DC circuit breakers and DC transmission systems

Abstract

A load located downstream of a DC circuit breaker in a DC power transmission system is protected by the DC circuit breaker more reliably than ever before. [Solution] A DC circuit breaker (1) disposed upstream of a load (LD) in a DC power transmission system (100) includes a semiconductor switch (SW) connected to a DC transmission line (81) in the DC power transmission system (100) and having a gate terminal (GT), a current sensor (11) that detects the current value of a current flowing through the semiconductor switch (SW) and a current change rate that is the time rate of change of the current value, and a control unit (20) that controls the semiconductor switch (SW) by supplying a gate voltage to the gate terminal (GT). The control unit (20) reduces the current flowing through the semiconductor switch (SW) when the semiconductor switch (SW) is in a conductive state by changing the gate voltage based on the current change rate detected by the current sensor (11).

Description

[Technical Field]

[0001] The following disclosure relates to a DC circuit breaker. [Background technology]

[0002] Various techniques have been proposed for semiconductor circuit breakers as DC circuit breakers. For example, Patent Document 1 listed below shows various configuration examples of semiconductor circuit breakers provided in DC power transmission systems. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 8-251907 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one aspect of the present disclosure is to provide more reliable protection than ever before for a load located downstream of a DC circuit breaker in a DC power transmission system by the DC circuit breaker. [Means for solving the problem]

[0005] A DC circuit breaker according to one aspect of the present disclosure is a DC circuit breaker that is disposed upstream of a load in a DC power transmission system, and includes: a semiconductor switch that is connected to a DC transmission line in the DC power transmission system and has a gate terminal; a current sensor that detects a current value of a current flowing through the semiconductor switch and a current change rate that is a time rate of change of the current value; and a control unit that controls the semiconductor switch by supplying a gate voltage to the gate terminal, and the control unit reduces the current flowing through the semiconductor switch when the semiconductor switch is in a conductive state by changing the gate voltage based on the current change rate detected by the current sensor. [Effects of the Invention]

[0006] According to one aspect of the present disclosure, it is possible to more reliably protect a load located downstream of a DC circuit breaker in a DC power transmission system by the DC circuit breaker than ever before. [Brief explanation of the drawings]

[0007] [Figure 1] 1 shows an example of the configuration of a DC power transmission system according to a first embodiment. [Figure 2] FIG. 4 is a diagram for explaining a first gate voltage and a second gate voltage. [Figure 3] 10 shows an example of the configuration of a DC power transmission system according to a second embodiment. [Figure 4] 10 is a flowchart illustrating a processing flow in the second embodiment. [Figure 5] 10 shows an example of a time chart of each signal value in the second embodiment. [Figure 6] 10 shows another example of a time chart of each signal value in the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Embodiment 1] The first embodiment will be described below. For convenience of explanation, components having the same functions as those described in the first embodiment will be denoted by the same reference numerals in the following embodiments, and the description thereof will not be repeated. For the sake of brevity, the description of well-known technical matters will also be omitted as appropriate.

[0009] Unless otherwise stated, the components and numerical values described in this specification are merely examples. Therefore, unless otherwise stated, the positional relationships and connection relationships of the components are not limited to the examples in the drawings.

[0010] (DC circuit breaker 1 and its peripheral configuration) Fig. 1 shows a configuration example of a DC power transmission system 100 according to a first embodiment. The DC power transmission system 100 in the example of Fig. 1 includes a DC circuit breaker 1, a DC power source DP, and a load LD. The DC circuit breaker 1 in the example of Fig. 1 may be arranged downstream of the DC power source DP and upstream of the load LD. Therefore, the load LD in the example of Fig. 1 is located downstream of the DC circuit breaker 1.

[0011] As will be described later, the DC circuit breaker 1 includes a semiconductor switch SW. As can be understood from this, the DC circuit breaker 1 is an example of a semiconductor circuit breaker. The DC power transmission system 100 is designed to supply power from a DC power source DP to a load LD via the DC circuit breaker 1. The DC circuit breaker 1 selectively interrupts a current (more specifically, a DC current) flowing from the DC power source DP to the load LD.

