JP2018157702A - Voltage compensator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage compensator capable of protecting from an excessive current when an excessive fault current flows to an electric power system.SOLUTION: A voltage compensator comprises: an input terminal; an output terminal; a power conversion part that includes a current passage toward a DC terminal from the input terminal; a first current transformer having a secondary winding connected to one input terminal; a second current transformer having the second winding connected to the other input terminal; a capacitor connected between the output terminals; an inductor connected serially between the second winding of the first current transformer and the first AC input terminal; a first rectifier element that flows a current toward the first DC output terminal from a node to which the secondary winding of a first current transformer and the inductor are connected; and a second rectifier element that flows the current toward the node from a second DC terminal.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to a voltage compensation device.

  In the power system, the power line impedance increases according to the distance from the substation, and therefore, the received voltage may decrease due to the voltage drop at the end of the system. In the electric power system, it is necessary to make a constant voltage available regardless of the distance from the substation.

  In a power system, an accident such as a ground fault occurs due to a lightning strike or the like, and an excessive current may flow in a device connected to the system, and it is necessary to protect the device from such an accident.

Yuji Sasaki, Takahiko Yoshida, Nagataka Seki, Toshiyuki Watanabe, Yuji Saito, “TVRs enabling high-speed response and their verification tests”, IEEJ Transactions B, Vol. 123 (2003)

  The embodiment provides a voltage compensator capable of protecting from an excessive current when an excessive fault current flows in the power system.

  The voltage compensator according to the embodiment is a voltage compensator that compensates the voltage of the power system. The voltage compensator includes a first DC terminal, a second DC terminal, a first AC terminal, a second AC terminal, a first current path from the first AC terminal to the first DC terminal, A second current path from the second DC terminal to the second AC terminal, a third current path from the second AC terminal to the first DC terminal, and from the second DC terminal to the first AC terminal A first transformer having a power converter including a fourth current path, a primary winding connected in series to the first power line of the power system, and a secondary winding connected to the first AC terminal. A second winding having a primary winding connected in series to a second power line of the power system, a secondary winding connected to the second AC terminal, the first DC terminal, and the first A capacitor connected between two DC terminals, a secondary winding of the first transformer, An inductor connected in series with one AC terminal, and a first rectifying element that allows current to flow from the node to which the secondary winding of the first transformer and the first inductor are connected toward the first DC terminal And a second rectifying element that allows current to flow from the second DC terminal toward the node.

1 is a block diagram illustrating a voltage compensation device according to a first embodiment. It is a block diagram for demonstrating operation | movement of a voltage compensation apparatus. It is a block diagram for demonstrating operation | movement of a voltage compensation apparatus. It is a block diagram for demonstrating operation | movement of a voltage compensation apparatus. It is a block diagram for demonstrating operation | movement of the voltage compensation apparatus of a comparative example. It is a block diagram for demonstrating operation | movement of the voltage compensation apparatus of a comparative example. It is a block diagram which illustrates the voltage compensating device concerning the modification of a 1st embodiment. It is a block diagram which illustrates the voltage compensation apparatus concerning a 2nd embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings.
In the present specification and drawings, the same elements as those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

(First embodiment)
FIG. 1 is a block diagram illustrating a voltage compensator according to this embodiment.
As shown in FIG. 1, the voltage compensation device 1 of this embodiment includes a voltage compensation unit 10. Voltage compensator 10 includes series transformers 11, 13, 15, first power converter 20, capacitor 40, filter circuit 50, and first bypass circuit 60. The voltage compensation unit 10 further includes a second bypass circuit 70, current detectors 75 and 76, and a control unit 80.

  The voltage compensator 1 is connected in series to the power system by the voltage compensator 10. The power system is a three-phase AC distribution system composed of a U phase, a V phase, and a W phase. Hereinafter, when viewed from the voltage compensator 1 connected in series to the power system, the substation side is referred to as upstream and the consumer side is referred to as downstream. The voltage compensator 1 is connected to the U-phase upstream 6a via the input terminal 2a, and is connected to the U-phase downstream 7a via the output terminal 3a. The voltage compensator 1 is connected to the upstream 6b of the V phase at the input terminal 2b, and is connected to the downstream 7b of the V phase at the output terminal 3b. The voltage compensator 1 is connected to the upstream 6c of the W phase at the input terminal 2c, and is connected to the downstream 7c of the W phase at the output terminal 3c. The voltage compensator 1 detects an increase or decrease in the voltage of the upstream 6a to 6c and the downstream 7a to 7c of the power system, and compensates the voltage of the power system so as to be within the target value range.

