JP2015142466A - Power conversion system, dc power transmission system, and control method of power conversion system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a protector of a power conversion device generally includes a function for protecting the power conversion device per se by opening a circuit breaker connected between the power conversion device and an AC system to stop operation of the power conversion device if overcurrent of an arm is detected, but if only one arm is short-circuited, a DC current flows to a side of the AC system, the current cannot be stopped and the circuit breaker cannot be safely opened.SOLUTION: The protector is configured to first disconnect another power conversion device being connected via a DC system from the AC system after the arm overcurrent is detected, and then disconnects the power conversion device of the protector's own from the AC system after the lapse of a time interval. Otherwise, after the arm overcurrent is detected, voltage output of all unit converters are substantially turned to 0 [V] and after all arms are substantially vertically short-circuited, the power conversion device is disconnected from the AC system.

Description

The present invention relates to a power conversion system, a DC power transmission system, and a method for protecting a power conversion device.

In recent years, power converters that convert alternating current to direct current or direct current to alternating current have been widely used.
This type of power converter is also applied to the field of high voltage. In that case, for example, by using a unit converter including a semiconductor switching element and a capacitor, each unit converter operates the switching element to output the stored energy of the capacitor. Used to connect in series. Such a configuration can withstand high voltages.

  In the case of using a unit converter group configured by connecting unit converters in series in this way, for example, the unit converter groups are connected in parallel, and an AC terminal is provided in a part of each unit converter group. On the other hand, the parallel connection end of the unit converter group is a DC terminal. This AC terminal is connected to the power system. And by controlling the operation | movement of each unit converter, the electric current which flows through each unit converter group is controlled, and electric power conversion is performed between an alternating current system and a DC terminal. In other words, each unit converter group is controlled so that a periodic current determined according to the frequency of the AC system to which the AC terminal is connected flows between the DC terminal and the AC terminal while handling a plurality of phases. Perform power conversion with.

Such a technique is described in Patent Document 1, for example.

JP 2010-233411 A

  In general, in a power converter, for example, a short circuit is formed due to a lightning strike in a part of a DC power transmission line or a power converter, and a short circuit current flows, etc. Connected through. That is, when an overcurrent of the unit converter group is detected, the circuit breaker connected to the AC system is opened and protected.

  However, for example, when only one group of unit converter groups connected in parallel is short-circuited, current balance may be lost among the unit converter groups, and a DC current may flow to the AC system side. . There is a problem in that the direct current flows through the circuit breaker, so that the current is not interrupted and the circuit breaker cannot be safely opened.

An object of the present invention is to provide a power conversion system capable of safely opening a circuit breaker even if the current balance is lost between unit converter groups due to an accident that occurs around the power converter or the power converter. Another object of the present invention is to provide a control method for a DC power transmission system and a power conversion system.

  A unit converter including a switching element and a power storage unit, wherein the unit converter charges and discharges the power storage unit by operation of the switching element, and a plurality of the unit converters are connected in series. A unit converter group, the unit converter group is connected in parallel, the parallel connection portion is a DC terminal, each of the unit converter group is connected to a first AC system through a circuit breaker, A first power conversion system that performs AC / DC power conversion with one AC system, and a configuration similar to that of the first power conversion system, is connected to the second AC system via a circuit breaker. There is a second power conversion system, wherein the first and second power conversion systems are connected to each other, and the first and second AC systems exchange power between the first and second power conversion systems. The unit of direct current flowing through the unit converter group When the unbalance between the converter groups becomes equal to or greater than a predetermined value, a signal for cutting off the circuit breaker of the second power conversion system connected via the DC output terminal is output, and then the first power It was configured to output a signal to shut off the circuit breaker on the conversion system side.

Specifically, after detecting the arm overcurrent, the protection device detects the short-circuit state of the unit converter group, and first shuts off the other power conversion devices connected via the DC system from the AC system, After a while, I tried to shut myself out of the AC system. Alternatively, after the arm overcurrent is detected, the protection device sets the voltage output of all the unit converters to almost 0 [V], and makes all the arms close to the upper and lower short circuit, and then turns the power conversion device into an alternating current. It was made to cut off from the system.

ADVANTAGE OF THE INVENTION According to this invention, in a power converter device, the electric current which flows into the AC system side interrupts appropriately with a simple structure, and it becomes possible to interrupt | block a power converter device from an AC system.

1 is a schematic configuration diagram showing a DC power transmission system in a first embodiment. It is a wave form diagram which shows the direct current of the power converter device in 1st Embodiment. It is a wave form diagram which shows the electric current / voltage of the alternating current system in 1st Embodiment. It is a figure which shows the circuit structure of the bidirectional chopper type unit converter in 1st Embodiment. It is a figure which shows the logic structure of the control and protection apparatus in 1st Embodiment. It is a figure which shows the logic structure of the control and protection apparatus in 1st Embodiment. It is a figure which shows the logic structure of the control and protection apparatus in 2nd Embodiment. It is a figure which shows the logic structure of the control and protection apparatus in 2nd Embodiment. It is a figure which shows the logic structure of the protection part in 1st Embodiment. It is a figure which shows the structure of the outline of the direct-current power transmission system in 3rd Embodiment. It is a figure which shows the logic structure of the control and protection apparatus in 3rd Embodiment. It is a figure which shows the logic structure of the control and protection apparatus in 4th Embodiment. It is a figure which shows the logic structure of the protection part in 3rd Embodiment. It is a figure which shows the electric current and voltage waveform of the power converter device 101a in 3rd Embodiment. It is a figure which shows the electric current and voltage waveform of the power converter device 102a in 3rd Embodiment.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

(Configuration of the first embodiment)

  FIG. 1 is a schematic configuration diagram showing a DC power transmission system 100 according to the first embodiment.

  The DC power transmission system 100 according to the first embodiment includes a power conversion device 102a, a power conversion device 102b, a circuit breaker 121a, a circuit breaker 121b, and a circuit breaker operation unit 153. In the DC power transmission system 100 of the first embodiment, a circuit breaker 121a, a power conversion device 102a, a power conversion device 102b, and a circuit breaker 121b are connected in series between an AC system 101a and an AC system 101b, and these four are disconnected. It is configured to be connected to the instrument operating unit 153.

  The power converter 102a includes a positive DC terminal Pa (output terminal) and a negative DC terminal Na (output terminal). The power conversion device 102b includes a positive DC terminal Pb and a negative DC terminal Nb. Between the power converter 102a and the power converter 102b, a positive DC terminal Pa and a positive DC terminal Pb are connected, and further, a negative DC terminal Na and a negative DC terminal Nb are connected. The connection between the positive DC terminals Pa and Pb and the connection with the negative DC terminals Na and Nb constitute a DC system (DC transmission line). Here, it is assumed that the voltages at the DC terminals Pa and Pb are higher than the voltages at the DC terminals Na and Nb. A DC voltage VDC is applied between the DC terminal Pa and the DC terminal Na. A DC current Idc can be passed through the DC system from the DC terminal Pa of the power converter 102a to the DC terminal Pb of the power converter 102b, or in the opposite direction. Hereinafter, in the case where the direct current Idc flows in the direction from the direct current terminal Pa of the power conversion device 102a to the direct current terminal Pb of the power conversion device 102b, input / output names of the respective terminals are given. The positive DC terminal Pa and the negative DC terminal Na form a DC output unit of the power converter 102a.

  The power converter 102a includes a failure signal terminal Ha (output terminal). The power converter 102b includes a failure signal terminal Hb. These terminals are connected to the circuit breaker operation unit 153 via the failure signal lines 152a and 152b.

  The power converter 102a includes primary terminals R, S, and T that are input terminals. These primary side terminals R, S, and T are connected to each phase of the AC system 101a through a circuit breaker 121a. The primary side terminals R, S, and T constitute an AC input unit of the power converter 102a. Note that the breaker signal to the breaker 121a is transmitted from the breaker operation unit 153 through the signal line 154a.