[0012] In the example of Fig. 1, the DC circuit breaker 1 is connected to a DC transmission line 81 in a DC power transmission system 100. The DC transmission line 81 includes a positive electrode line 82p and a negative electrode line 82n. Therefore, the DC circuit breaker 1 in the example of Fig. 1 has terminals Tpi and Tni on the upstream side (also referred to as the input side of the DC circuit breaker 1). Terminal Tpi is a positive terminal on the input side of the DC circuit breaker 1, and terminal Tni is a negative terminal on the input side of the DC circuit breaker 1.

[0013] Terminals Tpi and Tni are connected to a DC power supply DP. Specifically, terminal Tpi and the positive electrode of DC power supply DP are connected by a positive line 82p. Meanwhile, terminal Tni and the negative electrode of DC power supply DP are connected by a negative line 82n.

[0014] 1 has a terminal Tpo and a terminal Tno on the downstream side (also referred to as the output side of the DC circuit breaker 1). The terminal Tpo is a positive terminal on the output side of the DC circuit breaker 1, and the terminal Tno is a negative terminal on the output side of the DC circuit breaker 1.

[0015] The terminals To and Tno are connected to a load LD. Specifically, the terminal Tpo and the positive electrode of the load LD are connected by a positive line 82p. On the other hand, the terminal Tno and the negative electrode of the load LD are connected by a negative line 82n.

[0016] In the example of Fig. 1, the DC circuit breaker 1 includes a semiconductor switch SW, a current sensor 11, and a control unit 20. Both the current sensor 11 and the semiconductor switch SW are connected to a DC transmission line 81. In the example of Fig. 1, the current sensor 11 and the semiconductor switch SW are connected in series on the positive electrode line 82p. In the example of Fig. 1, the current sensor 11 is located upstream of the semiconductor switch SW. In this specification, the current detected by the current sensor 11 is referred to as I in It is written as I in may be referred to as the input current.

[0017] In the example in Figure 1, I in is the current flowing from the DC power supply DP to the terminal Tpi. I in can be interpreted as the current flowing from the DC power source DP to the load LD. I in is also the current flowing through the semiconductor switch SW. In this way, the current sensor 11 in the first embodiment is disposed so as to be able to detect the current flowing through the main semiconductor switch SW.

[0018] As described above, the current sensor 11 in the first embodiment detects the current value (i.e., I in In addition, the current sensor 11 in the first embodiment detects the value of I in In this specification, the time rate of change of I in The time rate of change of I is called the current rate of change. in The time rate of change of is typically dI in It is expressed as / dt. in By controlling the semiconductor switch SW in consideration of / dt, more diverse control of the semiconductor switch SW is possible. in and dI inThere are no particular limitations as long as / dt can be detected.

[0019] The semiconductor switch SW in the first embodiment only needs to have a gate terminal GT. In the first embodiment, the case where the semiconductor switch SW is a FET (Field Effect Transistor) will be exemplified.

[0020] However, as will be apparent to those skilled in the art, power semiconductor devices other than FETs can also be used as the semiconductor switch SW. For example, any type of IGBT (Insulated Gate Bipolar Transistor) can be used as the semiconductor switch SW.

[0021] The semiconductor switch SW is switched between a conductive state and a non-conductive state (cut-off state) according to the gate voltage supplied to the gate terminal GT. Therefore, by supplying a predetermined gate voltage to the gate terminal GT, the semiconductor switch SW is in can be selectively blocked.

[0022] The control unit 20 controls each unit of the DC circuit breaker 1. For this reason, the control unit 20 in the example of Fig. 1 has a switching control unit 21. The switching control unit 21 controls the semiconductor switch SW by supplying a predetermined gate voltage to the gate terminal GT. Specifically, the switching control unit 21 controls the conduction state of the semiconductor switch SW by supplying a gate voltage to the gate terminal GT.

[0023] In the first embodiment, the switching control unit 21 generates a gate voltage to be supplied to the gate terminal GT in accordance with the detection result of the current sensor 11. Then, the switching control unit 21 supplies the generated gate voltage to the gate terminal GT.

