JPH06113444A - Protective device of self-excited converter - Google Patents

Abstract

PURPOSE:To enhance the reliability of an apparatus when a self-excited converter is applied to the power transmission and transformation apparatus of an electric power system by protecting an overcurrent in the accident of the self-excited converter. CONSTITUTION:A diode 7, a thyristor rectifier 9 which is connected in parallel with it and a current-limiting reactor 8 are connected in series with a main circuit. In order to use the thyristor rectifier 9 in common as the charger of a DC circuit, a switch 10 for circuit changeover is installed. Thereby, by adding a simple circuit, a self-excited converter can be protected in its accident, and the reliability of an apparatus can be enhanced when the self-excited converter is applied to the power transmission and transformation apparatus of an electric power system. In addition, when a protective device is used in common as the charging circuit of a capacitor for a reactive-power compensation device, the device can be made compact and its cost can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power composed of an element having a self-extinguishing function (hereinafter referred to as a self-extinguishing element) used in a static var compensator, a DC power transmission system, a photovoltaic power generation system and the like. The present invention relates to a protective device for a self-excited converter that converts the AC power into AC power or the AC power into DC power.

[0002]

2. Description of the Related Art With the increase in withstand voltage and capacity of self-extinguishing elements, large-capacity self-excited converters to which such self-extinguishing elements are applied have come into practical use. FIG. 5 shows a conventional example of a self-excited converter, taking as an example the case where such a self-excited converter is applied to a static var compensator.

In the figure, 1 is an AC system, 2 is a conversion transformer of a self-excited converter 3, and 3 is a gate having a self-extinguishing function.
A self-excited converter (voltage source inverter) 4 and a self-excited type in which a diode D is connected in antiparallel with a turn-off thyristor (GTO), etc., and is composed of a single-phase or three-phase bridge connection. The rise of the current i flowing in the main circuit of the converter 3 (di /
dt) to suppress the reactor, 41 is a flywheel diode, 5 is a capacitor, 51 is a diode rectifier for charging the capacitor 5 in the initial stage of activation of the reactive power compensator, 52 is a transformer, 53 is A charging power source 6 is a control circuit for the voltage source inverter 3. Since the current flowing through the reactive power compensator flows according to the difference between the voltage of the system and the voltage of the device, it is possible to generate the reactive power from the lead to the delay by changing the amplitude of the output voltage of the voltage source inverter. it can.

[0004]

In the self-excited converter shown in FIG. 5, when an arm short circuit occurs in the voltage source inverter, there is a reactor 4 which suppresses the rise of the current flowing in the main circuit, but an accident occurs. If the protective operation for current detection or overcurrent suppression is delayed, there is a risk that the fault current will exceed the current value at which the self-arc-extinguishing element that constitutes the main circuit can be cut off, and destroy the self-arc-extinguishing element.

The present invention has been made in view of such circumstances, and it is possible to protect the self-exciting converter by simply adding a simple circuit and to downsize the device and reduce the cost. It is an object of the present invention to provide a protection device for a container.

[0006]

SUMMARY OF THE INVENTION A protective device for a self-excited converter according to the present invention is a self-excited converter for converting AC power composed of a self-extinguishing element into DC power or converting DC power into AC power. In the protection device, a diode connected between the self-excited converter and a DC power source or a capacitor on the DC side with a polarity that blocks a current flowing from the DC power source or the DC side to the main circuit of the self-excited converter. , A series circuit composed of a thyristor rectifier and a current limiting reactor connected in parallel to the diode, and a control means for controlling the output current of the thyristor rectifier.

The protection device for a self-excited converter according to the present invention comprises:
The control means is given a constant value as a current command value for the thyristor rectifier.

Further, the protective device for a self-excited converter according to the present invention is
The control means includes, as a current command value for the thyristor rectifier, the main circuit received from a control device which supplies a current command value to the main circuit of the self-exciting converter to control a current flowing through the main circuit. It is characterized in that a supplied current command value is given.

The protection device for the self-excited converter according to the present invention comprises:
The control means includes an addition means for setting a value obtained by adding a margin to the current command value for the thyristor rectifier as a current command value for the thyristor rectifier.

