JP6430294B2 - DC breaker - Google Patents

Description

  Embodiments described herein relate generally to a DC interrupter that isolates an accident point in a DC power transmission system.

  Renewable energy such as wind power generation and solar power generation is spreading from the viewpoint of reducing environmental load and diversifying power sources. Further, the scale of these power sources is increasing, and for example, wind power generation on the ocean, sunlight or solar thermal power generation in the desert area, etc. are beginning to be put into practical use. Oceans and deserts are often geographically distant from the urban areas where power is demanded, increasing the transmission distance. For such long-distance power transmission, high-voltage direct current (HVDC) may be applied instead of a commonly used AC power transmission system.

  When HVDC is applied to long-distance high-power power transmission, it is possible to construct a system with lower transmission loss and lower cost than conventional AC power transmission systems. However, in HVDC, when a system fault caused by lightning strikes or the like occurs, it is not easy to isolate the fault point. This is because, in alternating current, the current can be cut off at a point where the current crosses zero every half cycle at a frequency of 50 Hz or 60 Hz, but in direct current, there is no point where the current crosses zero. Therefore, even if the contact of the disconnector provided in the system is simply disconnected, an arc is generated between the contacts and current continues to flow.

  Thus, it has been proposed to perform high-speed disconnection by using a semiconductor circuit breaker instead of a mechanical disconnector. However, when a semiconductor breaker is connected in series to the power transmission system, conduction loss may occur, leading to a decrease in power transmission efficiency. Therefore, a DC circuit breaker having a configuration in which a semiconductor circuit breaker is connected in parallel to a mechanical disconnector has been proposed. An H bridge circuit having a plurality of switching elements and capacitors is connected in series to the semiconductor circuit breaker. In the event of an accident, output voltage control is performed using an H-bridge circuit, current is induced in a parallel circuit, and current interruption is performed at high speed by a semiconductor breaker.

JP 2014-235834 A

  The DC breaker provided with the parallel circuit described above can prevent conduction loss due to the semiconductor breaker because the current passes only through the mechanical disconnector during normal operation. However, the semiconductor circuit breaker provided in the parallel circuit needs to finally cut off the accident current that increases with time, and it is necessary to use one having a large current capacity. The H bridge circuit provided in the parallel circuit also needs to be configured by a semiconductor element having the same large current capacity as that of the semiconductor circuit breaker, which may increase the equipment capacity and cost.

  In view of the above-described problems, the present embodiment aims to provide a high-efficiency and low-cost DC interrupting device that reduces facility capacity and conduction loss while having a function of interrupting an accident current at high speed. .

  In order to achieve the above object, a DC interrupting device according to an embodiment includes a mechanical disconnector provided in a DC power transmission system, and a mechanical interrupter provided in the DC power transmission system and connected in series to the mechanical disconnector. A semiconductor breaker that is connected in parallel to the mechanical disconnector and the mechanical breaker, and that switches between supply and interruption of current of the DC power transmission system, and a reactor that is connected in series to the semiconductor breaker, An H-bridge unit comprising a plurality of switching elements and capacitors, connecting a parallel circuit comprising: a single point between the mechanical disconnector and the mechanical breaker; and a single point between the semiconductor breaker and the reactor. And an H-bridge circuit that controls a current flowing through the mechanical circuit breaker by output voltage control.

(A) is a figure which shows the structure of the direct current | flow interruption | blocking apparatus which concerns on 1st Embodiment, (b) is a figure which shows the structure of an H bridge unit. It is a figure which shows the operation | movement at the normal time of the direct current | flow interruption | blocking apparatus which concerns on 1st Embodiment. It is a figure explaining the electric current operation at the time of accident occurrence. It is a figure which shows the initial stage operation | movement at the time of the accident of the DC circuit breaker which concerns on 1st Embodiment. It is a figure which shows the operation | movement of the medium term at the time of the accident of the DC circuit breaker which concerns on 1st Embodiment. It is a figure which shows the operation | movement of the latter period at the time of the accident of the direct-current circuit interrupter which concerns on 1st Embodiment. It is a figure which shows the structure of the direct current | flow interrupting apparatus which concerns on 2nd Embodiment.

