JP6109649B2 - DC current interrupter - Google Patents

Description

  Embodiments described herein relate generally to a direct current interruption device.

  In recent years, the spread of renewable energy such as wind power generation, solar power generation, and solar thermal power generation has been promoted, but in order to cover higher-power renewable energy, offshore wind power generation, solar power generation in desert areas, etc. Solar power generation is beginning to be considered.

  In offshore wind power generation, large amounts of offshore generated power are transmitted to the cities where they are consumed by submarine cables, or large amounts of power generated in desert areas in the back of Africa and the mainland of China are used for example in Europe and coastal areas. It is necessary to transmit power efficiently over long distances to cities.

  In order to respond to such demands, DC power transmission can be installed more efficiently and at a lower cost than conventional three-phase AC power transmission. Being started.

  In DC power transmission, a power converter such as a converter that converts generated AC power into DC for DC power transmission or an inverter that converts transmitted DC power into AC in a power facility in a city is required. In this case, studies and commercialization of modular multi-level converter circuits that can output a voltage waveform close to a sine wave so that harmonic components associated with switching of converters and inverters do not flow into the AC power system will proceed. It has been.

  By the way, the DC power transmission system can be installed at a lower cost than the conventional AC power transmission system when applied to long-distance high-power transmission, and a high-efficiency system with less transmission loss can be constructed. . However, when a system accident occurs due to a lightning strike, there is a restriction that it is difficult to quickly shut off the point of the system accident.

  In the AC power transmission system, the mechanical contact breaker can cut off the current at a high speed using a point where the AC current crosses zero every half cycle of the AC frequency 50 Hz or 60 Hz. This is because there is no point where the DC current crosses zero, and therefore the mechanical contact breaker cannot quickly interrupt the DC current.

  Normally, when constructing a power transmission network, it is assumed that there will be a requirement that the accident point should be separated from the power transmission network at a high speed and the operation should be continued only with a healthy power transmission network. If there is a restriction that sometimes cannot cut off the accident current at high speed, it becomes impossible to construct a DC power transmission network as described above.

  Therefore, as shown in FIG. 5, a DC current interrupting device having a configuration in which a plurality of H-shaped bridge units 103,... Are connected in series at a required portion of a transmission line 101 of a DC transmission network has been proposed. Each H-type bridge unit 103 has a circuit configuration in which two legs 103a and 103b each having two switching elements such as IGBTs (insulated gate bipolar transistors) having self-extinguishing capability connected in series and a capacitor 103c are connected in parallel. is there.

  Here, the reason why the plurality of H-type bridge units 103 are connected in series is equivalent to the DC line voltage of the power transmission line 101 because the withstand voltage of the semiconductor switching elements constituting one H-type bridge unit 103 is small. In order to have a withstand voltage, a plurality of H-shaped bridge units 103,... Are connected in series.

  The DC current interrupting device of FIG. 5 turns on the required semiconductor switching elements of the legs 103a, 103b of each H-shaped bridge unit 103, ... during normal operation, and flows DC current during normal operation, and when a system fault occurs. The semiconductor switching element is turned off, and the self-extinguishing capability of the semiconductor switching element is utilized to cut off the DC fault current at high speed. As a result, it became possible to cut off the direct current at the time of an accident at a high speed even in the future direct current transmission system.

  However, in the circuit configuration capable of high-speed interruption as described above, since all of the transmitted power always passes through the semiconductor switching elements of the plurality of H bridge units 103,. The increase in the capacity of the device and the increase in power transmission loss due to the passage of current through a large number of semiconductor switching elements lead to a decrease in power transmission efficiency during normal operation, resulting in high costs and an increase in the size of the interrupting device.

  Therefore, in order to solve the above problems, a DC current interrupting device as shown in FIG. 6 has been proposed.

  This DC current interrupting device has a circuit configuration in which a serial connection circuit of a mechanical contact type current interrupter 104 and an auxiliary semiconductor circuit breaker 105 and a semiconductor circuit breaker 106 are connected in parallel to a required portion of a transmission line 101 of a DC power transmission network. It is.