  The power conversion device 102b includes DC terminals Pb and Nb that are input terminals and primary terminals R, S, and T (not shown) that are output terminals. The power converter 102b is connected to each phase of the AC system 101b via the circuit breaker 121b by these primary terminals R, S, T (not shown). In addition, the interruption | blocking signal to the circuit breaker 121b is transmitted through the signal line 154b from the circuit breaker operation part 153.

  The DC power transmission system 100 according to the first embodiment supplies, for example, the power of the AC system 101a to the AC system 101b. The DC power transmission system 100 is a power conversion device that converts AC to DC between primary terminals R, S, T and DC terminals Pa, Na in a power converter 102a and is connected via a DC system. At 102b, direct current is converted into alternating current between direct current terminals Pb and Nb which are input terminals and primary terminals R, S and T (not shown) which are output terminals.

  The circuit breaker 121a has a function of connecting or disconnecting a circuit between the power conversion device 102a and the AC system 101a. The circuit breaker 121a is connected to the circuit breaker operation unit 153 by the signal line 154a and is controlled by the circuit breaker operation unit 153.

  The circuit breaker 121b has a function of connecting or disconnecting a circuit between the power conversion device 102b and the AC system 101b. The circuit breaker 121b is connected to the circuit breaker operation unit 153 through the signal line 154b and is controlled by the circuit breaker operation unit 153.

  In this embodiment, the circuit breaker 121a is provided outside the power conversion device 102a, but may be provided inside the power conversion device 102a and on the secondary side of the transformer 103a. Moreover, although the circuit breaker 121b is provided in the outer side of the power converter device 102b, you may provide it in the inner side of the power converter device 102b and the secondary side of the transformer 103b.

  Next, although the structure of the power converters 102a and 102b is demonstrated, since these are substantially the same structures, it demonstrates centering on the power converter 102a here.

  The power converter 102a includes a transformer 103, an AC voltage sensor 110, an R-phase leg 104R, an S-phase leg 104S, a T-phase leg 104T, a control / protection device 112, a gate signal line 113, and a capacitor voltage. A detection line 114 and a DC voltage sensor 115 are provided.

  The R-phase leg 104R includes a positive arm 105RP that is a first arm and a negative arm 105RN that is a second arm, which are connected in series. The R-phase positive arm 105RP includes a unit converter group 106RP, an arm current sensor 111, and a reactor 107RP, which are connected in series. R-phase negative arm 105RN includes unit converter group 106RN, arm current sensor 111, and reactor 107RN, which are connected in series. The unit converter group 106RP and the unit converter group 106RN are each connected in series with M (M is a natural number of 2 or more) bidirectional chopper type unit converters 108 (unit converters). Each bidirectional chopper type unit converter 108 is operated by a signal generated by the control / protection device 112.

  The S-phase leg 104S includes a positive arm 105SP that is a first arm and a negative arm 105SN that is a second arm, which are connected in series. The S-phase positive arm 105SP includes a unit converter group 106SP, an arm current sensor 111, and a reactor 107SP, which are connected in series. S-phase negative arm 105SN includes unit converter group 106SN, arm current sensor 111, and reactor 107SN, which are connected in series. In the unit converter group 106SP and the unit converter group 106SN, M bidirectional chopper type unit converters 108 are connected in series.

  The T-phase leg 104T includes a positive arm 105TP that is a first arm and a negative arm 105TN that is a second arm, which are connected in series. The T-phase positive arm 105TP includes a unit converter group 106TP, an arm current sensor 111, and a reactor 107TP, which are connected in series. The T-phase negative arm 105TN includes a unit converter group 106TN, an arm current sensor 111, and a reactor 107TN. In the unit converter group 106TP and the unit converter group 106TN, M bidirectional chopper type unit converters 108 are connected in series, respectively.

  When the R-phase leg 104R, the S-phase leg 104S, and the T-phase leg 104T are not particularly distinguished, they are simply referred to as the leg 104. The leg 104 is installed for each AC phase. These are basically the same configuration. Symbols R, S, and T attached to the back of each leg 104 mean each phase of alternating current. Each leg 104 is a conversion circuit that converts alternating current into direct current or direct current into alternating current between an input terminal and an output terminal.

  Similarly, when the arms 105RP, 105RN, 105SP, 105SN, 105TP, and 105TN are not particularly distinguished, they are simply referred to as the arm 105. When the unit converter groups 106RP, 106RN, 106SP, 106SN, 106TP, and 106TN are not particularly distinguished, they are simply referred to as the unit converter group 106. When the reactors 107RP, 107RN, 107SP, 107SN, 107TP, and 107TN are not particularly distinguished, they are simply referred to as the reactor 107.

  In the first embodiment, the unit converter group 106 of each arm 105 employs a bidirectional chopper type unit converter. However, the present invention is not limited to this, and the unit converter group 106 of each arm 105 may employ another type of unit converter such as a full bridge type unit converter.

  The output side of the arm current sensor 111 is connected to the control / protection device 112. The arm current sensor 111 detects a current flowing through each arm 105 and outputs it to the control / protection device 112. The arm current sensor 111 detects the current flowing through the arms 105RP, 105SP, and 105TP. Arm current sensor 111 separately detects the current flowing through each of arms 105RN, 105SN, and 105TN. In order to detect separately, each phase may be connected by a separate connection line, or may be identified by assigning a different address for each phase as serial communication.

  The gate signal line 113 connects the bidirectional chopper type unit converter 108 and the control / protection device 112. The control / protection device 112 controls the operation of the bidirectional chopper type unit converter 108 by the gate signal line 113. The control / protection device 112 transmits a command for each phase, and the bidirectional chopper type unit converter 108 compares the received command with a carrier wave to generate a PWM signal to control on / off of its own switching element. . The carrier wave is generated so as to have a predetermined phase difference with the adjacent bidirectional chopper type unit converter 108 of the same phase.

The capacitor voltage detection line 114 is connected to the bidirectional chopper type unit converter 108 and the control / protection device 112. The control / protection device 112 detects the state of the bidirectional chopper type unit converter 108 by the capacitor voltage detection line 114. The voltage of each capacitor is sent to the control / protection device 112 by serial communication so that any one of the bidirectional chopper type unit converters 108 can be identified and identified.

  The AC voltage sensor 110 is connected to the secondary side of the circuit breaker 121a. The output side of the AC voltage sensor 110 is connected to the control / protection device 112. The AC voltage sensor 110 detects the system voltages VGR, VGS, and VGT of the AC system 101a and outputs them to the control / protection device 112.

  The transformer 103 transforms the three-phase AC voltage applied to the primary side and outputs it to the secondary side. The primary side of the transformer 103 is connected to the AC system 101a via the circuit breaker 121a. In the first embodiment, the node on the AC system 101a side is defined as the primary side of the transformer 103, and the primary side terminals are described as R, S, and T.

  The secondary side of transformer 103 is connected to R-phase leg 104R, S-phase leg 104S, and T-phase leg 104T, respectively. In the first embodiment, these connection points are described as terminals Ra, Sa, Ta.

  The control / protection device 112 has a DC output unit so that a predetermined output can be obtained at the primary side terminals R, S, T of the AC output unit or the positive DC terminal Pa and the negative DC terminal Na of the DC output unit. A command for performing power conversion between (Pa, Na) and the AC output unit (R, S, T) is generated. That is, a command is sent to each bidirectional chopper type unit converter 108 so that predetermined outputs can be obtained at the positive DC terminal Pa and the negative DC terminal Na of the DC output unit. Further, the current flowing through each arm 105 is monitored, a fault such as a short circuit or a ground fault in the DC power transmission system 100 is detected, and a fault signal CBTa ′ is transmitted to the circuit breaker operation unit 153 via the fault signal transmission line 152a. .

  The control / protection devices 112a and 112b communicate fault signals with each other via the signal line 155. A failure signal GBa (gate block) is transmitted from 112a to 112b, and a failure signal GBb is transmitted from 112b to 112a.

  Next, the circuit breaker operation unit 153 will be described.

  The circuit breaker operation unit 153 is connected to the terminal Ha of the power conversion device 102a and the terminal Hb of the power conversion device 102b via fault signal lines 152a and 152b. Further, signal lines 154a and 154b for operating the circuit breakers 121a and 121b to interrupt the circuit are output. Details will be described later.