  Hereinafter, a DC interrupter according to an embodiment will be described with reference to the drawings. In the description of the embodiment, “normal time” means a state in which a normal current is flowing in the DC power transmission system, and “at the time of an accident” means an excessive accident current due to a system fault caused by lightning or the like. The state that has occurred.

(First embodiment)
(Constitution)
As shown in FIG. 1, a transmission line connecting two DC transmission networks A and B is provided in the DC transmission system. Although the power transmission line has a positive side 100 and a negative side 101, the DC breaker 1 of the present embodiment is provided on the positive side. In the present embodiment, an example in which power is transmitted from the DC power transmission network A to the DC power transmission network B in the positive transmission line 100 will be mainly described.

  The DC breaker 1 includes a mechanical disconnector 2 and a mechanical breaker 20 connected in series to the power transmission line 100, a parallel circuit 3 connected in parallel to the mechanical disconnector 2 and the mechanical breaker 20, An H bridge circuit 5 that connects the power transmission line 100 and the parallel circuit 3 is configured. More specifically, the parallel circuit 3 includes a semiconductor circuit breaker 4 and a reactor 55 connected in series to the semiconductor circuit breaker 4, and an arrester 43 is connected in parallel only to the semiconductor circuit breaker 4. The H bridge circuit 5 is configured to connect one point between the mechanical disconnector 2 and the mechanical circuit breaker 20 of the transmission line 100 and one point between the semiconductor breaker 4 and the reactor 55 of the parallel circuit 3. Has been.

  The mechanical disconnector 2 can use various known configurations. In this embodiment, since the direct current is interrupted using the parallel circuit 3 as will be described later, the mechanical disconnector 2 itself does not need a current interrupting capability. It is sufficient if it has a mechanical contact and has a withstand voltage that can withstand the DC voltage necessary for disconnecting the accident point with the contact disconnected. For example, the mechanical disconnector 2 is provided with a rotating contact between the terminals of the circuit, and the rotating contact rotates to come in contact with and separate from the fixed contact attached to each terminal. It can be set as the structure which performs.

  The mechanical disconnector 2 is normally controlled to be in an on state, that is, in a state in which the contacts are in contact with each other. The current from the DC transmission network A flows through the mechanical disconnector 2 to the DC transmission network B. In the event of an accident, as will be described later, control is performed so that a current flows through the parallel circuit 3, and when the current flowing through the mechanical disconnector 2 becomes substantially zero, the circuit is disconnected.

  The mechanical circuit breaker 20 can use various known configurations. Any mechanical contact that has the ability to cut off a small current by opening the contact is sufficient. The mechanical circuit breaker 20 is provided with a rotating contact between terminals of a circuit, for example, and the rotating contact rotates to contact and separate from a fixed contact attached to each terminal. It can be set as the structure which performs interruption | blocking.

  The mechanical circuit breaker 20 is normally controlled to be in an on state, that is, in a state in which the contacts are in contact with each other. The current from the DC power transmission network A flows through the mechanical disconnector 2 and the mechanical circuit breaker 20 to the DC power transmission network B. At the time of an accident, the current flowing through the mechanical circuit breaker 20 increases. A current sensor (not shown) is attached to the mechanical circuit breaker 20. The current flowing through the mechanical circuit breaker 20 is measured by a current sensor, and the accident is detected by comparing it with a threshold value indicating the accident. Although details will be described later, in the event of an accident, control is performed so that a current flows through the H-bridge circuit 5 and the current flowing through the mechanical circuit breaker 20 becomes substantially zero. The mechanical circuit breaker 20 is switched to an off state when the flowing current becomes substantially zero, and the circuit is disconnected.

