JPH11275872A - Overvoltage protective device for capacitor of power conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a capacitor from an overvoltage without increasing the energy processed by means of nonlinear resistance elements and the overcurrent duty of a power converter, when such an accident as the interline short circuit or arm short circuit occurs. SOLUTION: In a power conversion circuit having series capacitors 31-33 connected between the AC terminal of a power converter and an AC power source 2, nonlinear resistance elements 41-43, switching means (51-53) which short-circuits capacitor terminals to each other, and voltage detecting means (61-63) which detect the voltages across the capacitor terminals are connected between the capacitor terminals, and a control means 200 which turns on a short-circuiting switch about one cycle after the point of time the voltage detecting means detect an overvoltage is provided. For an interline short- circuiting current which continues over one or more cycles, the short-circuiting current is by-passed to short-circuiting switches, and for one-cycle arm short circuit, the igniting pulse of the power converter is stopped before the short- circuiting switches are turned on, and the capacitors 31-33 suppress the short- circuiting current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to overvoltage protection of a capacitor, and more particularly, to a capacitor overvoltage protection device for a power conversion circuit for overvoltage protecting a capacitor used in a power conversion circuit.

[0002]

2. Description of the Related Art As a DC interconnection power conversion system, for example, Japanese Patent Laid-Open Publication No. Hei 8-228480 discloses a series connection between an AC terminal of a thyristor converter 1 and a conversion transformer T as shown in FIG. A circuit for connecting the capacitors 3 in series is disclosed. The thyristor converter 1 converts three-phase AC to DC or DC to three-phase AC,
AC voltage VS, DC voltage ED of converter 1 and DC current I
D is input and controlled by the control circuit 100 that generates a firing pulse. By the way, it is known that various advantages can be obtained by the series capacitor 3 in the power conversion system. As one advantage, the capacitor 3 is charged by the alternating current of the converter 1, which adds to the commutation voltage of the converter. Since the firing angle is set with respect to the AC system voltage 2, the converter performing the forward conversion operation has a small firing angle α.
Thus, a converter that performs an inverse conversion operation can operate at a large firing angle α. This means a reduction in the amount of reactive power generated as viewed from the AC system. As another advantage, even if the AC system voltage 2 is transiently reduced for some reason, the decrease in the commutation voltage is suppressed by the capacitor voltage, so that the commutation voltage can be maintained and the commutation failure can be prevented. .

[0003]

However, in a DC interconnection system having a series capacitor, if an overcurrent flows through the capacitor due to some accident, an overvoltage is generated in the capacitor, and the capacitor is destroyed. is there. On the other hand, a non-linear resistance element (for example, a ZnO type varistor) is connected between the capacitor terminals, and when the capacitor voltage exceeds a predetermined value, a current flows through the non-linear resistance element, thereby overcharging the capacitor. It is known to prevent. However, if the overcurrent continues, the energy to be processed by the nonlinear resistance element becomes enormous, and there is a problem that the nonlinear resistance element becomes very large. An object of the present invention is to provide a power conversion circuit suitable for protecting a capacitor from overvoltage without increasing the processing energy of a nonlinear resistance element and the overcurrent duty of a power converter in the event of a line short-circuit or an arm short-circuit. A capacitor overvoltage protection device is provided.

[0004]

The object of the present invention is to provide a voltage detecting means for detecting a voltage between capacitor terminals of a series capacitor connected between an AC terminal of an electric power converter and an AC power supply, or detecting an AC current of the converter. Current detecting means, and a switch for short-circuiting between the capacitor terminals is provided,
It is possible to solve the problem by providing control means for generating a switch-on signal when a predetermined time has elapsed from the time when the overvoltage of the capacitor or the overcurrent of the AC current is detected by the detection means, and for turning on the switch. You.