  Series transformers 11, 13, and 15 include primary windings 11p, 13p, and 15p, and secondary windings 11s, 13s, and 15s, respectively. The primary winding 11p of the series transformer 11 is connected between the input terminal 2a and the output terminal 3a, and is connected in series to the U phase of the power system. The primary winding 13p of the series transformer 13 is connected between the input terminal 2b and the output terminal 3b, and is connected in series to the V phase of the power system. The primary winding 15p of the series transformer 15 is connected between the input terminal 2c and the output terminal 3c, and is connected in series to the W phase of the power system. That is, the primary windings 11p, 13p, 15p of the three series transformers 11, 13, 15 are connected in series to each phase of the power system.

  The secondary windings 11s, 13s, and 15s of the series transformers 11, 13, and 15 are connected to each other through one terminal 12a, 14a, and 16a, and the other terminal 12b, 14b, and 16b are connected to the first power converter. The AC output terminals 22a, 22b and 22c of the vessel 20 are connected. That is, the secondary windings 11 s, 13 s, and 15 s of the series transformers 11, 13, and 15 are star-connected and connected to the output of the first power converter 20.

  The first power converter 20 includes a high voltage DC input terminal 21a and a low voltage DC input terminal 21b. A capacitor 40 is connected to the high voltage DC input terminal 21a and the low voltage DC input terminal 21b. A DC voltage is supplied to the high-voltage DC input terminal 21 a and the low-voltage DC input terminal 21 b via the second power converter 90.

  The first power converter 20 includes AC output terminals 22a, 22b, and 22c. The first power converter 20 outputs a three-phase AC voltage via the AC output terminals 22a, 22b, and 22c. The AC output terminals 22a, 22b, and 22c are connected to the secondary windings 11s, 13s, and 15s of the series transformers 11, 13, and 15 through the filter circuit 50.

  The first power converter 20 is an inverter device that converts a DC voltage applied between the high-voltage DC input terminal 21a and the low-voltage DC input terminal 21b into a three-phase AC voltage. The first power converter 20 includes, for example, six switching elements 23a to 28a. The switching elements 23a to 28a are self-extinguishing switching elements such as MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors).

  Diodes 23b to 28b are connected in antiparallel to the switching elements 23a to 28a, respectively. That is, when the switching element is an IGBT, the anode terminal of the diode is connected to the emitter terminal of the switching element. The cathode terminal of the diode is connected to the collector terminal of the switching element. When the switching element is a MOSFET, the diodes 23b to 28b may be diodes built in the MOSFET.

  The switching elements 23a to 28a are connected in series as a high side switch and a low side switch. Three arms connected in series are connected in parallel to form an inverter circuit. The inverter circuit of the first power converter 20 is not limited to this circuit configuration as long as it can convert a DC voltage into an AC voltage having a frequency higher than the frequency of the power system. The inverter circuit may be, for example, a multilevel inverter circuit or a modification thereof. The diodes 23b to 28b function as flywheel diodes that allow current to flow during the dead time period of the upper and lower switching elements, for example.

  Since the switching elements 23a to 28a are connected as described above, the diodes 23b to 25b serve as a current path through which current flows from the AC output terminals 22a to 22c to the high-voltage DC input terminal 21a. The diodes 26b to 28b serve as a current path through which a current flows from the low voltage DC input terminal 21b to the AC output terminals 22a to 22c.

  More specifically, the diode 23b is connected so that a current flows from the AC output terminal 22a toward the high-voltage DC input terminal 21a. The diode 24b is connected so that a current flows from the AC output terminal 22b toward the high-voltage DC input terminal 21a. The diode 25b is connected so that a current flows from the AC output terminal 22c toward the high-voltage DC input terminal 21a. The diode 26b is connected so that a current flows from the low-voltage DC input terminal 21b toward the AC output terminal 22a. The diode 27b is connected so that a current flows from the low-voltage DC input terminal 21b toward the AC output terminal 22b. The diode 28b is connected so that a current flows from the low-voltage DC input terminal 21b toward the AC output terminal 22c.

  Filter circuit 50 includes inductors 51a to 51c and capacitors 52a to 52c. The inductor 51a is connected in series between the terminal 12b of the secondary winding 11s and the AC output terminal 22a. The inductor 51b is connected in series between the terminal 14b of the secondary winding 13s and the AC output terminal 22b. The inductor 51c is connected in series between the terminal 16b of the secondary winding 15s and the AC output terminal 22c. The capacitor 52a is connected between the terminal 12b and the terminal 14b. The capacitor 52b is connected between the terminal 14b and the terminal 16b. The capacitor 52c is connected between the terminal 16b and the terminal 12b. That is, the capacitors 52a to 52c are delta-connected. Each connected node is connected to each terminal 12b, 14b, 16b.

  The capacitors 52a to 52c of the filter circuit 50 are not limited to the delta connection, and may be star-connected. The filter circuit 50 is not limited to an LC filter, and may be an LCR filter or the like. In the case of the LCR filter, a resistor is connected between each terminal 12b, 14b, 16b and the capacitors 52a to 52c.