Further, the protection device for a self-excited converter according to the present invention is
In a protective device for a self-excited converter that converts alternating-current power to direct-current power or direct-current power to alternating-current power, which is composed of a self-extinguishing element, between the self-excited converter and a direct-current power supply or a capacitor on the direct-current side. A series consisting of a diode connected with a polarity that blocks a current flowing from the DC power source or the DC side to the main circuit of the self-excited converter, and a thyristor rectifier and a current limiting reactor connected in parallel to the diode. Circuit, switching means for sharing the thyristor rectifier as a charging circuit for the DC-side capacitor, voltage detection means for detecting the voltage across the terminals of the capacitor, and current flowing in the main circuit of the self-excited converter. The current detection means for detection and the detection outputs of the voltage detection means and the current detection means are fetched, and the charging voltage and the size of the capacitor are calculated based on these detection outputs. And having a control means for controlling the output current of the static rectifier.

The protective device for a self-excited converter according to the present invention comprises:
The control means is a constant current control means for controlling the current flowing in the main circuit of the self-excited converter to be constant based on a current command value, and a voltage between terminals of the capacitor based on a command value of the charging voltage of the capacitor. Of the self-excited converter of the present invention, further comprising constant voltage control means for controlling the constant voltage and signal switching means for switching the signal output of the constant current control means and the constant voltage control means. The device, the current command value given to the constant current control means of the control means,
The feature is that when an accident occurs, a smaller value is set than in steady operation.

[0012]

In the protective device for a self-excited converter having the above-mentioned structure, a DC current for producing necessary reactive power is supplied through the diode during steady operation. Since the diode is connected in the opposite direction to the direct current flowing in the main circuit of the self-excited converter, the thyristor rectifier connected in parallel to the diode causes a circulating current to flow so that the direct current flows in the main circuit. Keep it.

When an excessive current is about to flow due to an arm short circuit accident of the self-excited converter, the current of the thyristor rectifier is throttled to prevent the current from flowing to the main circuit by the diode, and the accident current is connected in parallel to the diode. It is possible to prevent an excessive current from flowing into the main circuit of the self-excited converter by causing the current to flow into the current limiting reactor. If the excessive current is suppressed in this way, the self-extinguishing element constituting the self-excited converter is formed by shutting off the self-current by the element (GTO) having the self-extinction function of the voltage source inverter. Can be protected.

[0014]

FIG. 1 shows an embodiment in which the protective device for a self-excited converter according to the present invention is applied to a reactive power compensator. Since the elements having the same numbers as those in FIG. 5 have the same function, different elements will be described. 7 is a diode connected in the direction opposite to the direction in which the current of the circuit flows, and 8 is a diode. 7, a current limiting reactor for limiting the current connected in parallel to 7, a thyristor rectifier composed of a thyristor bridge, 90 a control circuit of the thyristor rectifier, 91 a transformer connected to the thyristor rectifier, 92 an AC power supply, 9
Reference numeral 3 is a DC current detector for detecting the current flowing in the main circuit.

To explain the operation of this circuit, since the diode 7 is connected in the direction opposite to the direction in which the current of the main circuit flows, the current of the main circuit does not flow. In order to allow the current to flow through the diode, it is apparent that the main circuit current flows through the diode 7 when the thyristor rectifier 9 causes a current larger than the current flowing through the main circuit by a margin. It will be the same. By always adjusting the current of the thyristor rectifier according to the current of the main circuit in this manner, the current can be passed through the voltage source inverter 3.
Next, the operation at the time of an accident will be described.

Now, consider the case where an arm short circuit occurs in the voltage source inverter 3. Since the DC circuit is short-circuited, the electric charge charged in the capacitor 5 is discharged through the diode 7. However, when the short-circuit current exceeds the set current of the thyristor rectifier 9, the current of the diode 7 is reversed, so that the diode 7 is blocked.

When the fault current further increases, the current tends to flow through the circuit composed of the thyristor rectifier 9 and the current limiting reactor 8 which are connected in parallel with the diode. However, the fault current is suppressed by the current limiting reactor 8. Although not shown in FIG. 1, if a separately provided accident detection signal is used, the self-extinguishing element can be prevented from being broken if the accident current is cut off by using the self-extinguishing element of the voltage source inverter.