  The terminal Ra is connected to a node (connection node) to which the upper arm 105RP and the lower arm 105RN of the R-phase leg 104R are connected. One end of the arm 105RP is connected to the DC terminal Pa. The other end of the arm 105RP is connected to one end of the arm 105RN and the terminal Ra. The other end of the arm 105RN is connected to the DC terminal Na. A current flowing from the AC system 101a side to the terminal Ra is defined as a system current IR.

  The terminal Sa is connected to a node (connection node) to which the upper arm 105SP and the lower arm 105SN of the S-phase leg 104S are connected. One end of the arm 105SP is connected to the DC terminal Pa. The other end of the arm 105SP is connected to one end of the arm 105SN and the terminal Sa. One end of the arm 105SN is connected to the DC terminal Na. A current flowing from the AC system 101a side to the terminal Sa is defined as a system current IS.

  The terminal Ta is connected to a node (connection node) to which the upper arm 105TP and the lower arm 105TN of the T-phase leg 104T are connected. One end of the arm 105TP is connected to the DC terminal Pa. The other end of the arm 105TP is connected to one end of the arm 105TN and a terminal Ta. One end of the arm 105TN is connected to the DC terminal Na. A current flowing from the AC system 101a side to the terminal Ta is defined as a system current IT.

  The voltage output from the unit converter group 106RP in the arm 105RP is the output voltage VRP. The current flowing through the unit converter group 106RP is an arm current IRP. The arm current IRP is detected by the arm current sensor 111. The arm current IRP has a positive direction from the terminal Ra to the DC terminal Pa.

  In the arm 105RN, a voltage output from the unit converter group 106RN is an output voltage VRN. The current flowing through the unit converter group 106RN is assumed to be an arm current IRN. The arm current IRN is detected by the arm current sensor 111. The arm current IRN has a positive direction from the DC terminal Na to the terminal Ra.

  A voltage output from the unit converter group 106SP in the arm 105SP is referred to as an output voltage VSP. The current flowing through the unit converter group 106SP is assumed to be an arm current ISP. The arm current ISP is detected by the arm current sensor 111. The arm current ISP has a positive direction from the terminal Sa to the DC terminal Pa.

  A voltage output from the unit converter group 106SN in the arm 105SN is defined as an output voltage VSN. The current flowing through the unit converter group 106SN is an arm current ISN. The arm current ISN is detected by the arm current sensor 111. The arm current ISN has a positive direction from the DC terminal Na to the terminal Sa.

  The voltage output from the unit converter group 106TP in the arm 105TP is referred to as an output voltage VTP. The current flowing through the unit converter group 106TP is assumed to be an arm current ITP. The arm current ITP is detected by the arm current sensor 111. The arm current ITP is positive in the direction from the terminal Ta to the DC terminal Pa.

  In the arm 105TN, the voltage output from the unit converter group 106TN is defined as an output voltage VTN. The current flowing through the unit converter group 106TN is an arm current ITN. The arm current ITN is detected by the arm current sensor 111. The arm current ITN is positive in the direction from the DC terminal Na to the terminal Ta.

  FIG. 2 is a waveform diagram showing a direct current of the power conversion device 102a in the first embodiment.

  The vertical axis in the figure indicates the current value. The horizontal axis of the figure indicates time. This figure shows that the power converter 102a converts the active power obtained from the system currents IR, IS, IT of the AC system 101a into a DC current Idc of 0.6 [pu].

  3A and 3B are waveform diagrams showing current / voltage of the AC system 101a in the first embodiment.

  FIG. 3A is a graph showing a current waveform of the AC system 101a in the first embodiment.

  The vertical axis | shaft of Fig.3 (a) has shown the electric current value (instantaneous value) of AC system | strain 101a. The horizontal axis of Fig.3 (a) has shown the time common with FIG.3 (b).

  The graph of FIG. 3A shows that the peak values of the system currents IR, IS, IT of the AC system 101a are 0.82 [pu].

  FIG. 3B is a graph showing a voltage waveform of the AC system 101a in the first embodiment.

  The vertical axis | shaft of FIG.3 (b) has shown the voltage value (instantaneous value) of AC system | strain 101a. The horizontal axis of FIG.3 (b) has shown the time common to Fig.3 (a).

  The graph of FIG. 3B shows voltage waveforms of VGR, VGS, and VGT when the secondary side phase voltage of the transformer 103 is defined as VGR, VGS, and VGT.

  FIG. 4 is a diagram showing a circuit configuration of the bidirectional chopper type unit converter 108 in the first embodiment.

  Here, the bidirectional chopper type unit converter 108 in the arm 105RP will be described. The bidirectional chopper type unit converter 108 provided in the arm 105SP, the arm 105TP, the arm 105RN, the arm 105SN, and the arm 105TN is configured similarly to the bidirectional chopper type unit converter 108 in the arm 105RP.

  The arm 105RP includes a unit converter group 106RP, an arm current sensor 111 that detects an arm current IRP that flows through the unit converter group 106RP, and a reactor 107RP. One end of the arm 105RP is connected to the terminal Ra. The other end of the arm 105RP is connected to the DC terminal Pa. The unit converter group 106RP includes a plurality of bidirectional chopper type unit converters 108, which are connected in series.

  The bidirectional chopper type unit converter 108 includes a parallel circuit of a high side switching element 201H and a high side freewheeling diode 202H, a parallel circuit of a low side switching element 201L and a low side freewheeling diode 202L, a capacitor 203 as energy storage means, and a drive. And a voltage sensor 204 that measures the voltage across the capacitor 203. The bidirectional chopper type unit converter 108 is connected to the control / protection device 112 (see FIG. 1) via a gate signal line 113 and a capacitor voltage detection line 114. The positive side terminal 208 (first terminal) of the bidirectional chopper type unit converter 108 is connected to the negative side terminal 209 (second terminal) of the other bidirectional chopper type unit converter 108 or the DC terminal Pa. It is connected to the. The negative-side terminal 209 (second terminal) of the bidirectional chopper type unit converter 108 is connected to the positive side terminal 208 of another bidirectional chopper type unit converter 108 or one end of the reactor 107RP. .

  A parallel circuit of the high side switching element 201H and the high side freewheeling diode 202H and a parallel circuit of the low side switching element 201L and the low side freewheeling diode 202L are connected in series to constitute a series switching circuit.

  The collector of the high-side switching element 201H is connected to one end of the capacitor 203 and one end of the voltage sensor 204. The other end of the capacitor 203 and the other end of the voltage sensor 204 are connected to the negative terminal 209. That is, the voltage sensor 204 is connected in parallel between one end and the other end of the capacitor 203. The voltage applied to both ends of the capacitor 203 is detected by the voltage sensor 204 and transferred to the control / protection device through the signal line 114 as the capacitor voltage VCjk. Of the symbols jk attached to the capacitor voltage VC, etc., j indicates the type of arm 105 (j = RP, SP, TP, RN, SN, TN), k is the order 1, 2,... , M.

  The collector of the high side switching element 201H is further connected to the cathode of the high side freewheeling diode 202H. The emitter of the high side switching element 201H is connected to the anode of the high side freewheeling diode 202H, and further connected to the collector of the low side switching element 201L.

  The collector of the low side switching element 201L is connected to the emitter of the high side switching element 201H and the cathode of the low side freewheeling diode 202L. The emitter of the low-side switching element 201L is connected to the anode of the low-side freewheeling diode 202L and the negative terminal 209.

  The positive-side terminal 208 of the bidirectional chopper type unit converter 108 is connected to a connection node between the collector of the low-side switching element 201L and the emitter of the high-side switching element 201H.

  The high-side switching element 201H and the low-side switching element 201L can output a stored energy source stored in the capacitor 203 between a terminal 208 (first terminal) and a terminal 209 (second terminal). It is. That is, the high-side switching element 201H and the low-side switching element 201L can output the voltage across the capacitor 203 between the terminal 208 (first terminal) and the terminal 209 (second terminal).