  According to this DC current interrupting device, at the time of steady operation, the mechanical contact current interrupter 104 and the auxiliary semiconductor circuit breaker 105 are turned on, and the semiconductor circuit breaker 106 is set off. At this time, a normal DC current flows through a series circuit of the mechanical contact type current breaker 104 and the auxiliary semiconductor breaker 105.

  On the other hand, when a system fault occurs, the auxiliary semiconductor circuit breaker 105 is turned off and the parallel-connected semiconductor circuit breaker 106 is turned on at the same time. As a result, all fault currents begin to flow through the parallel-connected semiconductor circuit breakers 106. After that, when the current flowing through the mechanical contact type current breaker 104 becomes zero, the mechanical contact type current breaker 104 is disconnected to ensure a dielectric strength, and the semiconductor breaker 106 on the parallel connection side is turned off. To cut off the accident current.

  Such a DC current interrupting device can reduce the conduction loss compared to the DC current interrupting device shown in FIG. 5 because the conduction loss during steady operation is only the conduction loss of the auxiliary semiconductor circuit breaker 105. There is still a problem that conduction loss of the auxiliary semiconductor circuit breaker 105 occurs, and there is still room for improvement.

International Publication No. 2011/12174 Pamphlet International Publication No. 2011/57674 Pamphlet

  The problem to be solved by the present invention is to provide a high-efficiency and low-cost DC current interrupting device having a function of interrupting a DC fault current at high speed and reducing the equipment capacity and conduction loss.

In order to solve the above problems, a DC current interrupting device according to an embodiment is a DC current interrupting device that is installed at a required portion of a transmission line of a DC power transmission network and disconnects an accident point of the transmission line at high speed.
A mechanical circuit breaker with a withstand voltage that can withstand the DC voltage necessary to isolate the accident point with a mechanical contact and a switching element with self-extinguishing capability connected to each other. Thus, at least two semiconductor circuit breakers connected in series, two legs connected in series with two switching elements having self-extinguishing capability, and a capacitor are connected in parallel to form an H-shaped bridge unit. An H-type bridge unit group in which one or more bridge units are connected in series, the mechanical circuit breaker is arranged in a current path during steady operation, and the semiconductor breaker and the H-type bridge unit group are connected in series. And a DC current interrupting device arranged in an accident current path connected in parallel to the steady operation current path.

The lineblock diagram showing one embodiment of the direct-current interruption device applied to a direct-current power transmission system. The block diagram of the simulation circuit which performs operation | movement verification of the direct-current interrupter of FIG. The figure explaining the simulation result by the simulation circuit shown in FIG. The block diagram which shows other embodiment of the direct-current interrupting device applied to a direct-current power transmission system. The block diagram of the conventional direct current interruption device. The block diagram of the other conventional DC current interrupting device.

Hereinafter, embodiments will be described with reference to the drawings.
(Embodiment 1)
FIG. 1 is a diagram showing a configuration of a DC current interrupting device according to the first embodiment.
The DC current interrupting device is installed at a required portion of the transmission line 11 of the DC power transmission network as in the conventional case.
The DC current interrupting device is a semiconductor that becomes a current path at the time of an accident with respect to a current path at the time of steady operation that is composed of a mechanical contact type current circuit breaker (hereinafter referred to as a mechanical circuit breaker) 13 that becomes a current path during normal (normal) operation. A series circuit of the circuit breaker 14 and the H-shaped bridge unit 16 is connected in parallel.

  The mechanical circuit breaker 13 has a mechanical contact, and is configured to have a withstand voltage that can withstand a DC voltage necessary for disconnecting an accident point in a state where the mechanical contact is disconnected.

  The semiconductor circuit breaker 14 includes two semiconductor switching elements 14a and 14b connected in series and having a self-extinguishing capability such as an IGBT (Insulated Gate Bipolar Transistor), a bipolar transistor, and a field effect transistor. As the two semiconductor switching elements 14a and 14b, the emitters are commonly connected, but the number of semiconductor switching elements may be two or more, and the number is not particularly limited.

  The semiconductor circuit breaker 14 is connected in parallel with a non-linear element arrester 15 having a function of conducting when a voltage higher than a certain voltage is applied to the semiconductor circuit breaker 14.

