Automated electric drive. Variable-frequency asynchronous electric drive - course of lectures General characteristics of the lecture notes

Kharkov National Academy of Municipal Economy

LECTURE NOTES

by discipline

"Automated electric drive"

(for 4th year full-time and part-time students in specialty 6.090603 – “Electrical power supply systems”)

Kharkov - KHNAGH - 2007

Lecture notes on the discipline “Automated electric drive” (for 4th year students of all forms of study, specialty 6.090603 – “Electrical power supply systems”). Auto. Garyazha V.N., Fateev V.N. – Kharkov: KHNAGH, 2007. – 104 pages.

CONTENT

GENERAL CHARACTERISTICS OF LECTURE NOTES

The automated electric drive is the main consumer of electricity. In industrialized countries, more than 65% of generated electricity is converted by electric drives into mechanical energy. Therefore, the development and improvement of the electric drive, which is the basis of the power supply of labor, contributes to increased productivity and increased production efficiency. Knowledge of the properties and capabilities of an electric drive allows an electrical engineer to ensure the rational use of an electric drive, taking into account the requirements of both technological machines and power supply systems. The subject “Automated electric drive” is studied in the seventh semester of the fourth year of study. The curriculum of the specialty “Electrical engineering systems of power consumption” allocates four credits for it. They are filled with six content modules, which are studied during lectures and practical classes, while performing laboratory work and calculation and graphic tasks.

This lecture notes contains material for studying the first three content modules of the subject “Automated Electric Drive”. In the first content module, an automated electric drive is considered as the basis for the development of the productive forces of Ukraine. In the second, the mechanical characteristics of engines are studied, showing the capabilities of the engine when operating both in motor mode and in electric braking mode. The third module studies typical components of automatic engine control circuits. Based on the properties of motors studied in the second module, typical units provide automatic starting, braking and reversing of motors in functions of time, speed and current with direct or indirect control of these quantities. Structurally, typical units are combined in the form of control stations. The share of control stations in the total number of electric drives used in Ukraine exceeds 80%.

Lecture 1.

1.1. Development of electric drive as a branch of science and technology

Since ancient times, people have sought to replace heavy physical labor, which was a source of mechanical energy (ME), with the work of mechanisms and machines. To do this, in transport and agricultural work, in mills and irrigation systems, he used the muscular power of animals, wind and water energy, and later the chemical energy of fuel. This is how the drive appeared - a device consisting of three significantly different parts: an engine (D), a mechanical transmission device (MTD) and a technological machine (TM).

Purpose of the engine: converting energy of various types into mechanical energy. The MPU is designed to transfer ME from the engine to the TM. It does not affect the amount of transmitted ME (without taking into account losses), but can change its parameters and, to coordinate types of motion, is performed in the form of belt, chain, gear or other mechanical transmissions.

In a technological machine, ME is used to change the properties, state, shape or position of the processed material or product.

In modern drives, various electric motors (EM) are used as a source of ME. They convert electrical energy (EE) into mechanical energy and therefore the drive is called an electric drive (ED). Its functional diagram is shown in Fig. 1.1. In addition to the mentioned elements, it includes a controlled converter (P), with the help of which the electrical energy is supplied from the network to the electric motor.

Changing the converter control signal U at, you can change the amount of EE coming from the network to the ED. As a result, the amount of ME produced by the engine and the amount of HM received will change. This, in turn, will lead to a change in the technological process, the efficiency of which is characterized by the controlled variable y(t).

Priority in creating an electric drive belongs to Russian scientists

B.S. Jacobi and E.H. Lenz, who invented the direct current motor in 1834, and in 1838 used it to propel boats. However, the imperfection of the engine and the uneconomical source of electrical energy (galvanic battery) did not allow this electric drive to find practical application.

In the middle of the 19th century, attempts to use electric motors with a direct current motor for printing and weaving machines were made by scientists in France and Italy. However, the DC system did not provide a satisfactory solution. By 1890, only 5% of total drive motor power came from electric motors.

The widespread use of electric drives is associated with the invention in 1889-1891 by the Russian engineer Dolivo-Dobrovolsky of a three-phase alternating current system and a three-phase asynchronous motor. The simplicity of the three-phase system, the possibility of centralized production of electricity, and the convenience of its distribution led to the fact that by 1927, already 75% of the total power of drive motors was made up of electric motors.

Currently, in leading industries, the ratio of the installed power of electric drives to the total installed power of drives with engines of all types (thermal, hydraulic, pneumatic) is approaching 100%. This is determined by the fact that electric motors are manufactured for a variety of powers (from hundredths of a watt to tens of thousands of kilowatts) and rotation speeds (from fractions of a shaft revolution per minute to several hundred thousand revolutions per minute); ED operates in an environment of aggressive liquids and gases at low and high temperatures; thanks to the controllability of the converter, the ED easily regulates the progress of the technological process, providing various parameters for the movement of the TM working bodies; it has high efficiency, is reliable in operation and does not pollute the environment.

Currently, the total installed capacity of electric generators in Ukraine exceeds 50 million kW. To distribute such power at all voltage levels, electrical networks have been created.

However, due to the decline, first of all, in industrial production, real electricity consumption in Ukraine is ensured at the expense of half of the specified capacity. Such a significant energy reserve is a reliable basis for the development of Ukraine’s production forces, associated with the introduction of new energy-saving technologies, the production of modern high-tech products, and the further development of automation and mechanization of production. The solution to all, without exception, of these problems is ensured by the use of various electric drive systems, an increase in the consumption of electrical energy by an electric drive, which in the existing consumption structure is already approaching 70%.

1.2. Principles of constructing control systems for automated electric drives

A distinctive feature of a modern electric drive is that it contains a converter control signal U at is formed by a special automatic control device (ACD) without direct human participation. Such control is called automatic, and the electric drive is called automated (AEP).

The AEP control system, like any other automatic control system, can be considered as a system that receives and processes information.

In the first channel, information about the required value of the controlled variable is generated q(t)(setting influence).

In the second channel, information about the actual value of the controlled variable can be obtained using sensors y(t) or other quantities characterizing EP.

The third channel can provide information about disturbances to the control system f i (t) as a signal x i (t).

Depending on the number of information channels used, there are three principles for constructing control systems for automated electric drives:

1) open-loop control principle;

2) closed-loop control principle;

3) the principle of combined control.

Let's consider the functional diagrams of the AED control systems.

The AEP control system, built on the principle of open-loop control, is called an open-loop system. It uses only one channel of information - about the required value of the controlled variable. q(t). The functional diagram of such a control system is shown in Fig. 1.2.

As in the previous case, the summation node at the input of the ACU receives information about q(t). Arrow indicating q(t), is directed to the undarkened sector of the summation node. This means that the master signal enters the summation unit with a “+” sign.

The automatic control device generates a converter control signal U y, using only information about the magnitude of the reference influence q(t), which is supplied to the input of the ACU from the command authority (CO). As a result of the fact that each element of the functional diagram is influenced by disturbing influences f i (t), the amount of mechanical energy supplied to the technological machine, and therefore the stroke

Rice. 1.2 - Functional diagram of the open-loop control system of the AED

technological operation will change. As a result, the actual value of the controlled variable y(t) may differ significantly from the required value q(t). The difference between the required and actual value of the controlled variable in steady state (when the controlled variable y(t) does not change over time) is called the control error Δx(t)= q(t)– y(t).

Open-loop AED systems are used if the occurrence of a control error does not lead to significant losses in the technology (reduced TM productivity, decreased product quality, etc.)

Otherwise, when the occurrence of a control error significantly reduces the efficiency of the technological process, the principle of closed-loop control is used to build the AED control system. Such a system is called closed.

It uses two channels of information: information about the required value of the controlled variable q(t) information about the actual value of the controlled variable is added y(t). The functional diagram of such a control system is shown in Fig. 1.3.

Information about the actual value of the controlled variable y(t) is fed to the summation unit using the main feedback loop (GOS). They say that the GOS “closes” the control system by connecting its output to the input.

Arrow indicating y(t), is directed to the dark sector of the summation node, i.e. The GOS signal enters the summation unit with a “–” sign and therefore the GOS is called negative feedback.

Rice. 1.3 - Functional diagram of the closed-loop control system of the nuclear power plant.

In the summation node as a result of algebraic (taking into account the sign) addition of signals q(t) And y(t) the magnitude and sign of the control error are determined Δx(t)= +q(t) – y(t). The error signal is sent to the input of the ACU. Thanks to this, the ACU, generating a control signal for the converter P based on information about the actual relationship between the given and actual value of the controlled variable, ensures the supply of such an amount of EE to the ED, and to the technological machine ME, that the control error can be reduced to an acceptable value or reduced to zero.

In addition to the GOS, the control system may have various feedback loops (FOC) internal to the GOS. They control intermediate parameters of the system, which improves the quality of the control process. A system containing only GOS is called single-circuit, and one that, in addition to GOS, also has VOS, is called multi-circuit.

In a system built on a combined principle, two structures are combined - closed and open. To the closed system, which is the main one, an open-loop structure is added via a third information channel x 1 (t) about the main disturbing influence f 1 (t). The functional diagram of the system is shown in Figure 1.4.

The main one is the disturbing influence, which has the largest component in the value of the control error.

Rice. 1.4 - Functional diagram of the combined control system of the nuclear power plant

In Fig. 1.4 as the main one, disturbing influence is taken f 1 (t). It is controlled by an intermediate element (IE) and information about it x 1 (t) fed to the summation unit. Thanks to this, the ACU introduces a component into the converter control signal that compensates for the influence f 1 (t) on the technological process and reduces the amount of control error. The influence of other disturbing influences on the error is eliminated by the main closed system.

The considered examples allow us to define the concept of “automated electric drive”.

An automated electric drive is an electromechanical system in which, firstly, electrical energy is converted into mechanical energy. Through this energy, the working parts of the technological machine are set in motion. And, secondly, the energy conversion process is controlled in order to ensure the required steady-state and transient operating modes of the TM.

Lecture 2.