  A semiconductor circuit breaker 4 is provided in the parallel circuit 3 connected in parallel to the mechanical disconnector 2 and the mechanical circuit breaker 20. The semiconductor circuit breaker 4 has a configuration in which a plurality of switching elements 41 are connected in series, and a diode 42 is connected in antiparallel to each switching element 41. In the example of FIG. 1, the semiconductor circuit breaker 4 includes two switching elements 41. As the switching element 41, for example, an element having a self-extinguishing capability such as an IGBT (insulated gate bipolar transistor), a bipolar transistor, or an electric field transistor is used. There are switching elements that have a collector terminal connected to the DC power transmission network A side and those that have a collector terminal connected to the DC power transmission network B side, so that a bidirectional current from the DC power transmission network A to B or B to A Can be turned on and off.

  The semiconductor circuit breaker 4 is switched between an on state, which is a conducting state, and an off state, which is a non-conducting state, by the input of a gate signal. In the conductive state, current is supplied from the DC power transmission system to the parallel circuit 3 via the semiconductor circuit breaker 4, and in the non-conductive state, the current from the DC power transmission system to the parallel circuit 3 is interrupted.

  The semiconductor circuit breaker 4 is connected in parallel with an arrester 43 made of a non-linear element that conducts when a certain voltage or more is applied. The arrester 43 absorbs the surge voltage and enables safe current interruption when the semiconductor circuit breaker 4 is switched to the off state.

  The H bridge circuit 5 has a configuration in which a plurality of H bridge units 50 are connected in series. Each H-bridge unit 50 has two legs 52 in which two switching elements 51 are connected in series. As the switching element 51, one having a self-extinguishing capability is used. A diode is connected to each switching element 51 in parallel. These two legs 52 are connected in parallel, and a capacitor 53 is connected in parallel with the two legs 52. The capacitor 53 is charged by a current flowing through the power transmission line 100 during steady operation.

  The reactor 55 is for reducing the rate of change in current, and will be described later in detail, but is provided to enable current control by the H-bridge circuit 5.

(Operation)
The operation of the DC interrupter 1 having the above configuration will be described separately with reference to FIGS. At normal times, the mechanical disconnector 2 and the mechanical circuit breaker 20 are controlled to be in an on state, and the semiconductor circuit breaker 4 and the H bridge circuit 5 are controlled to be in an off state. As shown in FIG. 2, the current from the DC power transmission network A flows only through the mechanical disconnector 2 and the mechanical circuit breaker 20 to the DC power transmission network B, and flows into the parallel circuit 3 and the H bridge circuit 5. Absent.

  In describing the operation of the DC interrupter 1 at the time of an accident, reference is made to FIG. FIG. 3 is a diagram illustrating an operation state of the simulation execution circuit, which was performed to explain the effectiveness of the DC interrupting device 1 described above. The simulation execution circuit is connected to the DC interrupter 1 shown in FIG. 1 in the circuit configuration simulating the current transmission network A, and after applying the DC voltage 320 KV to the DC interrupter 1, the simulated current A ground fault caused by lightning or the like has occurred in the power transmission line 100 of the power transmission network A. (I) indicated by a thick solid line in FIG. 3 indicates a current flowing through the mechanical circuit breaker 20. (Ii) indicated by an alternate long and short dash line indicates a current flowing through the H-bridge circuit 5. (Iii) indicated by a two-dot chain line indicates a current flowing through the semiconductor circuit breaker 4.

  When an accident occurs, the accident current increases with time. The DC blocking device 1 performs a two-stage blocking operation as a whole. First, the breaking operation of the mechanical circuit breaker 20 is performed at the initial stage where the fault current is small, and the fault current is commutated to the parallel circuit 3, and the breaking operation of the semiconductor circuit breaker 4 is performed at the later stage when the fault current increases. I do. Details will be described below.

When a ground fault occurs at time t1, the current flowing through the mechanical circuit breaker 20 increases as shown in (i). The current sensor attached to the mechanical circuit breaker 20 detects the current Idc_M flowing through the mechanical circuit breaker 20 and compares it with a preset accident occurrence detection threshold value Idc_J. At time t2 when the detected current Idc_M exceeds the threshold value Idc_J, the gate signal of the switching element 41 of the semiconductor circuit breaker 4 of the parallel circuit 3 is switched from OFF to ON. At the same time, the output voltage of the H bridge circuit 5 is controlled. Specifically, the output voltage V_H of the H bridge circuit 5 is calculated by the following formula and output.
V_H = G (s) × (IdcM-0)
(G (s) is control gain, s is Laplace operator)
G (s) is a control gain, for example, performing general proportional-integral control.

