JPS586389B2 - Emergency operation method for reactive power compensation converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises two three-phase bridge type converters connected to a three-phase AC power supply in a parallel connection relationship with each other on the input side, and connected in series or parallel with each other on the output side; The converter is controlled as a power commutation converter with a control angle lagging with respect to the power supply voltage, and the other converter is controlled as a forced commutation converter with a control angle leading in phase with respect to the power supply voltage, and The forced commutation converter relates to a method for the emergency operation of a reactive power compensating converter in which each of the bridge halves, each consisting of a controllable electric valve having a common output terminal, has an independent forced commutation circuit.

A reactive power compensation converter reduces the reactive power generated in the power supply system by offsetting the lagging reactive power generated by the power supply current converter with the leading phase reactive power generated by the forced commutation converter. It can be reduced to almost zero, and is particularly suitable for large-capacity cyclorectifiers or cycloconverters.

However, such a reactive power compensation type conversion device,
Due to the presence of a forced commutation device that performs commutation with the assistance of a forced commutation circuit, it has the disadvantage of being inferior in reliability compared to a normal converter that consists only of a power commutation converter, that is, there is a risk of commutation failure. The problem is that the probability is high.

As an emergency operation method in case of commutation failure of such a reactive power compensation converter, a method has already been proposed in which the control angle of the forced commutation converter is switched from phase leading to phase lagging when commutation failure is detected. (Patent application No. 51-124599).

According to this, forced commutation converters are composed of three-phase bridge-connected controllable electric valves (for example, thyristors) like power commutation converters, and the bridge halves share a common output terminal. An independent forced commutation circuit is provided for each.

The individual controllable electric valves of the forced commutation converter are then connected at the input side of a pulse amplifier that provides a firing pulse to a firing angle regulator that generates a control pulse at a normally advanced control angle α. However, if a commutation failure occurs, the control angle of the slow phase +
It is designed to be switched and connected to a firing angle regulator for a power supply commutator rectifier which generates a control pulse at α.

However, with this already proposed emergency operation method, if the control angle α is large, voltage fluctuations may occur during the above-mentioned switching transients, which may lead to a significant increase in the current.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide an improved emergency operation method that can reduce voltage fluctuations during the transition period of switching.

The present invention will now be described in detail with reference to the drawings.

FIG. 1 shows an example of the main circuit configuration of a reactive power compensation type converter to which the emergency operation method according to the present invention is applied.

This device consists of three-phase bridge-connected thyristors U1 to
It consists of a power commutation rectifier 1 consisting of Z1, and a forced commutation rectifier 2 consisting of three-phase bridge-connected thyristors U2 to Z2 and a forced commutation circuit.

3-phase AC input voltages eR1, e8, , eTt of rectifier 1 and 3-phase AC input voltages eR2, e32, eT2 of rectifier 2
are voltages with no twist in their mutually isolated phases that are changed from a three-phase AC power source via a transformer (not shown), and are voltages of equal magnitude.

The forced commutation rectifier 20 forced commutation circuit includes a commutation capacitor C1, a commutation reactor L1, and an inversion thyristor S1 for one bridge half U2, v2, W2,
The other bridge half portions X2, Y2, and Z2 are provided with a commutating capacitor C2, a commutating reactor L2, and an inverting thyristor S2, and further provided with a diode bridge DB.

This diode bridge DB not only forms a commutation circuit, but also serves as a rectifier that generates a DC voltage for supplementary electricity, and is used as a braking resistor r1 and a supplementary electricity thyristor to supplementally charge the commutating capacitor C1. S3 is provided, and a braking resistor r2 and a auxiliary current thyristor S4 are provided for supplementary current of the commutating capacitor C2.

Since this type of forced commutation circuit is well known, a description of its operation will be omitted here.

FIG. 2 shows an example of the basic configuration for realizing the emergency operation method according to the present invention.

Although only the portion corresponding to one bridge half portion U2, v2, W2 will be described here, the other bridge half portion X2, Y2, Z2 has a similar configuration.

In FIG. 2, 10 is commanded with a control angle magnitude α by a control input voltage, and a control pulse with a slow-phase control angle 10α for each thyristor U1 to Z1 of the power commutation rectifier 1, and a forced rotation control pulse. This is a control pulse generator that generates control pulses of phase advance control angle -α for the individual thyristors U2 to Z2 of the flow rectifier 2.

A switching gate 12 is provided on the input side of the pulse amplifier 11 attached to each of the thyristors U2, V2, and W2 of the forced commutation converter 2. During normal operation, this switching gate is in the switching position a and the thyristor U2 is ,v2
, W2 can be fired at a phase advance control angle -α.

The switching gate 12 also makes it possible in the switching position C to fire the thyristors U2, V2, W2 with a slow control angle of ten α.

Furthermore, in the switching position b of the switching gate 12, the control pulses from the control pulse generator 10 are prevented from being transmitted to the pulse amplifier 11, and furthermore, the pulse generator 15 is able to generate a special pulse for igniting the desired thyristor. It can also be transmitted to the pulse amplifier 11.