1.3. Classification of AED control systems

Classification of AED control systems can be carried out according to many criteria: according to the type of motor current, systems are divided into alternating and direct current. By type of information and control signals - continuous and discrete systems. Depending on the nature of the equations describing control processes - linear and nonlinear systems. They are often subdivided according to the type of converter or main equipment: system - DC generator - motor (G-D); system - thyristor converter - motor (TP-D); system - thyristor frequency converter - motor (TFC-D), etc.

However, the most widespread classification of AED control systems is based on the functions they perform in technological processes. There are five such functions.

1. Control systems for starting, braking, and reverse processes. Among them, in turn, three groups of systems can be distinguished.

The systems of the first group are open-loop. They are used in electric drives with asynchronous motors with a squirrel-cage rotor. The converter consists of a power switching device (SPU) that connects the motor directly to the network. All control equipment is relay-operated (contact or non-contact).

The control systems of the second group are also open-loop. They are used in electric drives with DC motors and asynchronous motors with a wound rotor; they have a more complex structure of SPUs that provide stepwise switching of resistors or other elements in the power circuits of the motor. Provide control of automatic starting and braking, which limits the motor current and torque. With manual control of the SPU, it is possible to regulate the speed in a small range.

Systems of the third group are designed to implement optimal processes of starting, braking, and reversing. In this case, optimal is understood as transient processes occurring in the minimum time. This is ensured by maintaining the engine torque at the permissible value during starting and braking.

Such systems are used in electric drives with intermittent operating modes, when the steady-state time is short or absent altogether. Therefore, the occurrence of a control error will not lead to losses in technology and the system may not have a GOS.

A closed control loop in such a system is formed by negative feedback on the motor torque (current). In Fig. 1.4 it is shown as BOS. The controlled variable in this case is the engine torque. Therefore, the ACU generates a control signal P in such a way that during the start-up and braking process the torque is maintained at the required level or changes over time according to the required law.

2. Systems for maintaining a constant set value of the controlled variable (stabilization systems). Adjustable quantities are those that characterize the movement of the working body of the TM and the engine shaft - speed, acceleration, torque, power, etc.

Stabilization systems are built on a closed principle and can have a functional diagram shown in Fig. 1.4. In such a system, the driving signal q(t)=const. Therefore, reducing the controlled variable y(t), caused by the appearance of a disturbing influence f 1 (t), will lead to an increase in the control error signal at the ACU input. The automatic control device generates a converter control signal depending on the control law (regulator type) used in it. With a proportional control law, a proportional (amplifying) link with a gain greater than unity (P – regulator) is used as a regulator. Therefore, as the signal increases, the error at the input of the P-regulator will also increase the converter control signal. As a result of this, the amount of EE and ME will increase, which will lead to an increase y(t) and reducing control error. However, it cannot be completely compensated, since in this case the signals at the input and output of the P-regulator will be equal to zero, no electrical energy will be supplied to the engine and the technological process will stop.

A stabilization system in which the control error is not reduced to zero, but only decreases to an acceptable value, is called static.

With a proportional-integral control law, the regulator consists of two links connected in parallel - proportional and integral (P-I - regulator). The error signal arrives simultaneously at the input of both links. The proportional part of the regulator, as in the previous case, will amplify the error signal. The integral part of the controller will sum the error signal, i.e. its output signal will increase as long as there is an error signal at the controller input. Since the controller output signal (converter control signal) is the sum of the output signals of the proportional and integral parts, then as long as there is an error signal at the controller input, its output signal will increase. As a result, the number of EE and ME in the system will increase and the control error will decrease. When the error signal at the controller input becomes equal to zero, the signal at the controller output will be greater than zero, due to the fact that the integral part of the controller, after the disappearance of the signal at its input, remembers the total value of the output signal. EE will be supplied to the engine and the technological process will continue.

A stabilization system in which the control error is reduced to zero is called astatic.

With a proportional-integral-differential control law, a differentiating link (P-I-D-regulator) is switched on in parallel to the P, I. - links.

The output signal of the differential part is directly proportional to the rate of change of the control error signal. Summed up with the signals P, I of the regulator parts, it additionally increases the converter control signal and the amount of electrical energy supplied to the engine. This helps to reduce the dynamic control error, i.e. the difference between the required and actual value of the controlled variable during a transient regime in the system.

Stabilization systems are used in cases where it is necessary to maintain a particularly precise technical process parameter, as well as when regulating engine speed over a wide range.

To form the starting and braking processes, the stabilization system can have internal feedback on the engine torque (BOC in Fig. 1.4).

An open control channel based on the main disturbance reduces the control error in static systems.

3. Tracking systems. Like stabilization systems, they are built on a closed principle. However, the driving signal q(t) in them the actual value of the controlled variable changes according to a random law y(t) must repeat (track) this law.

Used in technological machines, which require that when the input shaft is turned by any angle, the output shaft “follows” the input shaft and turns by the same angle.

When the position of the shafts coincides q(t) = y(t) and the control error is zero. When changing the position of the input shaft q(t) ≠ y(t). An error signal appears at the input of the ACU, the converter supplies electrical energy to the motor and the output shaft will rotate until it takes the position of the input.

4. Program control systems. They are used in technological machines with several electric drives. These drives can be built either on an open or closed principle. What they have in common is a device that changes the set value of the controlled variable of each electric drive according to a predetermined program. In this case, the engines of individual working parts automatically start, operate at specified speeds or are reversed, and the moving working parts of the technological machine do not interfere with each other.

5. Adaptive systems. They are used in cases where a system built on a closed principle, as a result of unforeseen changes in disturbing influences, is unable to perform its function, for example, stabilizing a controlled variable.

To ensure adaptation (adaptability) of a closed system, an additional circuit is introduced into its composition, the basis of which is a computing device. It controls the amount q(t), y(t), disturbing influences f i (t), analyzes the operation of the stabilization system and determines the changes in the parameters or structure of the control unit necessary for adaptation.

Lecture 3.

2.1. Bringing moments and forces of resistance, moments of inertia and inertial masses

The mechanical part of the electric drive includes the rotating part of the engine, the mechanical transmission device and the working element of the technological machine.

The rotating part of the engine (armature or rotor) serves as a source of mechanical energy.

With the help of the MPU, the rotational motion of the engine is converted into the translational movement of the TM working element, or by changing the ratio of the speeds of the input and output shafts of the MPU, the rotation speeds of the engine and the working element are coordinated. Cylindrical and worm gearboxes, planetary gears, a screw-nut pair, crank, rack, belt and chain drives can be used as MPUs.

The working body of a TM is a consumer of mechanical energy, which it converts into useful work. The working parts include the spindle of a lathe or drilling machine, the moving part of a conveyor, an excavator bucket, an elevator cabin, a ship propeller, etc.

The elements of the mechanical part of the electric drive are connected to each other and form a kinematic chain, each element of which has its own speed of movement, characterized by a moment of inertia or inertial mass, as well as a set of moments or forces acting on it. The mechanical motion of any of the elements is determined by Newton's second law. For an element rotating around a fixed axis, the equation of motion has the form:

Where
– vector sum of moments acting on the element;

J– moment of inertia of the element;

– angular acceleration of the rotating element.

For a translationally moving element, the equation of motion has the form:

,

Where
– vector sum of forces acting on the element;

m– inertial mass of the element;

– linear acceleration of a translationally moving element.

Using these equations, the interaction of any element with the rest of the kinematic chain can be taken into account. This is conveniently accomplished by bringing moments and forces, as well as moments of inertia and inertial masses. As a result of this operation (reduction), the real kinematic scheme is replaced by a calculated, energetically equivalent scheme, the basis of which is the element whose movement is being considered. As a rule, this element is the motor shaft M. This allows us to most fully study the nature of the movement of the electric drive and its operating mode. Knowing the parameters of the kinematic diagram, it is possible to determine the type of movement of the working body of a technological machine.

The reduction of moments of resistance from one axis of rotation to another is carried out on the basis of the power balance in the system.

During a technological operation, a working body rotating on its axis at a speed ω m and creating a moment of resistance M cm, consumes power R m =M cm ω m. Power losses in the MPU are taken into account by dividing the value R m on efficiency transfers η n. This power is provided by a motor rotating at a speed ω and developing moment M With, equal to the moment of resistance reduced to the axis of rotation of the motor shaft M cm. Based on the equality of powers, we obtain:

.

Then the expression for determining the reduced moment of resistance M With has the form:

,

Where
– MPU gear ratio.

Bringing resistance forces is done in a similar way. If the speed of translational movement of the working body of the TM is equal to υ m and during the technological operation a resistance force is created F cm, then taking into account the efficiency The MPU power balance equation will have the form:

.

Reduced moment of resistance M With will be equal to:

,

Where
– MPU reduction radius.

Each of the rotating elements of the kinematic scheme is characterized by a moment of inertia J і . The reduction of moments of inertia to one axis of rotation is based on the fact that the total reserve of kinetic energy of the moving parts of the drive, related to one axis, remains unchanged. In the presence of rotating parts with moments of inertia J d , J 1 , J 2 , … J n and angular velocities ω, ω 1 , ω 2 , … ω n it is possible to replace their dynamic action with the action of one element having a moment of inertia J and rotating at speed ω .

In this case, we can write the kinetic energy balance equation:

.

The total moment of inertia reduced to the motor shaft will be equal to:

,

Where J d– moment of inertia of the rotor (armature) M;

J 1 , J 2 , … J n– moments of inertia of the remaining elements of the kinematic scheme.

Bringing inertial masses m, moving translationally, is also carried out on the basis of the equality of kinetic energy:

,

Hence the moment of inertia reduced to the motor shaft will be equal to:

.

As a result of performing reduction operations, the real kinematic scheme is replaced by a calculated, energetically equivalent scheme. It is a body rotating on a fixed axis. This axis is the axis of rotation of the motor shaft. It is acted upon by the engine torque M and the reduced moment of resistance M With. The body rotates at the speed of the engine ω and has a reduced moment of inertia J.

In the theory of electric drives, such a design scheme is called a single-mass mechanical system. It corresponds to the mechanical part of the AED with absolutely rigid elements and without gaps.