  That is, by performing pulse width modulation control on the switching elements 51 of each leg 52 of each H-bridge unit 50 according to a predetermined on / off time ratio (duty), the current Idc_M flowing through the mechanical circuit breaker 20 is substantially zero. Continue to control to become. In other words, the output voltage V_H of the H bridge unit 50 is variably output by performing pulse width modulation control on the switching element 51 of each leg 52.

  By such control by the H bridge circuit 5, as shown in FIG. 3I, the current Idc_M flowing through the mechanical circuit breaker 20 is continuously controlled until it becomes substantially zero. In this state, the mechanical circuit breaker 20 is shifted to the off state. Since the current flowing through the mechanical circuit breaker 20 is substantially zero, even if the contact is shifted to the OFF state, the current does not continue to flow by pulling an arc as in normal DC current conduction. Therefore, current can be interrupted at high speed.

  When the output voltage control by the H bridge unit 50 is performed, the output voltage of the H bridge unit 50 is directly applied to the mechanical circuit breaker 20 having almost zero conduction resistance, a short circuit current flows, and there is a possibility that the current control cannot be performed. . However, in the present embodiment, the parallel circuit 3 connected to the H bridge circuit 5 is provided with a reactor 55 for reducing the current change rate. Since the reactor 55 prevents the output voltage of the H-bridge unit 50 from being directly applied to the mechanical breaker 20, the current flowing through the mechanical breaker 20 can be controlled.

More specifically, the rate of change dIdc_M / dt of the current Idc_M flowing through the mechanical circuit breaker 20 is expressed by the following equation using the inductance value L of the reactor 55.
dIdc_M / dt = V_H / L
In the absence of the reactor 55, the inductance value L = 0, so that the current change rate dIdc_M / dt becomes infinite unless the output voltage V_H of the H-bridge unit 50 is zero, and the current flowing through the mechanical circuit breaker 20 Idc_M cannot be controlled. In the present embodiment, by providing the reactor 55 in the parallel circuit 3, since the inductance value L is inserted in the above equation, the current change rate dIdc_M / dt becomes finite. Therefore, the current change rate dIdc_M / dt can be controlled according to the magnitude of the output voltage V_H of the H bridge unit 50. This prevents the output voltage of the H-bridge unit 50 from being directly applied to the mechanical circuit breaker 20 and enables current control to make the current Idc_M flowing through the mechanical circuit breaker 20 substantially zero.

  By the output voltage control by the H bridge circuit 5, the current Idc_M flowing through the mechanical circuit breaker 20 is continuously controlled until it becomes substantially zero. Specifically, as shown in FIG. 4, the current flowing through the transmission line 100 does not pass through the mechanical circuit breaker 20, passes through the H bridge circuit 5, and further passes through the parallel circuit 3 connected to the H bridge circuit 5. Return to the power transmission line 100. For this reason, the current Idc_M flowing through the mechanical circuit breaker 20 becomes substantially zero. In this state, the mechanical circuit breaker 20 is shifted to the off state. Since the current flowing through the mechanical circuit breaker 20 is substantially zero, even if the contact is shifted to the OFF state, the current does not continue to flow by pulling an arc as in normal DC current conduction. Therefore, current can be interrupted at high speed.