  The diodes 23 b to 28 b can be connected in series with the inductors 51 a to 51 c of the filter circuit 50. When a current flows from the secondary windings 11 s, 13 s, and 15 s to the inductors 51 a to 51 c in the event of a power system failure or the like, the current can charge the capacitor 40 via the diodes 23 b to 28 b. Therefore, the voltage compensation device 1 of the present embodiment includes the first bypass circuit 60 and the second bypass circuit 70 that bypass the current path from the secondary windings 11s, 13s, and 15s to the inductors 51a to 51c. Yes.

  The first bypass circuit 60 is connected between the terminals 12 b, 14 b and 16 b of the secondary windings 11 s, 13 s and 15 s and the capacitor 40. The first bypass circuit 60 bypasses the current path through the inductors 51 a to 51 c and causes a current to flow through the capacitor 40.

  The first bypass circuit 60 includes bypass diodes 61 to 66. The bypass diodes 61 to 63 are connected so that current flows from the terminals 12b, 14b, and 16b of the secondary windings 11s, 13s, and 15s toward the high-voltage DC input terminal 21a of the first power converter 20. The bypass diodes 64 to 66 are connected so that a current flows from the low-voltage DC input terminal 21b toward the terminals 12b, 14b, and 16b.

  Bypass diodes 61 to 66 are, for example, semiconductor rectifier elements. The bypass diodes 61 to 66 are full-wave rectification bridge circuits in this example. The full-wave rectification bridge circuit rectifies the AC voltage generated in the secondary windings 11 s, 13 s, and 15 s in the event of an accident and supplies the pulsating current to the capacitor 40.

  The second bypass circuit 70 is connected between the terminals 12b and 14b and between the terminals 14b and 16b. The second bypass circuit 70 is connected to the control unit 80. The second bypass circuit 70 operates according to a bypass control signal Ss supplied from the control unit 80. The second bypass circuit 70 short-circuits between the terminals 12b and 14b and between the terminals 14b and 16b when an active bypass control signal Ss is input.

  The second bypass circuit 70 includes thyristors 71 and 72 and electromagnetic contactors 73 and 74. The thyristors 71 and 72 each include two SCRs (Silicon Controlled Rectifiers), and the two SCRs are connected in antiparallel to each other. That is, in the thyristors 71 and 72, the anode terminal of one SCR and the cathode terminal of the other SCR are connected, and the cathode terminal of one SCR and the anode terminal of the other SCR are connected. The thyristor 71 is connected between the terminals 12b and 14b. The thyristor 72 is connected between the terminals 14b and 16b.

  The thyristors 71 and 72 are turned on by a trigger current supplied from a drive circuit (not shown) that receives the bypass control signal Ss and generates a trigger current. The thyristors 71 and 72 protect the first power converter 20 and the capacitor 40 by bypassing an excessive current generated at the time of the accident.

  The magnetic contactor 73 is connected between the terminals 12b and 14b. That is, the electromagnetic contactor 73 is connected in parallel with the thyristor 71. The magnetic contactor 74 is connected between the terminals 14b and 16b. That is, the electromagnetic contactor 74 is connected in parallel with the thyristor 72.

  The magnetic contactors 73 and 74 are turned on by a drive signal supplied from a drive circuit (not shown) that receives the bypass control signal Ss and generates a conduction signal.

  The electromagnetic contactors 73 and 74 have a longer delay time until they are turned on than the thyristors 71 and 72, but the DC resistance value when turned on is lower than the resistance value when the thyristors 71 and 72 are turned on. Therefore, the magnetic contactors 73 and 74 can flow a current larger than that of the thyristors 71 and 72 for a long time. The magnetic contactors 73 and 74 bypass the current flowing through the thyristors 71 and 72 after being turned on behind the thyristors 71 and 72.

  The control unit 80 inputs current data IL1 and IL2 detected by the current detectors 75 and 76. The control unit 80 compares the detected current data IL1 and IL2 with a preset threshold value It1, and outputs a gate block signal GB when the current data exceeds the threshold value. The gate block signal GB is supplied to the first power converter 20 and the second power converter 90. The first power converter 20 and the second power converter 90 that have received the gate block signal GB stop the switching operation and stop the power conversion operation regardless of the gate drive signals Vg1 and Vg2.

  The control unit 80 outputs a bypass control signal Ss when the acquired current data IL1 and IL2 exceed the threshold value It1. The bypass control signal Ss is supplied to the second bypass circuit 70. When the bypass control signal Ss is supplied to the second bypass circuit 70, the second bypass circuit 70 turns on and conducts the thyristors 71 and 72 and the magnetic contactors 73 and 74, thereby bypassing an excessive current at the time of an accident. .