A modern electric drive is a structural unity of an electromechanical energy converter (motor), a power converter and a control device. It ensures the conversion of electrical energy into mechanical energy in accordance with the operating algorithm of the technological installation. The scope of application of electric drives in industry, transport and everyday life is constantly expanding. Currently, more than 60% of all electrical energy generated in the world is consumed by electric motors. Consequently, the effectiveness of energy-saving technologies is largely determined by the efficiency of the electric drive. The development of high-performance, compact and economical drive systems is a priority direction in the development of modern technology. The last decade of the outgoing century was marked by significant advances in power electronics - the industrial production of insulated gate bipolar transistors (IGBTs), power modules based on them (racks and entire inverters), as well as intelligent power modules (IPM) with built-in key protection and interfaces was mastered for direct connection to microprocessor control systems. The growing degree of integration in microprocessor technology and the transition from microprocessors to microcontrollers with a built-in set of specialized peripheral devices have made irreversible the trend of mass replacement of analog drive control systems with direct digital control. Direct digital control means not only direct control from the microcontroller of each switch of the power converter (inverter and controlled rectifier, if any), but also providing the possibility of direct input of various signals into the microcontroller feedback(regardless of the type of signal: discrete, analog or pulse) with subsequent software and hardware processing inside the microcontroller. Thus, the direct digital control system is aimed at eliminating a significant number of additional interface boards and creating single-board drive control controllers. In the extreme, the embedded control system is designed as a single-chip system and, together with the power converter and actuator motor, is structurally integrated into one whole – the mechatronic motion module.

Let's consider the generalized structure of an electric drive (Fig. 6.25). In it, two interacting channels can be distinguished - power, which transfers and converts energy from electrical to mechanical, and information.

Depending on the requirements for an electric drive, various electrical machines are used as an electromechanical converter: asynchronous and synchronous alternating current, brushed and brushless direct current, stepper, switched reluctance, switched reluctance, etc.

The information channel is designed to control the flow of energy, as well as collect and process information about the state and functioning of the system, and diagnose its malfunctions. The information channel can interact with all elements of the power channel, as well as with the operator, other electric drive systems and the upper-level control system.

Rice. 6.25. Generalized electric drive structure

For a long time, the widespread use of variable speed drives was hampered by two factors:

relatively low permissible values ​​of currents, voltages and switching frequencies of power semiconductor devices;

limiting the complexity of control algorithms implemented in analog form or on digital microcircuits of low and medium integration.

The advent of thyristors for high currents and voltages solved the problem of a static converter for a DC electric drive. However, the need for forced closing of thyristors along the power circuit significantly complicated the creation of autonomous inverters for frequency-controlled AC electric drives. The emergence of powerful fully controllable field effect transistors, designated in foreign literature as MOSFET (Metal - Oxide - Semiconductor Field Effect Transistor), and bipolar transistors with an insulated gate IGBT (Isulated Gate Bipolar Transistor) led to the rapid development of converter technology and the constant expansion of the scope of application of asynchronous electric drives with frequency converters. Another factor that determined the possibility of mass implementation of frequency-controlled electric drives was the creation of single-chip microcontrollers with sufficient computing power.

Analysis of the products of the world's leading manufacturers of drive systems and materials of published scientific research in this area allows us to note the following pronounced trends in the development of electric drives:

The share of drive systems with DC motors is steadily decreasing and the share of drive systems with engines AC. This is due to the low reliability of the mechanical commutator and the higher cost of commutated DC motors compared to AC motors. According to experts, at the beginning of the next century the share of DC drives will be reduced to 10% of the total number of drives.

Currently, they are predominantly used drives with squirrel-cage asynchronous motors. The majority of such drives (about 80%) are unregulated. Due to the sharp reduction in the cost of static frequency converters, the share frequency-controlled asynchronous electric drives is increasing rapidly.

A natural alternative to brushed DC drives are drives with valve, i.e. electronically switched engines. As executive brushless dc machines(BMPT), synchronous motors with excitation from permanent magnets or with electromagnetic excitation (for high powers) are predominantly used. This type of drive is the most promising for machine tool building and robotics, however, it is the most expensive. Some cost reduction can be achieved by using a synchronous reluctance motor as an actuator.

The drive of the next century, according to most experts, will be a drive based on switched reluctance motor(VIEW). Engines of this type are easy to manufacture, technologically advanced and cheap. They have a passive ferromagnetic rotor without any windings or magnets. At the same time, high consumer properties of the drive can be ensured only by using a powerful microprocessor control system in combination with modern power electronics. The efforts of many developers in the world are concentrated in this area. For typical applications, self-excited inductor motors are promising, and for traction drives, inductor motors with independent excitation from the stator are promising. In the latter case, it becomes possible to have two-zone speed control, similar to conventional DC drives.

6.2.1. Asynchronous electric drives
with scalar control

Scalar control methods ensured the achievement of the required static characteristics and were used in electric drives with a “quiet” load. At the input of these systems, as a rule, intensity setters were turned on, which limited the rate of increase (decrease) of the input signal to such a value at which the processes in the system can be considered steady, that is, the term in the equation could be neglected , because .

In Fig. Figure 6.26 shows the mechanical characteristics of an asynchronous squirrel-cage motor for all four control laws for a linear model that does not take into account saturation of the magnetic circuit. It should be repeated that the listed control laws have been widely used and have proven themselves in electric drives, where control speed is not required and there are no sudden changes in load torque.

Rice. 6.26. Mechanical characteristics of AKZ
under different control laws

The simplest of the listed laws is the first: This law, when using an inverter with a sinusoidal PWM, is implemented in almost all semiconductor converters that are produced by numerous companies and offered on the market. The convenience of this law is that the electric drive can operate without negative speed feedback and have natural rigidity of mechanical characteristics in a limited speed control range.

In electric drives with scalar control, other relationships between frequency and voltage are used to regulate or stabilize speed. The choice of this ratio depends on the load torque and is determined from the conditions for maintaining the overload capacity:

Where M max – maximum torque of the AKZ, Μ N – load moment on the machine shaft.

The law of voltage and frequency changes that satisfies requirement (6.15) under the assumption r s= 0, installed
M.P. Kostenko. This law looks like

Where U NOM,f NOM,Μ NOM – nominal values ​​given in the machine's passport data.

If the law of torque change is known in advance, then the required voltage-frequency ratio at the inverter output can be determined. Let's consider three classic types of loads on the machine shaft:

M H= const, ; P H = M H wm = const, ; . (6.16)

Converters available on the market are often designed to be reconfigurable to accommodate all three laws. The electric drive circuit that implements the considered laws is shown in Fig. 6.27. The functional converter (FC) implements one of the dependencies (6.16), determined by the nature of the load. The semiconductor converter (SC) includes an autonomous inverter and its control system; the intensity generator (ISD), as already noted, generates a slowly increasing input signal. In this case, the increase in speed in the electric drive will not be accompanied by intense fluctuations in torque and current, which are observed during direct starting.

Rice. 6.27. Functional diagram of an open-loop asynchronous

For more complex loads, other scalar control laws are used, which are implemented using feedback. These laws are discussed above based on an analysis of the operation of an asynchronous machine in steady state.

Let's consider another scalar control law that is used in the construction of electric drives with autonomous current inverters - this is the law ψ R= const.

The implementation of this dependence in the electric drive is shown in the functional diagram (Fig. 6.28). Such systems are called frequency-current systems.

The PP block in the system can be implemented in two ways. In the first case (Fig. 6.28) it contains a controlled rectifier, a series inductive filter and an autonomous inverter. It should be emphasized that the inductive filter gives the inverter the characteristic of a current source. Such a current source is called parametric.

Rice. 6.28. Functional diagram of asynchronous
electric drive with scalar control

6.2.2. Asynchronous electric drives
with vector control

In Fig. Figure 6.29 shows the structure of a vector control AC drive. The actuator motor can be either a synchronous motor with an active magnetoelectric rotor or a synchronous reluctance motor. It is also possible to use this structure to control three-phase switched reluctance motors with different polarity power supply, as well as stepper motors in the mode of brushless DC motors.

An inverter based on IGBT switches or intelligent power modules is used as a power converter. Inverter switch drivers are connected directly to the outputs PWM generator microcontroller operating in mode pulse width modulation of base vectors(vector PWM modulation), which ensures the highest possible utilization of DC link voltage and minimization of dynamic losses in the inverter (more details below).

Rice. 6.29. Drive block diagram
AC vector control

Structure in Fig. 6.29 assumes the use of a pulse engine rotor position sensor. Signals from the sensor are input directly into the controller and processed in a position estimation unit, which can be implemented on the basis of a special peripheral device - timer with “quadrature” mode of operation. The code for the mechanical position of the rotor is converted by software into the code for the electrical position of the rotor within the pole division of the machine q. To implement the speed estimation unit, either special microcontroller peripheral devices can be used, the operating principle of which is based on measuring the time interval of the engine working out a given section of the path (speed estimators), or general purpose peripherals such as event processors or event managers. In the latter case, a timer operating in “quadrature” mode is the base one for one of the comparison channels. As soon as the engine has completed the specified distance, a comparison interruption will occur. In the service routine for this interrupt, the CPU will determine the time interval since the previous interrupt and calculate the current drive speed w. It is desirable that a timer operating in the “quadrature” mode allows initial initialization in accordance with the number of marks per revolution of the pulse position sensor, and also has a mode of automatic correction of its state based on the reference sensor. The speed estimator must operate with an adjustable resolution both in terms of the number of pulses per speed measurement period (from 1 to 255) and with an adjustable time resolution (maximum resolution 50 - 100 ns with a resolution adjustment range of 1:128). If the above requirements for the peripheral devices of the microcontroller are met, then it will be possible to measure speed in the range of at least 1:20000 with an accuracy of no worse than 0.1%. To measure electrical variables, the microcontroller must have built-in ADC with a resolution of at least 10 - 12 bits and a conversion time of at least 5 - 10 μs. As a rule, eight ADC channels are sufficient to receive not only phase current feedback signals, but also voltage and current feedback signals in the DC link, as well as external master signals. Additional analog signals are used to implement inverter and motor protection. The ADC will be more productive if the microcontroller allows automatic scanning and starting the conversion process. This is usually done either using a separate peripheral device − peripheral transaction processor, or using ADC autostart mode from an event processor or PWM signal generator. It is desirable that at least two analog signals be sampled simultaneously.