  The gate driver 205 is connected to the control / protection device 112 via the gate signal line 113. The output side of the gate driver 205 is connected to the gate and emitter of the high-side switching element 201H, and further connected to the gate and emitter of the low-side switching element 201L.

  The gate driver 205 is a drive unit of the bidirectional chopper type unit converter 108 and is controlled by a command from the control / protection device 112 to switch the high-side switching element 201H and the low-side switching element 201L on and off. Thus, the voltage of the capacitor 203 can be output between the positive terminal 208 and the negative terminal 209, and the output voltage Vjk is controlled. Here, the control / protection device 112 (FIG. 1) controls the gate driver 205 by generating a command so that the electric power obtained from the current transformer 207 becomes a predetermined value or more.

  The high-side freewheeling diode 202H and the low-side freewheeling diode 202L are connected in series in a direction in which no current flows with respect to the capacitor voltage VCjk. The high-side switching element 201H connected in parallel to the high-side freewheeling diode 202H and the low-side switching element 201L connected in parallel to the low-side freewheeling diode 202L are attached in a direction to discharge the capacitor voltage VCjk when the switching state is on. It has been.

  In the first embodiment, as already described, among the symbols jk attached to the capacitor voltage VC and the like, j indicates the type of the arm 105 (j = RP, SP, TP, RN, SN, TN), and k is The order 1, 2,..., M in the arm 105 is shown.

  In the first embodiment, the element connected to the higher voltage of the capacitor 203 is described as the high side and is given the symbol H. An element connected to a capacitor 203 having a lower voltage is referred to as a low side, and a symbol L is given.

  An output voltage Vjk output from the bidirectional chopper type unit converter 108 is applied between the collector and emitter of the low-side switching element 201L.

  In the first embodiment, IGBTs (Insulated Gate Bipolar Transistors) are employed for the high-side switching element 201H and the low-side switching element 201L. However, the present invention is not limited to this, and the high-side switching element 201H and the low-side switching element 201L include a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), a GCT (Gate Commutated Turn-off thyristor), and a GTO (Gate Turn Off thyristor). Other elements capable of on / off control may be employed.

  The bidirectional chopper type unit converter 108 includes a voltage sensor 204 that detects a capacitor voltage VCjk (j = RP, SP, TP, RN, SN, TN, k = 1, 2,..., M). The output side of the voltage sensor 204 is connected to the control / protection device 112 (see FIG. 1) via the capacitor voltage detection line 114.

  The gate driver 205 of the bidirectional chopper type unit converter 108 is based on the gate signal GHjk transmitted from the control / protection device 112 (see FIG. 1) via the gate signal line 113, and the gate / emitter of the high-side switching element 201H. A gate voltage is applied between them, and a gate voltage is applied between the gate and emitter of the low-side switching element 201L based on the gate signal GLjk.

  Hereinafter, the relationship between the output voltage Vjk of the bidirectional chopper type unit converter 108 and the on / off states of the high-side switching element 201H and the low-side switching element 201L will be described.

  When the high side switching element 201H is in the on state and the low side switching element 201L is in the off state, the arm current Ij (j = RP, SP, TP, RN, SN, TN) of the bidirectional chopper type unit converter 108 is set. Regardless, the output voltage Vjk is approximately equal to the capacitor voltage VCjk.

  When the high side switching element 201H is in the off state and the low side switching element 201L is in the on state, the output voltage Vjk is substantially equal to zero regardless of the arm current Ij.

  The control / protection device 112 receives signals from the AC voltage sensor 110, the DC voltage sensor 115, and the arm current sensors 111 provided in both of the power conversion devices 102 a and 102 b.

  The control / protection device 112 connects the capacitor voltage VCjkl (j = RP, SP, TP, RN, SN, TN, k = 1, 2,...) Of the bidirectional chopper type unit converter 108 via the capacitor voltage detection line 114. , M, l = a, b).

  FIG. 5 is a diagram illustrating a logical configuration of the control / protection device 112 according to the first embodiment. The control / protection device 112 includes a control unit 300, a protection unit 320, and a gate pulse output unit 340.

  The control unit 300 takes in the arm currents IRP, ISP, ITP, IRN, ISN, and ITN, generates gate signals GHjkc and GLjkc so that the input signal from the power converter 102 approaches a predetermined command value, and generates gate pulses. Output to the output unit 340. J indicates the type of arm 105 (j = RP, SP, TP, RN, SN, TN), and k indicates the order 1, 2,..., M in the arm 105. Since the present invention does not depend on the configuration of the control unit 300, description of the contents of the control unit 300 is omitted.

  When the arm current exceeds the threshold, the protection unit 320 outputs the gate block signal GBa and the circuit breaker trip signal CBT ′. GBa is output to the gate pulse output unit 340 and the signal line 155, and CBT ′ is output to the signal line 152. Details will be described later.

  Finally, the operation of the gate pulse output unit 340 will be described.

  The gate pulse output unit 340 outputs the gate signals GHjkc and GLjkc transmitted from the control unit 300 as they are to the signal line 113 as the gate signals GHjk and GLjk. However, when the GBa signal is output from the protection unit 320 or when the GBb signal is input, the outputs of GHjkc and GLjkc are ignored, and the gate signal is changed to a gate stop signal and transmitted.

  Next, the structure of the protection part 320 is demonstrated using FIG.

  The absolute value calculator 901 and the maximum value calculator 902 calculate the current maximum value Imax of the three arms by the equation (1).

[Equation 1]
Imax = max (| IRP |, | ISP |, | ITP |, | IRN |, | ISN |, | ITN |)

  The comparator 903 compares the arm overcurrent threshold value Ith and the arm current maximum value Imax, and outputs an overcurrent signal OC when Imax exceeds Ith.

  The signal holding circuit 904 holds the input of the overcurrent signal OC for a certain time (until the reset signal is input to the holding circuit), and outputs it as the gate block signal GBa.

  The moving average 905 calculates an average value between tac [s] of each arm current Ij and outputs it as a DC component Ijdc. Note that tac [s] is a length corresponding to one AC cycle of the AC system 101.

  The accumulator 906, the comparator 907, and the logical sum calculator 908 determine whether or not the DC component is flowing through the three-phase arm in different directions.

  If IRPdc, ISPdc, and ITPdc are all the same code, it is determined that there is no abnormality. At this time, if the current flowing through the DC system is large, it is considered that the DC system is abnormal. At this time, all the outputs of 906 are positive and the output of 907 is 0.

  On the other hand, when all are not the same code | symbol, it is considered that the arm has a short circuit failure. At this time, there are some in which the output of 906 becomes negative and the output in 907 becomes 1. When 908 detects a short-circuit fault in the unit converter group constituting the arm on either the P side or the N side, the AC flag signal is output.

  A logical product calculator 909 calculates a logical product of the OC signal holding result GBa and ACflag. That is, an arm overcurrent is detected, and if it is due to an arm short circuit failure, a signal OC2 is output.

  The signal OC2 is output as a circuit breaker trip signal CBT 'via a tac [s] delay circuit 910 and a tac [s] holding circuit.

  The above is the description of the control / protection device 112.

  Next, the configuration of the circuit breaker operation unit 153 will be briefly described with reference to FIG.

  The circuit breaker operation unit 153 receives the interruption signals CBTa ′ and CBTb ′ from the power converters 102a and 102b, and outputs the interruption signals 154a and 154b based on the signals.

  The circuit breaker operation unit 153 has two logical sum calculators 401 and outputs a signal when any of CBTa ′ and CBTb ′ is input. One OR operation unit 401 outputs a signal CBTa via a signal line 154a, and the other outputs a signal CBTb via a signal line 154b.

  However, the signal from the power converter 102a to the circuit breaker 121a is delayed by td [s] from the signal to the circuit breaker 121b. Similarly, the signal from the power converter 102b to the circuit breaker 121b is also delayed from the signal to the circuit breaker 121a. Therefore, a delay circuit 402 is provided.

  The above is the description of the configuration of the first embodiment.

  The present embodiment is characterized in that the circuit breakers on both the sound side and the accident occurrence side are opened in the event of an arm short circuit accident, but the circuit breaker opening on the accident occurrence side is delayed.