According to the present invention, an overvoltage or an overcurrent is detected by the voltage or current detection means, and a short-circuit switch is turned on about one cycle after the occurrence of the overvoltage or the overcurrent, whereby a line-to-line short-circuit current that continues for one cycle or more is provided. Is bypassed to the short-circuit switch, so that the capacitor can be protected from overvoltage while reducing the processing energy of the non-linear resistance element. In addition, for one cycle of arm short-circuit, the power converter is turned on before the short-circuit switch is turned on. , The short-circuit current can be suppressed by the capacitor.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 illustrates a capacitor overvoltage protection device for a power conversion circuit according to an embodiment of the present invention. In the present embodiment, the non-linear resistance elements 41 to 43 and the short-circuit switch 51 are connected between the terminals of the capacitors 31 to 33 of the conventional example shown in FIG.
To 53, voltage detectors 61 to 63 and a short-circuit switch control device 200 are provided. Reference numeral 7 denotes a power breaker.
The control device 200 for the short-circuit switch includes the voltage detectors 61 to 6.
3 inputs the overvoltage of the capacitors 31 to 33 to the overvoltage detecting means 201 and delays the overvoltage by the time delay means 202 for a predetermined time, and then inputs the closing signal to the switch drive circuit 203 to drive the short-circuit switches 51 to 53.

FIG. 2 shows the operation when the short-circuit switches 51 to 53 are not provided when the line-to-line short-circuit accident shown in FIG. 1A occurs. The non-linear resistance elements 41 to 43 have a voltage-current characteristic as shown in FIG. 3, and when an overvoltage occurs between terminals, a current flows through the non-linear resistance element to absorb energy, thereby suppressing a rise in voltage. . Now, when a line short circuit at point A in FIG. 1 occurs at the time shown in FIG. 2 (occurrence of an accident), the system voltage 2 is short-circuited via the capacitors 31 and 32. A current is generated (a rectangular wave usually indicates a current flowing in the main circuit), and the capacitors 31 and 32 are caused by this overcurrent.
Is overcharged, an overvoltage occurs. When this overvoltage exceeds the overvoltage protection level, the nonlinear resistance element 4
The overcurrent bypasses 1 and 42, and the capacitor voltage is kept close to the protection level. However, due to the current flowing through the nonlinear resistance elements 41 and 42, the processing energy of the nonlinear resistance elements 41 and 42 temporarily increases (illustrated as an integral value of the processing energy of the nonlinear resistance elements). When an accident occurs, the circuit breaker 7 is tripped. However, since a normal circuit breaker requires several cycles before tripping, in this case, it is necessary to use a nonlinear resistance element capable of processing the increased energy during the trip. That is, when the overcurrent continues, the energy to be processed by the nonlinear resistance element becomes enormous, so that the nonlinear resistance element needs to be very large.

On the other hand, when the short-circuit switches 51 to 53 are provided, even if a line-to-line short-circuit at the point A occurs, the short-circuit switch is turned on immediately after the occurrence of the overvoltage, thereby preventing the occurrence of the overvoltage of the capacitor. It is possible to reduce the processing energy of the resistance element. However, by providing the short-circuit switches 51 to 53, the effect of suppressing the arm short-circuit current is lost when an arm short-circuit occurs in the converter 1 instead of the short-circuit accident at the point A. Here, the effect of suppressing the arm short-circuit current means that when the arm short-circuit of the converter 1 occurs, the firing pulse of the converter is instantaneously stopped (hereinafter, this operation is referred to as a gate block), and the alternating current is applied. Since the overcurrent is removed in one cycle, it means that the arm short-circuit current can be suppressed. FIG. 4 shows an operation in which the effect of suppressing the arm short-circuit current is lost. Time point in Fig. 4 (occurrence of accident)
When an arm short-circuit accident occurs, the system voltage is short-circuited via a circuit impedance (not shown) and a capacitor, and a short-circuit current determined by both impedances flows. As a result, when the capacitor voltage rises, and when the capacitor voltage rises to the protection level, a short circuit switch is turned on by a turn-on signal to short-circuit the capacitor, the impedance of the short-circuit path of the system voltage is reduced. Increases from the solid line shown to the broken line. Since this arm short-circuit current flows through the converter 1, the overcurrent duty of the converter 1 is increased as compared with the case where the capacitor is not short-circuited. That is, when the capacitor is short-circuited, the arm short-circuit current cannot be suppressed. The capacitor voltage becomes zero as shown by the dotted line when the capacitor is short-circuited by the short-circuit switch.

