SU1580504A1 - Method of controlling direct semiconductor converter with discrete frequency control - Google Patents

Abstract

The invention relates to electrical engineering and can be used to control converters in an electric drive. The purpose of the invention is to expand the frequency control range and increase the smoothness of the control. A method of controlling a direct semiconductor frequency converter intended for stepwise control of the rotational speed of an asynchronous motor is to form a three-phase, symmetrized system of output voltages, the spectrum of which contains an intense useful harmonic of a lower frequency using a three-phase system of modulating voltages with a frequency corresponding to a given frequency engine rotation. The multiplicity of the ratio N of the repetition period T to the period of the voltage of the network T c is fixed by a number determined by the expression N = 3P + 4 (P = 1,2,3,4 ...), and the number of the useful harmonic K is fixed by the value from the numerical sequence K = 3P + 1. 2 Il.

Description

The invention relates to electrical engineering and can be used to control converters used to control the frequency of rotation of an asynchronous electric drive.

The aim of the invention is to expand the frequency control range and increase the smoothness of the control.

FIG. 1 shows diagrams explaining the method; in fig. 2 is a functional diagram of the device implementing the control method.

A device for implementing a control method comprises a converter 1 comprising valve switches 2, to the output of which motor 3 is connected, and a control device consisting of a unit 4 of pulse-phase control with a thyristors control angle adjuster 5 and a channel for setting the coefficients p and k containing the divider b frequency shaper 7 input signal and the block 8 setpoint. From the output of the divider 6, the signal is fed to a three-channel distributor 9, the output of which through frequency multipliers 10 with a setting node 11 is connected to the inputs of the coincidence elements 12. A 2-bit memory unit 13 is connected to unit 8 and to the inputs of the elements 12, the outputs of which are the outputs of the control device.

The device works as follows.

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Unit 4 generates a continuous sequence of pulses, a sample of the moment of switching on each thyristor with a delay of an angle a, Value sets, with unit 5, depending on the engine load 3, the former 7 generates a square signal with a frequency fc 1 / TC, which is nociyiacr by divider 6, the division factor of which is 4, 7, 10 ... is set by block 8. From the output of divider 6, a low-frequency signal defining a repeated period of the output voltage T PTS is applied to distributor 9, which forms t ehfaznoy system signals with period T, but shifted relative to each other pgslno T / 3. From the output of the distributor 9, signals with a period Г пТс are fed to a three-channel block of multipliers 10, in which the frequency increases by k - 1.4.7 ... times. The value of the multiplication factor k is set by node 11. The polarity of the mains voltage is compared with the modulation voltage UM supplied from the output of the multiplier block 10 by elements 12. The signs of these voltages coincide for at least half the voltage of the network voltage in block 13 In the next cycle of formation of the output curve, the corresponding element of the block 13 supplies the enable signal to the electronic 12, and the unlocking pulses are passed to the keys 2 of the converter 1.

The use of the method to expand the range of output frequencies of the converter, improves its energy and simplifies the power part, which increases the reliability of operation of the converter.

A significant advantage of the control method proposed is that with a fixed period of repetition of the output voltage T h Gf (Zp + 4) Tc (4; 7; 10; 13; 17 ...) TC and a fixed number of the useful harmonic k - Sp + 7; ten; 13; 17 ..., which corresponds to her er f 1 Zr + 4

35; 38.4 Hz), the required rapf is useful / it always has a direct sequence, the same as the first harmonic and mains supply. Consequently, these harmonics (with a clock

gota fa 0 form in the stator

Circular MDS motor having a direction of rotation coinciding with the direction of rotation of the mains phase phases Therefore when changing the frequency at the output of the converter, for example, from 28.8 to 35 Hz

frequency f (k) f (c)

(e.g. 28, 8;

the order of phase alternation and the direction of the motor 1 and the rotor of the engine remain unchanged, so that it simplifies the power part,

f- more than that, changing the value of P, ensure i expansion of the range of the output clock, as well as a significant convergence of the settled hours from the output of the converter, which increased the smoothness of the adjustable drive, especially in the upper part of the range. At T (3p + 4) TC, the network is Aomonic, i.e. the harmonic with the number k -Zo-I, has one direction of rotation with the puller, which contributes to an increase in the torque of the engine and, consequently, an increase in the electromechanical parameters of the electric drive,

Of the entire set of output frequencies of the converter, only those often Jbs are selected, who form the same direct (forward) port dt of phase alternation with the first harmonic h and the mains supply

Of the invention

5 with a discrete frequency control semiconductor converter, which means that the phase angle of control is set, measured from the moment of transition of the mains voltage through O1.

0 set the period t of the output voltage repetition equal to n periods of the mains voltage, the beginning of the repetition period of the voltage of each lagging phase lags T / 3 behind the start of the period of the capacitance

5 of the advancing phase, in each phase in the repetition period, a two-field rectangular modulating band is formed, the period of which is shorter than the repetition period, and at each half-period of the modulating voltage the evo polarity is compared with the polarity of the corresponding network phase, the intervals are fixed On which the polarities of the indicated voltages coincide, and on5 determine the duration of these intervals, turn on the corresponding converter gate on the interval of coincidence with the angle of control (X, polarity of stresses and stress

The 0 phases coincide during the half-period of the Phase voltage, characterized in that, in order to expand the frequency control range and increase the smoothness of the adjustment, the parameter is Rpf + 4, where p

5 - 0, 1, 2, „. & set the period of the modulating voltage to be k times less than the repetition period T, a k is set to 3.

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Claims (1)

Claim · A method of controlling a direct semiconductor converter with discrete frequency control, which consists in setting the phase angle of control a, counted from. the moment of transition through O the mains voltage, the output voltage repeatability period T is set equal to n periods of the mains voltage, the beginning of the voltage repeatability period of each lagging phase lags by T / 3 from the beginning of the repeatability period of the leading phase, and bipolar is formed for each phase in the repeatability period. a rectangular modulating voltage, the period of which is less than the repeatability period, and on each half-period of the modulating voltage compare its polarity with the voltage polarity of the corresponding phase of the network, fix the intervals at which the polarity of the indicated voltages coincide, and determine the duration of these intervals, turn on the corresponding converter valve on. the coincidence interval with the control angle a, if the polarity of the modulating voltage and the phase voltage coincide during the half-cycle of the phase voltage, characterized in that, in order to expand the frequency control range and increase the smoothness of regulation, set η = Зр + 4, where p = 0, 1 , 2 ..., and the period of the modulating voltage is set to k times smaller than the repeatability period T, and k is set equal to Zp + '1,