JPH07177743A - Controller for ac-dc converter - Google Patents

Abstract

PURPOSE:To make it possible to restrict a voltage during accident by permitting the operation of a converter during accident in an AC system by continuing the operation of an AC-DC converter when the line voltage does not rise even though a voltage to ground rises and stopping the operation of the converter when the line voltage also rises. CONSTITUTION:When a single-phase grounding accident occurs, the voltage to ground of AC voltage detectors 16 to 18, absolute value circuits 19 to 21 and a maximum value selection circuit (MS) 22 rises, and the level detector 23 becomes H. Also, the waveforms of the line voltage detectors 28 to 30, the absolute value circuits 31 to 33 and MS34 remain the same as normal state, and a level detector 36 remains as L. Therefore, in a converter protection circuit (CD) 25, the converter is operated by giving, for example, a command to operate with a firing angle a of 90 deg. to a firing angle controller 7. On the other hand, if an accident occurs in the same system and the rise of both the line voltage and the voltage to ground is detected, level detectors 23 and 35 become H. Because of this, CD 37 operate and a stop command is issued to the firing angle controller 7 and a pulse generator 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an AC / DC converter applied to a DC power transmission system, a frequency converter or a grid interconnection device in an electric power system.

[0002]

2. Description of the Related Art A converter applied to a general DC power transmission system, a frequency converter, or a system interconnection device has a configuration shown in FIG. A three-phase AC busbar 1 is connected to a converter 3 via a converter transformer 2. The converter 3 operates as a forward converter or an inverse converter, and has one pole grounded and the other pole connected to a non-grounded pole of a facing converter (not shown) via a DC reactor 4. A transformer for transformer is connected to another AC bus on the AC input side of the converter facing each other, and one converter is operated as a forward converter to convert AC power to DC power, and the other The converter operates as an inverse converter to convert DC power into AC power, so that the AC power is once converted into DC power, and then the AC power is exchanged to another AC system as AC power.

The converter 3 is composed of a thyristor bridge, and is operated by applying a gate pulse to each thyristor to ignite it. The gate pulse during normal operation is given as follows. The DC current detector 5 detects the DC current Id, and the DC voltage detector 6 detects the DC voltage Ed. The respective detected values are given to the firing angle controller 7, and the firing angle controller 7 determines and outputs the firing angle α signal 13 such that the direct current and the direct current voltage are the values as set values respectively.

On the other hand, the AC voltage detectors 8 to 10 provided on the AC bus 1 detect the phase of the AC voltage by the phase control circuit 11 which has detected each phase voltage of the AC bus, and outputs the phase angle θ signal 12. . The pulse generator 14 generates a pulse signal 15 by deciding the generation timing of the gate pulse given to each thyristor from these two signals 12 and 13. The signal 3 causes the thyristors to be fired in sequence, whereby the converter 3 is operated.

In order to protect this converter from disturbance caused by an AC system accident, the following protection control device is provided. The AC voltage detectors 16 to 18 detect the ground voltage of each phase, and the absolute value circuits 19 to 21 make the respective absolute values. The absolute value is given to the maximum value selection circuit (HVG) 22 to select the maximum value. As a result, respective signals when a one-phase ground fault occurs in the AC system are as shown in FIG. That is, if an accident occurs in the phase a, the relative ground voltage Va decreases, so the detected values by the AC voltage detectors 16 to 18 are shown in FIG. 6 (a).
It becomes a waveform like.

The output signals of the absolute value circuits 19 to 21 in which this is an absolute value are shown in FIG. 6 (b). Further, the signal having the maximum value of the three signals has a solid line waveform in FIG. 6C, which is the output of the maximum value selection circuit (HVG) 22. On the other hand, in the level detector 23, when the value of the output signal of the maximum value selection circuit 22 becomes lower than the protection voltage level Vo shown in FIG. Give 24. In the converter protection circuit 25, in order to protect the converter 3 from disturbance caused by an AC system accident, the firing angle α is set to a value close to 90 ° for the firing angle controller 7 so as to stop the converter 3. Give command 27 to do so.

