SU1636980A2 - Ac electric drive - Google Patents

Abstract

The invention relates to electrical engineering and can be used in electric drives with an asynchronous electric motor supplied from a transistor inverter with a pulse-width principle of frequency variation in cases when the motor switches to generator mode during deceleration. The aim of the invention is to increase reliability when braked from the maximum speed to a full stop. For this purpose, the AC drive is provided with a voltage sensor 22, a differential amplifier 23, a comparator 20, a voltage adjuster 25 connected in series with the current sensor 27, a recovery transistor switch 26 and a recovery resistor 28 connected in parallel with the sensor 22 voltage, two-input adder 32, on the first input and output connected between the output of the second smoothing filter 15 and the inputs of the integrator 17 and the zero-body 16, connected in series by the node 29 galvanich By a decoupling, a precision rectifier 30, a smoothing filter 31. An output connected to the second input of the adder 32. The inputs of the galvanically isolated node 29 are connected to the outputs of the current sensor 27 and the generator 9 rectangular pulses. The first input of the comparator 20 is connected via the differential amplifier 23 to the output of the voltage sensor 22, the second input of the comparator 20 is connected to the output of the voltage setting device 25, and the output is connected to the control input of the transistor regen 26. 1 il. About w ON O 00 S3

Description

The invention relates to electrical engineering, can be used in electric drives with an asynchronous electric motor, powered by a transit inverter With a pulse-width principle of frequency variation, in cases when the motor switches to generator mode during deceleration, and is an improvement of the invention according to the author. St. No. 1443074.

The purpose of the invention is to increase the reliability of operation when braking from the maximum speed to a full stop.

The drawing shows a diagram of the AC drive.

The AC drive contains power transistor switches 1.1-1.6, forming a transistor inverter 2, a power input connected to the output of the rectifier 3t, which is connected to the generator 4, a three-phase asynchronous motor 5, the stator winding of which is connected to the output of the transistor inverter 2, the power transistor the keys 1.1 - 1.6 of which are connected via the corresponding electronic keys 6.1 - 6.6 to the outputs of the inverter control unit 7.

A current sensor 8 is connected to the rectified current circuit, the output of the generator 9 rectangular pulses is connected to one input of the first galvanic isolation node 10, the other input of which is connected to the output of the current sensor 8, and the output of node 10 to the input of the first precision rectifier 11, the output of which is connected via the first smoothing filter 12 to the first input of the first comparator 13, the output of which is connected to each of the control inputs of the electronic keys 6.1-6.6.

The current limiter setpoint 14 is connected to the second input of the first comparator 13, the output of which is connected via the second smoothing filter 15 to the first input of the second adder, the output of which is connected to the inputs of the zero-body 16 and the integrator 17 with a reset.

The output of the current limiter setting device 14 is connected to the input of the first adder 18, the second input of which is connected to the response time setting device 19, the output of which is connected to the first input of the second comparator 20, the second input of which is connected to the output of the integrator 17 with a reset, the reset input of which is connected to the output null organ 16.

The output of the comparator 20 is connected to the control input of the three-phase disconnector 21, through which the input of rectifier 3 is connected to the output of generator 4. At the output of rectifier 3, an add-on sensor 22 is connected, the output of which is connected through a differential amplifier 23 to the first input of the third comparator 24, the second input of which is connected to the output of the voltage setting device 25, and the output is connected to the control input of the transistor recovery switch 26. At the output of the rectifier 3 in parallel with the voltage sensor 22, the voltages are connected in series between

0 is a second current sensor 22, a transistor switch 26, and a recovery resistor 28.

The generator 9 rectangular pulses connected to one input of the second node 29

5 galvanic isolation, the other input of which is connected to the output of the second current sensor 27, and the output to the input of a precision rectifier 30, the output of which through the third smoothing filter 31 is connected to

0 the second input of the second adder 32.

The AC drive operates as follows.

During normal system operation: transistor inverter 2 - rectifier 3 5 generator 4 current from generator 4 flows through three-phase breaker 21, rectifier 3, first current sensor 8, lower power transistor switches 1.2, 1.4 or 1.6 transistor inverter 2, three-phase asynchronous electric motor 5 and upper power transistor switches 1.1, 1.3 or 1.5 transistor inverter 2.

A voltage proportional to the current of the electric motor 5 flowing through

5, the transistor inverter 2 is removed from the first current sensor 8 and through the first galvanically isolated node 10, the first precision rectifier 11 and the first smoothing filter 12 is fed to the first

0 a comparator 13 with an adjustable current limiter 14 of the current limit level and a response threshold.

The node 10 galvanic uncoupling is required for unlocking high potential on

5 buses rectifier from the low potential of the control part of the transistor inverter 2. The voltage from the first Vtok sensor modulates the high-frequency voltage

0 is the generator output of 9 rectangular pulses whose frequency is, for example, 100,000 Hz.

At the output of the first galvanic isolation node 10, a two-pole modulated signal is obtained, the amplitude of which is proportional to the voltage taken from the first current sensor 8.