[0024] In the first embodiment, the semiconductor switch SW is in a conductive state during normal operation of the DC circuit breaker 1. Therefore, the switching control unit 21 supplies a first gate voltage to the gate terminal GT during normal operation of the DC circuit breaker 1. The value of the first gate voltage may be set to correspond to the conductive state of the semiconductor switch SW. However, the value of the first gate voltage is set to be larger than the value of a second gate voltage, which will be described later. As described above, the semiconductor switch SW can be made conductive by supplying the first gate voltage from the switching control unit 21 to the gate terminal GT.

[0025] In the first embodiment, the control unit 20 receives the I in The control unit 20 in the example of FIG. 1 therefore includes a current value comparison unit 22. The current value comparison unit 22 controls the conductive switch SW based on I in is compared with a current threshold (threshold for current). In this specification, the current threshold is denoted as th1.

[0026] Specifically, the current value comparison unit 22 compares I in That is, the current value comparison unit 22 determines whether or not the current value is equal to or greater than th1. I in ≧th1 …(1) Determine whether or not is satisfied.

[0027] The current value comparison unit 22 is in is equal to or greater than th1, that is, if it is determined that the formula (1) is satisfied, it supplies information indicating this to the switching control unit 21.

[0028] The switching control unit 21 is inWhen information indicating that the current value th1 is equal to or greater than th1 is acquired from the current value comparison unit 22, a cutoff gate voltage is generated as the gate voltage. The value of the cutoff gate voltage may be set to correspond to the cutoff state of the semiconductor switch SW. Therefore, the value of the cutoff gate voltage in the first embodiment is set to be smaller than the value of the first gate voltage and smaller than the value of the second gate voltage. Typically, the cutoff gate voltage is set to a value lower than 0 V (for example, see reference numeral 630 in FIG. 6 shown later). In this specification, the cutoff gate voltage is denoted as Vg0.

[0029] As described above, the semiconductor switch SW can be switched from the conductive state to the cut-off state by supplying Vg0 to the gate terminal GT from the switching control unit 21. This makes it possible to cut off the current flowing from the DC power supply DP to the load LD.

[0030] In addition, the control unit 20 in the first embodiment uses the dI in Therefore, for example, as described below, the control unit 20 controls the gate voltage supplied to the gate terminal GT based on dI in More specifically, the control unit 20 can change the gate voltage based on dI / dt. in By changing the value based on / dt, I in can be reduced.

[0031] 1 includes a current change rate comparison unit 23. The current change rate comparison unit 23 calculates dI in / dt is compared with a current change rate threshold (threshold for the current change rate). In this specification, the current change rate threshold is denoted as th2.

[0032] Specifically, the current change rate comparison unit 23 calculates dI in That is, the current change rate comparison unit 23 determines whether / dt is equal to or greater than th2. dI in / dt≧th2 …(2) Determine whether or not is satisfied.

[0033] The current change rate comparison unit 23 calculates dI in If it is determined that / dt is equal to or greater than th2, that is, if it is determined that the formula (2) is satisfied, it supplies information indicating this to the switching control unit 21.

[0034] The switching control unit 21 determines whether dI in When information indicating that / dt is equal to or greater than th2 is acquired from the current change rate comparison unit 23, the gate voltage supplied to the gate terminal GT is switched from the first gate voltage to the second gate voltage. The value of the second gate voltage is set to correspond to the conductive state of the semiconductor switch SW. The value of the second gate voltage is set to be smaller than the value of the first gate voltage.

[0035] More specifically, the value of the second gate voltage is set so as to operate the semiconductor switch SW in the active region, and may be determined by the designer of the DC circuit breaker 1 based on, for example, the specifications of the semiconductor switch SW.

[0036] (Explanation of the first gate voltage and the second gate voltage) 2 is a diagram for explaining the first gate voltage and the second gate voltage in the first embodiment. In the example of FIG. 2, the first gate voltage is denoted as Vg1, and the second gate voltage is denoted as Vg2. In the example of FIG. 2, Vg1=20 V, and Vg2=10 V. In the following description, the gate voltages may be collectively denoted as Vg.

[0037] FIG. 2 shows the current-voltage characteristics of the semiconductor switch SW when Vg=Vg1 and when Vg=Vg2. The horizontal axis of the graph in FIG. 2 represents a predetermined inter-terminal voltage of the semiconductor switch SW. In this specification, this voltage is referred to as V sw It is written as follows.