On the other hand, the pulse generator 14 is given a command 26 for stopping the generation of the ignition pulse. This operation is called a gate block. The command of the gate block is also given to the other converter connected to the tip of the DC terminal A, and by stopping both converters, the entire DC system is stopped, and DC voltage zero and DC current zero It becomes a state. In this way, in the conventional converter, it is detected that a fault such as a ground fault or a short circuit has occurred in the AC system and the voltage to ground has dropped,
Operates to shut down the converter.

As a protection control device for a self-excited converter, there is a system shown in FIG. The self-excited converter 3A according to this method is connected to the power system 1A via the converter transformer 2A and the circuit breaker 42 as shown in FIG. or,
The protection control device of this self-excited converter includes an AC overcurrent detected by the AC current detector 43 and the overcurrent relay 44 of the converter, and a DC detected by the DC current detector 5A and the DC overcurrent relay 45. When either of the overcurrents is operated via the OR circuit 46, the gate block signal 47 stops the converter, and the cutoff signal 48 trips the breaker to stop the protection. In this way, when some failure occurs in the self-exciting converter and an AC or DC overcurrent occurs, the converter is stopped and the breaker is protected and cut off.

[0009]

In the former case of the above-mentioned conventional method, the AC / DC converter in operation naturally consumes the reactive power of the AC system, and therefore, in general, in order to prevent the decrease of the AC voltage due to it, the AC / DC converter is generally used. A capacitor and AC filter for reactive power compensation are installed near the converter.
If an accident occurs in the AC system and the converter stops,
The reactive power consumption of the converter becomes zero, but since the phasing capacitor and AC filter are still connected to the AC bus 1, they serve as an extra reactive power supply source, and the AC voltage is healthy overvoltage during the accident. Due to this extra reactive power supply, the AC voltage after the accident elimination and before the converter is restarted becomes a high value.

In some cases, a large overvoltage that may damage the equipment may occur. The overvoltage after the accident is removed can be suppressed to some extent by tripping the capacitor.However, since the overvoltage during the accident is the overvoltage that appears immediately after the accident occurs, it is necessary to operate the circuit breaker such as capacitor trip. The measures do not make it in time.

In particular, when the AC system to which the converter 3 is connected is a non-grounded system or a high resistance grounded system, the ground voltage of the sound phase is not affected even if no capacitor is present at the time of one-line ground fault. Theoretically, it is about 1.73 times the steady state. That is, in the vector diagram shown in FIG. 7, in the case of a direct grounding system, as shown in FIG.
Is almost the same as in the steady state, but in the case of a non-grounded system or a high resistance grounded system, as shown in (b), the a-phase voltage Va is zero, that is, the ground potential and the sound relative ground voltages Vb and Vc are steady. 1.73 times the size.

In the case of a non-grounded system or a high resistance grounded system, the insulation design of the equipment is also designed to be higher in consideration of this. However, when the DC system is stopped and many capacitor components such as capacitors remain, the healthy relative ground voltage becomes a large value, and there is a high possibility that it will be more than twice the steady state voltage. The equipment may be damaged.
That is, in the conventional AC / DC converter, the converter is stopped at the time of an AC system fault, so that an extra capacitor remains in the system and a large overvoltage may occur during the fault or after the fault is eliminated.
Especially when the AC system is a non-grounded system or a high resistance grounded system,
There is a possibility that the sound relative ground voltage during a one-phase ground fault may exceed twice that in the steady state, which may damage the equipment.

On the other hand, in the latter case, when the self-excited converter reaches an overcurrent, the power system is caused by turning on a large capacity transformer, turning on a power capacitor, switching the system, etc. in addition to the failure of the converter itself. The disturbance may cause the transformer for the conversion device to be DC-biased, and as a result, the self-excited conversion device may be unable to continue operation due to overcurrent. In the case of a failure of the converter itself, it is necessary to quickly perform protective cutoff, but in the case of system disturbance, there is no abnormality in the converter itself, so there is no need to perform protective cutoff.
On the contrary, it is desirable that the operation is performed as soon as possible after the disturbance of the power system is converged, because the contribution to the power system is large.