After straightening the first precision rectifier 11 and smoothing the first smoothing filter 12 a single-polar signal proportional to the motor current is fed to the first input of the first comparator 13. From the first comparator 13 the relay signal goes to the control inputs of the electronic keys 6.1-6.6, which control the passage of the signal from the inverter control circuit 7 to the power transistor switches 1.1 to 1.6 transistor inverter 2.

When the engine is loaded, a current surge occurs on the shaft, as measured by the first current sensor 8. At the same time, the voltage at the first input of the first comparator 13 exceeds the response threshold set by the setting device 14 of the current limit, set to an acceptable value less than the emergency current, the first comparator 13 operates and issues a closing signal to the electronic switches 6.1-6.6, which remove the control signal power transistor switches 1.1 - 1.6 transistor inverter 2. The current decreases sharply and the first comparator 13 returns to its initial state, while removing the close signal from the electronic switches 6.1 - 6.6. As a result, in a closed circuit formed by the first current sensor 8, power transistor switches 1.1-1.6, rectifier 3, three-phase breaker 21 and generator 4, a self-oscillating process occurs at a high frequency, for example 3000 Hz, current limiting transistor inverter 2 is at the level set by the current limiter 14.

Continuous (more than 3 - 5 s) flow through transistor switches 1.1 - 1.6 transistor inverter 2 of a limited current, usually having a value of 0.7 - 0.9 of the maximum allowable current value of transistor inverter 2, with a switching frequency equal to the frequency of self-oscillations in the circuit current limitations, for example, 3000 Hz, can lead to the heating of power transistor switches 1.1 - 1.6 and to their thermal breakdown.

To limit the duration of operation of the device, the current limiting level is 3-5 seconds in case of emergency situations, the AC electric drive contains an integral protection circuit, i.e. limiting the time of operation of the current-limiting device with the subsequent disconnection (for example, in 3-5 sec) of the transistor inverter 2 from the generator 4, consisting of the second smoothing filter 15, the second adder 32, the zero-organ 16, the integrator 17 with a reset, the first adder 18, the second comparator 20, the setting device 19 of the response time and the three-phase breaker 21.

In case of emergency in the operation of the electric motor 5, the relay signal from the first comparator 13 with a frequency of, for example, 3000 Hz, is smoothed by the second smoothing signal.

filter 15 and through the second adder 32 is fed to the input of the zero-body 16 and to the input of the integrator 17. In the absence of a signal at the output of the second smoothing filter 15 and respectively at the output of the second summator 32, the zero-body 16 outputs a signal to the input of the integrator 17 As a result, the integrating capacitance is ehuntied with low ohmic resistance and the voltage at the output of the integrator 17 is absent. When a voltage appears at the output of the second smoothing filter 15 and respectively at the output of the second adder 32, the zero body 16 removes the Reset signal from the integrator 17, which starts

0 integrate the input voltage with a given time constant. The voltage from the output of the integrator 17 is fed to the first input of the second comparator 20, the second input of which receives the voltage from the stroke of the first adder 18, which determines the threshold of the second comparator 20, i.e. response time of current limiting device

0Pressure formed first

the adder 18 depends on the initial time setting set by the response time setting unit 19, as well as on the magnitude of the current limit level.

5The initial setting of the device response time is set by the response time setting unit 19, for example, 3 to 5 seconds, with a current limit level set by the current limit level setting unit 14,

0 equal to 0.7 of the maximum allowable current for power transistor switches 1.1 - 1.6 transistor inverter 2. With an increase in the current limit more than 0.7 from the maximum allowable current for power transistor switches 1.1 - 1.6 transistor inverter 2, the device operation time is proportionally reduced i.e. the trigger threshold of the second comparator 20 is reduced.

0 When the signal from the integrator 17 is exceeded with the reset threshold of the second comparator 20, the latter triggers and outputs a signal to the control input of the three-phase breaker 21, which disconnects the transistor inverter 2 from the generator 4.

When the electric motor 5 of the AC drive operates with a greater inertial load, the kinetic energy stored in the load when the engine is braked,

goes into the capacity of the filter rectifier 3 in the form of voltage jump, as the engine goes into generator mode.

The greater the inertial load on the shaft of the electric motor 5 and the sharper the deceleration of the motor rotating at maximum speed occurs, the greater the increase in voltage on the filter capacity of the rectifier 3.

A sharp increase in the voltage on the buses of the rectifier 3, as well as the transistor inverter 2, can lead to a breakdown on the voltage of the transistors in the power transistor switches 1.1 to 1.6 of the transistor inverter 2.

To limit the voltage surge during engine braking with inertial load 5, there is a voltage limiting circuit on the filter capacitor 3, consisting of a voltage sensor 22, a differential amplifier 23, a third comparator 24, a transistor switch 26 and a recovery resistor 26.

Voltage sensor 22 continuously measures the voltage on the buses of the rectifier 3, and part of this voltage, proportional to the voltage on the tires, is removed from it by a differential amplifier 23, which simultaneously serves as a galvanic isolation between high potential on the buses of the rectifier 3 and the low potential of the control circuit of the transistor switch 26, which includes the third comparator 24 and the voltage adjuster 25.