In the vector PWM modulation block, the components of the voltage vector are first converted to the polar coordinate system (g, r) associated with the longitudinal axis of the rotor, and then, taking into account the current position of the rotor q, the working sector, the intra-sector angle are determined, and the components of the base vectors in absolute coordinate system associated with the stator. Voltages applied to the motor windings U a, U b, U c are formed. All of the above coordinate transformations (direct and inverse Park and Clark transformations) must be performed in real time. It is desirable that the microcontroller used to implement the vector control system have built-in library of functions, adapted for efficient motor control, including coordinate transformation functions. The implementation time for each of these functions should not exceed a few microseconds.

A distinctive feature of the vector control system for asynchronous motors is the need to use an additional computing unit, which evaluates the current angular position of the rotor flux linkage vector. This is done based on the system's real-time decision differential equations, compiled in accordance with the mathematical model of the engine. Naturally, such an operation requires additional computing resources of the central processor.

6.2.3. Valve and contactless
DC machines

Contactless DC machines (BMPT) and switched-type machines (VM) are a synchronous motor in a closed system (Fig. 6.30), implemented using a rotor position sensor (RPS), a coordinate converter (PC) and a power semiconductor converter (SPC).

The difference between BMPT and VM lies only in the method of generating voltage at the output of the power semiconductor converter. In the first case, a pulse voltage (current) is formed on the windings of the machine. In the second case, a sinusoidal or quasi-sinusoidal voltage (current) is formed at the output of the SPP.

It should be noted that BMPTs differ from stepping machines in that they are included in a closed voltage generation system. In them, the voltage is formed depending on the position of the rotor, and this is their fundamental difference from stepper ones, in which the position of the rotor depends on the number of control pulses.

Rice. 6.30. Functional diagram of BMPT and VM

Standing apart from the range of synchronous machines are hysteresis and jet engines. These machines are rarely used in electric drive.

Of all the types of synchronous machines considered in controlled systems, valve machines are considered the most promising.

In a number of applications, for example, for drives with switched reluctance and brushless DC motors, it is quite sufficient to maintain a specified fixed current level in the motor winding during the commutation interval. The structure of the control system is noticeably simplified. The peculiarity of the circuit (Fig. 6.31) is that the PWM generator provides two functions at once: automatic switching of motor phases based on position sensor signals and maintaining the current at a given level by regulating the voltage applied to the motor windings.

The first function can be implemented automatically if the generator has a built-in output control unit, allowing commands to be received from the event processor. The second function is traditional and is implemented by changing the duty cycle of the output PWM signals. To estimate the position of the motor rotor, you can use either a Hall-element position sensor or a more expensive pulse position sensor. In the first case, signals from the position sensor are entered into the microcontroller at the inputs event processor capture modules.

The execution of each whole step by the engine is identified by the event processor and causes auto-commutation of the inverter keys. The interruption that occurs each time an edge of the signal from the sensor is captured is used to estimate the time between two adjacent switchings and, further, the drive speed. In the second case, it is possible to obtain more accurate information about the current position of the motor rotor and its speed, which may be required in drives with intelligent control of the commutation angle as a function of speed. Thus, full-fledged vector control systems for AC drives require for their implementation high-performance microcontrollers with a wide range of the above-mentioned built-in peripheral devices that allow joint operation and require minimal resources from the central processor for their maintenance.

Rice. 6.31. Control system block diagram
brushless DC motor

6.3. Power semiconductors
converters in the system
automated electric drive

Power semiconductor converters in automation systems perform the function of regulating the speed and torque of an electric motor. They are connected between the power consumer (usually an electric motor) and the main power source (Fig. 6.32). According to the principle of operation, power converters are divided into the following basic types:

controlled rectifiers (RC), which convert alternating, usually sinusoidal, voltage from a constant-frequency power source (usually industrial
f and = 50 Hz or f and = 400 Hz) and with a constant effective value (usually U and = 220 V or U and = 360 V), into adjustable DC output voltage ( U n = var, f n = 0).

pulse width converters (PWC), which convert the DC voltage of the power source
(U And = const, f and = 0) to a constant regulated DC voltage output ( U n = var, f n = 0).

autonomous inverters (AI), which convert the DC supply voltage ( U And = const, f and = 0) into alternating voltage output with adjustable effective value and adjustable frequency ( U n = var, f n = var).

direct frequency converters (NPC) convert alternating, usually sinusoidal, voltage of constant frequency ( f and = 400 Hz or f and = 50 Hz) constant rms value (usually 220 V) into alternating voltage output with adjustable rms value and adjustable frequency ( U n = var, f n = var).

Rice. 6.32. Basic Uses of Power Converters

It should be noted that here the constant voltages ( f= 0) are characterized by average values U i.sr, U p.sr, and variables ( f¹ 0) – effective values ​​( U And, U p).

Thus, power converters HC, SHIP can be used to control (voltage, current, power) DC consumers. Moreover, the latter can be not only electric motors, but also consumers with active (resistive) loads (such power converters are used in regulated power supplies). If the power source is an alternating current network, then either a shock wave or a combination of a rectifier and a power supply can be used.

For AC consumers (which is most often an AC machine), an AI is used, and when powered from an AC source, an NPCh, or a combination of a shock wave and an AI, or a rectifier and an AI.

6.3.1. Controlled rectifiers

The energy source for controlled rectifiers is an alternating current network. The control principle is that during the positive half-cycle of the supply voltage, an electronic switch (usually a thyristor) opens and supplies voltage to the consumer only part of this half-cycle. The voltage and current at the output of the controlled rectifier contain DC and AC components. By changing the moment (phase) of opening the electronic key, the average voltage value at the input of the power consumer is changed. Controlled rectifiers are most often used to control a DC motor via an armature circuit.

There is a large number various schemes controlled rectifiers. According to the principle of operation and construction, they can be divided into two groups: half-wave (circuits with a neutral wire), in which only one half-wave of the network voltage is used, and full-wave (bridge circuits), where both half-waves of the alternating network voltage are used.

Let's consider the operation of the simplest full-wave thyristor circuit with a purely active load R n (Fig. 6.33).

To the source of sinusoidal mains voltage U and with amplitude n through a thyristor bridge
VS1 – VS4. Diagonal thyristors VS1, VS4 And VS2, VS3 open in pairs, alternately at a time determined by the opening angle a.

In interval α < w t< 180° voltage is applied to the load U n = U m sin w t.In Fig. 6.35, the load voltage curve is shaded dark.

Since the load is active (resistive), the current curve follows the voltage curve. At time w t = 180° the current is reduced to zero and the corresponding pair of diagonal thyristors is closed. This process is repeated every half cycle. Thyristors are controlled by pulses of short duration with a fairly steep leading edge, which reduces power losses in the thyristor when turned on, and, consequently, its heating.

The considered phase control method can be implemented using phase-shifting methods, one of which is vertical method control based on a comparison of a reference voltage (usually a sawtooth waveform) and a constant voltage control signal. The equality of the instantaneous values ​​of these voltages determines phase a, at which the circuit generates a pulse, then amplified and supplied to the control electrode of the thyristor. Changing the phase a of the control pulse is achieved by changing the voltage level of the control signal U ex. The functional control diagram is shown in Fig. 6.34. The reference voltage generated by the sawtooth voltage generator GPN and synchronized with the mains voltage using the SU synchronizing device is supplied to the CC comparison circuit, which simultaneously receives the input voltage (control signal). The signal from the comparison circuit is supplied to a pulse shaper (PI), then to a pulse distributor (PD), to power amplifiers (P), from where it is supplied to the control electrode in the form of a powerful, steep-edged, phase-adjustable pulse.

Lectures on the discipline “Automated electric drive” Literature 1. Chilikin M.G., Sandler A.S. General course of electric drive (EP).-6th ed. -M.: Energoizdat, – 576 p. 2. Moskalenko V.V. Electric drive - M.: Mastery; Higher school, –368 p. 3. Moskalenko V.V. Electric drive: Textbook for electrical engineering. specialist. -M.: Higher. school, – 430 s. 4. Handbook of automated electric drives / Ed. V.A. Eliseeva, A.V. Shiyansky.-M.: Energoatomizdat, 1983. – 616 p. 5. Moskalenko V.V. Automated electric drive: Textbook for universities. - M.: Energoatomizdat, p. 6. Klyuchev V.I. Electric drive theory. - M.: Energoatomizdat, p. 7. GOST R –92. Electric drives. Terms and definitions. Gosstandart of Russia. 8. Agricultural Electrical Engineer's Handbook. production / Textbook.-M.: Informagrotekh, p. 9. Guidelines for performing laboratory work on the basics of electric drives for students of the Faculty of Electrification of Agriculture. / Stavropol, St. State Agrarian University, “AGRUS”, – 45 p. 10. Savchenko P.I. Workshop on electric drives in agriculture. – M.: Kolos, p. Recommended sites on the Internet: Lectures on the discipline “Automated electric drive” Literature 1. Chilikin M.G., Sandler A.S. General course of electric drive (EP).-6th ed. -M.: Energoizdat, – 576 p. 2. Moskalenko V.V. Electric drive - M.: Mastery; Higher school, –368 p. 3. Moskalenko V.V. Electric drive: Textbook for electrical engineering. specialist. -M.: Higher. school, – 430 s. 4. Handbook of automated electric drives / Ed. V.A. Eliseeva, A.V. Shiyansky.-M.: Energoatomizdat, 1983. – 616 p. 5. Moskalenko V.V. Automated electric drive: Textbook for universities. - M.: Energoatomizdat, p. 6. Klyuchev V.I. Electric drive theory. - M.: Energoatomizdat, p. 7. GOST R –92. Electric drives. Terms and definitions. Gosstandart of Russia. 8. Agricultural Electrical Engineer's Handbook. production / Textbook.-M.: Informagrotekh, p. 9. Guidelines for performing laboratory work on the basics of electric drives for students of the Faculty of Electrification of Agriculture. / Stavropol, St. State Agrarian University, “AGRUS”, – 45 p. 10. Savchenko P.I. Workshop on electric drives in agriculture. – M.: Kolos, p. Recommended Internet sites:

Electrical energy source (EES) Control device (CU) Converting device (PDB) Electric motor device (ED) M Transmission device (TD) Mechanical energy consumer (PME) U,I,f M d, ω d U d,I d,f d F d, V d M m (F m), ω m (V m) tasks Figure 3 – Block diagram of the AED

3 AED efficiency coefficient As for any electromechanical device, an important indicator is the AED efficiency coefficient = PRB · ED · PRD Since the efficiency of PRB and PRD1 depends little on the load, the AED is determined by ED, which is also quite high and at rated load is 60-95%.