[0038] As mentioned above, the semiconductor switch SW may be a FET. In this case, V in the example of FIG. sw represents the drain-source voltage of the FET as a semiconductor switch SW (the magnitude of the potential at the drain terminal of the FET relative to the potential at the source terminal of the FET). The vertical axis of the graph in Figure 2 is I in Represents I in corresponds to the drain current of the FET (the current flowing through the drain terminal of the FET).

[0039] As mentioned above, the semiconductor switch SW may be an IGBT. In this case, V in the example of FIG. sw represents the collector-emitter voltage of the IGBT as the semiconductor switch SW (the magnitude of the potential at the collector terminal of the IGBT relative to the potential at the emitter terminal of the IGBT). in corresponds to the collector current of the IGBT (the current flowing through the collector terminal of the IGBT).

[0040] As shown in Figure 2, in both the cases of Vg=Vg1 and Vg=Vg2, V sw With the increase of I in However, as mentioned above, when Vg=Vg2, the semiconductor switch SW operates in the active region. sw With the increase of I in increases, but I in This is the operating region of the semiconductor switch SW, where an increase in

[0041] On the other hand, in the example of Fig. 2, when Vg = Vg1, the semiconductor switch SW operates in the non-active region. sw With the increase in in This means the operating region of the semiconductor switch SW where an increase in

[0042] From these facts, V when Vg=Vg2 sw With the increase in inThe increasing trend of I is gentler than that when Vg=Vg1 and when Vg=Vg2. More specifically, in the example of FIG. in is a constant current value I clamp In this specification, I clamp is also called the clamp current. I clamp is determined according to the specifications of the semiconductor switch SW. clamp It is preferable that the semiconductor switch SW is selected so that is smaller than th1.

[0043] As described above, the switching control unit 21 controls dI in When / dt is equal to or greater than th2, Vg2, which is lower than Vg1, is supplied to the gate terminal GT. As can be seen from FIG. 2, by switching Vg from Vg1 to Vg2, the semiconductor switch SW is maintained in a conductive state while I in can be reduced.

[0044] (effect) In general, dI in When / dt is large, I in It is highly likely that an overshoot of I in (i.e., I as an overcurrent in ) flowing into a load may cause deterioration or damage to the load. Therefore, it is desirable to protect the load by a DC circuit breaker located upstream of the load.

[0045] In the above-mentioned Patent Document 1, dI in This shows an example of the configuration of a DC circuit breaker having a fuse that blows when dI / dt is large. in When / dt is large, the fuse blows and I in In this manner, in this configuration example, the load is protected from overcurrent using a fuse.

[0046] However, it generally takes a certain amount of time for the fuse to completely blow, so the DC circuit breaker configuration example described in Patent Document 1 may cause an overcurrent to flow into the load for a certain period of time.

[0047] On the other hand, according to the DC circuit breaker 1 of the first embodiment, Vg is set to dI in By changing the value based on / dt, I in As an example, as can be seen from FIG. 2, by switching Vg from Vg1 to Vg2, the semiconductor switch SW is maintained in a conductive state, and I in I clamp from values greater than I clamp In this way, by switching Vg from Vg1 to Vg2, the operating region of the semiconductor switch SW can be shifted from the inactive region to the active region.

[0048] Therefore, unlike the DC circuit breaker of Patent Document 1, the DC circuit breaker 1 can protect the load from an overcurrent without the need to blow a fuse. in Therefore, the DC circuit breaker 1 can protect the load more reliably than conventional circuit breakers.

[0049] [Embodiment 2] In embodiment 2, another configuration example of a DC circuit breaker according to an aspect of the present disclosure will be described. Fig. 3 shows a configuration example of a DC power transmission system 100 according to embodiment 2. The DC power transmission system 100 in the example of Fig. 3 includes a DC circuit breaker 1A instead of the DC circuit breaker 1.

[0050] The DC circuit breaker 1A includes a control unit 20A instead of the control unit 20. The control unit 20A further includes a Joule heat calculation unit 24 and a Joule heat comparison unit 25 in addition to a switching control unit 21, a current value comparison unit 22, and a current change rate comparison unit 23.