  Next, as shown in FIG. 5, all the switching elements 51 of the H bridge unit 50 are turned off (see (ii) of FIG. 3). Then, the voltage stored in advance in the capacitor 53 of the H bridge unit 50 is applied in a direction to reduce the accident current that continues to flow through the mechanical disconnector 2. As a result, the fault current flowing through the mechanical disconnector 2 is reduced. Since the accident current flowing through the mechanical disconnector 2 is reduced, the accident current is commutated to the parallel circuit 3 connected in parallel to the mechanical disconnector 2. As shown in (iii) of FIG. 3, the current flowing through the semiconductor breaker 4 increases, and eventually the current flowing through the mechanical disconnector 2 becomes zero with the passage of time, so that all fault currents are interrupted by the semiconductor. It flows through the vessel 4. At this timing, the mechanical disconnector 2 is turned off. Since no current flows through the mechanical disconnector 2, an arc is not generated when the contact is disconnected, and the current does not continue to flow.

  Finally, as shown in FIG. 6, the gate signal of the switching element 41 of the semiconductor circuit breaker 4 is switched from on to off, and the accident current flowing through the parallel circuit 3 is interrupted. The surge voltage generated at this time is absorbed by the arrester 43, and the current interruption is completed.

(effect)
As described above, in the first embodiment, the DC breaker 1 includes the mechanical disconnector 2 provided in the power transmission line 100, the mechanical breaker 20 connected in series to the mechanical disconnector 2, and the machine And a parallel circuit 3 connected in parallel to the mechanical disconnector 2 and the mechanical breaker 20. The parallel circuit 3 includes a semiconductor circuit breaker 4 that switches between supply and interruption of the current of the power transmission line 100 to the parallel circuit 3 and a reactor 55 that is connected to the semiconductor circuit breaker 4 in series. The DC breaker 1 further includes an H bridge circuit 5 that connects a point between the mechanical disconnector 2 and the mechanical breaker 20 and a point between the semiconductor breaker 4 and the reactor 55. The H bridge circuit 5 includes an H bridge unit 50 including a plurality of switching elements 51 and a capacitor 53. The H bridge circuit 5 controls the current flowing through the mechanical circuit breaker 20 by output voltage control.

  At normal times, since the current passes only through the mechanical disconnector 2 and the mechanical circuit breaker 20, the conduction loss can be reduced, and the efficient DC breaker 1 can be provided. In the event of an accident, the output voltage control using the H-bridge circuit 5 can induce the current in the parallel circuit 3 and the current flowing through the mechanical disconnector 2 can be disconnected without causing an arc. For example, by setting it to substantially zero, even in the case of the mechanical disconnector 2 having no current interruption capability, the accident point can be safely separated. Furthermore, high-speed current interruption can be realized by the semiconductor breaker 4 provided in the parallel circuit 3. Such an effect can contribute to improvement in power transmission efficiency, cost reduction, and improvement in reliability in DC power transmission.

  Further, the H bridge circuit 5 is installed in such a manner that one point between the mechanical disconnector 2 and the mechanical circuit breaker 20 and one point between the semiconductor circuit breaker 4 and the reactor 55 are connected. Therefore, a current flows through the H bridge circuit 5 only in the initial stage where the fault current that performs the breaking operation of the mechanical breaker 20 is small. That is, the maximum value of the current flowing through the H bridge circuit 5 is an accident current at the time when the mechanical circuit breaker 20 is turned off. Thereafter, the fault current that increases when a further time elapses before the mechanical disconnector 2 is turned off flows through the parallel circuit 3, so that the maximum current capacity of the semiconductor switching element 51 constituting the H-bridge circuit 5 is It is possible to reduce the capacity to a much smaller capacity than the maximum current capacity of the switching element 41 constituting the semiconductor circuit breaker 4. Moreover, since the reactor 55 is installed in the parallel circuit 3, the output voltage of the H bridge circuit 5 is not directly applied to the mechanical circuit breaker 20, and accurate current control is possible.

  The H bridge circuit 5 includes a plurality of H bridge units 50 connected in series. As the number of capacitors 53 provided in each H-bridge unit 50 increases, the amount of charge / discharge also increases, so that a large accident current can be dealt with.

(Second Embodiment)
A second embodiment will be described with reference to FIG. In the second embodiment, only points different from the first embodiment will be described, and the same parts as those in the first embodiment will be denoted by the same reference numerals and detailed description thereof will be omitted.