However, it is difficult to separate the phenomenon of overcurrent due to its cause, and there is a problem in the timing of restarting the operation. In this way, when the overcurrent protection element of the self-excited converter operates, the protection must be stopped regardless of the cause. This is because there was no easy and economical way to isolate the cause of the overcurrent and the timing of the self-excited converter restart. The present invention has been made in view of the above circumstances, and continues to operate the converter as much as possible even in the event of an AC system accident or disturbance,
Another object of the present invention is to provide a control device for an AC / DC converter, which is capable of promptly restarting and improving the stability and reliability of electric power.

[0015]

According to a first aspect of the present invention, there is provided a control device for an AC / DC converter, which detects a voltage to ground in an AC system to which the AC / DC converter is connected and which detects that the voltage to ground is equal to or higher than a set value. Means, a line voltage detecting means for detecting that the line voltage of the AC system to which the AC / DC converter is connected is a set value or more, the ground voltage detecting means operates, and the line voltage detecting means is While not operating, the operation of the AC / DC converter is continued, and means for stopping the operation of the AC / DC converter when both the ground voltage detecting means and the line voltage detecting means are in operation.

In a control device for an AC / DC converter according to claims 2 to 4 of the present invention, when the overcurrent relay operates while the self-exciting converter is operating, the cause of the overcurrent relay is considered and the device itself is abnormal during system disturbance. Except in the case of, the converter is restarted without protection stop, or is started a plurality of times until it becomes operable.

[0017]

The control device for the AC / DC converter according to the first aspect of the present invention has a condition that the line voltage does not rise even if the ground voltage rises due to an accident, such as an ungrounded system or a high resistance grounded system. The AC / DC converter continues to operate at the time of the one-phase ground fault and consumes the reactive power, so that the overvoltage generated during the accident or after the accident is eliminated can be suppressed. On the other hand, if the line voltage also rises, immediately stop the operation of the converter,
It is possible to prevent unnecessary stress from being applied to the thyristor.

The self-excited AC / DC converter according to claims 2 to 4 of the present invention promptly restarts the device even if the overcurrent relay operates, if the device itself is not abnormal.

[0019]

Embodiments will be described below with reference to the drawings. First, the concept of the present invention will be described. The AC / DC converter is generally shown in FIG.
It is based on a 6-phase bridge as shown in. In order to reduce harmonics, two bridges of this configuration are often combined, but the basic operation can be explained using a 6-phase bridge.
Here, during normal operation of the converter, the thyristor valve is u
The DC voltage Ed is created by repeating firing in the order of → z → v → x → w → y. The valve is always energized in one of uvw and one of xyz. Moreover, the upper and lower valves such as u and x are not energized at the same time. Considering a state where the valves u and z are energized, for example, the terminal B is applied with the a-phase voltage Va and the terminal C is applied with the c-phase voltage Vc.

That is, a voltage of Vb-Va is applied between the poles of the valve v, a voltage of Vc-Va is applied between the poles of the valve w and the valve x, and a voltage of Vc-Vb is applied between the poles of the valve y. When is in the forward direction, each valve can fire. The value obtained by subtracting the ground voltage of another phase from the ground voltage of another phase is the line voltage, and in the AC / DC converter using the thyristor bridge configured as shown in FIG.
It can be said that the commutation is performed by the line voltage. Therefore, even if the ground voltage drops or rises, if the line voltage drops or rises, the converter can normally commutate and operate.

That is, a line voltage detector is provided in addition to the ground voltage detector for detecting an AC system fault, and the line voltage is monitored.
Even if the ground voltage rises, if the line voltage does not rise, some method is used, for example, the converter is operated with a constant firing angle,
If the line voltage also rises, normal commutation may not be possible and may give great stress to the thyristor valve. Therefore, command the firing angle controller 7 and pulse generator 14 to stop the converter. Give out.