FIG. 5 shows the operation of the embodiment of FIG. In the present embodiment, if a line short circuit occurs at the time point (accident occurrence) in FIG. 5, the system voltage 2 is short-circuited via the capacitors (31 to 33). Occurs, and the capacitor (31-33)
Is overcharged, an overvoltage occurs. When the overvoltage exceeds the overvoltage protection level of the nonlinear resistance elements (41 to 43), the overcurrent bypasses the nonlinear resistance elements (41 to 43), and the capacitor voltage is suppressed to the vicinity of the protection level. This protects the capacitor from overvoltage. At the same time, the voltage detectors (61 to 63) detect an overvoltage of the capacitor voltage, and input this overvoltage detection signal to the overvoltage detection means 201 of the control device. In this case, if the time delay by the time delay means 202 is about one cycle,
After a time delay of about one cycle by the time delay means 202, that is, after the three overvoltage detection signals shown in FIG.
The closing signal of 3) is generated, and the short-circuit switches (51 to 53) are driven by the switch driving circuit 203 to short-circuit the capacitors (31 to 33). Thereby, the period during which the current flows through the nonlinear resistance elements (41 to 43) is suppressed to about one cycle, so that the processing energy (integral value) of the nonlinear resistance element can be reduced as compared with FIG. If an arm short circuit occurs at the time point (accident occurrence) in FIG. 5, the converter 1 is gate-blocked instantaneously (within one cycle).
Therefore, the short-circuit switches (51 to 53) are turned on after the gate block. In other words, when the arm is short-circuited, until the converter 1 is gate-blocked,
Since the short-circuit switches (51 to 53) are not turned on, the capacitors (31 to 33) are present in the system voltage short-circuit path, thereby preventing the arm short-circuit current from increasing. That is, the effect of suppressing the arm short-circuit current can be maintained by the capacitor. As described above, in the present embodiment, when an accident such as line-to-line short-circuit or arm short-circuit occurs, the capacitor can be protected from overvoltage without increasing the processing energy of the nonlinear resistance element and the overcurrent duty of the converter.

FIG. 6 shows another embodiment of the present invention. The operation is shown in FIG. FIG. 6 shows a part of the control device 200 of the embodiment shown in FIG. 1 and is provided with a means 204 for masking an overvoltage signal for a predetermined time. In FIG. 6, when an overvoltage signal is input to the overvoltage detection means 201 as shown in FIG. 7, the masking means 204 masks the overvoltage signal for about one cycle after the overvoltage detection. , A closing signal is generated by the subsequent overvoltage signal. Then, this input signal is transmitted to the switch drive circuit 20.
3 to drive the short-circuit switch. Further, when an arm short-circuit accident occurs, the short-circuit switches (51 to 53) are not turned on by the mask of the overvoltage signal until the converter 1 is gate-blocked. This allows
The same effect as that of the embodiment of FIG. 1 can be realized, and at the same time, if an accident is eliminated during the mask period, no closing signal is generated, so that the operation can be continued as it is.

FIG. 8 shows another embodiment of the present invention. The operation is shown in FIG. FIG. 8 shows a part of the control device 200 of the embodiment shown in FIG. 1, and includes an absolute value means 205 for generating positive and negative capacitor voltages as absolute values, and an integrating means for integrating the absolute values of the capacitor voltages after an overvoltage occurs. 2
06, a comparison means 207 for generating a closing signal when the integrated value exceeds a predetermined judgment level. FIG.
In FIG. 9, a line-to-line short-circuit accident occurs as shown in FIG.
When an overvoltage signal is input to the overvoltage detection means 201, the integration start signal is transmitted from the overvoltage detection means 201 to the integration means 206.
Output to The integrating means 206 integrates the absolute value of the capacitor voltage, and generates a closing signal from the comparing means 207 when the integrated value exceeds a predetermined judgment level. Then, this input signal is input to the switch drive circuit 203 to drive the short-circuit switch. Further, when an arm short-circuit accident occurs, the integrated value of the absolute value of the capacitor voltage does not reach the predetermined determination level until the converter 1 is gate-blocked, so the short-circuit switches (51 to 53) are turned on. Never. Thereby, the same effect as that of the embodiment of FIG. 1 can be realized, and at the same time, the processing energy of the nonlinear resistance element can be indirectly evaluated based on the integral value of the absolute value of the capacitor voltage, so that the capacity of the nonlinear resistance element is reduced. be able to.