4 Advantages of AED 1) low noise level during operation; 2) no pollution environment; 3) wide range of powers and angular speeds of rotation; 4) availability of regulation of the angular speed of rotation and, accordingly, the productivity of the technological installation; 5) relative ease of automation, installation, and operation compared to heat engines, for example, internal combustion.

AUTOMATED ELECTRIC DRIVE

Course of lectures for specialty students

"Metalworking machines and tools"

CHAPTER 1 GENERAL QUESTIONS FOR AEP. MECHANICS OF AEP

1.1. Basic concepts and definitions

1.1. Mechanical characteristics of working machines and electric motors

1.2. Mechanical characteristics of DPT

1.3. Mechanical characteristics of IM

1.4. Mechanical characteristics of SD

CHAPTER 2 METHODS FOR CALCULATING POWER AND SELECTING ELECTRIC MOTORS

2.1. Forces and moments acting in the ED

2.2. Bringing moments of resistance and inertia to the motor shaft

2.3. General notes . Engine heating and cooling

2.4. Average loss method . Equivalent methods.

2.5. Series of electric motors used in machine tools

CHAPTER 3 ELEMENTS OF POWER AND REGULATING PART OF PDS

Classification of electronic devices SEP

3.1. Thyristor converters

3.2. Transistor converters

3.3. Typical sensors

3.4. Typical electronic protection units

3.5. Typical regulators

CHAPTER 4 TYPICAL SEP OF METAL-CUTTING MACHINES

4.1. Principles for constructing standard SEPs

4.2. Single-circuit DC PDS

4.3. SPR EP DC with single-zone control

4.4. SPR EP DC with dual-zone control

4.5. AC PDS with AIN and AIT (circuits with OS for speed and current)

4.6. Systems for stabilizing technological parameters when cutting metals

CHAPTER 5 TRACKING SEP OF METAL-CUTTING MACHINES

5.1. Typical structures of tracking electronic devices and their elements

5.2. Tracking ED with subordinate regulation of parameters

5.3. Tracking electronic feed of copy-milling machines

LITERATURE

1. Automated electric drive of standard production mechanisms and technological complexes: Textbook for universities / M.P. Belov, V.A. Novikov, L.N. Reasons. – M.: Publishing center “Academy”, 2004. – 576 p.

2. Engineering of electric drives and automation systems: textbook. aid for students higher textbook institutions / M.P. Belov, O.I. Zementov, A.E. Kozyaruk et al.; under. ed. V.A. Novikova, L.M. Chernigov. – M.: Publishing Center “Academy”, 2006. – 368 p.

3. Kovchin S.A., Sabinin Yu.A. Electric drive theory: Textbook for universities. – St. Petersburg: Energoatomizdat, 2000. – 496 p.

4. Shestakov V.M., Dmitriev B.F., Repkin V.I. Electronic devices of automatic control systems: Textbook. – St. Petersburg: Publishing house. Leningrad State Technical University, 1991.

CHAPTER 1. GENERAL ISSUES OF AEP. MECHANICS OF AEP.

1.1. Basic concepts and definitions

There are various types of drives, but due to efficient storage, ease of transmission, summation and divisibility properties, electrical energy is more widely used compared to other forms of energy. Currently, the most commonly used is an automated electric drive (GOST R 50369-92).

Electric drive (ED) is an electromechanical system designed to set in motion the working parts of machines, purposefully control these processes and consisting of transmission, electric motor, converter, control and information devices.

Transfer device designed to transform forms of movement and transfer mechanical energy from the propulsion device to the working parts of the machine.

Propulsion device converts electrical energy into mechanical energy and forms, together with the transmission device, specified forms of movement of the working bodies.

Converter device serves to connect the PDS with a source of electricity (industrial network or autonomous), to convert one form of electricity to another (for example, rectifying alternating current).

Control and information devices are intended for the formation of specified laws for controlling the flow of energy and the movement of working parts of machines.

Classification of EP

1. By purpose: a) main (for example, main movement);

b) auxiliary (for example, feeds).

2. By the type of current consumed by the motor: a) direct current;

b) alternating current.

3. By type of power switches: a) thyristor;

b) transistor;

c) microprocessor

4. By type of automatic control system (ACS):

a) analogue (continuous) electronic transmission systems (EPS);

b) digital (discrete) electronic transmission systems;

c) digital-analog SES;

d) linear or nonlinear SEP;

e) static or astatic SEP;

5. By functions performed:

a) rough speed control (open PDS);

b) precise speed control (closed PDS);

c) tracking arbitrarily changing input signals (tracking systems);

d) program processing of tasks (SEP with program control);

e) interconnected regulation of parameters (multi-motor and interconnected PDS);

Functions a)-e) are considered basic. Additional functions include: alarm (diagnostics) and electronic protection.

Mechanical characteristics of asynchronous motors (IM)

1) Mechanical characteristics of 3-phase IM

An asynchronous electric motor has a three-phase stator winding. When a three-phase voltage is applied to it with a frequency of , a magnetic field is formed, rotating at an angular speed of , where is the number 10

pairs of stator poles (determined by winding placement).

The IM rotor is most often squirrel-cage (“squirrel cage”). In lifting and transport machines, a wound rotor is used, where the rotor winding is brought out through contact rings to a stationary base and connected to additional resistances.

Currently, IM is used by default to drive most objects.

When describing the IM, the electrical parameters of the motor have indices: 1 – stator; 2 – rotor.

When R 1 =0 the mechanical characteristic is described by the formula

, where is the critical moment; - sliding.

1 – natural ();

1" – reverse (two of the three phases are swapped);

4 – IM with wound rotor, .

braking modes

5 – dynamic braking: direct current is supplied to the stator winding, then the spinning rotor will be braked;

6 – counterflow (reverse): (two phases change places);

7 – recuperation, torque reverse. Braking to zero requires an inverter that continuously reduces .

Starting an IM: To limit the starting currents of a high-power IM or to obtain a smooth start of an asynchronous drive, use:

1) inclusion of active or inductive resistances in the stator circuit, which are output at the end of the start;

2) “frequency” starting through a converter that smoothly changes the frequency of the motor supply;

3) start with wound rotor;

4) reactor start-up - inclusion of inductive reactors in the rotor circuit. At the beginning of starting, the frequency of the current in the rotor is close to the mains frequency, the inductive reactance is large and limits the starting current.

2) Mechanical characteristics of two-phase IM

Available in power up to 1 kW. Can be made with a solid or hollow rotor. OV, OU – excitation and control windings, respectively; To shift the phases, a capacitor with a capacity of 1-2 μF is connected in series to the OF circuit for every 100 W.

With single-phase switching on.

Note: with frequency control, the characteristics will become linear and parallel to each other, with phase control - only linear.

General notes

1) The task is to correctly select an electric motor for a given mechanism (unit), taking into account permissible heating and overload in current and torque.

Losses are divided into:

Constants - mechanical and in steel - do not depend on the motor current;

The variables - in copper - are a function of the square of the motor current.

Relationship between losses and efficiency:

, Where R– shaft power; P 1 – power consumption.

2) Heating and cooling of the electric motor during long-term operation.

- the amount of heat released (generated) by the electric motor;

Heat capacity of the engine;

- heat transfer.

At a constant ambient temperature, the engine temperature will increase according to the law , where is the heating time constant, s; , deg.

3) Engine operating modes

a) long-term (S1)

b) short-term (S2)

c) intermittent (S3, S4)

ON duration , where is the duty cycle;

standardized PV% = 15, 25, 40, 60%

4) Insulation classes and permissible operating temperatures of motors.

In accordance with international standards, the following insulation classes are distinguished:

General purpose motors use class B and F insulation.

5) Climatic design of electrical machines

6) Degrees of protection of electrical machines (GOST 14254-80 and GOST 17494-72)

The general designation of the type of protection (International Protection) is IP, where

1st digit: degree of protection of personnel from contact with moving parts of equipment and from the entry of solid foreign bodies into the shell;

2nd digit: degree of protection against water getting inside the equipment.

*) Does not apply to fans of electrical machines

The standard motor protection is IP 54. On request, higher degrees of protection IP 55 and IP 65 are provided.

Drives operating with a large number of switches

Drives with additional inertial mass (inertial impeller)

Converter-controlled drives with control ranges over 1:20

Converter controlled drives that maintain rated torque at low speed or in the stop position

Power calculation methods

The choice of engine power at a stationary load is carried out according to the condition (the nearest larger one in the catalog). In this case, the engine overheated.

Let's consider the choice of engine power under variable load:

1. Average loss method (direct method).

The method is based on a load diagram. Let's consider the direct method of accounting for losses in the engine

1) The average power on the motor shaft is calculated using the formula

, Joule-Lenz law

Motor losses are proportional to active power. Thus, engine heating is determined not by , but by . This raises the problem of calculating losses.

2) choice of engine power,

Where k= 1.2...1.3 – safety factor, taking into account the proportionality of losses to the square of the current;

3) Calculation of losses at various loads using catalog curves according to the formula

4) the average losses per cycle are determined ;

5) selection of engine power according to the condition, where - the engine has warmed up;

6) The selected motor must be tested for overload and starting conditions

DPT: , ;

HELL: ,

Equivalent Methods

These methods are indirect, since they indirectly take into account losses in the electric machine.

1) Equivalent current method.

A certain equivalent current is calculated, the losses from which are equivalent to the actual ones under variable load because

2) Equivalent moment method at Ф-const

; - the engine has warmed up.