  A plurality of the H-shaped bridge units 16 are connected in series. Specifically, each H-type bridge unit 16 is a circuit in which two legs 16a and 16b each having a self-extinguishing capability, for example, two semiconductor switching elements such as IGBTs connected in series and a capacitor 16c are connected in parallel. It has a configuration. Although two H-shaped bridge units 16 are connected in series, two or more H-shaped bridge units 16 may be used, and the number is not particularly limited.

  Next, the operation of the DC current interrupting device as described above will be described.

  At the time of steady operation, the DC current interrupter operates with the mechanical circuit breaker 13 turned on and the semiconductor circuit breaker 14 and the H-shaped bridge units 16 and 16 turned off. When power is interchanged using the transmission line 11 of the DC transmission network, the normal current flows from the upstream side of the transmission line 11 to the downstream side of the transmission line 11 through the mechanical circuit breaker 13.

  On the other hand, when a system fault occurs, the semiconductor switching elements 14a and 14b of the semiconductor circuit breaker 14 are turned on, and the current flowing through the mechanical circuit breaker 13 is substantially zero by the output voltage control of the H-type bridge units 16 and 16. Control is performed as follows.

  Hereinafter, the control which makes the electric current which flows into the mechanical circuit breaker 13 zero is demonstrated.

  The current IdcM flowing through the mechanical circuit breaker 13 is detected by, for example, a current sensor (not shown). The detected current IdcM is compared with a preset accident occurrence detection threshold value IdcJIKO. When the detected current IdcM exceeds the accident occurrence detection threshold value IdcJIKO, the semiconductor switching element 14a of the semiconductor circuit breaker 14 is detected. , 14b is switched from off to on, and the output voltage VH of the H-type bridge units 16, 16 is calculated and output based on the following control algorithm.

VH = G (s) × (IdcM-0)
In the above equation, G (s) is a control gain, and s is a Laplace operator. G (s) is a control gain, and for example, general proportional integral control is performed.

  That is, by performing pulse width modulation control on the semiconductor switching elements of the legs 16a and 16b of each H-shaped bridge unit 16 according to a predetermined on / off time ratio (duty), the current IdcM flowing through the mechanical circuit breaker 13 is Continue to control to be almost zero. That is, the output voltage VH of the H-type bridge units 16 and 16 is variably output by performing pulse width modulation control on the semiconductor switching elements of the legs 16a and 16b.

  And the mechanical circuit breaker 13 is made into an OFF state in the state which became almost zero. Since no current flows through the mechanical circuit breaker 13, even if the mechanical contact is set to the OFF state, the current does not continue to flow by pulling the arc as in the normal DC current conduction, and the current interruption It is also possible to interrupt the current using an incapacitating circuit breaker.

  In this state, by switching the gate signals of the semiconductor switching elements 14a and 14b constituting the semiconductor circuit breaker 14 from on to off, the fault current flowing through the semiconductor circuit breaker 14 is caused by the self-extinguishing capability of the semiconductor circuit breaker 14. Eventually shut off.

  Next, FIG. 2 and FIG. 3 are diagrams showing the configuration of the simulation execution circuit and the operation state of the simulation performed to explain the effectiveness of the DC current interrupting device according to Embodiment 1 described above.

  The simulation execution circuit is connected to the DC current interrupting device shown in FIG. 1 in a circuit configuration simulating a current transmission network, and after applying a DC voltage of 320 KV to the DC current interrupting device, the simulated current transmission is performed. A ground fault caused by lightning, etc. occurred on the transmission line of the network. Here, the four H-shaped bridge units 16 are connected in series.

FIG. 3A shows a change state of the voltage Vmain-brk across the semiconductor circuit breaker when the semiconductor circuit breaker 14 is turned off. That is, when the semiconductor breaker 14 is turned off, a voltage close to 500 KV, which is the set voltage of the arrester 15, appears at both ends of the semiconductor breaker, and then current flows through the arrester 15, so that power energy is consumed in the arrester 15. The voltage Vmain-brk at both ends of the semiconductor circuit breaker 14 decreases until it is used up. That is, after the semiconductor circuit breaker 14 is turned off, the voltage of the DC current interrupting device is clamped at the set voltage 500 KV of the arrester 15, and the fault current is attenuated by the difference from the system voltage 320 KV.