  Note that the gate block signal GB may be generated under other conditions. For example, the control unit 80 may output the gate block signal GB when the current data IL1 and IL2 detected by the current detectors 75 and 76 exceed another threshold value It2. For example, the other threshold value It2 is a value lower than the threshold value It1. That is, the voltage compensator 1 determines that an excessive current has flowed through the series transformers 11, 13, and 15 due to a lower current value, and substantially stops its operation. Thereafter, when a larger current is detected, the control unit 80 outputs the bypass control signal Ss to protect the voltage compensation unit 10 from an excessive current at the time of the accident.

In addition to the protection operation described above, the voltage compensation device 1 performs a voltage compensation operation for the system voltage in a normal operation state. The voltage compensation unit 10 performs series compensation of the voltage of the power system with the configuration described below.
Voltage compensation unit 10 further includes a second power converter 90, inductors 101 and 102, parallel transformers 103 and 104, AC voltage detectors 111 to 114, and a DC voltage detector 115.

  The second power converter 90 includes a high voltage DC terminal 91a and a low voltage DC terminal 91b. The high voltage DC terminal 91 a and the low voltage DC terminal 91 b are connected to the capacitor 40. Second power converter 90 includes AC terminals 92a, 92b, and 92c. One end of the inductor 101 is connected to any one of the AC terminals 92a, 92b, and 92c, in this example, the AC terminal 92a. In this example, one end of the inductor 102 is connected to the AC terminal 92c. That is, the second power converter 90 operates as a converter device that converts AC power input to the AC terminals 92a to 92c into DC and supplies it to the capacitor 40 that is a DC link. The second power converter 90 supplies active power to the capacitor 40. The second power converter 90 may be an inverter circuit having the same circuit format as the first power converter 20, or may be a different circuit format.

  The primary winding of the parallel transformer 103 is connected between the U-phase and V-phase downstream lines 7a and 7b. The primary winding of the parallel transformer 104 is connected between the lines on the downstream side 7b and 7c of the V phase and the W phase. One of the secondary windings of the parallel transformer 103 is connected to the other end of the inductor 101, and the other is connected to the AC terminal 92 b of the second power converter 90. The secondary winding of the parallel transformer 104 is connected to the other end of the inductor 102, and the other is connected to the AC terminal 92 b of the second power converter 90. That is, the secondary windings of the parallel transformers 103 and 104 are V-connected to the AC terminals 92a to 92c of the second power converter 90 via the inductors 101 and 102.

  The current detector 105 is connected in series between the AC terminal 92a and the secondary winding. The current detector 106 is connected in series between the AC terminal 92c and the secondary winding. Current detectors 105 and 106 detect respective alternating currents flowing through inductors 101 and 102, and output current data IL3 and IL4.

  The AC voltage detectors 111 and 112 are connected to the upstream 6a to 6c side of the power system. The AC voltage detector 111 is connected between the U-phase and V-phase lines, and detects the line voltage between UV. The AC voltage detector 112 is connected between the lines of the V phase and the W phase, and detects a line voltage between the VWs. The AC voltage detectors 113 and 114 are connected to the downstream side 7a to 7c of the power system. The AC voltage detector 113 is connected between the u-phase and v-phase lines and detects a line voltage between the uv. The AC voltage detector 114 is connected between the lines of the v phase and the w phase, and detects a line voltage between the vw. AC voltage detectors 111-114 include, for example, an instrument transformer and a transducer that converts the output of the instrument transformer to an appropriate voltage level. The AC voltage detectors 111 to 114 detect voltages at both ends of the primary windings 11p, 13p, and 15p of the series transformers 11, 13, and 15, step down the voltage with an instrument transformer, and input the voltage to the control unit 80 using a transducer. It converts into the alternating voltage data VAC1-VAC4 which are possible signals, and outputs them.

  DC voltage detector 115 detects the DC voltage across capacitor 40 and outputs DC voltage data VDC.

  In a normal operation state, the control unit 80 receives the AC voltage data VAC1 to VAC4 and obtains a voltage difference between the upstream side and the downstream side from these. The control unit 80 compares the target value of the voltage difference between the upstream side and the downstream side set in advance with the measured value. The control part 80 supplies the voltage of each phase according to the difference to the secondary winding of the series transformers 11, 13, 15 according to the target value according to the measured value. The control unit 80 is set to output a voltage having the same phase as that of the power system when the measured value is lower than the target value. The control unit 80 is set to output a voltage having a phase opposite to that of the power system when the measured value is equal to or greater than the target value.

  Control unit 80 controls the operation of second power converter 90 based on current data IL3 and IL4 flowing through inductors 101 and 102 and DC voltage data VDC.

  Based on the AC voltage data VAC1 to VAC4, the current data IL3 and IL4, and the DC voltage data VDC, the control unit 80 appropriately operates the first power converter 20 and the second power converter 90 to drive the gate drive signal Vg1. , Vg2 are generated. The first power converter 20 and the second power converter 90 perform an appropriate power conversion operation based on the gate drive signals Vg1 and Vg2.