3) Equivalent power method for Ф-const, -const

; - the engine has warmed up.

The selected motor must then be tested for overload and starting conditions.

The widest application is for the equivalent current method, the narrowest for the equivalent power method. The equivalent current and power methods are not applicable for two-zone control since they contain blocks of products in formulas, . More accurate is the average loss method (direct method).

Note: In intermittent mode, the motor is selected from the condition.

;

Here, the methods of equivalent torque and current are practically not used. If the load is not the same in different cycles, calculate the average duty cycle taking into account n cycles.

Thyristor converters

Advantages: a) reliability; b) low mass; c) low control power; d) high performance; d) high efficiency (0.95-0.97)

Disadvantages: a) cannot withstand overloads; b) reduction of cos at low loads; c) generation of higher harmonic oscillations into the network when switching valves (to combat them, TOP is turned on)

1. TP diagrams and control methods:

1) Zero reversible drive circuit

m=3 – converter phase. Advantages: fewer thyristors. Used in low-power drives.

2) Bridge circuit for rectifying a reversible drive (Larionov circuit)

m=6; Advantages: a) fewer smoothing chokes; b) smaller class of thyristors; Used in medium and high power drives.

2. Methods of controlling reversible transformer transformers:

a) separate, when groups of thyristors are controlled alternately.

Advantages: 1) absence of equalizing current and, therefore, the need to turn on equalizing reactors (UR);

Disadvantages: 1) wide zone of intermittent currents; 2) nonlinearity of mechanical characteristics at the origin; 3) slow reverse of the converter voltage.

At the same time, separate control of TP is used more often.

b) coordinated, when both groups of thyristors are controlled jointly, according to the condition , and , ;

Advantages: 1) linear characteristic; 2) narrow zone of intermittent currents; 3) fast reverse.

Disadvantages: 1) the presence of static and dynamic equalizing currents. To combat them, equalization reactors (UR) are activated.

3. Mathematical description of TP

1) Thyristor converter control system (TCC) or pulse-phase control system (PFC)

a) with stabilized sawtooth reference voltage . Does not contain higher harmonics in the reference voltage, ensures clear opening of thyristors and is used in medium and high power transformers.

b) with an unstabilized sinusoidal reference voltage . It is used in low-power transformer stations with a wide range of speed control of the transformer.

c) if the SUTP is digital, then the opening angle of the thyristors, where is the number code.

2) Power part of the transformer substation.

Described by the expression , Where - maximum rectified EMF of the TP. In addition, TP has a delay, which is statistically average. At m=6 .

a) SUTP with a stabilized sawtooth reference voltage.

Nonlinear dependence .

b) SUTP with an unstabilized sinusoidal reference voltage.

; - linear dependence !

From the figures it is clear that fluctuations in the AC voltage (dashed line) affect the output EMF in case a) and do not affect in case b).

3) TP load (motor). Forms the nature of the converter current, which can be continuous, borderline continuous and intermittent.

The nature of the current affects the characteristics of the drive. In the continuous current zone, the characteristics are rigid because the internal resistance of the converter is small. With intermittent current, the internal resistance of the TC increases significantly, which reduces the rigidity of the characteristics. , where is the switching resistance. is formed in continuous current mode when the phases overlap. - dynamic resistance of thyristors.

The intermittent current zone is extremely unfavorable for regulation, since the rigidity of the drive characteristics decreases and a nonlinear dependence appears (see figure).

Typical sensors

Let's consider the sensors of the domestic universal system of block regulators of analog design (UBSR-AI).

1) Current sensor DT1-AI The use of an operational amplifier (OA) allows you to decouple the power and control circuits of the drive, which is also necessary for safety reasons. Gain is selected so that the maximum measured current corresponds to .

2) Voltage sensor DN1-AI. The gain is selected so that the maximum measured voltage corresponds to.

3) EMF sensor

3) Speed ​​sensors. Precision tachogenerators of direct and alternating current are used as speed sensors.

4) Position sensors

a) Resolver. It works on the principle of a sine-cosine rotating transformer (SCRT). In a rotating transformer, the rotor consists of a coil (winding), which, together with the stator winding, forms the transformer. In principle, the resolver is designed in exactly the same way, with the only difference being that the stator is made not of one, but of two windings located at an angle of 90° to each other. The resolver is used to determine the absolute position of the motor shaft within one revolution. In addition, the speed value is determined from the resolver signal and an incremental encoder for position control is simulated. The resolver rotor is fixed to the motor shaft. In order to be able to transmit an alternating carrier voltage to the rotor without brushes, additional windings are placed on the stator and rotor. From two output sinusoidal voltages and , shifted by 90° (Fig. 7), it is possible to determine the rotor rotation angle, speed and incremental position signal (simulation of an incremental encoder).

b) Photoelectric sensors of the PDF series. No temperature or time drift. 500-5000 imp/rev.

5) Mismatch sensors. Used in tracking systems.

a) Potentiometric mismatch sensors

b) Selsyns in transformer mode. Selsyn has a 2-phase stator winding and a 3-phase rotor winding. The selsyn-sensor axis is driven by the master device, and the selsyn-receiver axis is driven by the actuator. When there is a difference in angles (i.e., tracking error), a voltage is generated across the stator winding. Selsyns work with error angles of up to 90 degrees, then the signal “overturns” (see figure). There are also inductosyns - linear analogues of selsyns.

Typical regulators

1) Statics is described by algebraic equations (EA), and dynamics - by differential equations. To facilitate the study of the dynamics of complex electromechanical systems using the Laplace transform pass from the time t-domain to the p-domain of images, where p (s) is the differentiation operator (Laplace), . In this case, the remote control is replaced by the automatic control unit.

The transfer function (TF) W(p) is the ratio of Laplace images of the output variable to the input variable (see TAU course).

2) Indicators of the quality of the transition process. Let's consider the transient process in a closed system:

a) Static error ;

b) Transition time – time of the last entry of the controlled variable into the 5% zone;

c) Overshoot ;

3) Standard regulators. Used in closed systems to obtain the required quality indicators. The most commonly used are proportional (P), proportional-integral (PI) and proportional-integral-derivative (PID) controllers. The choice of controller type is determined by the transfer function of the control object. Transfer functions of regulators

; ;

Implementation of an analog circuit	Gain
;
; ;

Single-circuit PDS

MINISTRY OF EDUCATION AND SCIENCE

RUSSIAN FEDERATION
FEDERAL EDUCATION AGENCY
STATE EDUCATIONAL INSTITUTION

HIGHER PROFESSIONAL EDUCATION
UFA STATE OIL

TECHNICAL UNIVERSITY

V.I.BABAKIN

Course of lectures on the discipline:

"Automated electric drive of standard

production mechanisms and technological

complexes."
Part 2.

Ufa 2007

1.AEP with asynchronous motor 4

1.1AEP with blood pressure with rheostatic regulation 4

1.2AEP with AKZD with adjustable voltage supplied to the stator AD 5

2. Current state of AED with AC motors 7

2.1 Problems of synthesis and control of AED 7

3. Automated asynchronous electric drive using synchronous

Electric machine frequency converters 9

4. Automated asynchronous electric drive using asynchronous

Electric machine frequency converters 11

5. Automated electric drive with an AC motor with static frequency converters (SFC) 11

5.1 Frequency converter with DC link 12

6. Autonomous inverters (AI)……………………………………………………………… 13

7. AEPT with a state of emergency having a controlled rectifier in its structure………………………….14

8.Speed ​​regulation in AED with inverter with HC……………………………………………………………… ...17

9. Start-up in an AEP with an inverter with a shock wave………………………………………………………………………………………… …18

10. Braking in an AED with a shock………………………………………………………………… ..19

10.1.Braking by counter-switching (TC)……………………………………………………………………..19

10.2.Dynamic braking……………………………………………………………… 19

10.3.Reverse…………………………………………………………………………………. ..20

11.Advantages and disadvantages of AED with IF with HC…………………………………………… .20

12. Automated electric drive using an inverter with WID……………… ….20

13.Speed ​​regulation, starting and braking in AED with WID…………………………… ...21

13.1 Speed ​​control in AED with WID……………………………………………………………… …21

13.2 Start-up in AEP with WID……………………………………………………………… ….22

13.3 Braking in AED with WID………………………………………………………………………………… 22

14 Automated electric drive using PWM inverter…………………...22

15 Operating principle of PWM inverter……………………………………………………………..23

16 Schematic diagrams of inverter with PWM………………………………………………………24

17 inverter with PWM based on non-lockable thyristors…………………………………………......25

18 Element base of modern frequency converters……………………………...26

18.1 Power filters…………………………………………………………………………………27

18.2 Characteristics of modern powerful power switches with double-sided heat sink

19 Circuit diagrams of the inverter based on IGBT transistors……………………………………...29

20 Speed ​​control in AED with PWM inverter……………………………………………………………….29

21 Start-up in an AED with an inverter with PWM…………………………………………………………………………………..29

22 Braking in an AED with an inverter with PWM………………………………………………………..29

23 Emergency modes in AED with inverter with PWM……………………………………………………………29

24 Influence of the length of the installation cable on overvoltages at the motor terminals……….30

25 Principles and fundamentals of vector control……………………………………………...34

26 Implementation of vector control………………………………………………………..36

27 Automated AC electric drive with direct conversion

Vanium frequency (NCF)…………………………………………………………………… ..38

28 Automated AC electric drive in cascade circuits………….40

29 Automated electric drives with electric electric machine cascades………………………………………………………………………………………………………… 42

30 Automated electric drives with electromechanical electric machine cascades…………………………………………………………………………………………………………..43

31 Automated electric drives with asynchronous valve cascades (AVC).44

32 Automated AC electric drives with dual power supply machines

Niya………………………………………………………………………………………. .45

33 Automated AC electric drives with dual power machines in synchronous mode………………………………………………………………………………… 46

34 Automated AC electric drives with dual power supply machines

Niya in asynchronous mode………………………………………………………………..48

35 Automated AC electric drives with valve motors ...50

36 Automated AC electric drives of servo type……… …….52
1. AED with an asynchronous motor
1.1 AED with blood pressure with rheostatic regulation.