(Description of operation of the first embodiment)
Next, the operation of the first embodiment will be described with reference to FIGS.

  During normal operation, both arm currents Ij are smaller than threshold value Ith. Therefore, the signal OC is not output, and neither CBT nor GB is output. Therefore, the circuit breakers 121a and 121b are operated in a closed state, and gate signals GHjk and GLjk are also output.

  Here, when one arm is short-circuited, for example, a case where the terminals Pa and Ra of the power conversion device 102a are short-circuited is considered. Then, a great amount of short-circuit current flows in the direction from Pa to Ra, and | IRP | becomes a large value.

  At this time, in the power converter 102a, Imax> Ith, the comparator 903 outputs the OC signal, the holding circuit 904 outputs the GBa signal, and the gate signals GHjk and GLjk are turned off (gate block).

  Further, since a short circuit current flows in the direction of Pa from the terminals Sa and Ta, the sign of IRP and the sign of ISP / ITP are reversed (the short circuit current flows in this way, the sign of IRP and the sign of ISP / ITP are The reverse phenomenon is defined as the current imbalance between phases). Therefore, the ACflag signal is output and the CBT ′ signal is also output. However, the opening of the circuit breaker is delayed more than the gate block. Let this delay be tcb [s].

  After the gate block, the cell current flows only in one direction from terminals 209 to 208. This is because the switching elements 201H and 201L are both off, and a reverse voltage is applied to the diode 202H by the voltage stored in the capacitor 203, so that current flows only through the diode 202L.

  Therefore, the arm which is not short-circuited, from bottom to top, flows from the Na and Nb terminals and flows out from the AC terminals Ra, Sa, Ta, Rb, Sb and Tb, and the AC terminals Ra, Sa, Ta and Rb. , Sb, and Tb, current flows only in the direction of flowing out to the Pa and Pb terminals. Since there is no current inflow source at the N-side terminal, no current flows through the N-side arm. On the other hand, in the case of the P-side arm, regarding 105SPa, 105TPa, 105RPb, 105SPb, and 105TPb, current can flow only in the direction from the AC terminals Rb, Sb, Tb, Sa, Ta to Pa, Pb. On the other hand, since 105RPa is short-circuited, a current flows in both directions. Therefore, current flows from the AC terminals Rb, Sb, Tb, Sa, Ta to the AC terminal Ra via the DC terminal Pa.

  From the above, it can be seen that IRPa <0 [A]. In the case of the arms 105SPa and 105TPa, when the forward voltage is applied to the diode 202L, ISPa> 0 [A], ITPa> 0 [A], and when the reverse voltage is applied, ISPa = 0 [A], ITPa = 0 [A]. In addition, since current flows only from the bottom to the top in all arms, the power converter 102d satisfies Idc <0 [A].

  The current flowing in the system is expressed by the equations (3) to (5) when the transformer 103 is Y-Δ connected and the excitation current, loss, and zero phase current of the system are ignored.

[Equation 2]
IR = (IRP-IRN) / √3- (ISP-ISN) / √3 Equation 3

[Equation 3]
IS = (ISP-ISN) / √3- (ITP-ITN) / √3 Equation 4

[Equation 4]
IT = (ITP-ITN) / √3- (IRP-IRN) / √3 Equation 5

  Since | IRP | is larger than | ISP | and | ITP |, the short-circuit current is IT> 0 [A] when IR <0 [A]. Also, the IS direction changes with time.

  On the other hand, since the arm on the system 101b side is not short-circuited, a current flows with a waveform close to a normal three-phase alternating current.

  From the above, a short-circuit current flows through the arm and system after the gate block. At this time, the direction of the current flowing through 121a is such that the R phase is always from the power converter 102a to the AC system 101a, the T phase is the opposite direction, and the current is not interrupted except for the S phase. After the S phase is interrupted, the currents in the R phase and T phase are attenuated and the current is interrupted. However, since a long time is required, 121a cannot be safely interrupted unless the circuit breaker has a large withstand capability.

  On the other hand, since a current close to a normal three-phase alternating current flows through 121b, the current is interrupted once every half cycle of the alternating current in each phase, and can be safely shut off.

  After tcb [s] from the occurrence of the accident, CBTb is output and the circuit breaker 121b is opened. At this time, no current flows through the DC circuit, and Idc = 0 [A]. Here, when a reverse voltage is applied to the diodes 202L of the arms 105Sa and 105Ta, IS and IT become 0 [A], and 121a can be safely shut off.

After tcb + td [s] from the occurrence of the accident, CBTa is output and the circuit breaker 121a is opened.

(Effects of the first embodiment)

  Conventionally, when an overcurrent such as an internal short circuit is detected by the power converter 102a, a cutoff signal is output to both of the circuit breakers 121a and 121b. For this reason, in the case of a one-arm short circuit accident as in this embodiment, the circuit breaker 121a on the side where the short circuit occurred cannot be opened safely when the withstand capability of the circuit breaker is small.

  Therefore, in the present embodiment, the following effect (A) is realized by first shutting off the circuit breaker 121b connected to the power converter 102b in which no short circuit accident has occurred.

(A) When an arm short circuit accident occurs in either of the power converters 102a and 102b of the DC power transmission system 100, not the circuit breaker connected to the AC terminal of the power converter on the short circuit side but the side on which the short circuit occurs By first opening the circuit breaker 121b connected to the AC terminal of the power converter, the DC power transmission system 100 can be safely disconnected from the AC systems 101a and 101b.

(Configuration of Second Embodiment)

  The configuration of the DC power transmission system 100 according to the second embodiment will be described. In the present embodiment, description of FIGS. 1 and 4 used in common with the first embodiment will be omitted, and only points different from the first embodiment will be described with reference to FIGS.

  FIG. 7 is a diagram illustrating a logical configuration of the control / protection device 112 according to the second embodiment. The same elements as those of the control / protection device 112 (see FIG. 5) of the first embodiment are denoted by the same reference numerals.

  The AND operator 311 calculates the logical product of the CBT and GLjk, turns on GLjk unconditionally when the CBT is output, and directly outputs the operation result of the AND operator 306 when the CBT is not output. Output as GLjk.

  FIG. 8 is a diagram illustrating a logical configuration of the circuit breaker operation unit 153 according to the second embodiment. This is used instead of FIG. 6 showing the logical configuration of the circuit breaker operation unit 153 of the first embodiment.

  In the second embodiment, the signal CBTa ′ received from the power converter 102a is transmitted as it is to the circuit breaker 121a as the circuit breaker signal CBTa. In addition, the signal CBTb ′ received from the power conversion device 102b is transmitted as it is to the circuit breaker 121a as the circuit breaker signal CBTb.

  The above is the description of the configuration of the second embodiment.

  The present embodiment is characterized in that when the cut-off signal CBT is output, the L-side switching elements of all the arms on the side where the arm short circuit occurs are turned on and all the arms are short-circuited.

(Operation of Second Embodiment)
Next, it will be described that the same effect as in the first embodiment can be obtained when the configuration and control of the DC power transmission system 100c in the second embodiment are adopted.

  The operation immediately after the one-arm short circuit is the same as that of the first embodiment. After one arm is short-circuited, both 102a and 102b are gate-blocked, and a short-circuit current flows through the arm and system after the gate block.

  After tac [s] from the occurrence of the accident, both CBT ′ and GB are output in a state where the grid currents IR and IT are not interrupted.

  However, at the same time, all the switching elements 201L of all six arms are turned on, and all the arms are short-circuited. Therefore, IR, IS, and IT can cause a short-circuit current close to three-phase alternating current to flow and 121a can be safely shut off.

The effect of this embodiment is the same as that of the first embodiment.

(Configuration of Third Embodiment)

  FIG. 10 is a diagram illustrating a schematic configuration of a DC power transmission system according to the third embodiment.

  The DC power transmission system 100b according to the third embodiment is configured using voltage-type power converters 102c and 102d, as in the first and second embodiments. However, the power converters 102c and 102d of the third embodiment are different from the power converters 102a and 102b of the first and second embodiments in circuit configuration. Except for the power converters 102c and 102d, the configuration is the same as that shown in FIG.