  FIG. 3B shows a change state of the DC line current ilinek that is the sum of the mechanical circuit breaker current isub and the semiconductor circuit breaker current imain when the semiconductor circuit breaker 14 is turned on when a system fault occurs. At this time, the semiconductor circuit breaker 14 is turned off at the time when the peak of the DC line current ilinek is reached (see FIG. 3A). From FIG. 3B, the DC line current ilinek is zero within 3 ms after the occurrence of the ground fault. Therefore, this direct current interruption device can interrupt the direct current accident current at high speed.

  FIG. 3C shows a change state of voltages Vcell-1 to Vcell-4k of the capacitor 16c of the 4-series H-type bridge unit 16.

  FIG. 3D shows the operation start timing of the H-shaped bridge unit 16, the opening of the mechanical circuit breaker 13, and the opening timing of the semiconductor circuit breaker 14.

  Therefore, if this DC current interrupting device is controlled according to the above-described control procedure when a system fault occurs, the DC fault current can be finally interrupted at high speed as shown in FIG.

  Therefore, according to the configuration of the DC current interrupting device according to the first embodiment, since the power interchange current flows only through the mechanical circuit breaker 13 during the steady operation, the conduction loss hardly occurs only by the mechanical circuit breaker 13 and is highly efficient. A direct current interruption device can be provided.

(Embodiment 2)
FIG. 4 is a diagram showing a configuration of the DC current interrupting device according to the second embodiment.
The second embodiment has a configuration in which a DC current interrupting device in which, for example, five DC current interrupting units 21,... Are connected in series at a required portion of the transmission line 11 of the DC power transmission network.

  The internal configuration and control operation of these DC current interrupting units 21 are substantially the same configuration and control operation as those of the DC current interrupting device described in the first embodiment, and are particularly different in each DC current interrupting unit 21. That is, the withstand voltage is 1/5 of the first embodiment.

  The configuration of the DC current interrupting device as described above is realized for the following reason. That is, the DC current interrupting device according to the second embodiment, for example, in the DC current interrupting device according to the first embodiment, the required withstand voltage increases as the DC voltage of the transmission line 11 of the current transmission network increases. It was invented to facilitate the structure (configuration) of the mechanical circuit breaker 13.

  The mechanical circuit breaker 13 needs to take a longer distance between the contacts in accordance with the withstand voltage in order to ensure the withstand voltage at the time of off, but as the distance becomes longer, the time taken to complete the off operation becomes longer, resulting in a DC accident. The current interruption completion time becomes longer accordingly.

  Therefore, in the second embodiment, it is possible to shorten the operation time by shortening the distance between the contacts by adopting a configuration in which five mechanical circuit breakers 13 having a dielectric strength of 1/5 are connected in series. Is. However, if the mechanical circuit breaker 13 in the circuit configuration of the first embodiment is simply replaced with a five-divided circuit, voltage concentration occurs due to variation in operating time between the five circuit breakers, and the breakdown voltage is destroyed. There are concerns that will happen. In order to solve this problem, the semiconductor breaker 14 and the H-type bridge unit 16 connected in parallel are also divided into five parts and connected individually, thereby suppressing overvoltage caused by variation in operation time. .

  After turning off each mechanical circuit breaker 13 of each hybrid circuit breaker 21, if only four semiconductor circuit breakers 14 are turned off among the five semiconductor circuit breakers 14,..., The arrester voltage in the entire series circuit is 400 kV. The accident current decay rate can be made slower than in the first embodiment. By using this, it is possible to continue the accident current while suppressing an increase in the accident current, and it is possible to control the accident current necessary for system operation such as identification of the accident point.

  If the DC current interrupting device according to the second embodiment is used, the power interchange current flows only to the mechanical circuit breaker 13 of each hybrid circuit breaker 21 during steady operation as in the first embodiment. Therefore, the conduction loss hardly occurs and only a high-efficiency DC current interrupting device can be provided.

  Therefore, it can be applied to a high-voltage DC power transmission system, and the attenuation rate of the accident current can be adjusted, thereby facilitating system operation.