These circuits are used for IMs with a wound rotor.

Operating principle: By changing the active resistance of the rotor circuit, we thereby influence the sliding, and the angular velocity changes.

One of the most important indicators quality of regulation – smoothness. In this case, it depends on the number of stages of additional resistance introduced into the rotor circuit, which in turn is limited by standard control equipment using relay contactor circuits. An increase in the number of stages will entail an increase in the number of relays and contacts, which in turn will lead to a decrease in the speed and reliability of the system as a whole. In addition, such electric drives have low energy indicators, low efficiency in the field of deep regulation, and with a significant increase in additional resistance, the rigidity of the characteristic sharply decreases, which will affect the stability of the electric drive.

In order to increase the smoothness of regulation, pulse parametric control is used. The essence of this method is to alternately introduce and remove additional resistance in the rotor circuit, with the average value being:

where t 1 is the duration of the closed state of the key;

T 2 - duration of the open state of the key.

Fig.2

ω will change smoothly in the range between two boundary characteristics ε=1 and ε=0

The range of speed control in electric drives with rheostat control is limited to:

1. 
   Large power losses (low efficiency)
2. 
   Low stability (D=1.5÷1).

• 
  pulsed;
• 
  continuous.

Until recently, pulse control methods were mainly used.

The simplest circuit diagram of pulse control:
Fig.3
In this case, the frequency of closing and opening is commensurate with the network frequency f ≤ 200 Hz. When the duty cycle of control pulses changes, the effective voltage value changes:
When ε=1, the engine operates at a natural mechanical characteristic, while the keys K are constantly closed. As ε decreases, the angular velocity decreases. At the same time, the critical moment M KR decreases, as a consequence of which the overload capacity (rigidity) of the working part decreases mechanical characteristics. At small duty cycle values, i.e. At low speeds the drive is unstable.

Flaws:

• 
  Low energy performance, which is associated with an increase in voltage and speed, as well as with transient electromagnetic processes caused by turning on and off the stator windings of the motor.
• 
  Such electric drives can only operate in continuous mode, because do not provide short-term starting and stopping of the engine.

The KN is turned on during the off-state intervals of the KV keys, with ε=0 pulses controlling the KV keys. The electric drive will operate in counter-switching braking mode. The family of mechanical characteristics in such electric drives will be more rigid in the working part (overload capacity is lower).

The difference in mechanical characteristics between pulse voltage regulation and pulse phase rotation (in the working part the electric drive operates more stably). At very small values ​​of ε, the characteristics move into the region of back-on braking, which allows you to quickly stop the engine. Such electric drives are for intermittent and short-term modes, but these electric drives have even lower energy indicators, because the superposition of motor and braking modes causes almost continuous electromagnetic transient processes, accompanied by large power losses.

Flaws:

A decrease in supply voltage at constant power on the motor shaft will lead to a decrease in the voltage at the rotor terminals, an increase in the rotor current, a decrease in the engine power factor and a decrease in efficiency.

Quality indicators:

1. 
   Low energy levels;
2. 
   Low regulation stability:
3. 
   Regulation range D=1.5÷1;
4. 
   Smoothness is high;
5. 
   The direction is single-link “down”;

Currently, electric generators with continuous voltage regulation are widely used:

• 
  RN-BP;
• 
  TRN-AD.

^ Advantages of EP using the TRN-AD system: In terms of initial costs, it is 30-40% cheaper than an electric drive with a frequency converter; Maintenance costs are reduced by 20-50%.

^ Disadvantages of EP according to the TRN-AD system: Low regulation range D=2÷1.

This drawback, to some extent, can be eliminated by using an AED with an adjustable EMF in the stator winding, i.e. regulating not voltage, but EMF.

^ 2. Current state of AED with AC motors.

2.1 Problems of synthesis and control of AED.
Control object –

1. 
   ED (electromechanical converter);
2. 
   SP (power electrical converter);
3. 
   IP (measuring transducer).

1) ED(electromechanical converter).

The widest class of electric motors used in modern electric drives AKZD for general industrial use. These motors are intended for use in adjustable electric drives, for direct connection to an industrial network. Basically, changes in this area are in the nature of some design improvements to the electric motor. Special modifications of ACPDs are being developed and mass-produced for use in variable-frequency electric drives (Siemens has been developing and mass-producing ACPDs for five years for use at low and high power supply frequencies of 500-1000 Hz). In addition, there is an increase in the production of LEDs with excitation from permanent magnets (non-contact). These EDs have improved weight, size and price indicators, and are not inferior in terms of technical and energy indicators. Among the promising electric motors is an induction motor, which, according to the developers, has significantly better technical and energy characteristics and requires a very simple power converter (the cost of the electric drive is much lower). A synchronous reluctance electric motor has weight and size indicators that are in the range between AD and SD and at the same time significantly higher energy efficiency at a significantly lower cost.
2) SP(power electrical converter);

In the field of joint ventures in electric drives with DC motors, converters with a rectifier structure - AIN are currently mainly used. Moreover, if until 2000 the requirements for the quality of rectification were not regulated, now a number of regulatory documents have appeared that strictly regulate the presence of rectifier devices in the structure of joint ventures. These are IEEE-519, IEC555 standards - integration standards; GOST 13109. To improve the quality indicators of modern joint ventures, in particular to improve the quality of power consumption, namely increasing the power factor, rectifiers on fully controlled power switches with output voltage stabilization are currently used. Circuits with additional inductance and circuits with a switching input switch are implemented using smart technology. However, joint ventures with uncontrolled rectifiers seem to be more efficient and cheaper. The JV currently uses a modern base that uses modern electronic devices such as MGT or IGST thyristors and fully controlled IGBT transistors. In addition, transistors with a voltage resolution of 6-10 kV are currently being developed.

Currently, the most promising mode of operation of the joint venture is the high-frequency PWM mode with a modulation frequency of 20 kHz and vector control (action through the torque-forming and flux-forming components of the stator current). This mode is most favorable for motors with a rated frequency of 500-1000 Hz because in this case, the problem of matching the modulation frequency with the frequency of the voltage supplying the motor is solved much easier. At present, a promising type of joint venture is also the NPC, which has a matrix structure with a matrix control system. The advantage of such converters is the absence of reactive elements, i.e. capacitances and inductances in the power circuit, almost sinusoidal shape of the output voltage and current, as well as the ability to operate in the leading cosφ mode.
3) IP(measuring transducer).

Traditionally known means are currently used as primary meters, which include commercially produced current and voltage sensors, Hall sensors, tachogenerators, photopulse and code displacement and position sensors, electromagnetic revolvers, synchronizers, etc. The volume of use of such modern sensors as capacitive and laser is practically zero. The most promising type of MT are indirect meters, in which, based on easily measured parameters, such as active and inductive reactance of the motor, speed and position of the rotor, etc. When using such measuring systems, there is no need to use a large number of sensors and, in particular, a rotation speed sensor. Such measurement systems are called sensorless.
^ Electric drive control tasks:

The most common type of control problem is the problem of direct regulation of the rotation speed of the electric motor. In addition, there are specially adjustable drives that perform the tasks of regulating electromagnetic torque, power, acceleration, regulating the rotor position, and regulating any technological parameter. In addition, there are tasks of stabilization, tracking, positioning, ensuring invariance (consists of ensuring independence or weak dependence on uncontrolled disturbances), ensuring autonomy (ensuring the independence of any parameter of the object from other parameters).

Synthesis of ED control comes down to finding a sufficiently conditioned ED model, which currently represents in most cases a system of Kirchhoff equations according to the second law of electromagnetic circuits of ED and SP. Typically, these equations are written for an equivalent two-phase machine, as well as a system of Newton's equations for mechanical electric circuits.

The main problem when creating an ES model:

• 
  Taking into account the saturation of the motor magnetic circuit;
• 
  Accounting for elastic mechanical connections;
• 
  Accounting for nonlinear connections.

There are two types of electric machine inverters:

1. 
   Electric machine synchronous frequency converter (EMSFC);
2. 
   Electric machine asynchronous inverter (EMAC).

AEP with electric machine frequency control.

The main element of such a system is a three-phase synchronous generator matched in power to the drive motor. In this case, the output voltage and frequency are determined by the angular velocity of the generator shaft and the magnitude of the excitation magnetic flux. When the speed changes, the output voltage will change. If we take the voltage at the stator winding phase terminals, it is obvious that when Ф=const with an increase in the shaft rotation speed, simultaneously with an increase in frequency, the effective value of the output voltage will also increase. In this case, only the proportional control law can be implemented.

Fig.6

The PC includes:

• 
  The main link is a three-phase synchronous generator (G2);
• 
  DPT NV (D2) output G-D systems connected via a shaft to the SG;
• 
  Auxiliary drive motor AKZ (D1) with unregulated speed.

• 
  
• 
  Low efficiency, high cosφ;
• 
  P mouth min = 400%

Advantages of AED with ESP:

• 
  
• 
  Easy to control.

• 
  Disadvantages of AED with ESPC:
• 
  Low efficiency;
• 
  
• 
  
• 
  The ability to regulate only according to the proportional law.

^ 4. Automated asynchronous electric drive using asynchronous electric machine frequency converters.
The main element of such a system is a three-phase asynchronous generator matched in power to the drive motor.

Fig.7

Quality indicators:

• 
  Regulation is two-zone, smooth, stable;
• 
  Low efficiency, high cosφ;
• 
  P mouth min = 200-400%

Advantages of AED with ESP:

• 
  No negative impact on the network;
• 
  Easy to control.

Disadvantages of AED with ESPC:

• 
  Low efficiency;
• 
  The presence of a large number of rotating parts;
• 
  Unsatisfactory weight and size indicators;
• 
  Possibility to regulate by any law.
• 
  The need to use autotransformers.

HRO is classified according to the following criteria:

1. 
   According to the structure of energy conversion.

• 
  HRC with direct conversion.
• 
  VHF with DC link.

1. 
   By type of inverters they are divided into:

• 
  Inverters with grid-driven inverters.