  Next, although the structure of the power converters 102c and 102d is demonstrated, since these are substantially the same structures, it demonstrates focusing on the power converter 102c here.

  The power conversion device 102c includes an AC voltage sensor 110, a transformer 130, an arm 105 for each phase (an R-phase arm 105R, an S-phase arm 105S, and a T-phase arm 105T), an AC current sensor 140, and a control. A protection device 112, a gate signal line 113, a capacitor voltage detection line 114, and a DC voltage sensor 115 are provided.

  The power converter 102c is connected to the AC system 101a via the circuit breaker 121a. In the third embodiment, the AC system 101a side of the transformer 130 is a primary side, and each line is a primary side terminal R, S, T. In the third embodiment, the secondary side positive side of each phase of the transformer 130 is set as the secondary side positive terminals Rb, Sb, Tb, and the neutral point of the secondary side of each phase of the transformer 130. Is connected to the secondary negative terminal Nx (negative DC terminal Nc).

The R-phase arm 105R includes a unit converter group 106R and an arm current sensor 111 , which are connected in series. In the unit converter group 106R, M (M is a natural number of 2 or more) bidirectional chopper type unit converters 108 are connected in series.

The S-phase arm 105S includes a unit converter group 106S and an arm current sensor 111 , which are connected in series. In the unit converter group 106S, M bidirectional chopper type unit converters 108 are connected in series.

The T-phase arm 105T includes a unit converter group 106T and an arm current sensor 111 , which are connected in series. In the unit converter group 106T, M bidirectional chopper type unit converters 108 are connected in series.

  Next, the internal configuration of the transformer 130 will be described.

  The transformer 130 includes iron cores 131R, 131S, and 131T, windings 132RA, 132RB, and 132RC, windings 132SA, 132SB, and 132SC, and windings 132TA, 132TB, and 132TC, and further includes primary side terminals R and S. , T, secondary side positive terminals Rb, Sb, Tb, and secondary side negative terminal Nx. The secondary negative terminal Nx is connected to the negative DC terminal Nc that is the second DC terminal.

A winding 132RB that is a first secondary winding and a winding 132SC that is a second secondary winding are wound around the iron core 131R by the same number of turns. Further, a winding 132RA, which is a primary winding, is wound around the iron core 131R in the same direction as the winding 132SC.

A winding 132SB that is a first secondary winding and a winding 132TC that is a second secondary winding are wound around the iron core 131S by the same number of turns. Further, a winding 132SA, which is a primary winding, is wound around the iron core 131S in the same direction as the winding 132TC.

A winding 132TB that is a first secondary winding and a winding 132RC that is a second secondary winding are wound around the iron core 131T by the same number of turns. Further, a winding 132TA, which is a primary winding, is wound around the iron core 131T in the same direction as the winding 132RC.

  The transformer 130 includes the plurality of iron cores 131R, 131S, and 131T.

  Hereinafter, when the iron cores 131R, 131S, and 131T are not particularly distinguished, they are simply referred to as the iron core 131. When the windings 132RA to 132TC are not particularly distinguished, they are simply referred to as windings 132. These windings 132 are wound in the same direction around the iron cores 131R, 131S, and 131T.

  In each iron core 131, the terminal in the direction of the secondary side positive terminals Rb, Sb, Tb in the drawing is called a positive side terminal. A terminal in the direction of the secondary negative terminal Nx (negative DC terminal Nc) in the figure is referred to as a negative terminal.

  Positive terminals of windings 132RA, 132SA, and 132TA are connected to primary terminals S, T, and R, respectively. The negative terminals of the windings 132RA, 132SA, and 132TA are connected to the primary terminals R, S, and T, respectively, and are delta-connected (Δ-connected). That is, the windings 132RA, 132SA, and 132TA, which are primary windings, are connected to the secondary side of the circuit breaker 121a by Δ connection.

  The positive terminals of the windings 132RB, 132SB, and 132TB that are the first secondary windings are the positive terminals of the windings 132RC, 132SC, and 132TC that are the second secondary windings wound around the iron cores 131 of different phases. Connected to the side terminal.

  The negative side terminals of the first secondary windings 132RB, 132SB, and 132TB are connected to the secondary side positive terminals Rb, Sb, and Tb, respectively.

  The negative terminals of the windings 132RC, 132SC, 132TC, which are the second secondary windings, are all connected to the secondary negative terminal Nx (negative DC terminal Nc).

  Here, a case is considered where the same DC current flows from the secondary positive terminals Rb, Sb, Tb toward the secondary negative terminal Nx (negative DC terminal Nc). In the iron core 131R, the magnetic flux generated in the winding 132RB and the magnetic flux generated in the winding 132SC have opposite directions and the same strength, and thus cancel each other. In the iron core 131 </ b> S, the magnetic flux generated in the winding 132 </ b> SB and the magnetic flux generated in the winding 132 </ b> TC have opposite directions and the same strength, and thus cancel each other. In the iron core 131T, the magnetic flux generated in the winding 132TB and the magnetic flux generated in the winding 132RC are in the opposite direction and have the same strength, and thus cancel each other.

  Thereby, the power converters 102c and 102d can flow the current Idc of the DC system independently of the system current of the AC systems 101a and 101b.

  One end of the R-phase arm 105R is connected to the secondary side positive terminal Rb of the transformer 130. The other end of the R-phase arm 105R is connected to a DC terminal Pc (first DC terminal). The voltage output from the unit converter group 106R in the arm 105R is the output voltage VRa. An arm current IRa flows through the arm 105R in the direction from the secondary positive terminal Rb to the DC terminal Pc. In the output voltage VRa and the arm current IRa, the direction from the secondary side positive terminal Rb to the DC terminal Pc is positive.

  One end of the S-phase arm 105 </ b> S is connected to the secondary side positive terminal Sb of the transformer 130. The other end of the S-phase arm 105S is connected to a DC terminal Pc (first DC terminal). The voltage output from the unit converter group 106S in the arm 105S is the output voltage VSa. An arm current ISa flows through the arm 105R in the direction from the secondary positive terminal Sb to the DC terminal Pc. In the output voltage VSa and the arm current ISa, the direction from the secondary side positive terminal Sb to the DC terminal Pc is positive.

  One end of the T-phase arm 105T is connected to the secondary-side positive terminal Tb of the transformer 130. The other end of the T-phase arm 105T is connected to a DC terminal Pc (first DC terminal). The voltage output from the unit converter group 106T in the arm 105T is assumed to be the output voltage VRa. An arm current ITa flows through the arm 105T in the direction from the secondary positive terminal Tb to the DC terminal Pc. In the output voltage VTa and the arm current ISa, the direction from the secondary side positive terminal Tb to the DC terminal Pc is positive.

  In the third embodiment, the other end of each arm 105 is connected to a DC terminal Pc that is a first DC terminal, and the secondary negative terminal Nx of the transformer 130 is a negative DC terminal that is a second DC terminal. It is connected to the terminal Nc. However, the present invention is not limited to this, and the other end of each arm 105 may be connected to the negative DC terminal Nc, and the secondary negative terminal Nx of the transformer 130 may be connected to the positive DC terminal Pc.

  Next, the operation of the control / protection device 112 will be briefly described. In the present embodiment, the turns ratio (windings 132RA, 132RB, 132TC), (windings 132SA, 132SB, 132RC), and (windings 132TA, 132TB, 132SC) of the transformer 130 are 2: 1: 1, respectively. This will be described assuming the case. However, the present invention is not limited to this, and the turn ratio may be (X: 1: 1). As a result, the power converters 102c and 102d can cause the zero-phase component current to flow through the arms 105R, 105S, and 105T without flowing the system currents IR, IS, and IT.

  The control / protection device 112 receives signals from the AC voltage sensor 110, the DC voltage sensor 115, each arm current sensor 111, and the AC current sensor 140 included in both of the power conversion devices 102 c and 102 d.

  The control / protection device 112 receives the capacitor voltage VCjkl (j = R, S, T, k = 1, 2,..., M, l = c of the bidirectional chopper type unit converter 108 via the capacitor voltage detection line 114. , D).