  In the second embodiment, a plurality of DC current interrupting units 21,... Are configured, but by controlling the number of these DC current interrupting units 21,. You may operate | move so that an accident electric current may be reduced in steps.

  In addition, each said embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 11 ... Transmission line of DC power transmission network, 13 ... Mechanical circuit breaker (mechanical contact type current breaker), 14 ... Semiconductor circuit breaker, 14a, 14b ... Semiconductor switching element with self-extinguishing capability, 15 ... Arrester, 16 ... H-shaped bridge unit, 16a, 16b ... leg, 16c ... capacitor, 21 ... DC current interruption unit.

Claims (5)

A DC current interrupting device that is installed at a required location of a transmission line of a DC transmission network and disconnects the accident point of the transmission line at high speed,
A mechanical circuit breaker that has a mechanical withstand voltage and withstands the DC voltage necessary to isolate the accident point with the mechanical contact disconnected.
A semiconductor breaker in which at least two switching elements having self-extinguishing ability are connected in series by connecting the emitters;
Two legs with a self-extinguishing capability connected in series and a capacitor are connected in parallel to form an H-shaped bridge unit, and one or more H-shaped bridge units are connected in series. With a group of bridge units,
The mechanical circuit breaker is disposed in a current path during steady operation, and the semiconductor circuit breaker and the H-shaped bridge unit group are connected in series and disposed in a current path during an accident connected in parallel to the current path during steady operation. A direct current interrupting device characterized by: The direct current interrupting device according to claim 1,
At the time of steady operation, the mechanical circuit breaker is turned on, the semiconductor breaker and the H-bridge unit group are set to an off state, and a current during steady operation flows through the mechanical circuit breaker;
When a system fault occurs, the semiconductor circuit breaker shifts to an on state, and the current flowing through the mechanical circuit breaker is controlled to be substantially zero by the output voltage control of the H bridge unit group; and
And a means for interrupting an accident current with the semiconductor circuit breaker after the mechanical circuit breaker is shifted to an off state when the current flowing through the mechanical circuit breaker is in a zero current state. Shut-off device. A DC current interrupting device that is installed at a required location of a transmission line of a DC transmission network and disconnects the accident point of the transmission line at high speed,
A mechanical circuit breaker with a withstand voltage that can withstand the DC voltage necessary to isolate the fault point with a mechanical contact and a switching element with self-extinguishing capability connected to each other. Thus, at least two semiconductor circuit breakers connected in series, an arrester connected in parallel to the semiconductor circuit breaker and conducting when applied over a certain voltage, and two switching elements having self-extinguishing capability are connected in series. An H-type bridge unit in which two or more connected legs and a capacitor are connected in parallel, and one or more H-type bridge units connected in series; and the mechanical circuit breaker is arranged in a current path during steady operation, In addition, the semiconductor circuit breaker including the arrester and the H-shaped bridge unit group are connected in series and connected in parallel to the steady-state current path. Constitute a direct current blocking unit by placing,
A DC current interrupting device comprising at least two DC current interrupting units connected in series. In the direct current interruption device according to claim 3,
At the time of steady operation, the mechanical circuit breaker in each DC current breaker unit is set to an on state, the semiconductor breaker and the H-shaped bridge unit are set to an off state, and a current during steady operation is passed through the mechanical breaker. Means,
When a system fault occurs, the semiconductor circuit breaker is 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-shaped bridge unit;
And a means for interrupting an accident current with the semiconductor circuit breaker after the mechanical circuit breaker is shifted to an off state when the current flowing through the mechanical circuit breaker is in a zero current state. Shut-off device. In the direct current interruption device according to claim 3,
At the time of steady operation, the mechanical circuit breaker in each DC current breaker unit is set to an on state, the semiconductor breaker and the H-shaped bridge unit are set to an off state, and a current during steady operation is passed through the mechanical breaker. Means,
When a system fault occurs, the semiconductor circuit breaker is 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-shaped bridge unit;
When the current flowing through the mechanical circuit breaker is in a zero current state, means for shifting the mechanical circuit breaker to an off state;
A DC current interrupting device comprising: means for controlling the number of semiconductor circuit breakers of the plurality of DC current interrupting units to be turned off so as to reduce the accident current stepwise.

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