An embodiment of a control device for an AC / DC converter according to claim 1 of the present invention will be described with reference to FIG. In FIG.
The same parts as those in FIG. 5 are designated by the same reference numerals and the description thereof will be omitted. Reference numerals 28 to 30 detect an AC bus voltage by an AC voltage detector, absolute values are taken by absolute value circuits 31 to 33, and maximum values are taken by a maximum value selection circuit (HVG) 34. The waveform of this maximum value is similar to the case of the ground voltage of FIG. 6C, but the steady value is 1.73 times as large as that of the case of the ground voltage. The level detector 35 judges whether it is below a certain set value, and if it is above the set value, the output is "1".
Build up.

The set value is, for example, about 1.73 times Vo in the case of the ground voltage. The output of this level detector 36
Is judged by the NOT circuit 38, the judged signal and the output 24 of the level detector 23 are ANDed by the AND circuit 39, and the ANDed signal is given to the converter protection circuit 25. In the converter protection circuit 25, when the input signal becomes "1", the converter is operated by normal firing angle control or some kind of protection control.
A converter control signal is supplied to the firing angle controller 7.

The protection control includes, for example, a method of operating the ignition angle at a value closer to 90 ° than in the normal control, a constant ignition angle control, and the like. Note that FIG. 2A is a line voltage waveform, and FIG. 2B is a waveform showing an absolute value. On the other hand, the output 36 of the level detector 35 is given to the converter protection circuit 37, and in the converter protection circuit 37, when the input signal becomes "1", the ignition angle controller 7 and the pulse generator 14 are supplied. Then, commands 26 and 27 for stopping the converter are given. Other configurations are the same as those in FIG.

Next, the operation of the control device for the AC / DC converter according to claim 1 will be described. Consider a case where the AC / DC converter is connected to a non-grounded system and a one-phase ground fault occurs in that system. In this case, since the ground voltage of the sound phase rises due to the ground fault, the AC voltage detectors 16 to 18 and the absolute value circuit 19
21 and the waveform obtained by full-wave rectifying the ground voltage obtained by the maximum value selection circuit 22 rises, and the output 24 of the level detector 23 detects the voltage rise and becomes "1".

On the other hand, the line voltage at the time of one-phase ground fault in the non-grounded system becomes a vector diagram as shown on the right side of FIG. 7 (b). The magnitude is 1.73 times the steady voltage to earth, and the vector diagram is a three-phase equilibrium with a phase shift of 30 °. This is exactly the same as the vector diagram of the line voltage in the normal state. Therefore, the line voltage detectors 28 to 30, the absolute value circuits 31 to 33, and the maximum value selection circuit 34
The waveform obtained by (3) does not change at all in the steady state, and the output 36 of the level detector remains "0" as in the steady state. The output of the NOT circuit 38 is "1" because the signal 36 is "0", and the output of the AND circuit 39 is "1" because the signal 24 is also "1".

Since this is given to the converter protection circuit 25, the converter protection circuit 24 gives a command to the firing angle controller 7 to operate, for example, with the firing angle α set to 90 °, and the converter receives the command. Driven according to. Since the signal 36 is "0", the converter protection circuit 37 does not operate.

Further, when a fault occurs in the same system and an increase in the line voltage along with the ground voltage is detected, both the output 24 of the level detector 23 and the output 36 of the level detector 35 become "1". Since the signal 36 becomes "1", the converter protection circuit 37 operates to issue a stop command to the firing angle controller 7 and the pulse generator 14 to stop the converter. As a result, even if an accident occurs in the AC system and the AC line voltage does not rise even if the AC ground voltage rises, the converter continues to operate and consume reactive power.

Therefore, for example, when a one-phase ground fault occurs in a non-grounded system or a high-resistance grounded system, a healthy phase overvoltage generated during an accident can be quickly suppressed. Furthermore, even if a short circuit or a ground fault occurs in the same manner in the same manner, if the line voltage rises as a result, the converter operation will be stopped immediately to give unnecessary stress to the thyristor. Can be prevented.