  In this way, the voltage compensator 1 of the present embodiment can compensate the voltage of the power system for each phase.

Next, the operation of the voltage compensator 1 of this embodiment will be described.
2 to 4 are block diagrams for explaining the operation of the voltage compensator.
5 and 6 are block diagrams for explaining the operation of the voltage compensator of the comparative example.
As shown in FIG. 2, when an accident such as a ground fault occurs in the power system and a large accident current flows, at least one of the primary windings of the series transformers 11, 13, and 15 of the voltage compensator 10. One excessive current flows. An excessive current at the time of an accident can be several tens of times that of normal. In one of the secondary windings, a current several tens of times that in a normal state flows according to the turn ratio.

  The line current flowing through the power system is detected by current detectors 75 and 76. The detected current data IL1 and IL2 are transmitted to the control unit 80. The control unit 80 compares the current data IL1 and IL2 with the threshold value It1, and when at least one of the current data IL1 and IL2 exceeds the threshold value, the control unit 80 controls the gate block signal GB and the bypass control. The signal Ss is output.

  The first power converter 20 receives the gate block signal GB, and the switching elements 23a to 28a stop operating. The first power converter 20 stops the power conversion operation. At this time, the second power converter 90 also receives the gate block signal GB and stops the power conversion operation.

  A current Iinc based on the accident current induced in the secondary winding flows through the first bypass circuit 60. In this example, the current Iinc is input to the anode terminal of the bypass diode 63 and flows into the capacitor 40 via the cathode terminal. The current Iinc charges the capacitor 40 and flows into the anode terminals of the bypass diodes 64 and 65, and the secondary winding of the series transformer 15 through the cathode terminal and the secondary windings of the series transformers 11 and 13. Return to.

  The ratio of the current that is shunted to the bypass diode 64 and the bypass diode 65 is determined by the impedance of the current path including the secondary windings of the series transformers 11 and 13.

  In the initial stage of occurrence of the accident current, the current Iinc flows as described above. Therefore, the current Iinc does not flow through the inductors 51a to 51c of the filter circuit 50. Moreover, since the diodes 23b to 28b of the first power converter 20 are also bypassed by the bypass diodes 63 to 65, no current flows.

  While the current Iinc flows through the first bypass circuit 60, the control unit 80 supplies the bypass control signal Ss to the second bypass circuit 70. However, due to the turn-on and conduction delay times of the thyristors 71 and 72 and the magnetic contactors 73 and 74 of the second bypass circuit 70, they are non-conductive and no current flows through the second bypass circuit 70.

  As shown in FIG. 3, when the turn-on time of the thyristors 71 and 72 elapses after the second bypass circuit 70 receives the bypass control signal Ss, the thyristors 71 and 72 are turned on. The turn-on time is, for example, about several μs to several tens of μs. After the thyristors 71 and 72 are turned on, the current Iinc flows through the thyristors 71 and 72. Since the ON voltage of the thyristors 71 and 72 is lower than the voltage of the capacitor 40 via the first bypass circuit 60, the current Iinc almost flows through the second bypass circuit 70.

  As shown in FIG. 4, after the second bypass circuit 70 receives the bypass control signal Ss, when the conduction delay time of the magnetic contactors 73 and 74 elapses, the magnetic contactors 73 and 74 become conductive. The conduction delay time is, for example, several tens ms to several hundreds ms. After the electromagnetic contactors 73 and 74 are conducted, the current Iinc flows through the electromagnetic contactors 73 and 74. Since the voltage at the time of conduction of the magnetic contactors 73 and 74 is lower than the on-voltage of the thyristors 71 and 72, the current Iinc almost flows through the electromagnetic contactors 73 and 74.

  In this way, the voltage compensating apparatus 1 of the present embodiment can bypass an excessive current at the time of an accident for a long time.

  Although not shown, the distribution system where the abnormality has occurred is shut off by the substation that monitors the abnormality of the power system, and then the distribution system from the other substation is connected to the customer's system via the voltage compensation device 1. The

  The voltage compensation device 1 is released from the protection state against excessive current and restarted.

The operation of the voltage compensator of the comparative example will be described.
As shown in FIG. 5, the voltage compensator of the comparative example does not include the first bypass circuit 60. Therefore, the current Iinc ′ flowing through the secondary winding caused by the accident current flows as follows.

  When an accident current flows through the power system, a current Iinc ′ corresponding to the turn ratio flows through the secondary winding. The current Iinc ′ has a value several tens of times that in the normal state, as in the case of the voltage compensator 1 of the embodiment.

  The current Iinc 'at this time is detected by a current detector, and the detected current data IL1' and IL2 'are transmitted to the control unit. The control unit compares the current data IL1 ′ and IL2 ′ with the threshold value It1, and when at least one of the current data IL1 ′ and IL2 ′ exceeds the threshold value It1, the control unit outputs the gate block signal GB. And the bypass control signal Ss is output.

  The first power converter 220 receives the gate block signal GB and stops the power conversion operation.

  The bypass circuit 270 receives the bypass control signal Ss, but cannot bypass the current Iinc ′ due to a delay due to the turn-on time of the thyristor.

  Therefore, the current Iinc 'induced in the secondary winding 215s flows so as to charge the capacitor 240 via the inductor 251c and the diode 225b of the filter circuit. The current charged in the capacitor 240 returns to the secondary winding of the series transformer 215 via the diodes 226b and 227b, the inductors 251a and 251b, and the secondary windings of the series transformers 211 and 213. The currents shunted to the diodes 226b and 227b and the inductors 251a and 251b are determined depending on the impedance including them.

  As shown in FIG. 6, the bypass circuit 270 turns on the thyristors 271 and 272 after the turn-on time of the thyristors 271 and 272 has elapsed. The bypass circuit 270 causes the magnetic contactors 273 and 274 to conduct after the lapse of the conduction delay time of the magnetic contactors 273 and 274. Therefore, the current Iinc ′ is bypassed to the thyristors 271 and 272 and the magnetic contactors 273 and 274.

  Since current flows through the inductors 251a to 251c of the filter circuit 250 before the bypass circuit 270 is turned on, energy is accumulated in the inductors 51a to 51c due to the flowing current. Even if the bypass circuit 270 conducts, the inductors 251a to 251c continue to pass current until the stored energy is released. Therefore, even though the bypass circuit 270 is operating, the current Iinc ′ continues to flow through the diode and continues to charge the capacitor 240.

  When the current Iinc 'exceeds the allowable current of the diode, the diode may be damaged due to overcurrent or the like. If the capacitor 240 is continuously charged via the diode, the voltage across the capacitor 240 exceeds the rated voltage, and the capacitor 240 may be damaged by the overvoltage.

The operation and effect of the voltage compensator of this embodiment will be described.
The voltage compensation device 1 according to the present embodiment includes a first bypass circuit 60. The first bypass circuit 60 is connected so as to bypass the filter circuit 50 from the secondary windings of the series transformers 11, 13, and 15 to the capacitor 40 that is a DC link. Therefore, an excessive current that flows in response to an accident current flowing in the secondary winding flows in the first bypass circuit 60, thereby preventing a current from flowing through the inductors 51 a to 51 c in the filter circuit 50.

  The voltage compensator 1 includes a second bypass circuit 70 that bypasses a current that flows according to an accident current that flows through the secondary winding. The second bypass circuit 70 includes thyristors 71 and 72 and electromagnetic contactors 73 and 74. Since the excessive current that flows in response to the accident current flows to the first bypass circuit 60 and then to the thyristors 71 and 72 and the electromagnetic contactors 73 and 74 of the second bypass circuit 70, the voltage compensation device 1 has an excessive current. In contrast, it is possible to energize for a longer time. Therefore, the bypass diodes 61 to 66 of the first bypass circuit 60 are only required to allow an excessive current for a short period until the thyristors 71 and 72 are turned on, and a small and low-cost diode bridge, for example, can be used. .

  In this way, the voltage compensation device 1 can be restarted immediately after the accident state is resolved, and the availability of the power system can be increased.

(Modification)
FIG. 7 is a block diagram illustrating a voltage compensator according to a modification of the first embodiment.
In the voltage compensation device 1 according to the above-described embodiment, the secondary windings 11s, 13s, and 15s of the series transformers 11, 13, and 15 are star-connected. The secondary windings 11s, 13s, and 15s are not limited to the star connection, and may be a delta connection.
The voltage compensator 301 of the present modification is the same as the voltage compensator 1 of the first embodiment except for the connection of the secondary windings 11 s, 13 s, and 15 s of the series transformers 11, 13, and 15. Constituent elements are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 7, in the voltage compensator 301 of this modification, one terminal 12a, 14a, 16a of the secondary windings 11s, 13s, 15s of the series transformer 11 of the voltage compensator 310 is at the start of winding. Yes, the other terminals 12b, 14b, 16b are the end of winding. One terminal 12a is connected to the other terminal 14b, one terminal 14a is connected to the other terminal 16b, and one terminal 16a is connected to the other terminal 12b. A connection node of the terminals 12 a and 14 b is connected to the AC output terminal 22 b of the first power converter 20. A connection node of the terminals 14 a and 16 b is connected to the AC output terminal 22 c of the first power converter 20. A connection node of the terminals 16 a and 12 b is connected to the AC output terminal 22 a of the first power converter 20. That is, the secondary windings 11 s, 13 s, and 15 s of the series transformers 11, 13, and 15 are delta-connected and connected to the AC output terminals 22 a, 22 b, and 22 c of the first power converter 20.

  When a star-connected series transformer is connected to the output of the first power converter 20, one terminal of the secondary winding is connected to the output of the first power converter 20, so that the wiring work is facilitated. There are advantages. On the other hand, in the star connection, the other terminals of the secondary winding are connected to each other as a neutral point, but the neutral point is not connected to the other, and voltage distortion occurs due to the nonlinearity of the transformer, etc. Occasionally, the current distortion cannot be caused to flow elsewhere, which may cause a problem that the voltage distortion phenomenon is hardly eliminated.

  When a series transformer of delta connection is connected to the output of the first power converter 20, the connection work becomes complicated by connecting the secondary windings of each phase to each other, but in the secondary winding. A reflux current can flow. Therefore, the voltage compensator 301 is unlikely to generate voltage distortion and can link high quality power to the power system.

  In the voltage compensator 301 of this embodiment, since the secondary windings 11s, 13s, and 15s of the series transformers 11, 13, and 15 connected to the output of the first power converter 20 are delta-connected, voltage distortion High-quality power connection with less power is possible.

  The secondary windings 11 s, 13 s, and 15 s of the series transformers 11, 13, and 15 can employ either star connection or delta connection in other embodiments described below.

(Second Embodiment)
FIG. 8 is a block diagram illustrating the voltage compensator of this embodiment.
In the above-described embodiment, when an accident current occurs, the capacitor 40 is charged with a current that flows according to the accident current. For this reason, the voltage across the capacitor 40 may reach an excessive voltage. In the voltage compensator of this embodiment, protection is performed so that an excessive voltage is not applied across the capacitor 40.

  As illustrated in FIG. 8, the voltage compensation device 401 according to the present embodiment includes a voltage compensation unit 410 and a control unit 480. Voltage compensation unit 410 includes a discharge circuit 460. Discharge circuit 460 includes a resistor 461 and a switch element 462. The resistor 461 and the switch element 462 are connected in series, and this series connection is connected to both ends of the capacitor 40. A control terminal of the switch element 462 is connected to the control unit 480.

  The switch element 462 is turned on by a signal from the control unit 480. When the switch element 462 is turned on, both ends of the capacitor 40 are short-circuited via the resistor 461. The diode 463 clamps the surge voltage generated by the inductance including the wiring when the switch element 462 is turned off and the current flowing through the resistor 461 is cut off, and protects the switch element 462 from overvoltage.

  Discharge control signal Ss1 for driving switch element 462 is generated, for example, under the same conditions as gate block signal GB.

  The bypass circuit 70 is controlled by the bypass control signal Ss2 generated by the control unit 480, as in the case of the first embodiment.

The operation of the voltage compensator of this embodiment will be described.
In the voltage compensator 401 of the present embodiment, the control unit 480 causes the gate block signal GB, the discharge control signal Ss1, and the bypass control signal when at least one of the current data IL1 and IL2 exceeds the threshold value Ith. Ss2 is generated.

  The first power converter 20 and the second power converter 90 receive the gate block signal GB and stop the power conversion operation.

  The discharge circuit 460 receives the discharge control signal Ss1 and turns on the switch element 462. Here, the current that flows according to the accident current flows into the first power converter 20 via the inductors 51 a to 51 c of the filter circuit 50. This current charges the capacitor 40, but is shunted to the resistor 461 by the switched switch element 462. Since the resistance value of the resistor 461 is set appropriately, the voltage across the capacitor 40 is prevented from becoming higher than the rated voltage, for example.

  Thereafter, the thyristors 71 and 72 of the bypass circuit 70 receiving the bypass control signal Ss2 are turned on to bypass a part of the current.

  At this time, the current continues to flow to the inductors 51a to 51c of the filter circuit 50 so as to release the energy corresponding to the current that has been flowing so far. The discharge circuit 460 short-circuits both ends of the capacitor 40 via the resistor 461. Therefore, the impedance of the first power converter 20 viewed from the AC output terminals 22a to 22c is lower than that before the operation of the discharge circuit 460. Therefore, the energy accumulated in the inductors 51a to 51c completes the discharge in a shorter time than when the discharge circuit 460 is not provided. After the energy stored in the inductors 51a to 51c is released, all of the current that flows according to the accident current flows to the bypass circuit 70.

The operation and effect of the voltage compensator of this embodiment will be described.
The voltage compensation device of this embodiment includes a voltage compensation unit 410 including a discharge circuit 460. The discharge circuit 460 is operated by the discharge control signal Ss1 output from the control unit 480. The discharge circuit 460 is connected to discharge the capacitor 40. Since the discharge control signal Ss1 is generated and output when it is detected that an excessive current flows, the discharge circuit 460 includes the inductors 51a to 51c of the filter circuit 50 and the diodes 23b to 23b of the first power converter 20. The increase in both-end voltage due to the charging current of the capacitor 40 flowing through 28b is suppressed.