(Constitution)
In the present embodiment, the DC cutoff device 1 does not include the H bridge circuit 5. Two sets of semiconductor breakers 4A and 4B are connected in series to the parallel circuit 3 connected in parallel to the mechanical disconnector 2 and the mechanical breaker 20.

  The semiconductor circuit breaker 4A has a configuration in which two or more switching elements 41a having a self-extinguishing capability are connected in series, and a diode 42a is connected in antiparallel to each switching element 41a. In the example of FIG. 7, an example in which three are connected is shown. The semiconductor circuit breaker 4A has a collector terminal connected to the DC power transmission network A side.

  The semiconductor circuit breaker 4B has a configuration in which two or more switching elements 41b having a self-extinguishing capability are connected in series, and a diode 42b is connected in antiparallel to each switching element 41b. In the example of FIG. 7, an example in which three are connected is shown. The semiconductor circuit breaker 4B has a collector terminal connected to the DC power transmission network B side. That is, the switching element 41b of the semiconductor circuit breaker 4B has the collector and emitter oriented in the opposite direction to the switching element 41b of the semiconductor circuit breaker 4A.

  The semiconductor circuit breakers 4 </ b> A and 4 </ b> B are connected to each other via a reactor 55. Although this reactor 55 is installed in order to reduce the current change rate of the parallel circuit 3, the reactor 55 can also be abbreviate | omitted by utilizing wiring inductance. Moreover, in the example of FIG. 7, although the reactor 55 is installed between the semiconductor circuit breakers 4A and 4B, an installation position is not restricted to this. Even if the parallel circuit 3 is installed next to the DC power transmission network A side of the semiconductor circuit breaker 4A or adjacent to the DC power transmission network B side of the semiconductor circuit breaker 4B, there is no difference in function.

  A reverse current generation circuit 6A is connected in reverse parallel to one of the switching elements 41a constituting the semiconductor circuit breaker 4A. The reverse current generation circuit 6A includes a switching element 61a, a diode 62a connected in antiparallel with the switching element 61a, and a capacitor 63a connected in series with the switching element 61a. The collector side of the switching element 41a of the semiconductor circuit breaker 4A is connected to the emitter side of the switching element 41a of the reverse current generation circuit 6A. The collector side of the reverse current generation circuit 6A is connected to the positive terminal of the capacitor 63a. The negative terminal of the capacitor 63a is connected to the emitter side of the switching element 41a of the semiconductor circuit breaker 4A.

  A reverse current generation circuit 6B is connected in reverse parallel to one of the switching elements 41b constituting the semiconductor circuit breaker 4B. The reverse current generation circuit 6B includes a switching element 61b, a diode 62b connected in antiparallel with the switching element 61b, and a capacitor 63b connected in series with the switching element 61b. The collector side of the switching element 41b of the semiconductor circuit breaker 4B is connected to the emitter side of the switching element 41b of the reverse current generation circuit 6B. The collector side of the reverse current generation circuit 6B is connected to the positive side terminal of the capacitor 63b. The negative terminal of the capacitor 63b is connected to the emitter side of the switching element 41a of the semiconductor circuit breaker 4A. That is, the switching element 61b of the reverse current generation circuit 6B is installed so as to conduct current in the opposite direction to the switching 61a of the reverse current generation circuit 6A.

  As the switching elements 61a and 61b constituting the reverse current generating circuits 6A and 6B, those having a capacity smaller than the maximum current capacity of the switching elements 41a and 41b constituting the semiconductor circuit breakers 4A and 4B may be used.

  The reverse current generation circuits 6A and 6B are connected in antiparallel to one of the switching elements 41a and 41b constituting the semiconductor circuit breakers 4A and 4B, respectively. On the other hand, you may make it connect in antiparallel. In the example of FIG. 7, the semiconductor circuit breakers 4A and 4B have three switching elements 41a and 41b, respectively. Therefore, the reverse current generation circuits 6A and 6B have two or three switching elements 41a and 41b. You may make it connect in antiparallel.