FIG. 3 shows an embodiment of a control device for a self-exciting AC / DC converter according to claim 2 of the present invention. The same parts as those in FIG. In FIG. 3, 49 is a waveform distortion detector for detecting the waveform distortion of the system, which is connected to the power system via the voltage detector 50. When disturbance occurs in the system, a signal is transmitted from the waveform distortion detector 49 when the voltage distortion exceeds the set value. On the other hand, due to the waveform distortion of the power system, the AC-side overcurrent relay 44 or the DC overcurrent relay 45 operates and the protection signal is transmitted.

The self-exciting converter immediately gate-blocks and stops by the protection signal, but if the waveform distortion continues, the cutoff signal is blocked by the NOT circuit 51 and the AND circuit 52, and protection such as tripping of the breaker is performed. It does not stop. or,
The relay is reset by the logical product of the protection signal and the waveform distortion signal and is not treated as a failure. If the waveform distortion is recovered, the signal from the waveform distortion detector is not transmitted, but the gate deblock signal is transmitted and the self-excited AC / DC converter is restarted.

On the other hand, when the AC side overcurrent relay 44 or the DC overcurrent relay 45 operates and the protection signal is transmitted without the cause of the waveform distortion, the logical product 52 of the negation of the waveform distortion detection signal and the protection signal is obtained. Self-excited converters immediately stop protection. In this way, even if the overcurrent relay of the self-excited converter operates, the cause is isolated, and if the disturbance of the power system is the cause, it can be restarted promptly and completely, and In other cases, the protection can be stopped immediately.

FIG. 4 shows an embodiment of a control device for a self-exciting AC / DC converter according to a fourth aspect of the present invention. The same parts as those in FIG. In FIG. 4, 53 is a detector for detecting the DC bias magnetism of the transformer for the converter. When configuring a conversion device by multiplexing multiple self-exciting converters,
The AC side currents flowing through the converters are equal, but a difference occurs when the converter transformer 2A is DC biased. Deflection detector 53
Uses that phenomenon to detect the DC bias of the transformer for the converter.

Now, due to the waveform distortion of the electric power system, the DC overcurrent relay 45 of the AC side overcurrent relay 44 operates and the protection signal is sent out. The self-excited converter immediately blocks the gate by the protection signal and stops, but if the bias magnetism detector 53 operates at the same time, the NOT circuit 51 and the AND circuit 52 block the shutoff signal, and stop the protection such as tripping the circuit breaker. Does not reach.
Further, the relay is reset by the logical product of the protection signal and the bias detection signal, and at the same time, the gate deblocking signal is sent and the self-excited converter is restarted. If the disturbance continues in the power system, the overcurrent relay operates again, but since the bias magnetism detection operates, it does not stop protection and restarts again.
As described above, the restart can be performed any number of times as long as the bias magnetism detection operates.

On the other hand, when the AC overcurrent relay or the DC overcurrent relay is operated and the protection signal is transmitted without the cause of the waveform distortion, the self-excited type is generated by the negation of the bias detection signal and the logical product of the protection signals. The converter immediately stops protection. Since the restart signal and the cutoff signal require time coordination, the time relay 54,
55 are provided. In this way, the cause is isolated even if the overcurrent relay of the self-excited converter operates, and if it is caused by the disturbance of the power system, it will not stop protection and will be restarted multiple times until it is completely restarted. The restart operation can be continued, and otherwise the protection can be stopped immediately.

