SU817974A1 - Static converter control device - Google Patents

Description

(54) DEVICE FOR CONTROL OF STATIC CONVERTER

one

The invention relates to electrical engineering, in particular, to converter technology, and can be used to form a reference sinusoidal voltage in pulse-phase control systems of static converters.

A device known for forming a reference sinusoidal voltage in converter control systems, made in the form of a passband active filter 1, is known

However, in this device, the bandpass filter reduces the output voltage, has a frequency dependence of the output voltage phase, exacerbated by the presence of frequency-dependent phase shifters in the reference voltage-forming circuits, and in transient processes forms a parasitic feedback current on the converter load that can lead to self-oscillation m

The closest to the technical essence of this invention is a device containing, for each phase of the supply voltage, a summing device, current and voltage transformers, the primary windings of which are connected to the power supply panel. The secondary voltage of the voltage transformer is fed to the first input of the summing device, and the current of the transformer secondary winding, the current to the second input of the summing device 2.

The drawbacks of the device are that the reference active-inductive resistance in the secondary circuit of the current transformer is essentially a current differentiator, and with a decrease in the ratio of the active component to the reactive component, which occurs when the power source increases, the area of differentiation the side

high frequencies and reduced immunity of the device. In addition, this device cannot be used for static converters powered from networks with varying reactance, for example, when powered from networks in which technological or emergency switching, switching on and off of synchronous generators are performed, as in these cases it is impaired proportionality of reference resistance and internal resistance of the network as a power source. The purpose of the invention is to expand the field of application, increase the noise immunity and reliability of the device for controlling a static converter. The goal is achieved by the fact that the known device is equipped with a logic unit and for each phase it supplies the network with a bandpass filter and a switch, the common contact of which is connected to the input of its summing amplifier, and the other two respectively to the secondary winding of the voltage transformer and the output of the bandpass filter which is connected to the input of the control unit, the input of the bandpass filter is connected to the output of the summing amplifier, and the control input of the switch is connected to the output of the logic unit, the inputs of which are connected s to the secondary windings of current transformers of the switched phases of the supply network. In addition, to improve reliability, additional inputs of the logic unit are connected to the outputs of the control node. On fi1. 1 shows a functional diagram of the device; ka fig. 2 is an example of an as-M. implementation of a logical block; in fig. 3 - time diagrams that show his work. Phase buses 1 ---- 3 of the supply voltage are connected to the input of the converter 4, loaded on the active-inductive load. Control pulses for converter 4 are formed by a control unit 5 whose inputs are connected to the outputs of shapers 6-8 of the reference sinusoidal voltage, each of which contains a switch, common contact 9 of which is connected to the input of summing amplifier 10, band-pass filter And is connected to one of the contacts 12 switch, the other contact 13 of which is connected to the secondary winding of the voltage transformer 14, and the control input 15 of the switch is connected to the output of logic unit 16, the remaining outputs of which are connected with E shaper 7 and 8, and the inputs to the secondary windings of the current transformers -19 primary windings and the primary winding of the transformer 14 are connected to a voltage supply network phases 1-3. FIG. 1 also shows the possible connections of the logic device 16 with the outputs of the control unit 5 of the converter. Logic block 16 (Fig. 2) contains two groups of comparators 20 and 21, with the outputs of current transformers connected to non-inverting inputs of comparators 20 and to inverting inputs of comparators 21. Opposite inputs of comparators 20 and 21 are connected to the zero bus power source of a logic device. The outputs of the comparators of each group are pairwise connected to the inputs of the elements AND 22-24 and 25-27, and the output of each of the elements AND is connected to one of the inputs of the elements OR 28-30. The outputs of the OR elements are connected to the control inputs of the switches. The diagram (Figs. 1 and 2) also shows the option of using the signal from the output, block 5, to increase the reliability of the device. The control pulses from the output of the control unit 5 are fed to a single input of the trigger 31, the zero input of which is connected to the output of the one-vibrator 32, the input of which is connected to the output of the element 28. The single-vibrator 32 generates narrow pulses from the cut of the pulses from the output of the element 28. The signal from the output of the trigger 31 (with this embodiment of the logic unit 16) is supplied to the control input 15 of the switch 6 of the generator 6. To switch the other drivers 7 and 8, the logic device is supplied with similar circuit (trigger 31, one-shot 32) connected to the corresponding outputs of the control system 5 and the elements 29 and 30. The timing diagram (Fig. 3) shows the change in voltage at the output of the voltage transformer 14, corresponding to the change in phase voltage of the converter 4 (bus 1). This voltage contains switching failures (four for the period in the case of a three-phase converter bridge circuit), due to voltage drops on the internal resistance of the supply mains during switching time (parallel connection of reactants of 1 and 2 and 3, respectively). The output signals of current transformers 17-19 acting on the inputs of logic device 16 are also shown in a time diagram (Fig. 3). The conductivity intervals of the thyristors of the converter in accordance with the diagram are approximately 120 el. hail. During switching of the thyristors of the converter 4, there are simultaneously signals of positive or negative polarity at the outputs of transformers 17 and 19, 17 and 18. Switching corresponding to the simultaneous presence of signals at the outputs of transformers 18 and 19 (switching of buses 2 and 3) does not cause distortion of the phase voltage. busbar 1 (voltage at the output of the voltage transformer 14). Thus, at the output of element 28, pulses are formed, the durations of which correspond to the duration of commutation, in which bus 1 of the phase voltage of the network is involved. The output of the one-shot 32 from the pulse slices at the output of the 28 produces narrow pulses that set the trigger 31 to the zero state, the control pulses from the output of the control block 5, also shown in the diagram, set it in one state.