  The basic functions of the control / protection device 112 are the same as those in the first embodiment. Details will be described in detail later with reference to FIG.

  Since the functional configuration of the control / protection device 112d is the same as that of the control / protection device 112c, the following description is omitted.

  FIG. 11 is a diagram illustrating a logical configuration of the control / protection device 112c according to the third embodiment. 112c includes a control unit 300, a protection unit 3320, and a gate pulse output unit 340.

  The control unit 300 generates the gate signals GHjkc and GLjkc so as to bring the input signal from the power conversion device 102c close to a predetermined command value, and outputs the gate signals GHjkc and GLjkc to the gate pulse output unit 3340. J indicates the type of arm 105 (j = R, S, T), and k indicates the order 1, 2,..., M in the arm 105. Since the present invention does not depend on the configuration of the control unit 300, description of the contents of the control unit 300 is omitted.

  Next, the operation of the protection unit 3320 will be described with reference to FIG.

  The absolute value calculator 901 and the maximum value calculator 902 calculate the current maximum value Imax of the three arms by the equation (6).

[Equation 5]
Imax = max (| IRa |, | ISa |, | ITa |)

  The comparator 903 compares the arm overcurrent threshold value Ith and the arm current maximum value Imax, and outputs an overcurrent signal OC when Imax exceeds Ith.

  The signal holding circuit 904 holds the input of the overcurrent signal OC for a certain time (until the reset signal is input to the holding circuit), and outputs it as the gate block signal GBa.

  The moving average 905 calculates an average value between tac [s] of each arm current Ij and outputs it as a DC component Ijdc. Note that tac [s] is a length corresponding to one AC cycle of the AC system 101.

  The accumulator 906, the comparator 907, and the logical sum calculator 908 determine whether a DC component is flowing in the arm in different directions.

  If IRadc, ISadc, and ITadc are all the same code, it is determined that there is no abnormality. At this time, if the current flowing through the DC system is large, it is considered that the DC system is abnormal. At this time, all the outputs of 906 are positive and the output of 907 is 0.

  On the other hand, when all are not the same code | symbol, it is considered that the arm has a short circuit failure. At this time, there are some in which the output of 906 becomes negative and the output in 907 becomes 1. When an arm short circuit failure is detected, 908 outputs an ACflag signal.

  A logical product calculator 909 calculates a logical product of the OC signal holding result GBa and ACflag. That is, an arm overcurrent is detected, and if it is due to an arm short circuit failure, a signal OC2 is output.

  The signal OC2 is output as a circuit breaker trip signal CBT 'via a tac [s] delay circuit 910 and a tac [s] holding circuit.

  The operation of the gate pulse output unit 3340 is the same as that of the first embodiment, and a description thereof is omitted.

  The above is the description of the control / protection device 112c.

The present embodiment is characterized in that the circuit breakers on both the sound side and the accident occurrence side are opened in the event of an arm short circuit accident, but the circuit breaker opening on the accident occurrence side is delayed.

(Description of operation of the third embodiment)

  Hereinafter, the operation of the third embodiment will be described with reference to FIGS. 11 and 13. Note that the effective value of the line voltage of 101a is 1 [pu], the frequency is 60 [Hz], the winding ratio of the transformer 130a is 3: 1: 1, the secondary-side rated phase voltage is 0.33 [pu], DC The rated voltage is 0.63 [pu], and there is no power interchange before an arm short circuit accident, that is, Idc = 0 [A].

  Further, the overcurrent determination value Ith = 9 [pu], the time tcb [s] required for breaking the circuit breakers 121a and 121b is 70 [ms], and the failure signal output delay time td [s] on the accident occurrence side is 33 [ms]. ]

  During normal operation, both arm currents Ij are smaller than threshold value Ith. Therefore, the signal OC is not output, and neither CBT nor GB is output. Therefore, the circuit breakers 121a and 121b are operated in a closed state, and gate signals GHjk and GLjk are also output. The waveforms at this time are shown in FIGS.

  Here, when one arm is short-circuited, for example, a case where the terminals Pc and Rb of the power converter 102a are short-circuited is considered. Then, a great amount of short-circuit current flows in the direction from Pc to Rb, and | IRa | becomes a large value.

  At this time, Imax> Ith in the power converter 102a, the comparator 903 outputs an OC signal, and the gate signals GHjk and GLjk are turned off (gate block).

  Further, since a short-circuit current flows in the direction of Pa from the terminals Sa and Ta, the signs of IRP and ISP / ITP are reversed. Therefore, the ACflag signal is output and the CBT ′ signal is also output. However, the opening of the circuit breaker is delayed more than the gate block.

  After the gate block, the cell current flows only in one direction from terminals 209 to 208. This is because the switching elements 201H and 201L are both off, and a reverse voltage is applied to the diode 202H by the voltage stored in the capacitor 203, so that current flows only through the diode 202L.

  Therefore, a current flows through the arm that is not short-circuited only from the bottom to the top, flowing in from the Nc and Nd terminals and flowing out from the Pc and Pd terminals. Since the current flows out from the shorted 105RPa, the current flows from the AC terminals Sb and Tb through the DC terminal Pa in the direction of the AC terminal Ra.

  From the above, it can be seen that IRa <0 [A]. In the case of the arms 105Sa and 105Ta, ISa> 0 [A], ITa> 0 [A] when a forward voltage is applied to the diode 202L, and ISa = 0 [A], ITa when a reverse voltage is applied. = 0 [A]. In addition, since current flows only from the bottom to the top in all arms, the power converter 102d satisfies Idc <0 [A].

  The current flowing through the system is expressed by equations (7) to (9) when the excitation current and the loss are ignored. Therefore, while IR <0 [A], IS> 0 [A] and IT> 0 [A]. Here, R is a ratio of the secondary side voltage to the primary side of the transformer 130, and in this embodiment, R = 1 [pu].

[Equation 6]
IR = (IRa−Idc / 3) · R Equation 7

[Equation 7]
IS = (ISa−Idc / 3) · R Equation 8

[Equation 8]
IT = (ITa−Idc / 3) · R Equation 9

  From the above, a short-circuit current flows through the arm and system after the gate block. At this time, the current always flows through 121a and is not interrupted. Therefore, 121a is in a state where it cannot be safely blocked. The waveform at this time is shown in FIG.

  On the other hand, since a current close to a normal three-phase alternating current flows through 121b, the current is interrupted once every half cycle of the alternating current in each phase, and can be safely shut off. The waveform is shown in FIG.

  After tcb [s] from the occurrence of the accident, CBTb is output and the circuit breaker 121b is opened. At this time, no current flows through the DC circuit, and Idc = 0 [A]. Here, when a reverse voltage is applied to the diodes 202L of the arms 105Sa and 105Ta, IS and IT become 0 [A], and 121a can be safely shut off. The waveform at this time is shown in FIG.

After tcb + td [s] from the occurrence of the accident, CBTa is output and the circuit breaker 121a is opened. The waveform at this time is shown in FIG.
(Effect of the third embodiment)

  Conventionally, when an overcurrent such as an internal short circuit is detected by the power converter 102c, a cutoff signal is output to both of the circuit breakers 121a and 121b. For this reason, in the case of a one-arm short circuit accident as in this embodiment, the circuit breaker 121a on the side where the short circuit occurred cannot be opened safely when the withstand capability of the circuit breaker is small.

  Therefore, in the present embodiment, the following effect (A) is realized by first shutting off the circuit breaker 121b connected to the power converter 102d in which no short circuit accident has occurred.

(A) When an arm short circuit accident occurs in one of the power conversion devices 102c and 102d of the DC power transmission system 100b, the side where the short circuit is occurring, not the circuit breaker connected to the AC terminal of the power conversion device on the short circuit side By first opening the circuit breaker 121b connected to the AC terminal of the power converter, the DC power transmission system 100b can be safely disconnected from the AC systems 101a and 101b.