• 
  Inverter with autonomous inverter

• 
  IF with AIN
• 
  IF with AIT
• 
  Inverter with AI with alternating commutation (inverter with incomplete control voltage)
• 
  AI inverter with individual switching (inverter with full control voltage)

^ 5.1 Frequency converter with DC link
Currently, this type of frequency converters is the most widespread type, and, unlike NP+Ch, it is supplied as an independent element of the electric drive.

Fig.8

Where U 1 is a three-phase alternating voltage with constant amplitude.

P 1 – controlled or uncontrolled rectifier, which is designed to convert the input sinusoidal voltage into an output constant (pulsating) voltage.

F – current or voltage filter is designed to smooth out ripple from the rectifier output.

P 2 – autonomous current or voltage inverter, designed to convert smoothed direct current or voltage into three-phase alternating current.

M – three-phase AC motor with a squirrel-cage rotor.
In the proposed block diagram, block P 1 can operate in both controlled and uncontrolled modes. In this case, in the first case, the AI ​​performs the functions of changing only the output frequency of the converter, and the functions of influencing the amplitude of the output voltage are performed by the rectifier. In the second case, the AI ​​performs the functions of changing the output frequency and the effective value of the output voltage.

The HC option has an undoubted advantage, namely, a significant simplification of the control system, despite the presence of a control unit. At the same time, the entire system is significantly cheaper.

In the case of the NV option, the compatibility of the entire system with the electrical network is significantly improved. However, in this case, the control scheme becomes significantly more complicated and, accordingly, the entire system becomes much more expensive.
^ 6. Autonomous inverters (AI).
According to the degree of controllability, AIs are divided into:

• 
  AI with alternating switching.
• 
  AI with individual switching.

Let's consider the principle of operation of an AI with alternating switching using the example of a single-phase AI in which the power switches are locked using a switching capacitor.

T 1,T2 – working thyristors

Let at time t = 0 T2 be open, T1 be closed; the input voltage is applied to Rн2, after a time interval equal to the switching period T2, an unlocking pulse is applied to T1. In this case, the input voltage is applied to Rn1, and through the open circuit T1, Rn1, Rn2, a reverse voltage with Sk is applied to T2, as a result of which T2 is locked, etc. Switching period is the duration of opening the key.

According to the shape of the output voltage and current, Ai is divided into: For AIT, the shape of the output voltage depends both on the sequence and duration of switching of the power switches and on the nature of the load, and the shape of the output current depends only on the sequence and duration of switching of the power switches.

With AIN, the shape of the output current depends both on the sequence and duration of switching of the power switches and on the nature of the load, and the shape of the output voltage depends only on the sequence and duration of switching of the power switches.

External difference between AIT and AIN: AIT has an input L - filter, and an input L or LC filter. In addition, if the inverter circuit uses incompletely controllable power switches, then there is one capacitor for each phase of the AIT, while the AIT has one switching capacitor for each power switch.

Let's consider the operation of a single-phase AIT.

T1, T3 – power switches of the anode group

T2, T4 – power switches of the cathode group

S K – switching capacitor

L – input filter.
At the first moment of time, two cross-lying power switches are in the open state - the first from the anode group, the second from the cathode group. At the moment the other two power keys are unlocked, the first two are locked, etc. Moreover, if the keys T3 and T2 are open, the capacitor is charged in the forward direction; when the keys T1 and T4 are open, the capacitor is recharged in the opposite direction.

Fig.11

At time t = 0, an unlocking pulse is sent to T1 and T4. the capacitor Sk at this moment is pre-charged, and when T1 and T4 are unlocked, it discharges to T3 and T2 in the direction of negative polarity, thereby closing T3 and T2. in the next period of time equal to the switching period T1 and T4, the current through the load resistance will flow in the positive direction. After a period of time, the capacitor is recharged in the opposite direction. At this moment, an unlocking pulse is applied to T3 and T2, the capacitor is discharged in the direction of negative polarity, locks T1 and T4, the current flows through T4, Zn, and open T2 and will have a negative direction.

^ 7. AEPT with a state of emergency having a controlled rectifier in its structure.
Currently, there is a tendency to expand the scope of application of controlled rectifiers in the inverter structure, in particular in those electric drives that, due to technological conditions, require frequent braking (i.e. for an electric drive operating in intermittent mode S5). This is due to the fact that carbon fiber has such an important property as two-way conductivity. This allows the use of such an energy-efficient type of braking as regenerative. But the negative properties of hydrocarbons cannot be completely eliminated. Currently, converters are used that contain two input blocks: the first is an uncontrolled rectifier that participates in the operation of the drive in motor mode; the second is the shock wave, which participates in the operation of the inverter in braking mode.

Let's consider the circuit and principle of operation of an inverter with a thyristor HF and a thyristor AIT, in which switching of power switches is carried out using switching capacitors.

-Fig.12

The input block of the converter is a shock wave, built using a six-cycle bridge three-phase rectification circuit. The main function of the CF, in addition to rectification, is to regulate the effective value of the output voltage of the converter. To smooth out the ripple of the rectifier output current, a series L-filter is used.

AIT consists of six power switches, three of which T1, T3, T5 have a common anode and form an anode group; the other three T2, T4, T6 have a common cathode and form a cathode group. The operating principle of AIT is based on the fact that at the first moment of time there are two cross-lying power switches in the open state: one from the anode group, the second from the cathode group. Unlocking of power keys is carried out at the moment of supply of control pulses from the BUI (multi-channel control system). In this case, the sequence of pulses supplied to each valve corresponds to their serial number. The power switches are locked when any of the three capacitors are discharged in the direction of negative polarity and also corresponds to the order of alternating power switch numbers.

At output frequency f 2 = 50Hz the converter operates in the following mode: the interval between two adjacent control pulses is
, the duration of opening each key will be 120 0. In this case, the locking capacitors C1, C2, C3 must have such a capacity that a time equal to 60 0 holds the charge necessary to lock the next key.
We demonstrate the operation of the converter using a diagram:

1. 
   The current from the rectifier output has an ideal rectified shape.
2. 
   Direction of currents in the phases of the converter-motor installation cable
   • 
     from P to D - positive.
   • 
     from D to P - negative.

1. t = 0 Open T1, T6. The circuit current flows through the power switch T1, phase A of the cable and through open T6 returns to phase C. In this case, C3 is pre-charged, in the time interval 0-60 0 C1 is recharged, and C3 retains its charge.

2. t = 60 0 An unlocking pulse is sent to T2. In this case, C3 discharges onto T6 and locks it. In the time interval 60 0 - 120 0 T1 and T2 are open. Current flows through phase A to the motor, and through phase B from the motor to the converter. . During this period of time, C2 is recharged, C1 retains its charge.

3. t = 120 0 An unlocking pulse is sent to T3. In this case, C1 discharges onto T1 and locks it. In the time interval 120 0 - 180 0 T2 and T3 are open. Current flows through phase B to the motor, and through phase C from the motor to the converter. . During this period of time, C3 is recharged, C2 retains its charge.

4. t = 180 0 An unlocking pulse is sent to T4. In this case, C2 discharges onto T2 and locks it. In the time interval 180 0 - 240 0 T3 and T4 are open. Current flows through phase B to the motor, and through phase A from the motor to the converter. . During this period of time, C1 is recharged, C3 retains its charge.

5. t = 240 0 An unlocking pulse is sent to T5. In this case, C3 discharges onto T3 and locks it. In the time interval 240 0 - 300 T4 and T5 are open. Current flows through phase C to the motor, and through phase A from the motor to the converter. . During this period of time, C2 is recharged; C1 guards its charge.

6. t = 300 0 An unlocking pulse is sent to T6. In this case, C1 discharges onto T4 and locks it. In the time interval 300 0 - 360 T5 and T6 are open. Current flows through phase C to the motor, and through phase B from the motor to the converter. . During this period of time, C3 is recharged; C2 guards its charge.

To increase the output frequency it is necessary to reduce the gap between control pulses; for this we increase the control angle β. Accordingly, with the control law, the effective value of the output voltage will change, in particular, with a proportional control law, as the frequency increases, the rectifier control angle α will decrease in proportion to the increase in angle β.

A significant drawback of the considered circuit is the need to use high-power capacitors necessary to maintain charges in the interval between two switchings. The use of AIs with cut-off diodes can partially get rid of this drawback.

Fig.14

Here, in the cathode and anode circuits of the power switches, cut-off diodes D1, D3, D5 and D2, D4, D6 are connected in series. Their number is equal to the number of keys. These diodes prevent the discharge of capacitors during the switching period of the switch and due to this significantly improve the readings of the inverter.

^ 8. Speed ​​control in an AED with an inverter with a shock wave.
In an AED with a frequency converter and a controlled rectifier in its structure, speed control ω is carried out in a wide range, while ensuring fairly high quality indicators. Regulation of ω is carried out by influencing the AI ​​with the help of a control device while simultaneously influencing the shock wave with the help of a control device in accordance with the regulation law. In this case, two-zone regulation is possible. However, for mechanisms with M C = const, and for mechanisms with linearly increasing M WITH upward regulation is limited by the fact that it requires simultaneous increase in frequency relative to f NOM, increase tension. As a result, an insulation breakdown may occur. Regulation of ω up is used much less frequently than in the down range and in small ranges.

In general, the family of control characteristics will have the form:

Fig.15
Regulation quality indicators:

1. 
   Stability during frequency regulation is high because characteristics in the working part have the same rigidity.
2. 
   Smoothness is practically unlimited.
3. 
   High efficiency, however, with deep regulation down from the fundamental frequency, which requires a significant reduction in the control angle α of the rectifier and the power factor of the drive as a whole can be very low.
4. 
   Regulation is mainly carried out when M C = const on the motor shaft.
5. 
   The direction is two-zone, downward regulation is mainly used.
6. 
   Regulation range D=100÷1.

^ 9. Start-up in an AED with an inverter with a shock wave.
Starting begins at a reduced voltage and at a minimum frequency, which accordingly ensures the absence of current inrush or minimization of current and at the same time large starting torques. In this case, the inverter operates with long switching periods of power switches, and the HC with a control angle α = P/2. The energy efficiency of start-up in such a system is reduced due to the fact that at the beginning of start-up the drive consumes a large amount of reactive component.

Fig.16