  In the voltage compensator 401 of the present embodiment, a current that flows according to the accident current flows through the diodes 23 b to 28 b of the first power converter 20, but the impedance is lowered by the discharge circuit 460 connected to both ends of the capacitor 40. Therefore, the current can be continued for a short time, and the accident current can be protected without increasing the current capacity of the diodes 23b to 28b.

  Therefore, in the voltage compensator 401 of this embodiment, the increase in the voltage across the capacitor 40 due to the charging current of the capacitor 40 is suppressed, so that the capacitor 40 has a smaller capacitance and a lower voltage rating. Can do. This can contribute to reduction of the area occupied by the voltage compensator 401 and cost.

  The discharge circuit 460 of the present embodiment can also be applied to the voltage compensator of the first embodiment and its modifications. By applying the discharge circuit 460 also to the voltage compensator of the first embodiment and its modification, the charging current to the capacitor 40 can be reduced, and the voltage rise across the capacitor 40 can be suppressed. It is possible to perform the protective operation in the event of an accident more effectively.

  According to the embodiment described above, it is possible to realize a voltage compensator that can protect against an excessive current when an excessive accident current flows in the power system.

  As mentioned above, although some embodiment of this invention was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and the equivalents thereof. Further, the above-described embodiments can be implemented in combination with each other.

  DESCRIPTION OF SYMBOLS 1 Voltage compensation apparatus, 10 Voltage compensation part, 11, 13, 15 Series transformer, 20 1st power converter, 21a High voltage DC input terminal, 21b Low voltage DC input terminal, 22a-22c AC output terminal, 23a-28a Switching element , 23b-28b Diode, 40 Capacitor, 50 Filter circuit, 51a-51c Inductor, 60 First bypass circuit, 61-66 Bypass diode, 70 Second bypass circuit, 71, 72 Thyristor, 73, 74 Electromagnetic contactor, 75, 76 current detector, 80 control unit, 90 second power converter, 101, 102 inductor, 103, 104 parallel transformer, 105, 106 current detector, 111-114 AC voltage detector, 115 DC voltage detector, 301 Voltage compensation device, 310 Voltage compensation unit, 401 Voltage compensation Location, 410 voltage compensation unit, 460 discharge circuit, 461 a resistor, 462 a switch element, 463 a diode, 480 control unit

Claims (6)

A voltage compensator for compensating the voltage of the power system,
A first DC terminal, a second DC terminal, a first AC terminal, a second AC terminal,
A first current path from the first AC terminal toward the first DC terminal;
A second current path from the second DC terminal to the second AC terminal;
A third current path from the second AC terminal to the first DC terminal;
A fourth current path from the second DC terminal to the first AC terminal;
A power converter including
A first transformer having a primary winding connected in series to a first power line of a power system, and a secondary winding connected to the first AC terminal;
A second transformer having a primary winding connected in series to a second power line of the power system, and a secondary winding connected to the second AC terminal;
A capacitor connected between the first DC terminal and the second DC terminal;
An inductor connected in series between the secondary winding of the first transformer and the first AC terminal;
A first rectifying element that allows current to flow from the node to which the secondary winding of the first transformer and the first inductor are connected toward the first DC terminal;
A second rectifying element that allows current to flow from the second DC terminal toward the node;
A power compensation device comprising: A current detector for detecting a current flowing through the first power line;
A control unit that compares a current value detected by the current detector with a preset threshold value and outputs a control signal when the current value is equal to or greater than the threshold value;
A bypass circuit connected between the secondary winding of the first transformer and the secondary winding of the second transformer, and short-circuiting between the secondary windings by the control signal;
The voltage compensator according to claim 1, further comprising:   The voltage compensation device according to claim 2, wherein the bypass circuit includes a thyristor.   The voltage compensation device according to claim 2, wherein the bypass circuit includes an electromagnetic contactor.   The voltage compensation apparatus according to claim 2, further comprising a discharge circuit that discharges the capacitor based on the control signal. A voltage compensator for compensating the voltage of the power system,
A first AC input terminal, a second AC input terminal, a first DC output terminal, a second DC output terminal,
A first current path from the first AC input terminal to the first DC output terminal;
A second current path from the second AC input terminal to the second DC output terminal;
A third current path from the second AC input terminal to the first DC output terminal;
A fourth current path from the first AC input terminal to the second DC output terminal;
A power converter including
A first transformer having a primary winding connected in series to a first power line of a power system, and a secondary winding connected to the first AC input terminal;
A second transformer having a primary winding connected in series to a second power line of the power system, and a secondary winding connected to the second AC input terminal;
A capacitor connected between the first DC output terminal and the second DC output terminal;
An inductor connected in series between the secondary winding of the first transformer and the first AC input terminal;
A current detector for detecting a current flowing through the first power line;
A control unit that compares the detected current value with a preset threshold value and outputs a control signal when the current value is equal to or greater than the threshold value;
A discharge circuit for discharging the capacitor based on the control signal;
A voltage compensation device comprising:

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