The switching control logic circuit for switching the switching gate 12 is designated at 13, and the commutation failure detection circuit belonging to the bridge half U2, v2, W2 is designated at 14.

The commutation failure detection circuit 14 is comprised of, for example, known means for detecting commutation failure from the relationship between the control pulse and current of each thyristor.

For example, if a thyristor that should be turned off continues to conduct current even though a predetermined period of time has passed after a commutation command was given by a control pulse, or if current does not rise to a thyristor that should be turned on, the switch will start. It is determined that the flow has failed.

The switching control logic circuit 13, which receives the commutation loss detection signal from the commutation failure detection circuit 14, immediately switches the switching gate 12 to the switching position b, and stores the thyristor that could not receive current due to the commutation failure.

Furthermore, the switching control logic circuit 13 monitors the control pulses with a delayed control angle of ten α and switches the switching gate 12 to the switching position C as soon as the control pulse corresponding to the storage thyristor arrives.

The special pulses generated by the pulse generator 15 will be described later, and the pulse generator 15 will not be considered for now.

FIG. 3 shows a waveform diagram when operating according to the emergency operation control method according to the present invention, where the magnitude of the control angle is O.
It is in the range of ≦α≦30°.

In the figure, a is the output voltage e of the forced commutation rectifier 2.

ut,b is the potential e of the positive side output terminal of the forced commutation converter 2
, and the waveform of the potential en of the negative output terminal.

And C is the control angle of phase advancement - 1α, and the thyristor U2, v2,
The conduction sequence when W2 is conduction controlled, d is the conduction sequence when the slow phase control angle is ten α, and e is the conduction sequence according to the present invention.

In the figure, it is shown that a commutation failure occurs at time t1.

Before the time t1, the individual thyristors in the rectifier 2 are ignited at a phase-advanced control angle -α, each time carrying out commutation with the aid of a forced commutation circuit.

Immediately before time t1, thyristors W2 and Y2 carry the load current Id, as can be seen from FIGS. 3C and 3E.

At time t1, a firing pulse is applied to Zyristor U2;
Assume that the load current Id should have been commutated from the thyristor W2 to the thyristor U2, but this has failed, for example, due to an abnormality in the forced commutation circuit.

As soon as this commutation failure is detected, the commutation failure detector 14
The output signal of is transmitted to the switching control logic 13.

The switching control logic circuit 13 immediately switches the switching gate 12 to the switching position b and remembers the thyristor U2 which could not draw current.

By switching to switching position b, pulse amplifier 1
The ignition pulse originating from 1 is blocked.

The thyristor W2 continues to flow the current Id, but as soon as the control pulse with the slow phase control angle 0α corresponding to the previously stored thyristor U2 rises at time t2, the switching control logic circuit 13 moves the switching gate 12 to the switching position. Switch to C.

As a result, an ignition pulse is given to thyristor U2, and load current Id is commutated from thyristor W2 to U2 due to power commutation.

From now on, the thyristor U of the bridge half of the forced commutation converter 2
2, v2, and W2 are controlled by a slow-phase control angle of ten α, and perform commutation operation using the power supply voltage.

Thyristors X2, Y2, of the other healthy bridge half;
Z2 continues to be controlled at the control angle -α of the creeping phase.

By the way, if the effective value of the line voltage is V, then the average value of the output voltage eouf of the rectifier controlled by the phase advance control angle -α can be expressed as is well known.

On the other hand, if one of the bridge halves U2, V2, W2 is controlled with a slow phase control angle +α, and the other bridge half is controlled with a fast phase control angle -α, e.

The average value leoutl of ut is as shown in FIG. 3, which is the same as the average value during normal forced commutation.

Figures 4a and b show α (≒54
FIG. 3 shows waveforms corresponding to FIGS. 3a and 3b.

In this case as well, the output voltage e. It can be easily confirmed that the average value of ut is expressed by the same formula both before and after the occurrence of commutation dissipation.

In FIG. 5, the output voltage waveform e is for the case of α-150°.

ut is shown, (a1) is when the emergency operation method according to the present invention explained so far is followed, (a2) is when the emergency operation method that is further developed is followed, and (a3) is the case when the emergency operation method according to the present invention is followed.
The case is shown in which the emergency operation method described in Japanese Patent No. 1-124599 is followed.

Time t1 represents the time when commutation dissipation occurs, and thyristor W2
Assume that even though the current is extinguished and the thyristor U2 should be conductive, the current continues to flow through the thyristor W2 and the thyristor U2 is unable to accept the current.

The waveform shown by the broken line after time t2 is the waveform assuming that no commutation failure has occurred, and therefore the shaded area represents the voltage error during the switching transition period of the control pulse.

In the case (a1) of the method of the present invention explained so far, only the bridge half where commutation failure has occurred is switched to operation at a slow phase control angle 1α, and the healthy bridge half is left with a phase advance. In the conventional method (a3), without distinguishing between the bridge half where the commutation failure occurred and the healthy bridge half, both are phase-delayed at the same time. This is a method of switching to operation at a control angle of -α.