[0036]

As described above, according to the present invention, not only can the converter be protected from accidents, but also possible conditions can be separated and operation can be continued. Further, according to the control device of the AC / DC converter according to claim 1 of the present invention, when an accident occurs in the AC system to which the AC / DC converter is connected, even if the AC ground voltage rises, the AC line voltage rises. Under an accident condition that does not cause a rise in voltage, the converter can continue to operate to suppress AC overvoltage, and at the same time, the AC line voltage rises and the pole voltage applied to the thyristor valve rises. Under such an accident condition, by stopping the operation of the converter, it is possible to prevent an abnormal phenomenon such as the interelectrode overvoltage of the thyristor valve and protect the devices constituting the converter. Further, according to the second to fourth aspects of the present invention, even if the overcurrent relay operates, the cause thereof can be separated, and when there is no abnormality in the device itself, it can be restarted promptly and completely.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a control device for an AC / DC converter according to claim 1 of the present invention.

2 is an AC voltage detector of FIG. 1 and FIG. 8, an absolute value circuit,
The figure explaining the relationship between the output waveform of the maximum value selection circuit, and the setting voltage level.

FIG. 3 is a diagram showing a configuration of an embodiment of a control device for a self-excited AC / DC converter according to claim 2 of the present invention.

FIG. 4 is a diagram showing an embodiment according to claim 4 of the present invention.

FIG. 5 is a configuration diagram of a control device for a conventional AC / DC converter.

FIG. 6 is a diagram for explaining the relationship between output waveforms of an AC voltage detector, an absolute value circuit, and a maximum value selection circuit and a set voltage level.

FIG. 7 is a vector diagram of the ground voltage and the line voltage when a one-phase ground fault occurs in a direct ground system and a non-ground system.

FIG. 8 is a configuration diagram of a thyristor bridge.

FIG. 9 is a diagram showing a configuration of a general self-excited converter.

[Explanation of symbols]

 1 AC Bus 2 Transformer for Transformer 3 AC / DC Converter 4 DC Reactor 5 DC Current Detector 6 DC Voltage Detector 7 Firing Angle Controller 8-10, 16-18 AC Voltage Detector 11 Phase Detection Circuit 12 Phase Angle 13 Ignition angle 14 Pulse generator 15 Ignition pulse 19 to 21, 31 to 33 Absolute value circuit 22,34 Maximum value selection circuit 23,35 Level detector 24,36 Protection operation signal 25,37 Converter protection circuit 26,27 Converter stop command 28 to 30 Line voltage detector 38 NOT circuit 39 AND circuit 44 Overcurrent relay 45 DC overcurrent relay 46 OR circuit 47 Gate block signal 48 Break signal 49 Waveform distortion detector 51 Negative circuit 52 AND circuit 53 Magnetic field detector 54, 55 Time relay

Claims (4)

[Claims] 1. A control device for an AC / DC converter, wherein ground voltage detection means for detecting that the AC voltage connected to the AC / DC converter is greater than or equal to a set value, and AC system connected to the AC / DC converter. The line voltage detection means for detecting that the line voltage of is not less than a set value, and the ground voltage detection means operates, and while the line voltage detection means is inoperative, while continuing the operation of the AC-DC converter. A control device for an AC / DC converter, comprising: a protection unit that operates to stop the operation of the AC / DC converter when both the ground voltage detection unit and the line voltage detection unit are in operation. 2. A control device for an AC / DC converter, comprising: an AC overcurrent detection means for detecting an AC overcurrent connected to the AC / DC converter; and an DC overcurrent connected to the AC / DC converter. The direct current overcurrent detection means, the waveform distortion detection means for detecting the waveform distortion of the electric quantity of the alternating current system, and the AC-DC converter when at least one of the AC overcurrent detection means and the DC overcurrent detection means operates. AC / DC conversion, comprising: a protection means for gate-blocking and outputting a protection signal for disconnecting from the AC system; and a blocking means for blocking the trip from the protection means by the operation of the waveform distortion detection means. Control device. 3. The control device for an AC / DC converter according to claim 2, further comprising restarting means for restarting the AC / DC converter when the operation of the waveform distortion detecting means is restored. 4. The AC / DC converter according to claim 2 or 3, further comprising a bias magnetism detecting means for detecting a DC bias magnetism of the transformer for the transformer, instead of the waveform distortion detecting means. Control device.