SU1446684A1 - Device for controlling multiphase rectifiers - Google Patents

Abstract

The invention relates to electrical engineering and is intended for use in devices for controlling multiphase rectifiers with an increased stability of the output voltage at an unstable frequency of the supply network with a high symmetry of the control pulses. The aim of the invention is to increase the stability of the output voltage of the rectifier during change of voltage with the frequency of the mains supply and high symmetry of the thyristor control pulses. The device contains a multi-phase generator of control sequences of pulses containing in each channel a controlled linear saw voltage generator 6, a feedback circuit including an auxiliary comparator 9, a gated key 4 and a memory 6, and one obverse reference voltage source 11 The amplitude of the sawtooth voltage of each channel is compared with the reference voltage, and at the time of comparison, a control signal is generated by the sawtooth generator, memorized for one iodine. This eliminates the mismatch with the reference voltage. Due to the speed of the feedback loop, when the frequency is changed, there is no noticeable change in the delay angles of the control pulses and the output voltage does not change. 3 il. (L with 4ib 4i F 05 00 .4 l "/

Description

The invention relates to an electrical machine station and can be used in converter equipment for controlling multiphase outputs.

The circuit of the invention is an increase in the stability of the output voltage of the voltage at a variable frequency of the supply network and high symmetry of the control pulses.

FIG. 1 shows a block diagram of the proposed device; Fig. 2 shows an embodiment of a gated key; Fig. 3 shows diagrams illustrating the operation of the device.

The device contains a multichannel generator 1 of pulses synchronized with a network voltage (FIG. 1) connected to the multiphase network, and outputs two each to a channel for generating a delayed thyristor control pulse (outputs 2 and 3 for the first channel), each which includes gated generator 1 key 4, connected to the output to the storage device 5, the generator. 6 of the sawtooth voltage, connected to the output of memory 5, and output to the first input of the comparator 7, the output of which controls the driver 8 of the rectifier thyristor, parallel to the first input of the comparator 7, is connected to the first input of the auxiliary comparator 9, The second input of the comparator 7 is connected to the source 10 of the phase shift control signal, common to all channels, and to the input of the auxiliary comparator 9 is the source 11 of the reference signal, common to all channels, output d auxiliary comparator connected to the input of the gated key 4,

The device works in the following way.

The multiphase voltage of the t-phase network and fed to the m inputs of the generator 1 are synchronized with the voltage of the network of pulses, which, to improve the synchronism of the input pulses with phase voltages during asymmetry of the amplitudes of the phase voltages, is synchronized at the moments of zeroing phase voltages. The pulses of the generator 1 synchronize the generator 6 of the saw-tooth voltage of each channel through the input of the chilling (Fig. 3, Po,), the saw-tooth voltage

0

five

0

five

0

five

0

five

and the control signal 11 jp from the source 10 of the phase shift control signal 10 is compared with a comparator 7, the signal from which the driver 8 starts, and at the time of the comparison, a thyristor control pulse of the rectifier Ug is generated. The sawtooth voltage 11 is also compared with the comparator 9 (FIG. 3, Ug) with reference voltage from source 11. The signal Ug from the comparator is fed to a gated key 4, the purpose of which is to change the value of the constant voltage at the output of the storage element 5 in proportion to the duration of the signal p matching signals at the input of the comparator a 9, The schematic solution of the gated key 4 and the storage device 5 is shown in FIG. 2, A memory line 5 is inserted with a dotted line, Transistors 12-15, elements 16 and 17 of coincidence, inverters 18 and 19 of the pulse signal constitute a gated switch 4, which through a resistor 20 charges the storage capacitor 21,

Gated key works as follows. Through one inverter, the first inputs of the matching elements are fed from the output of the comparator 9. To the second input of one matching element, the strobe signal tr is sent, to the second input of the other matching element, an inverted signal 1C, Depending on the error sign of the input signals the comparator 9 has a positive or negative polarity at the time of changing the polarity of the strobe signal and the signal and at the input of the key. Depending on the sign of this signal, one of the matching elements produces a pulse U, length elnost which is proportional to the misalignment of the reference voltage and the linear edge of the sawtooth voltage (FIG. 3) at the time of changing the polarity of the strobe signal, and unlocks shoulder charge or discharge the storage capacitor. The voltage U on it varies by the magnitude of the LI, and the slope of the linear portion of the sawtooth voltage changes so much that most of the mismatch is eliminated (ideally, completely), so that in the next period the duration

impulse, provided that a further change in the repetition period ceases, constitutes an insignificant fraction of the previous value (ideally zero), and thus, the symmetry of the pulses and their synchronism with the mains voltage are almost restored {ideally completely) already during the first period .

The ideal case is characterized by the ratio

t20 DO

t IT

(one)

where T is the network repetition period.

Let us find the required RC value, which characterizes the process of discharge (charge) of the memory voltage, which is a capacitor with capacitance C, discharged (charged) through the resistor R, This process characterizes the equality 4p

.U4 th i.jo

R-c

(2)

where Q4 is the magnitude of the change in charge

containers;

I is the charge (discharge) current, which in the case of t 5 T is performed with great accuracy, since in this case I (t) 2; const (t), Considering the previous equality, we get

Cs t

(3)

Actually, relation (3) is exact for the device shown in FIG. 2, is not fulfilled, since the period T itself changes. Therefore, the amplitude equalization of the sawtooth voltage occurs after several periods according to the law of geometric progression. If equality (3) is fulfilled with an accuracy of no worse than 20%, then the geometric progress kills faster than the exp (-t / T) law, and, therefore, the constant of the restoration time of the symmetry of the pulses of the proposed device is less than T, which significantly better than in known devices. In this case, the linearity of the sawtooth stresses in the proposed device can be broken only at the time of gating, i.e. at maximum delay angles, respectively

current minimum values for 11r —pairs at the output of the rectifier. Since the process of changing the inclination of the linear portion of the sawtooth voltage with the frequency change is the same in all channels, during the change of the symmetry frequency of the control pulses undergoes a smooth and uniform change across all channels.

Claims (1)

Invention Formula A device for controlling multiphase rectifiers, containing a multichannel generator synchronized with a voltage network of pulses in each channel, controlled by a sawtooth voltage generator, a comparator and a pulse shaper, and the outputs of the multichannel oscillator synchronized with a voltage network of pulses are connected to the inputs of zero generators of sawtooth voltage generators the first inputs of the comparators are connected to the outputs of the saw-tooth generators, the second are intended to be connected to regular enrollment control voltage the outputs are connected to the inputs pulse conditioners, in that, in order to control the stability of the output voltage of the rectifier at a varying frequency of the supply network and high symmetry of the control pulses, it is additionally equipped with one auxiliary comparator, a gated key, a memory device for each of the pulse shaping channels control thyristors and one common source of voltage, and in each channel one input of the auxiliary comparator is connected to the output of the sawtooth generator, The comparator is connected to the input of a gated key, the gated input of which is connected to a multi-phase generator, and the output to the input of the storage device, the output of which is connected to the control input of the sawtooth generator, and for all channels the second inputs of the auxiliary The comparators are connected to a common source of reference voltage. Oh oh r u ui