FIG. 10 shows another embodiment of the present invention.
In the present embodiment, current detectors 81 to 83 for detecting an alternating current are provided in place of the voltage detectors 61 to 63 for detecting the capacitor voltage in the embodiment shown in FIG. An overcurrent detection means 208 is provided instead of the overvoltage detection means 201 of the switch control device 200, and an overcurrent signal of an alternating current is used instead of the capacitor overvoltage signal. In FIG. 10, when a line short-circuit accident occurs and the current detectors (81 to 83) detect an overcurrent, an overcurrent signal is input to the overcurrent detecting means 208. In this case, as in the embodiment of FIG. Assuming that the time delay by the time delay means 202 is about one cycle, after a time delay of about one cycle by the time delay means 202, a closing signal of the short-circuit switch (51-53) is generated.
The short circuit switches (51 to 51) are switched by the switch driving circuit 203.
53) and short-circuit the capacitors (31-33). When an arm short circuit accident occurs, the converter 1 is gate-blocked instantaneously (within one cycle), so that the short-circuit switches (51 to 53) are turned on after the gate block. Thereby, the same effect as the embodiment of FIG. 1 can be realized. Here, since the capacitor voltage is the integral of the current, the detection of the overvoltage is slower than the detection of the overcurrent. Therefore, according to the present embodiment, in particular, the accident can be detected at a higher speed than the embodiment of FIG. Since the generation of the signal can be hastened, the processing energy of the nonlinear resistance element can be further reduced.

FIG. 11 shows another embodiment of the present invention.
In this embodiment, instead of the voltage detecting means 61 to 63 for detecting the capacitor voltage in the embodiment shown in FIG. 1, current detecting means 81 to 83 for detecting an AC current are provided, and a current detecting means 9 for detecting a DC current is provided. In addition, in place of the overvoltage detection means 201 of the short-circuit switch control device 200 of the embodiment shown in FIG. 1, an accident occurrence signal is generated when an overcurrent occurs only in an alternating current from an alternating current and a direct current, An accident judging means 213 which does not generate an accident occurrence signal when an overcurrent occurs in both currents is provided. In FIG. 11, when a DC ground fault occurs on the DC side of converter 1, current detecting means 81 to 83 for detecting an AC current are provided.
And the current detecting means 9 for detecting a direct current simultaneously detect an overcurrent. At this time, the accident determination means 213 determines that a DC ground fault has occurred, and does not generate an accident occurrence signal. Therefore, control device 200 does not turn on short-circuit switches 51 to 53, and shifts the firing angle of converter 1 to reduce overcurrent by means (not shown) incorporated in control circuit 100. Thus, in the present embodiment, the operation can be restarted at a high speed after the accident is eliminated. On the other hand, when only the current detecting means 81 to 83 for detecting an alternating current detect an overcurrent, the fault determining means 213 determines that there is a line short-circuit or an arm short-circuit and generates a fault occurrence signal. It operates in the same way as the form. Thereby, the same effect as the embodiment of FIG. 1 can be realized, and at the same time, in the case of the DC ground fault, the operation can be restarted at high speed after the removal of the fault.

In the above embodiment, a thyristor is described as a short-circuit switch for a capacitor. However, the same applies to other semiconductor switches such as GTO or high-speed mechanical switches that can be turned on in about several ms. The effect is obtained. Although the reactor is described as the impedance connected in series to the short-circuit switch, it is also possible to connect a resistor, a series circuit of the resistor and the reactor, or a circuit combining a resistor, a reactor, and a capacitor.

[0015]

As described above, according to the present invention,
When a predetermined time has elapsed from the point when the overvoltage of the capacitor or the overcurrent of the AC current is detected at the time of the occurrence of the line short-circuit accident, by turning on the short-circuit switch, Capacitors can be protected from overvoltage while reducing the processing energy of the non-linear resistance element, and when an arm short circuit occurs, the point of the power converter before the short circuit switch is turned on for one cycle of arm short circuit. Since the arc pulse stops, the effect of suppressing the short-circuit current can be maintained by the capacitor. As a result, the capacitor can be protected from overvoltage without increasing the processing energy of the nonlinear resistance element and the overcurrent duty of the power converter. Further, by detecting the overcurrent of the alternating current instead of detecting the overvoltage of the capacitor voltage, an accident can be detected at high speed, and the processing energy of the nonlinear resistance element can be further reduced. In addition, when a DC ground fault occurs, by shifting the firing angle of the power converter and reducing the overcurrent without short-circuiting the capacitor, the operation can be restarted at high speed after the fault is eliminated.