From the output of the differential amplifier 23, a voltage proportional to the voltage on the buses of the rectifier 3 is fed to the first input of the third comparator 24, to the second input of which voltage is supplied from the voltage setting unit 25, which determines the threshold of the third comparator 24. the nominal rectifier 3 busses (for example, up to 350 V at the nominal rectifier voltage of 310 V), the voltage at the output of the differential amplifier 20 is less than the response threshold of the third comparator 24 The sensors 25, a voltage signal at the output of the third comparator 26 closes the transistor switch recovery.

When the voltage on the rectifier buses 3, which occurs when the engine 5 goes to the generator mode when braking increases, the voltage from the output of the differential amplifier 23 exceeds the threshold of the third comparator 24, which, having triggered, generates a signal to OTKPJ

power transistor switch 26, which creates a circuit to discharge the capacitor-filter rectifier 3 through the regeneration resistor 28.

In this case, the regeneration resistor 28 is the load for the electric motor 5 operating in a generator mode when braking, which contributes to the reduction of the braking time.

0 When reducing the voltage from the output of the differential gain of the amplifier 23, due to the rapid discharge of the filter capacity of the rectifier 3 with a large current through the opened recovery key 26 and

5, a regeneration resistor 28, below the operation threshold set by the voltage selector 25, the third comparator 24 returns to its initial state and turns off the recovery transistor switch 26. If the electric motor 5 is still in the generating mode, the voltage on the rectifier 3 tires rises again.

Thus, in a closed circuit formed by the rectifier 3, the sensor 22

5, a differential amplifier 23, a third comparator 24, a second current sensor 27, a recovery transistor switch 26 and a recovery resistor 28, a self-oscillating process occurs with

0 by a high frequency, for example 2000 Hz, the voltage limits on the buses of the rectifier 3 at a predetermined voltage level of 25,

To limit the operating time of the system, limiting the voltage in the most unfavorable case (braking the electric motor 5 from the maximum speed at maximum inertial load), for example, less than 1 s,

0 uses an integral protection of the voltage limiting system, consisting of a second current sensor 27, a second galvanic isolation node 29, a second precision rectifier 31, a third smoothing filter 31 and working in conjunction with the integral protection of a transistor inverter 2 consisting of the second smoothing filter 15, the second adder 32, the integrator 17 with a reset, zero-body 16,

0 of the second comparator 20, the first adder 18, the response time setting knob 19, the current limiter setting knob 14 and the three-phase breaker 21.

A voltage proportional to the razart5 current flowing through the circuit of the second current sensor 27, the transistor recovery key 26 and the recovery resistor 28 is removed from the current sensor 27 and fed through the second galvanically isolated node 29 to the second precision rectifier 30,

The galvanic isolation node operates similarly to the galvanic isolation node 10 and a two-pole modulated signal is obtained at the input of the second precision rectifier 30, the amplitude of which is proportional to the discharge current. After this signal is rectified by the second precision rectifier 30 and smoothed by the third smoothing filter 31, it is fed to the second input of the second totalizer 32 consisting in the integral protection circuit of transistor inverter 2. When the motor 5 is braked to the second input of the second adder 32 respectively to the input an integrator 17 with a reset and a zero organ 16 is supplied with a signal from a voltage limiting system. When there is current through the second current sensor 27, which indicates the operation of the voltage limiting system, the null organ 16 removes the Reset signal from the integrating capacitor of integrator 17 with a reset, which begins to integrate the input signal with a given time constant. If there is a discharge current through a regeneration resistor 28 with a duration of, for example, more than 1.2-1.5 s, there is an emergency situation in the operation of the voltage limiting system (for example, a transistor breakdown in the transistor regen key 26) A three-phase disconnect switch 21 is activated, which disconnects rectifier 3 from generator 4.

Thus, increasing the reliability of an AC electric drive with a three-phase asynchronous electric motor with a strong increase in the voltage on the filter capacity of the rectifier is due to the relay self-oscillatory process of limiting the voltage at a given level by discharging

filter through active resistance with high current, and with analysis of the flow time of the discharge current through the active discharge resistance with the subsequent disconnection of the transistor inverter in case of a long flow of discharge current from the three-phase alternator.

Claims (1)

Claims of the invention AC electric power according to the author fsfe 1443074, characterized in that, in order to increase reliability during deceleration from maximum rotational speed to a complete stop, a voltage sensor connected at the output of the rectifier, a differential amplifier, a third comparator, a voltage adjuster, connected in series with the current sensor, transistor regen key and regeneration resistor connected at the output of the rectifier parallel to the voltage sensor, the second two-input adder at the first input and output connected between the output of the second Smoothing phi and the inputs of the integrator and the zero-organ, serially connected second galvanic isolation node, precision rectifier, third smoothing filter, output connected to the second input of the second adder, and inputs of the second electrical isolation node connected to the outputs of the second current sensor and rectangular generator pulses, the first input of the third comparator is connected via a differential amplifier to the output of the voltage sensor, the second input of the third comparator is connected to the output of the voltage setting device, and the output is connected with Aulus yuschim input transistor recovery key.