A specific example of the control circuit 90 of the thyristor rectifier 9 is shown in FIG. An adder 901 adds the command value COM, the margin setting value MAG, and the current detection value signal of the main circuit with the polarities shown in the figure. In this case, COM is a command value of the current flowing through the thyristor rectifier 9. In this case, since the current value corresponding to the amount of reactive power of the static var compensator is set to the set value, it corresponds to the reactive power to be output from the reactive circuit compensator from the control circuit 6 of the self-excited converter 3. The current value to be applied may be received as the set value. It is obvious that the current command value of COM may be a constant value of the rating of the reactive power compensator.

Reference numeral 902 denotes an operational amplifier which operationalally amplifies the output of the adder 901. A constant current control circuit is configured by the adder 901 and the operational amplifier 902. A phase control circuit 903 outputs an ignition pulse of the thyristor rectifier according to the output of the operational amplifier. The phase control circuit 903 controls so that a current having a value obtained by adding the margin setting value MAG to the command value COM flows into the diode 7. If the margin setting value is selected to be about 10% of the rated current, if the fault current exceeds the operating current plus 10% of the rated current, the fault current will be suppressed by the source reactor. .

Although the arm short circuit of the self-excited converter has been described as an example of the accident, the overcurrent can be suppressed even in the case of an AC system accident. Even in this case, it is clear that the operation is the same as when the arm is short-circuited, and the protective device of the present invention can suppress the current flowing in the self-excited converter at the time of an accident.

Another embodiment of the present invention is shown in FIG. In FIG. 3, the thyristor rectifier inserted for overcurrent protection in FIG. 1 is also used as a charging circuit for the capacitor 5. Since the same numbers as those in the previous figure show the same function, different ones will be described. 10 is a changeover switch for changing the thyristor rectifier 9 into a circuit for charging the capacitor 5 and a circuit for supplying a reflux current to the diode 7. Is a control circuit for issuing an ignition pulse to the thyristor rectifier 9 for using the thyristor rectifier 9 for charging and reflux current, and 95 is a DC voltage detector for detecting the terminal voltage of the capacitor 5.

The details of one embodiment of the control circuit 94 of the thyristor rectifier 9 are shown in FIG. 904 to 90 compared to FIG.
6 is added to charge the capacitor 5. 90
Reference numeral 4 denotes an adder for obtaining the deviation between the command value COM2 and the detection value of the DC voltage detector 95, and 905 denotes an operational amplifier for performing operational amplification on the output of the adder. The adder 904 and the operational amplifier 905 constitute a constant voltage control circuit. is doing. A signal switching circuit 906 switches the input of the phase control circuit 903 according to another signal of the command value COM3. In this case, the command value COM2 is given the voltage command value of the charging voltage of the capacitor 5.

To explain the operation of the circuit, first, the changeover switch 10 is changed over to the contact a side, and the capacitor 5 is charged by the thyristor rectifier 9. Next, the control circuit 94 controls the firing pulse of the thyristor rectifier 9 so that the voltage across the terminals of the capacitor 5 becomes a specified value.

When the voltage across the terminals of the capacitor 5 is charged to the specified value, the changeover switch 10 is changed over to the contact b side for use for the return current of the diode 7 this time, which is necessary for the reactive power compensator. A thyristor rectifier 9 supplies a freewheeling current to the diode 7 by supplying a current command value.

After that, the voltage source inverter 3 is started to operate as a predetermined reactive power compensator. The operation of the protection circuit at the time of steady operation during operation as a reactive power compensator and at the time of an accident is the same as described in the embodiment shown in FIG.

In the control circuit 94 of FIG. 4, in the event of an accident, the accident current is suppressed to a small value by setting the current command value input to the adder 901 forming the constant current control circuit to be smaller than that in steady operation. Therefore, the self-extinguishing element forming the self-excited converter can be more reliably protected.

In the above embodiments, the case where the protection device for the self-excited converter is applied to the static var compensator has been described. However, the power conversion device for direct current transmission, the power conversion device for solar cells, and the power conversion for fuel cells. When the self-excited converter is applied to the device or the like, the protection device of the present invention can be similarly applied.