The device (for example for phase 1) works as follows.

If converter 4 does not work, the voltage of phase 1, and hence the voltage at the output of transformer 14, does not contain switching distortion. At the output of the element 28, and hence at the control input 15 of the switch, a zero signal takes place, as a result of which the common contact 9 of the switch is closed with contact 13, i.e., the input of the summing amplifier 10 receives the undistorted sinusoidal voltage from the transformer output 14 voltages The output of the band-pass filter 11 has the same sinusoidal voltage as at the input of the amplifier 10 (the phase shift is zero, the amplitudes of the two voltages are the same).

When the converter 4 is turned on and the current commutation switches in the buses 1-2 and 1-3, the output of the element 28 (logic device 16) appears, single pulses affecting the switch control input 15 and calling its switching that are closed pins 9–12 appear. As a result, the input of summing amplifier 10 is connected to the output of band pass filter 11, a closed system is formed of amplifier 10 and filter 11 disconnected from the distorted network and continuing to form a reference sinusoid in otvetstvii with the initial conditions which preceded switching interval.

At the completion of the switching process, the contact 9 of the switch closes with the contact 13 and the amplifier 10 is connected to the undistorted voltage from the output of the transformer 14. Thus, the output of the filter 11 all time is undistorted sinusoidal voltage, having a zero phase shift relative to the phase (bus 1) voltage proportional to it amplitude. To ensure the stability of a real device implemented according to this principle, the loop gain of an open-loop system of amplifier 10 and filter 11 must be close to unity, and the phase shift in a closed loop at frequencies close to the frequency of its natural oscillations is close to zero.

Logic device 16, designed to control the switch, is connected to current transformers 17-19 and operates in accordance with the equation to ar $ t + a, Ci + a gji-f where, the output logic signal

element 28;

 - logical signals that take a single value in the presence of positive signals at the outputs of transformers 17-19 current.

atCzCt-logic signals that take a single value in the presence of negative signals at the outputs of current transformers 17-19: The functions of determining the presence and polarity of currents in converter 4 are performed by comparators 20 and 21. Due to the delay of pulses at the output of element 28, caused by the imperfection of comparators 20 and 21 and current transformers 17-19, in a sinusoidal voltage at the output of the amplifier 10, there can be switching dips of a negligible width. But the width of the dips does not depend on the magnitude of the load current of the converter, and the band-pass filter 11, due to the insignificant width of the dips, easily suppresses them, does not introduce phase and amplitude errors in the formation of the reference sinusoidal voltage at its output. In addition, the described phenomenon can be eliminated by connecting additional inputs of the logic device 16 with the outputs of the control system 5 (or systems) by the converter 4 (converters connected to a common power source 1-3).

Thus, the proposed device allows to form a reference sinusoidal voltage for controlling (synchronizing) the converters, without introducing phase and amplitude errors with changes in the wide limits of the load current and output reactance of the supply network. In this case, the formation of the reference sinusoidal voltage occurs without performing a differentiation operation and does not require a rigid proportional dependence of the parameters of its components and the internal resistance of the power source, which can vary over a wide range.

Claims (2)

1. A device for controlling a static converter, comprising a control unit and, for each phase of the supply network, a summing amplifier, current and voltage transformers, the primary windings of which are connected to the corresponding power supply bus, characterized in that, in order to expand the application area and increase the noise immunity, it is equipped with a logic unit and for each phase of the mains supply a bandpass filter and a switch, the common contact of which is connected to the input of the summing amplifier, and the other two are respectively to the secondary winding of the voltage transformer and the output of the bandpass filter, which is connected to the input of the control unit, the input of the bandpass filter is connected to the output of the summing amplifier, and the control input of the switch is connected to the output of the logic unit, whose inputs are connected to the secondary windings of the current transformers of the switched phases of the supply network. 2. An apparatus according to claim I, characterized in that, in order to increase reliability, the logic unit is provided with additional inputs connected to the outputs of the control unit. Sources of information taken into account in the examination 1.Sanina E.G., Skopitseva G.I. Multichannel control system using integrated circuits. Proceedings of VNIIEM, 1977, v. 51, p. 96-108. 2. The patent of Switzerland No. 516982, cl. H 02 R 13/24, 1972. jbixodf Exit 7. bModw Sxods 31 2 sxoie entrance input 8