SU1365327A1 - Device for controlling revolutions of induction motor - Google Patents

Abstract

The invention relates to electrical engineering and can be used in electric drives for lifting machines and passenger elevators. The purpose of the invention is to increase the smoothness of controlling the rotational speed of an asynchronous electric motor. This goal is achieved by providing a change in the synchronous frequency of rotation of the asynchronous motor when using only one phase as the voltage synchronizing. In addition, the device, by changing the main harmonic, allows us to significantly expand the family of artificial mechanical characteristics at which stable operation of an asynchronous electric motor is possible within the limits of the step of discrete frequency control. 1 il. (WITH (/)

Description

WITH

ABOUT)

SP

WITH

HS

The invention relates to electrical engineering and can be used in electric drives for lifting machines and passenger elevators.

The purpose of the invention is to increase the smoothness of controlling the rotational speed of an asynchronous electric motor.

The drawing shows a block diagram of a device for adjusting the frequency of a vrash, asynchronous electric motor.

A device for controlling the rotational speed of an asynchronous motor 1 contains a non-reversible thyristor converter 2 of an alternating voltage, the input terminals of which are intended to be connected to a power source, and the output terminals to be connected to the stator winding of the motor 1, three units 3-5 of pulse-phase control with three each of the inputs are connected in series with a block 6 of forming rectangular pulses, the input of which is intended to be connected to the terminals of one of the phases and the neutral wire of the power source ani, counter 7 pulses with control and sync. inputs, the output of the block 6 of the formation of rectangular pulses connected to the clock input of the counter 7 pulses and the block 8 of the distribution of pulses with three pairs of outputs that are connected to the first and second inputs of the corresponding blocks 3-5 of the pulse-phase control, the outputs of which are connected to non-reversible thyristor converter 2 control electrodes,

The control inputs of the pulse counter 7 are connected to the outputs of the comparators 9-13, the number of which must correspond to the required number of discrete values of the rotation frequency, one input of each of the comparators 9-13 is connected to the output of the corresponding 14-18 reference voltage unit, and the other inputs of each of the comparators 9-13 are combined and connected to the output of the frequency setting knob 19.

The output terminal of the rotational speed sensor 20 mounted on the shaft of the electric motor 1 is connected to one of the inputs of the speed controller 21, to another input of which the output of the rotation speed setting device 19 is connected, and the output of the speed regulator 21 is connected to the third input of each

blocks 3-5 of pulse-phase thyristor control.

The device works as follows.

Block 6 of forming rectangular pulses, the input of which is connected to the terminals of one of the phases, and the Zero wire of the power source forms

pulse sequence, which is fed to the clock input of the pulse counter 7 with the control of the conversion factor. The pulses from the output of the pulse counter 7 are fed to the input of the pulse distribution unit 8, which is an annular counting circuit that forms two three-phase pulse systems with a shift of 120 e. hail and

displaced one relative to the other by 180 e. hail.

Both systems of impulses come respectively to the first and second inputs of blocks 3-5 of the pulse-phase

controlling the thyristors of the non-reversible thyristor converter 2. As a result, the control electrodes of the thyristors of the non-reversible thyristor converter 2 receive a frequency-modulated sequence of control pulses from the outputs of blocks 3-5 of the pulse-phase control. B.depending on the conversion factor of the counter 7 pulses

In a non-reversible thyristor converter switched by thyristors of 2 phases, a system of intermittent currents is formed, the first harmonic components of which create a rotating

a magnetic field with a frequency and order of phase following, corresponding to the modulation signal. Therefore, the asynchronous motor 1 operates at a synchronous rotational speed excellent

from the synchronous frequency of rotation on its natural characteristic.

The signals at the outputs of the block 14-17 reference voltages correlate with each other in proportion to the set

a discrete number of rotational frequencies. A rotational speed sensor 19 generates an analog reference signal that varies from zero to the highest reference voltage of one of the blocks.

14-18 reference stresses. At the same time, when the signal value of the task is reached at the inputs of the comparators 9-13 of one of the reference voltages, the corresponding

the comparator and its output signal changes its value from a high level (signal one) to a low (signal zero).

As a result, the logical combination of signals at the control inputs of the pulse counter 7 changes and, accordingly, its conversion factor changes, i.e. The discrete synchronous frequency of the rotation of the NIN of the asynchronous motor 1 varies.

When the reference signal changes within the range of stresses, respectively. corresponding to the neighboring values of the reference voltages of the blocks 14-18, for example, blocks 14 and 15, the logical combination of signals at the control inputs of the pulse counter 7 is kept and the synchronous frequency of rotation of the asynchronous motor 1 does not change, but since the reference signal at the control input the speed torus 21 is compared with the signal from the rotational speed sensor 20 of the asynchronous electric motor 1 and the resulting error is fed to the third input of each of the blocks 3-5 of the pulse-phase control of the non-reversing thyristors A 2, then it changes from the moment the frequency-modulated control pulses are applied to the thyristors of the non-reversible thyristor converter 2 and the voltage of the main harmonic on the motor 1 is changed

This makes it possible to obtain a family of artificial mechanical characteristics, in which the asynchronous motor 1 can be operated stably within the limits of the discrete frequency control step.

The proposed device provides the ability to smoothly control the rotational speed within each step of the discrete control of the asynchronous rotational frequency, at which the asynchronous motor can work steadily.

5 0 5 About

five

„

five

0

Claims (1)

Invention Formula A device for controlling the frequency of rotation of an asynchronous electric motor, comprising an irreversible thyristor AC voltage converter, the input terminals of which are intended for. connections to the power source, and the output terminals of the thyristor AC voltage converter are designed to be connected to the stator winding of the motor, three pulse-phase control units with three inputs each, connected in series to a rectangular pulse generation unit, the input of which is intended to be connected to the terminals of one from the phases and the neutral wire of the power source, a pulse counter with controllable and synchronizing inputs and a pulse distribution unit with three pairs of outputs that are connected us with first and second inputs of the corresponding blocks of pulse-phase control, whose outputs are connected to a s a control electrodes of the thyristors of the thyristor converter irreversibly, Otley. In addition, in order to increase the smoothness of the rotation frequency control, five comparators, five voltage reference blocks, a frequency frequency adjuster, a rotation speed sensor, and a speed controller are entered into it, the outputs of the comparators are connected to the control inputs of the counter pulses, one input of each comparator is connected to the output of the corresponding reference voltage block, and the other inputs of each of the comparators are combined and connected to the output of the frequency rotation speed setting device, the output of the rotation speed sensor is connected to one and input speed regulator of the torus, the other input of which is connected to the output setpoint rotational speed and the output speed regulator torus connected to the third input of the blocks to azhdogo pulsed fazovogs control thyristors. 3 -380B, 50ri4 G9 . f