[0051] Semiconductor switch SW in When a current flows, Joule heat is generated in the semiconductor switch SW. By taking the Joule heat generated in the semiconductor switch SW into consideration, more diverse control of the semiconductor switch SW can be realized.

[0052] Therefore, the Joule heat calculation unit 24 calculates the Joule heat generated in the semiconductor switch SW. In this specification, the value of the Joule heat calculated by the Joule heat calculation unit 24 is represented as Q. There is no particular limitation on the method of calculating Q by the Joule heat calculation unit 24. In the second embodiment, the Joule heat calculation unit 24 calculates Q during the period when Vg2 is supplied to the gate terminal GT (in other words, the period when the semiconductor switch SW is operating in the active region) by multiplying I detected by the current sensor. in The following mainly illustrates the case where calculation is performed based on the above.

[0053] When Q is relatively large, a relatively large I in is considered to flow through the semiconductor switch SW. Therefore, when Q is relatively large, a relatively large I in is considered to flow to the load LD. For this reason, when Q is relatively large, it is considered preferable to switch the semiconductor switch SW from the conducting state to the blocking state to protect the load LD.

[0054] Therefore, the Joule heat comparator 25 determines whether to switch the semiconductor switch SW from the conductive state to the cut-off state based on Q calculated by the Joule heat calculator 24. As an example, the Joule heat comparator 25 compares Q with a Joule heat threshold (a threshold for Joule heat). In this specification, the Joule heat threshold is denoted as th3.

[0055] Specifically, the Joule heat comparator 25 determines whether Q is equal to or greater than th3. That is, the Joule heat comparator 25 uses the following formula (3): Q≧th3 …(3) Determine whether or not is satisfied.

[0056] When the Joule heat comparator 25 determines that Q is equal to or greater than th3, that is, when it determines that the formula (3) is satisfied, it supplies the switching control unit 21 with information indicating that fact.

[0057] The switching control unit 21 switches Vg to Vg0 when it receives information indicating that Q is equal to or greater than th3 from the Joule heat comparator 25. By supplying Vg0 to the gate terminal GT from the switching control unit 21, the semiconductor switch SW can be switched from the conductive state to the cut-off state, thereby protecting the load LD.

[0058] Q is I in It can be expressed as a quantity proportional to the square of I in and the above V sw Therefore, the DC circuit breaker 1A in the example of FIG. 3 further includes a voltage sensor 12 in addition to the current sensor 11. The voltage sensor 12 detects V sw It is sufficient that the sensors are arranged so that they can detect the signals.

[0059] In the example of FIG. 3, the voltage sensor 12 measures the potential difference between the first node Np1 and the second node Np2 as V sw As described above, the semiconductor switch SW may be a FET. In this case, in the example of FIG. 3, the source terminal of the FET serving as the semiconductor switch SW is connected to the second node Np2. On the other hand, the drain terminal of the FET is connected to the first node Np1.

[0060] As mentioned above, the semiconductor switch SW may be an IGBT. In this case, in the example of Fig. 3, the emitter terminal of the IGBT serving as the semiconductor switch SW is connected to the second node Np2. On the other hand, the collector terminal of the IGBT is connected to the first node Np1.

[0061] The control unit 20A in the example of FIG. 3 detects the current I from the current sensor 11. inand V from voltage sensor 12. sw In this case, for example, the Joule heat calculation unit 24 obtains the following equation (4): Q=I in ×V sw ×t Q …(4) Q can be calculated according to the following: Q represents a predetermined time period. Q The value of I may be determined by the designer of the DC circuit breaker 1A based on, for example, the specifications of the semiconductor switch SW. in and V detected by voltage sensor 12 sw Q may be calculated based on the above.

[0062] (Example of processing flow in DC circuit breaker 1A) 4 is a flowchart illustrating the flow of processing in the DC circuit breaker 1A. In the example of FIG. 4, the processing of step S2 and the processing of steps S3 to S6 are executed in parallel. Throughout the period in which the series of processing in FIG. 4 is executed, the control unit 20A receives the current I from the current sensor 11. in and V from voltage sensor 12. sw It is assumed that the following has been obtained.

