SU1515301A1 - Method of pulse-width control of three-phase self-excited voltage inverter - Google Patents

Abstract

The invention relates to electrical engineering, in particular, to methods for controlling a three-phase, self-contained voltage inverter with a pulse-width control, used, for example, in an AC electric drive. The purpose of the invention is to improve the harmonic composition of the inverter output voltage. For this purpose, control pulses are formed and supplied to thyristors of different phases. For each phase in the range from 60 to 120 al. form the main impulses and pauses separately of equal duration. On the interval from 0 to 60 and from 120 to 180 el.grad. form additional impulses and pauses. Set the duration of an additional pause γ = 0.4 (60 / N-β), where β is the duration of the main pause, N is the number of main pauses in the conduction interval. The number of additional pauses M = 4LOG ₂ N-6, the distance from the edge of the conduction interval to the center of the nearest additional pause L = 42 / N + 0.3β, the distance between the centers of adjacent additional pauses M = 60 / N. 3 il.

Description

The invention relates to electrical engineering, in particular, to methods of controlling a three-phase autonomous voltage inverter with a pulse-width control, used, for example, in an AC electric drive.

The aim of the invention is to improve the harmonic composition of the inverter output voltage by eliminating the fifth, seventh, reducing the eleventh, thirteenth harmonic components when using the pulse-width control.

Figure 1 shows the diagram, the ma switching main thyristors i

three phase voltage inverter; 2 shows the phase of the inverter; FIG. 3 is a functional diagram of the device for implementing the control method.

The inverter (Fig. 2) consists of main thyristors connected in a half-bridge circuit and connected to a power source, reverse diodes connected in parallel with them, connected in parallel with switching commutators, switching capacitors and drossels.

The device for implementing the control method consists of the master oscillator I and the analog-digital DSP.

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equalizer 2, which, through counting unit 3 and the persistent storage devices 4, 5 and 6, are connected to the elements HE 7, 8 and 9 and block 10. multiplexers. The outputs of the block 10 multiplexers through the elements 11, 12 and 13 are connected to the inputs of the block 14 to form the duration of the control pulses, the outputs connected to the inputs of the block 15 of the output driver,

The device works as follows.

The master oscillator 1 generates rectangular pulses with a frequency that is a multiple of the fundamental frequency of the inverter output voltage. The frequency of the master oscillator 1 is controlled by the voltage U ,, The impulses of the master oscillator I are fed to a scoring unit 3, which forms a code at the outputs. corresponding to the pulse number of the master oscillator 1, counted from the beginning of this 60-degree interval, as well as the code corresponding to the number of this 60-degree interval on the algorithm period (for example, 0-60 el, degrees, interval 1, 60-120 el , deg, - interval 2 and tod,), the code of the pulse number is fed to the inputs of permanent storage devices (ROM 4, 5 and 6 together with the code corresponding to the specified value formed by the analog-to-digital converter 2 and the code corresponding to the number of main pauses n, In each of ROM 4, 5 and 6 for Isana information sufficient for the formation of any infinite sequence consisting of the corresponding 60-degree intervals (0-60, 60-120, 120-180,) depending on the given g and f, ..

Thus, a rigid functional relationship is established between the duration and the number of main and additional pauses in accordance with the proposed control method,

Received at the outputs of the ROM 4, 5 and 6 pulse sequences, as well as inverse pulse sequences. L9, step on the inputs of the multiplexer unit 10, which is controlled by the code of the slot number: depending on the slot number, a sequence of pulses corresponding to this slot is sent to the output of this multiplexer.

Thus, three thyristor switching charts are formed, shifted relative to each other by 60 e, degrees.

Switching diagrams for the remaining three main thyristors are formed at the outputs of the HE elements 11, 12 and 13. The generated switching diagrams arrive at a block 14 for forming time intervals in which the temporal characteristics of the logical control signals of the main and switching thyristors are formed. The resulting sequences of control signals are fed to a block of 15 output drivers, which make a potential separation of control signals and their amplification in power before being fed into the thyristor control circuits.

The application of the invention allows to improve the quality of the output voltage of the inverter, to reduce losses due to the elimination or reduction of the level of a number of higher harmonics in the output voltage of an autonomous inverter.

Claims (1)

Invention Formula The method of controlling a three-phase autonomous inverter, voltage with a pulse-width control, which consists in forming and serving to the main thyristors of different phases of the inverter control pulses with a mutual phase shift of 60 e, degrees, for each main thyristor during one half period from O to 180 el, hail, form the conduction interval, during the other half period from 180 to 360 zl.grad, form the interval of the closed state, in the interval from 60 to 120 el.grad, form the main pulses and pauses separately equal to In addition, at intervals from 0 dL 60 and from 120 to 180 e, hail, additional impulses and pauses are formed, in the closed state interval for each of the pauses of the conduction interval, a corresponding impulse of the same duration as the pause is formed, with the purpose of improving the harmonic composition of the output voltage, the duration of the additional pause is set equal to .A (-; 3), where (b - the duration of the main pause. e, hail ,; y - the duration of an additional pause, email. hail,; n is the number of basic pauses of the conduction interval (, 8.16, ..,), I the number of additional pauses in the conduction range is defined as m 41о§2П 6, where m is the number of additional pauses in the intervals of proliferation, the distance from the edge of the conduction interval from the center of the nearest additional pause, expressed in electrical degrees, is L in - + 0,3 / e, where L is the distance from the edge of the conduction interval to the center of the nearest additional pause, the distance between the centers of the adjacent additional pauses in zl, hail is 60 M "- P 20 where M is the distance between the centers of adjacent additional pauses. - ABOUT f $ FIG. 2  1G 7 A / ky WV A / V A A y J 7t 7k CM 55 to 7 GZH