[Brief description of the drawings]

FIG. 1 is a capacitor overvoltage protection device for a power conversion circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an operation when there is no short-circuit switch in FIG. 1;

FIG. 3 is a voltage-current characteristic diagram of a nonlinear resistance element.

FIG. 4 is an explanatory diagram of an operation when there is no time delay unit in FIG. 1;

FIG. 5 is an operation explanatory diagram of the embodiment of FIG. 1;

FIG. 6 shows another embodiment of the present invention.

FIG. 7 is an operation explanatory view of the embodiment of FIG. 6;

FIG. 8 shows another embodiment of the present invention.

FIG. 9 is an operation explanatory diagram of the embodiment in FIG. 8;

FIG. 10 shows another embodiment of the present invention.

FIG. 11 shows another embodiment of the present invention.

FIG. 12 is a configuration diagram of a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Thyristor converter, 31-33 ... Capacitor, 41
~ 43 ... nonlinear resistance element, 51-53 ... short circuit switch,
61: voltage detector, 81: current detector, 9: current detector, 100: converter control circuit, 200: short-circuit switch control device, 201: overvoltage detection means, 202: time delay means, 203: switch driving means, 204 ... mask means,
205: absolute value means, 206: integrating means, 207: comparing means, 208: overcurrent detecting means, 213: accident determining means

Claims (6)

[Claims] 1. A power converter circuit comprising: a power converter for converting three-phase AC to DC or DC to three-phase AC; and a series capacitor connected between an AC terminal of the power converter and an AC power supply. A non-linear resistance element is connected between the capacitor terminals, switch means for short-circuiting between the capacitor terminals, and voltage detection means for detecting the voltage between the capacitor terminals are connected, and a predetermined value is detected from the time when the overvoltage is detected by the detection means. A capacitor overvoltage protection device for a power conversion circuit, further comprising control means for turning on the switch when time has elapsed. 2. A power conversion circuit comprising: a power converter for converting three-phase AC to DC or DC to three-phase AC; and a series capacitor connected between an AC terminal of the power converter and an AC power supply. A non-linear resistance element is connected between the capacitor terminals, and switch means for short-circuiting between the capacitor terminals and voltage detection means for detecting the voltage between the capacitor terminals are connected, and the overvoltage signal of the detection means is detected from the time of detection of the overvoltage. A capacitor overvoltage protection device for a power conversion circuit, comprising a control unit for masking for a predetermined period and turning on the switch when the mask period has elapsed. 3. A power conversion circuit comprising: a power converter for converting three-phase AC to DC or DC to three-phase AC; and a series capacitor connected between an AC terminal of the power converter and an AC power supply. A non-linear resistance element is connected between the capacitor terminals, and switch means for short-circuiting between the capacitor terminals and voltage detection means for detecting the voltage between the capacitor terminals are connected, and the capacitor is connected from the time when the overvoltage is detected by the detection means. Integrating the absolute value of the voltage,
A control device for turning on the switch when the integrated value reaches a predetermined value is provided. 4. A power conversion circuit having a power converter for converting three-phase AC to DC or DC to three-phase AC, and a series capacitor connected between an AC terminal of the power converter and an AC power supply. A non-linear resistance element is connected between the capacitor terminals and switch means for short-circuiting between the capacitor terminals is connected, and further, current detecting means for detecting an alternating current of the converter is provided, and overcurrent is detected by the detecting means. Control means for turning on the switch when a predetermined time has elapsed from the time when the power supply circuit has been turned on. 5. A power converter circuit comprising: a power converter for converting three-phase AC to DC or DC to three-phase AC; and a series capacitor connected between an AC terminal of the power converter and an AC power supply. Connecting a non-linear resistance element between the capacitor terminals and connecting a switch means for short-circuiting between the capacitor terminals; furthermore, a current detection means for detecting an AC current of the converter and a current detection for detecting a DC current of the converter. And a control means for deciding whether or not to turn on the switch according to the type of accident determined from the AC current and the DC current. 6. The switch according to claim 5, wherein when the overcurrent is detected only by the current detecting means for detecting the alternating current of the converter, the switch is turned off when a predetermined time has elapsed from the time when the overcurrent was detected. When the over current is detected from both the current detecting means for detecting the AC current of the converter and the current detecting means for detecting the DC current of the converter, the firing angle of the converter is shifted to A capacitor overvoltage protection device for a power conversion circuit, characterized in that the current is reduced.