It can be seen that the voltage error in the transient period after such switching until reaching a steady state is significantly improved in the method (a1) of the present invention compared to the conventional method (a3).

Furthermore, according to the developed form of the present invention which will be explained next, the second
As can be seen from Figure (a2), the voltage error can be further reduced.

This development according to the invention consists in the provision of special ignition pulses by the pulse generator 15 in FIG. 2 under predetermined conditions.

This is based on the following recognition.

That is, by the switching control circuit 13, the thyristor U2, v2
, W2, during the period when the firing pulses of α
In the case of >120°, commutation operation is possible by power supply commutation by firing a specific thyristor determined by the thyristor that caused the commutation failure.

For example, in FIG. 5(a2), if the thyristor W2 is not extinguished at time L1 and continues to flow, and the thyristor U2, which should be conducting, is unable to accept the current, the commutation failure detector 14 The pulse generator 15 generates a control pulse that fires the thyristor v2.

Since the switching gate 12 is at this time in the switching position b, its control pulse is transmitted to the pulse amplifier 11 and a firing pulse is given to the thyristor v2.

When α>120°, since es2>eT2 at this time, the line voltage es2-eT2 is applied as a reverse bias voltage to the thyristor W2 via the thyristor v2, and therefore power commutation is possible.

In this way, load current Ld is commutated from thyristor W2 to thyristor v2.

At this time, thyristor Y2 is conducting in the other bridge half, so that rectifier 2 is in bypass operating mode with zero output voltage.

In this manner, when a special control pulse is issued from the pulse generator 15, the memory thyristor of the switching control circuit 13 is changed by the output signal of the pulse generator 15.

That is, at time t1, the switching control circuit 13 remembers that the thyristor U2 was unable to accept the current based on the information from the commutation failure detection circuit 14, and controls the slow phase control angle 0α of the thyristor U2. When a pulse arrives, the switching gate 12 is waiting to be switched to the switching position C, but when the output signal of the pulse generator 15 is applied, the storage thyristor is changed from U2 to another thyristor W2 with an advanced phase.

In this case, the switching gate 12 is switched into the switching position C at time t3.

By doing so, voltage fluctuations during the transition period from forced commutation to natural commutation can be significantly reduced.

In addition, if only the emergency operation method as shown in FIG. Since switching is performed from to C, the switching control logic circuit 13 has an extremely simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of the main circuit configuration of a reactive power compensation converter to which the emergency operation method of the present invention is applied; FIG. 2 is a block diagram showing an example of the basic configuration of the emergency operation method of the present invention;
3 to 5 are waveform diagrams for explaining the emergency operation method according to the present invention. DESCRIPTION OF SYMBOLS 1...Power commutation converter, 2...1 Forced commutation converter, 10...1 Control pulse generator, 11...
...Pulse amplifier, 12...Switching gate, 13...Switching control logic circuit, 14...
...Commutation failure detector, 15...Pulse generator.

Claims (1)

[Claims] 1. Two three-phase bridge type converters are connected to a three-phase AC power source in a parallel connection relation to each other on the human power side, and two three-phase bridge type converters are connected in series or parallel to each other on the output side. As a power commutation converter, it is controlled with a control angle that is lagging in phase with respect to the power supply voltage, and the other converter is controlled as a forced commutation converter with a control angle that is in phase leading with respect to the power supply voltage, and the other converter is controlled as a forced commutation converter with a control angle that is in phase leading with respect to the power supply voltage. In a reactive power compensation converter in which each half of a bridge consisting of a controllable electric valve with a common output terminal has an independent forced commutation circuit, the converter is a forced commutation converter. An emergency operation method for a reactive power compensation type converter, characterized in that when a commutation failure occurs, only the half of the bridge that caused the commutation failure is switched to control at a slow phase control angle. 2. In the method described in claim 1, switching to control using a slow phase control angle is performed immediately upon detection of a commutation failure by all controllable electric valves in the half of the bridge where the commutation failure has occurred. After the ignition pulse is once blocked, the control pulse is simultaneously generated with a slow-phase control angle corresponding to the controllable electric valve that could not draw current due to commutation failure. A method of controlling a reactive power compensation type converter. 3. In claim 2, a controllable device in which the current cannot be drawn due to a commutation error after the ignition pulse is blocked, provided that the magnitude of the control angle in each case is greater than 120°. A method for controlling a converter with reactive power compensation, characterized in that a controllable electric valve (for example V2) in the bridge half to be fired next to the electric valve (for example U2) is additionally fired. . 4 In claim 3, when the additional ignition is performed, switching to control at a slow-phase control angle may result in failure of commutation to draw current. The change is made to occur simultaneously with the occurrence of a control pulse of a slow phase control angle corresponding to the controllable electric valve (e.g. W2) in the bridge half to be fired before the control electric valve (e.g. U2). A method of controlling a reactive power compensation type converter characterized by: