SU1661941A1 - Frequency converter - Google Patents

Abstract

The invention relates to electrical engineering and can be used as a converter for alternating voltage of one frequency into alternating voltage of another frequency. Its goal is to improve energy performance by reducing reactive power consumption. The converter contains two bridges formed by thyristors 1 - 12. The DC outputs of the bridges are connected through reactors 14, 15. The phase terminals of the first bridge are inputs to the converter, and the second outputs are outputs. Capacitors 15 to 23 connect the inputs and the outputs so that each of the outputs is connected to each input. The control system consists of six-phase pulse generators, respectively. input and output frequencies, a high-frequency generator and twelve two-input elements I. The outputs of the input frequency generator are connected to one input of the first six I elements, and their outputs through amplifiers to the inputs of the corresponding thyristors of the first bridge. The outputs of the output frequency generator are connected to one input of the second six elements I, and their outputs through amplifiers to the inputs of the corresponding thyristors of the second bridge. Other inputs of all elements And connected to the output of the high-frequency generator. 3 il.

Description

The invention relates to electrical engineering and can be used as a converter for a three-phase alternating voltage of one frequency into a three-phase alternating voltage of another frequency.

The purpose of the invention is to improve the energy performance by reducing the consumption of reactive power from the power source.

1 shows a diagram of the power part of the frequency converter; 2 is a block diagram of a control system; Fig. Zad d - high-frequency pulse diagrams fo, six-phase pulses of the input frequency fi-fe, six-phase pulses of the output frequency, input phase voltages UA, UB, Uc, output phase voltages Ua, Ub, Uc, respectively.

The frequency converter contains

thyristors 1–12, the first six of which form the first bridge, and the second six form the second bridge, the phase outputs of the first bridge are inputs to the frequency converter, and the second are outputs.

The anode groups of the thyristors of the first bridge are connected to the cathode groups of the thyristors of the second bridge through the reactor 13, and the cathode groups of the thyristors of the first bridge are connected to the anode groups of the thyristors of the second bridge through the reactor 14. The capacitors 15-17, 18-20 and 21-23 are connected respectively into three phases the star and connected to the phase outputs and inputs, and zero points - respectively to the outputs. The control system (FIG. 2) consists of six-phase impulse input 24 and output 25 frequencies, a high frequency pulse generator 26 and twelve two-input elements AND 27. The outputs of generator 24 are connected to one input of the first six And elements, and their outputs through an amplifier - the inputs of the corresponding thyristors of the first bridge. The outputs of the generator 26 are connected to the same inputs of the second six elements And, and their outputs through the amplifier to the inputs of the corresponding thyristors of the second bridge. Other inputs of all elements And connected to the output of the generator 26.

The frequency converter operates as follows.

A three-phase symmetric system of sinusoidal voltages UA, UeUc is connected to the input terminals A, B, C (Fig. 3g) ..

The thyristors K 16 of the first bridge receive control pulses FK fo-fk (fig. Sa.b).

The control pulses are synchronized with the input voltage UA, Us. Uc in such a way that the first bridge works in

unmanaged rectifier mode. This makes it possible to reduce the consumption of reactive power from the source of input voltages. On thyristors K 712 second

the bridge receives control pulses FK fo tc (fig. 3a, c).

If control pulses are absent, then between zero points a, b, with capacitor banks 15-23

are zero. Let at the zero moment of time, at which f5 f6 0, an impulse 1b arrives (Fig. 3). In this case, the thyristors K 5,6,7 and 12 receive control pulses FK fofK. Thyristors open

and oscillating circuits are formed: the first is from the elements 5,14,7 and 17, the second - 12,13,6 and 19. The current flowing through the oscillating circuits, the reverse half-wave cancels the thyristors 5,6,7 and 12 and recharges the capacitors 17 and 19. The natural frequency of the circuits is determined by the inductances of the reactors 13 and 14 and the capacitance of the capacitors.