[0028]

As described above, according to the protection device for a self-excited converter of the present invention, a diode is connected in series to the main circuit of the self-excited converter, and a thyristor rectifier and a current limiting reactor are connected in parallel to the diode. Since it is configured, it is possible to protect the self-excited converter in the event of an accident by adding a simple circuit, and it is possible to improve the reliability of the device when the self-excited converter is applied to the power transmission and transformation equipment of the power system. Further, by sharing the protection device also as a charging circuit for the capacitor of the reactive power compensating device, the device can be downsized and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a protective device for a self-excited converter according to the present invention.

2 is a block diagram showing a specific configuration of a control circuit of the thyristor rectifier in FIG.

FIG. 3 is a circuit diagram showing the configuration of another embodiment of the protective device for a self-excited converter according to the present invention.

4 is a block diagram showing a specific configuration of a control circuit of the thyristor rectifier in FIG.

FIG. 5 is a circuit diagram showing a configuration of a static var compensator for explaining the prior art of the present invention.

[Explanation of symbols]

 1 AC system 2 Transformer 52 Transformer 91 Transformer 3 Self-exciting converter 4 Reactor 41 Flywheel diode 5 Capacitor 51 Diode rectifier 53 AC power supply 92 AC power supply 7 Diode 8 Current limiting reactor 9 Thyristor rectifier 6 Control circuit 90 Control circuit 94 Control circuit 93 DC current detector 95 DC voltage detector 10 Changeover switch 901 Adder 904 Adder 902 Operational amplifier 905 Operational amplifier 903 Phase control circuit 906 Signal switching circuit

Claims (7)

[Claims] 1. A protective device for a self-exciting converter that converts AC power to DC power or DC power to AC power, which is composed of a self-extinguishing element, comprising: A diode connected between the capacitor and a DC power source or a polarity that blocks a current flowing from the DC side to the main circuit of the self-excited converter, a thyristor rectifier connected in parallel with the diode, and a current limiting A protective device for a self-excited converter, comprising: a series circuit including a reactor; and control means for controlling an output current of the thyristor rectifier. 2. The protective device for a self-excited converter according to claim 1, wherein a constant value is given to the control means as a current command value for the thyristor rectifier. 3. The control means receives, as a current command value for the thyristor rectifier, a control device which supplies a current command value to the main circuit of the self-excited converter for controlling a current flowing through the main circuit. The self-excited converter protection device according to claim 1 or 2, wherein a current command value supplied to the main circuit is given. 4. The control means has an adding means for setting a value obtained by adding a margin to a current command value for the thyristor rectifier as a current command value for the thyristor rectifier. Self-excited converter protection device. 5. A protective device for a self-exciting converter that converts alternating-current power to direct-current power or direct-current power to alternating-current power, which is composed of a self-extinguishing element, comprising: A diode connected between the capacitor and a DC power source or a polarity that blocks a current flowing from the DC side to the main circuit of the self-excited converter, a thyristor rectifier connected in parallel with the diode, and a current limiting A series circuit composed of a reactor, a switching means for sharing the thyristor rectifier as a charging circuit for the capacitor on the DC side, a voltage detecting means for detecting a terminal voltage of the capacitor, and a main part of the self-exciting converter. Current detection means for detecting the current flowing in the circuit, and the detection outputs of the voltage detection means and the current detection means are fetched, and based on these detection outputs, the capacitor A protection device for a self-excited converter, comprising: a control unit that controls a charging voltage and an output current of a thyristor rectifier. 6. The constant current control means for controlling the current flowing in the main circuit of the self-excited converter to be constant based on a current command value, and the control means based on a command value of a charging voltage of the capacitor. 6. The constant voltage control means for controlling the voltage between the terminals of the capacitor to be constant, and the signal switching means for switching the signal output of the constant current control means and the constant voltage control means. Self-excited converter protection device. 7. The self-excited conversion according to claim 6, wherein the current command value given to the constant current control means of the control means is set to a smaller value when an accident occurs as compared with a steady operation. Protective device.