(Operation)
The operation of the DC circuit breaker 1 having the above configuration will be described separately for normal times and accidents. In the case of an accident, a case where a DC short-circuit accident occurs in the DC power transmission network B will be described. During normal operation, the mechanical disconnector 2 and the mechanical circuit breaker 20 are turned on, and the switching elements of the semiconductor circuit breakers 4A and 4B and the reverse current generation circuits 6A and 6B are controlled to be turned off. The current from the DC power transmission network A flows only through the mechanical disconnector 2 and the mechanical circuit breaker 20 to the DC power transmission network B and does not flow into the parallel circuit 3.

  When an accident occurs, when the current sensor attached to the mechanical circuit breaker 20 detects a current Idc_M exceeding the threshold value Idc_J, the switching element 41a of the semiconductor circuit breaker 4A whose collector is connected to the DC power transmission network A side is turned on. At the same time, the switching element 61b of the reverse current generation circuit 6B connected in reverse parallel to the semiconductor circuit breaker 4B is turned on.

  The diode 42b of the semiconductor circuit breaker 4B, the mechanical circuit breaker 20, the mechanical disconnector 2, the direct current power transmission whose collector is connected to the direct current power transmission network B side by the capacitor voltage charged in advance in the capacitor 63b of the reverse current generation circuit 6B. A circuit that passes through the switching element 41a and the reactor 55 of the semiconductor circuit breaker 4A with the collector connected to the network A side is configured. By this one-round circuit, a current in the opposite direction to the accident current flowing through the mechanical circuit breaker 20 in the event of an accident is superimposed. As a result, the current Idc_M flowing through the mechanical circuit breaker 20 is controlled to be substantially zero. In this state, the mechanical circuit breaker 20 is shifted to the off state. Since the current flowing through the mechanical circuit breaker 20 is substantially zero, even if the contact is shifted to the OFF state, the current does not continue to flow by pulling an arc as in normal DC current conduction. Therefore, current can be interrupted at high speed.

  Next, the switching element 61b of the reverse current generation circuit 6B is turned off. Further, the mechanical disconnector 2 is turned off. The accident current that increases with the passage of time flows through the parallel circuit 3 only. Here, the fault current is finally cut off by switching the gate signal of the switching element 41a of the semiconductor circuit breaker 4A from on to off.

  When an accident occurs on the DC power transmission network A side, the operation is reversed to the left and right when an accident occurs on the DC power transmission network B. That is, the switching element 41b of the semiconductor circuit breaker 4B whose collector is connected to the DC power transmission network B side is turned on, and the switching element 61a of the reverse current generation circuit 6A is turned on. The diode 42a of the semiconductor circuit breaker 4A, the mechanical disconnector 2, the mechanical circuit breaker 20, and the DC power transmission whose collector is connected to the DC power transmission network A side by the capacitor voltage precharged in the capacitor 63a of the reverse current generation circuit 6A. A circuit that passes through the switching element 41b and the reactor 55 of the semiconductor circuit breaker 4B having a collector connected to the network B side is formed. By this one-round circuit, a current in the opposite direction to the accident current flowing through the mechanical circuit breaker 20 in the event of an accident is superimposed. The current Idc_M flowing through the mechanical circuit breaker 20 is controlled to be substantially zero, and in this state, the mechanical circuit breaker 20 is shifted to the off state.

(effect)
(1) As described above, in the second embodiment, instead of including the H bridge circuit 5 in the DC circuit breaker 1, the parallel circuit 3 includes two sets of semiconductor circuit breakers 4A and 4B, and further includes the semiconductor circuit breaker 4A. , 4B are provided with reverse current circuits 6A, 6B connected in antiparallel. The semiconductor circuit breakers 4A and 4B are configured by connecting a plurality of switching elements 41a in series, and are installed so as to conduct currents supplied from the power transmission line 100 in directions opposite to each other. The reverse current generation circuits 6A and 6B are connected in reverse parallel to one or more of the switching elements 41a and 41b constituting the semiconductor circuit breakers 4A and 4B, and have a current opposite to the current flowing through the mechanical circuit breaker 20. Is superimposed.