At small inductances

In reactors 13 and 14, the oscillation period of the circuits and the open state of the thyristors 7 and 12 will be sufficiently short (the time is equal to the half-period of oscillations).

Reload time yes capacitors in

this case is also small, and the voltage before the start of the recharge and equal to the voltage after the recharge and even with a minus sign. The limitation on the recharge rate is the time of thyristor locking.

After recharging the capacitors, a potential difference is formed between the zero point a and the capacitor bank 15D6 and 17 and the zero point b of the capacitor bank 18.19 and 20. If we take the potential of the zero point formed by the voltage system UA, UB, Uc for zero, then the potential of the point a Ua UB is Uba, and the points b-Ub are Uc-Ucb, where Uij is the voltage between points i A, B, C and ja, b, c. Since Uc and Uca were positive before the arrival of FS and F pulses, after recharging the capacitors Ua 0. Since UB and Ueb before the arrival of pulses, Fe and Fia were negative, after recharging Ub 0.

Under the influence of the potential difference between the points a and b, the load connected to the terminals a, bc, currents flow and the capacitors begin to recharge in such a way that their voltages will tend to the voltages UA, UB, UC, and Ua, Ub, Uc - to zero. At the moment of arrival of the second pulse fo, the control pulses Fi.Fe.F and Fi2 arrive at thyristors 1,6,7 and 12 and all the processes are repeated.

At the moment of arrival of the third pulse f0, the control pulses Fi, F2, F and FB are sent to thyristors 1,2,7 and 8. As a result, after recharging the capacitors, the potential of point a will be positive and points c will be negative.

Further processes proceed similarly. On phase outputs a, b, c a three-phase voltage system is formed. The frequency of the output voltage is determined by the frequency of the pulses f7, ..., f 12, and the effective value by the frequency of the pulses f0.

The shape of the output voltage curve can be improved by modulating the frequency of the pulses fo and the corresponding selection of the pulse duty cycle, TC: K 112.

Since the structure of the converter is symmetric with respect to the conclusions of AVC and ABC, in order to transfer energy from the terminals a, b, c, to terminals A, B, C it is necessary to change the control of the bridges - transfer the second bridge to rectification mode, and the first in inverter mode, in which the distribution pulses must be synchronized with the frequency of the network.

In the proposed frequency converter, the main load is taken by capacitors. The time during which the thyristors are in the conducting state is short. The consumption of reactive power from the network is also reduced. The latter is provided by the operation of the bridge connected to the network in the unmanaged rectifier mode.

Claims (1)

Claims A frequency converter comprising two three-phase thyristor bridges, the first phase terminals of which form an input, and the second an output, a reactor connecting the cathodes of the thyristors of the first bridge to the anodes of the second, a three-phase capacitor bank connected to the output terminals, and a control system consisting of two generators of six-phase impulses of input and output frequency, characterized in that, in order to improve the energy characteristics by reducing the consumption of reactive power from the source power supply, it is equipped with a reactor that connects the anodes of the thyristors of the first bridge to the cathodes of the second and two three-phase capacitor banks, which are connected, like the first one, to a star and are connected to the outputs by phase outputs, and to the third pulse generator, high frequency output connected to one of the inputs of the twelve entered two-code elements And, the other inputs of the first six of which are connected to the corresponding output of the generator six-phase symmetric pulses of the input frequency, and their outputs to strokes corresponding to the thyristors of the first bridge, the other inputs of the other six AND gates respectively connected to the outputs of the pulse generator symmetric six-phase output frequency, and their outputs - to the inputs of the respective thyristors of the first bridge. fa VlAS E f M I M I r I M ,, hh-5-1ht-mHnhr-ih-   3 P i i: m I 2 | | I "I I I | sl I I | g S  I7 I1 igi i1 l; / I I1 i, "I - § l IIJ l I I (“L jg {j I | J1 i | j I1. ftff { Ua at LK I I I I I I I I I I I I I w i KKMV i   W uc i I I I I I I I I I I I I I Vi   W Kkkkiyf AT /. J