SU1690162A1 - Method of control of rotation frequency of three-phase induction motor - Google Patents

Abstract

The invention relates to electrical engineering and can be used in an automated electric drive for frequency control of three-phase asynchronous electric motors for general industrial use. set engine speed, three hydrochloric system modulating voltages triangular shape with a frequency twice the frequency of the rectangular voltage. The switch thyristors, which transmit the positive and negative half-waves of the phase voltage, are opened in accordance with the polarity of the rectangular voltages of a lower frequency, and the control pulses to the thyristors are formed when the half-wave voltage coincides with the corresponding triangular voltage. Due to this, energy and control characteristics are improved and the drive is operated in a continuous mode in the low-frequency region of the output voltage. 2 Il. (Ls

Description

The invention relates to electrical engineering and can be used in an automated electric drive for frequency control of three-phase asynchronous electric motors for general industrial use.

The purpose of the invention is to expand the range of speed control and improve the energy performance of an electric motor.

FIG. 1 is a functional diagram of an apparatus for implementing a method for controlling rotational speed; on

FIG. 2 - time diagrams of currents and voltages, showing the operation of the device

An apparatus for implementing the method comprises a common control unit 1, units 2-4 of phase control and a power-less, low-voltage thyristor converter 5, consisting of three pairs of anti-parallel thyristors 6-8. A low-voltage converter 5 is connected between the power supply terminals and the asynchronous motor 9. The first output of the common control unit 1 is connected to the first inputs of the phase control units 2-4 outputs

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which are connected to the control electrodes peer thyristors 6-8. The second, third and fourth outputs of the common control unit 1 are connected to the second inputs of the first, second and third blocks 2-4, respectively, of the phase control. Phase control unit 2, as well as similar blocks 3 and 4, contains a transformer 10, two one-half-period rectifier 11 and 12, two comparison circuits 13 and 14, a reversible counter 15 with a digital-to-analog converter (D / A converter) 16 at the output, two AND elements -HE17 and 18, two amplifiers 19 and 20 of power, two pulse transformers 21 and 22 and an element NOT 23. The primary transformer 10 is connected to the corresponding phase of the supply network, and the secondary winding through one half-wave rectifiers 11 and 12 is connected to the first inputs circuits 13 and 14 comparison, the outputs of which The first inputs of the first and second elements are NOT-17 and 18, the outputs of which are connected to pulse transformers 21 and 22 through the respective power amplifiers 19 and 20, the outputs of which form the outputs of the phase control unit 2. The first and second inputs of the reversible counter 15 form the corresponding inputs of the phase control unit 2. The second input of the counter 15 is connected to the second input of the NAND 17 element directly and to the second input of the NAND 18 element NO 23. The common control unit 1 consists of a series-connected controlled oscillator 24, a frequency divider 25 and a pulse distributor 26, outputs which form the second, third and fourth outputs of block 1, the first output of which is formed by the output of the generator 24. The device operates as follows.

The frequency of the oscillator 24 (Fig. 2a) may vary depending on the magnitude of the voltage UBX arriving at its input. The pulses from the output of the generator 24 are fed to the inputs of the reversible counters 15 of the blocks 2-4 of the phase control and to the input of the frequency divider 25 (PM). From the output of DC 25 (Fig. 26), these pulses are fed to the input of the pulse distributor 26, at outputs A, B, C of which (Fig. 2, c, d, e) we have signals that ensure the operation of the phase control units 2-4. Consider the operation of the phase 2 control unit L (BUFA). The operation of blocks 3 and 4 of phase B control. C is similar.

If there is a high level at the output A of the distributor 26, the pulses from the output of the controlled generator 24 pass to the reversible village counter 15 and from its output

arrive at the input of the DAC 16, forming pulses of a lower frequency and a triangular shape (Fig. 2e). The triangular modulating voltage is applied to

inputs of circuits 13 and 14 of the comparison. The rectified phase voltage of the network is applied to the second inputs of the comparison circuits 13 and 14 (Fig. 2e). The one-half-voltage / voltage corresponding to the positive half-wave of the phase voltage of the network is fed to the input of the comparison circuit 13, and the one-half-full voltage corresponding to the negative half-wave of the phase voltage of the network is fed to the input of the circuit 14 compared to. At the moment of equality of the values of the modulating triangular shape and half-wave phase voltage at the inputs of the comparison circuits 13 and 14, a high uroz signal appears at their outputs. This signal from the output of the comparison circuit 13 goes to one of the inputs of the NAND element 17, and from the output of the comparison circuit 14 to one of the inputs of the NE input 18. If there is a high level at the output of the distributor 26, there is a high level at the second input of the element AND-NOT 17 and a low level (due to inverter 23) at the second input of the element AND-NOT 18. Therefore, the pulse only from the output of the element AND-NOT 17 through

0 a power amplifier 19 and a pulse transformer 21 turn on one of the counter-parallel thyristors 6, which transmit one-half-phase phase pulses

5 of positive polarity (Fig. 2g).

If the output A of the distributor 26 is low, the signal at the second input of the NAND 17 element has a prohibiting low voltage level, and on the second input of the NAND 18 element, on the contrary, we have a high signal level. Therefore, pulses from the output of the comparison circuit 14 pass the AND-NE.18 element, the pulse amplifier 20, the pulse transformer 22 and

5, a second of two anti-parallel thyristors 6 is switched on, which transmits one-half-phase negative polarity phase pulses (Fig. 2g).

Thus, the method of regulation allows, in comparison with the prototype, to improve its energy and control characteristics and to ensure the operation of the electric drive in the long-term mode in

Claims (1)

5 low frequency output voltage. Claims of Invention A method for controlling the rotational speed of an asynchronous three-phase electric motor. each winding of which is connected to the corresponding phase of the re phase supply network through a pair of anti-parallel thyristors, in which a three-phase system of rectangular voltage of a lower frequency, corresponding to a given motor rotation frequency, is formed, and for each thyristor pair, control pulse sequences are formed, distinguished by the fact that, in order to expand the range of controlling the rotation frequency and improve the energy performance of the electric motor, a three-phase modulating system is formed The triangular voltages, whose frequency is twice the frequency of the rectangular voltages, and the maximum modulating voltage coincides with the beginning of the half-period of the rectangular voltage in each phase, and the control pulses for one of the two opposite-parallel thyristors, positive polarity in each phase is formed by comparing the half-wave voltage corresponding to the positive polarity of the phase voltage in during one half-cycle of the reduced frequency of rectangular pulses of a given phase with a triangular modulating voltage of the same phase, the moments of time are determined when the values of the modulating and single-half-phase phase voltages coincide, and at these times the specified thyristor of this phase controls the pulses for the second of two opposite-parallel thyristors, which transmits negative polarity voltages, is formed in each phase by comparing the half-wave voltage corresponding to polarity of phase voltage during the next second half-period of the reduced frequency of rectangular pulses of this phase c. By modulating the voltage of a triangular form of the same phase, the moments of time are determined when the values of the modulating and single-half-phase phase voltages coincide, and at these times the specified second thyristor of this phase is switched on. 040B & C Cj hdc Editor N. Himchuk Compiled With Pozdnukhov Tchred M MorgetalKorrektor M. Pojo H-j