  By adopting such a configuration, as in the first embodiment, the current passes through only the mechanical disconnector 2 and the mechanical circuit breaker 20 at normal times, so that the conduction loss can be reduced and the efficiency is improved. It is possible to provide a direct current interrupting device 1 with good quality. In the event of an accident, the reverse current generation circuits 6A and 6B superimpose a current in the opposite direction to the current flowing through the mechanical circuit breaker 20, so that the current flowing through the mechanical circuit breaker 20 can be made substantially zero, so Can be separated. Furthermore, high-speed current interruption can be realized by the semiconductor breaker 4 provided in the parallel circuit 3. Such an effect can contribute to improvement in power transmission efficiency, cost reduction, and improvement in reliability in DC power transmission.

  In addition, since the reverse current generation circuits 6A and 6B are connected in parallel to the semiconductor circuit breakers 4A and 4B, current is supplied to the reverse current generation circuits 6A and 6B only at the initial stage where the fault current is small when the breaking operation of the mechanical circuit breaker 20 is performed. Flowing. That is, the maximum value of the current flowing through the reverse current generation circuits 6A and 6B is up to the accident current at the time when the mechanical circuit breaker 20 is turned off. After the mechanical circuit breaker 20 is turned off, the accident current increased with the passage of time flows through the semiconductor circuit breakers 4A and 4B connected in parallel with the reverse current generation circuits 6A and 6B. Therefore, the maximum current capacity of the switching elements 61a and 61b constituting the reverse current generating circuits 6A and 6B can be made smaller than the maximum current capacity of the switching elements 41a and 41b constituting the semiconductor circuit breakers 4A and 4B. Therefore, it is possible to reduce the cost of the DC interrupter 1.

(2) The parallel circuit 3 includes a reactor 55 connected in series to the semiconductor circuit breaker 4A and the semiconductor circuit breaker 4B. The current flowing through the parallel circuit 3 can be smoothed by the reactor 55, the rate of current change can be reduced, and accurate output voltage control is possible.

(Other embodiments)
The present invention is not limited to the above-described embodiments as they are, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

DESCRIPTION OF SYMBOLS 1 DC circuit breaker 2 Mechanical disconnector 20 Mechanical circuit breaker 3 Parallel circuit 4, 4A, 4B Semiconductor circuit breaker 41, 41a, 41b Switching element 42, 42a, 42b Diode 43 Arrester 5 H bridge circuit 50 H bridge unit 51 Switching Element 52 Leg 53 Capacitor 55 Reactor 6A, 6B Reverse current generation circuit 61a, 61b Switching element 62a, 62b Diode 63a, 63b Capacitor 100 Positive transmission line 101 Negative transmission line A, B DC transmission network

Claims (3)

A mechanical disconnector provided in the DC transmission system;
A mechanical circuit breaker provided in the DC power transmission system and connected in series to the mechanical disconnector;
A semiconductor breaker that is connected in parallel to the mechanical disconnector and the mechanical breaker, and that switches between supply and interruption of current of the DC power transmission system; and a reactor that is connected in series to the semiconductor breaker. A parallel circuit;
One point between the mechanical disconnector and the mechanical circuit breaker, and one point between the semiconductor breaker and the reactor are connected, and an H bridge unit including a plurality of switching elements and capacitors is provided, and output voltage control is performed. And a H-bridge circuit for controlling a current flowing through the mechanical circuit breaker. When an accident occurs in the DC transmission system,
The semiconductor circuit breaker and the H bridge unit are turned on, and the current flowing through the mechanical circuit breaker is controlled to be substantially zero by the output voltage control of the H bridge circuit, and the mechanical circuit breaker is turned off. Let
The H bridge unit is turned off, a fault current is commutated to the parallel circuit by applying a voltage of the capacitor of the H bridge circuit, and the mechanical disconnector is turned off. 2. The DC circuit breaker according to claim 1, wherein the fault current is interrupted by a circuit breaker.   3. The DC interrupter according to claim 1, wherein the H bridge circuit includes a plurality of the H bridge units connected in series.

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