(Configuration of Fourth Embodiment)

  A configuration of a DC power transmission system 100c according to the fourth embodiment will be described. In this example, the description of FIG. 10 used in common with the third embodiment and FIG. 8 used in common with the embodiment of FIG. 2 is omitted, and only the differences from the second and third embodiments are omitted. This will be described with reference to FIG.

  FIG. 12 is a diagram illustrating a logical configuration of the control / protection device 112 according to the fourth embodiment. The same elements as those of the control / protection device 112 (see FIG. 11) of the third embodiment are denoted by the same reference numerals.

  The AND operator 311 calculates the logical product of the CBT and GLjk, turns on GLjk unconditionally when the CBT is output, and directly outputs the operation result of the AND operator 306 when the CBT is not output. Output as GLjk.

  The above is the description of the configuration of the second embodiment.

  The present embodiment is characterized in that when the cut-off signal CBT is output, the L-side switching elements of all the arms on the side where the arm short circuit occurs are turned on and all the arms are short-circuited.

(Operation of Fourth Embodiment)
Next, it will be described that the same effect as in the third embodiment can be obtained when the configuration and control of the DC power transmission system 100b in the fourth embodiment are adopted.

  The operation immediately after the one-arm short circuit is the same as that of the third embodiment. After one arm is short-circuited, both 102c and 102d are gate-blocked, and a short-circuit current flows through the arm and system after the gate block.

  After tac [s] from the occurrence of the accident, both CBT ′ and GB are output in a state where the grid current is not interrupted.

  However, at the same time, all the switching elements 201L of all three arms are turned on, and all the arms are short-circuited. Therefore, IR, IS, and IT can cause a short-circuit current close to three-phase alternating current to flow and 121a can be safely shut off.

  The effect of this embodiment is the same as that of the third embodiment.

100, 100b, 100c DC power transmission system 101 AC system 101a AC system (first AC system)
101b AC system (second AC system)
102a, 102b Power converter 102c Power converter (first power converter)
102d Power converter (second power converter)
103 transformer 104 leg 105RP, 105SP, 105TP arm (first arm)
105RN, 105SN, 105TN Arm (second arm)
105R, 105S, 105T Arm 106 Unit converter group 107 Reactor 108 Bidirectional chopper type unit converter 110 AC voltage sensor 111 Arm current sensors 112, 112a, 112c, 112d Control unit 113 Gate signal line 114 Capacitor voltage detection line 115 DC voltage Sensor 120 Initial charging device 121 Circuit breaker 130 Transformer 131 Iron core 132RA, 132SA, 132TA Winding (Primary winding)
132RB, 132SB, 132TB Winding (first secondary winding)
132RC, 132SC, 132TC Winding (secondary winding)
140 AC current sensor 150, 150c Control / protection device 201H, 201L Switching element 202H, 202L Free-wheeling diode 203 Capacitor (energy storage means)
204 Voltage sensor 205 Gate driver (control unit)
208 terminal 209 terminals Pa, Pb, Pc, Pd Positive DC terminal (first DC terminal: DC output section)
Na, Nb, Nc, Nd Negative DC terminal (second DC terminal: DC output unit)
R, S, T Primary side terminal (AC output section)

Claims (10)

A unit converter including a switching element and a power storage unit, wherein the unit converter charges and discharges the power storage unit by operation of the switching element, and a plurality of the unit converters are connected in series. A unit converter group, the unit converter group is connected in parallel, the parallel connection portion is a DC terminal, each of the unit converter group is connected to a first AC system through a circuit breaker, A first power conversion system that performs AC / DC power conversion with one AC system, and a configuration similar to that of the first power conversion system, is connected to the second AC system via a circuit breaker. There is a second power conversion system, wherein the first and second power conversion systems are connected to each other, and the first and second AC systems exchange power between the first and second power conversion systems. The unit of direct current flowing through the unit converter group When the unbalance between the converter groups becomes equal to or greater than a predetermined value, a signal for cutting off the circuit breaker of the second power conversion system connected via the DC output terminal is output, and then the first power A power conversion system that outputs a signal for interrupting a circuit breaker on the conversion system side.
2. The AC system according to claim 1, wherein the AC system is an AC voltage having a predetermined cycle, and a moving average of the current flowing through one unit converter group for the predetermined cycle flows through another unit converter group. A power conversion system that outputs the signal to be cut off when the current is in a direction opposite to the moving average of the predetermined period.
3. The unit converter group according to claim 2, wherein the number of unit converter groups is three, and the product of the moving averages of two of the unit converter groups is calculated, and the signal to be cut off is output based on the calculation. Power conversion system characterized by
4. The power storage unit according to claim 1, wherein the power storage unit is a capacitor, the switching element is configured as a first switching element and a second switching element, and the unit converter includes a first terminal and A second terminal, wherein the first switching element is capable of outputting a stored energy source stored in the capacitor between the first terminal and the second terminal; The second switching element is capable of short-circuiting the first terminal and the second terminal, and when the current flowing through the unit converter group exceeds a predetermined value, either all or a predetermined A power conversion system, characterized in that a selected unit converter sends a command to the second switching element so as to short-circuit the first terminal and the second terminal.
5. The method according to claim 4, wherein the unbalance between the unit converter groups corresponding to the direct current flowing through the unit converter group is greater than or equal to a predetermined value, and the current flowing through the unit converter group exceeds a predetermined value. The power conversion system outputs the signal to be cut off and sends a command to the second switching element so that the unit converter short-circuits the first terminal and the second terminal. .
6. The power conversion device according to claim 1, wherein a sensor that detects a voltage of a power storage unit of the unit converter is provided, and the unit converter is controlled based on an output of the sensor.
In Claim 1, the said DC terminal was comprised from the 1st DC terminal and the 2nd DC terminal, and the primary winding, the 1st secondary winding, and the 2nd secondary winding were wound. A transformer having a plurality of iron cores and the primary winding are connected to a first AC system via the circuit breaker, one end of the unit converter group is connected to the first DC terminal, Each end is connected to one end of the first secondary winding, and the other end of the first secondary winding is connected to one end of the second secondary winding wound around a different phase iron core. The other end of the second secondary winding is connected to the second DC terminal, and the second power winding system has the same configuration as the first power conversion system. There is a second power conversion system that is connected to the AC system via a circuit breaker, and the DC section of the first and second power conversion systems is connected. In the power conversion system for accommodating power between the first and second AC systems, when the current flowing through the unit converter group exceeds a predetermined value, the AC circuit breaker on the second power conversion system side After outputting the signal which opens | releases, the interruption | blocking signal which opens the said circuit breaker by the side of a 1st power conversion system is output, The power converter device characterized by the above-mentioned.
2. The power converter according to claim 1, wherein each of the AC systems is connected to a midpoint of the unit converter group.
A unit converter including a switching element and a power storage unit, wherein the unit converter charges and discharges the power storage unit by operation of the switching element, and a plurality of the unit converters are connected in series. A unit converter group, the unit converter group is connected in parallel, the parallel connection portion is a DC terminal, each of the unit converter groups is connected to an AC system via a circuit breaker, and the DC terminal is the other A DC power transmission system that is connected to another power conversion device via a circuit breaker and transmits the power of the AC system to another power converter via the DC terminal, the DC flowing through the unit converter group Signal that shuts off the AC system side circuit breaker to which another power converter connected via the DC output terminal is connected when the unbalance between the unit converter groups for the current exceeds a predetermined value. Output, then before DC transmission system and outputs a signal to cut off the circuit breaker.
  A unit converter including a switching element and a power storage unit, wherein the unit converter charges and discharges the power storage unit by an operation of the switching element, and a plurality of the unit converters are connected in series. Power for controlling a power conversion system which is a converter group, the unit converter group is connected in parallel, the parallel connection portion is a DC terminal, and each of the unit converter groups is connected to an AC system via a circuit breaker A method for controlling a conversion system, wherein when an unbalance between the unit converter groups corresponding to a DC current flowing in the unit converter group becomes equal to or greater than a predetermined value, another unit connected via a DC output terminal The control method of the power conversion system which outputs the signal which interrupts | blocks the circuit breaker by the side of the alternating current system with which a power converter device is connected, and outputs the signal which interrupts | blocks the said circuit breaker after that.