[0063] First, in step S1, the switching control unit 21 supplies Vg1 (first gate voltage) to the gate terminal GT, thereby operating the semiconductor switch SW in the inactive region.

[0064] In the example of FIG. 4, step S2 and step S3 each follow step S1. First, step S2 will be described. In step S2, the current value comparison unit 22 compares I in is equal to or greater than th1. That is, the current value comparing unit 22 determines whether the above-mentioned formula (1) is satisfied.

[0065] If the answer is YES in step S2, that is, I inIf the result of step S2 is NO, that is, if I is equal to or greater than th1, the process proceeds to step S7. The process of step S7 will be described later. in If is less than th1, return to step S2. in Step S2 is repeated until th1 is reached.

[0066] Next, step S3 will be described. In step S3, the current change rate comparison unit 23 compares dI in It is determined whether / dt is equal to or greater than th2. That is, the current change rate comparison unit 23 determines whether the above-mentioned formula (2) is satisfied.

[0067] If the answer is YES in step S3, that is, dI in If / dt is equal to or greater than th2, proceed to step S4. On the other hand, if the result of step S3 is NO, that is, if dI in If / dt is less than th2, return to step S3. in Step S3 is repeated until / dt reaches th2.

[0068] In step S4, the switching control unit 21 switches Vg from Vg1 to Vg2 (second gate voltage). Then, the switching control unit 21 supplies Vg2 to the gate terminal GT. This allows the operating region of the semiconductor switch SW to transition from the inactive region to the active region.

[0069] Next, in step S5, the Joule heat calculation unit 24 calculates the Joule heat Q. As an example, the Joule heat calculation unit 24 may calculate Q according to the above-mentioned formula (4).

[0070] Next, in step S6, the Joule heat comparator 25 determines whether or not Q is equal to or greater than th3. That is, the Joule heat comparator 25 determines whether or not the above-mentioned formula (3) is satisfied.

[0071] If the answer is YES in step S6, i.e., if Q is equal to or greater than th3, proceed to step S7. On the other hand, if the answer is NO in step S6, i.e., if Q is less than th3, return to step S1. Therefore, if Q is less than th3, the operating region of the semiconductor switch SW can be returned from the active region to the inactive region.

[0072] As described above, if the answer is YES in step S2 or if the answer is YES in step S6, the process proceeds to step S7. In other words, if at least one of the above formulas (1) and (3) is satisfied, the process proceeds to step S7. If at least one of formulas (1) and (3) is satisfied, it is considered preferable to switch the semiconductor switch SW from the conductive state to the cut-off state to protect the load LD.

[0073] Therefore, in step S7, the switching control unit 21 supplies Vg0 (cut-off gate voltage) to the gate terminal GT, thereby switching the semiconductor switch SW from the conductive state to the cut-off state.

[0074] (Example of a time chart for each signal value) FIG. 5 shows an example of a time chart of each signal value in the second embodiment. In FIG. 5, reference numeral 510 denotes I in The graph showing the time course of dI is shown. in 5 shows a graph indicating the time course of / dt, and a graph indicating the time course of Vg is shown at 530. The horizontal axis (t) in each graph in FIG.

[0075] 5 illustrates a case where a short circuit fault occurs in the DC power transmission system 100. In the example of FIG. in reaches a value greater than th1, but dI in / dt remains at a value less than th2. Therefore, the example of Fig. 5 shows a case where the above formula (1) is satisfied but the formula (2) is not satisfied. That is, the example of Fig. 5 shows a case where the answer is YES in step S2 of Fig. 4 but NO in step S3.

[0076] FIG. 6 shows another example of a time chart of each signal value in the second embodiment. FIG. 6 is a diagram paired with FIG. 5. In FIG. 6, reference numeral 610 denotes I in A graph showing the time course of dI is shown, and reference numeral 620 indicates in A graph showing the time course of / dt is shown, and reference numeral 630 shows a graph showing the time course of Vg.

[0077] 6 also illustrates an example in which a short circuit fault occurs in the DC power transmission system 100. However, in the example of FIG. 6, I in The increase in dI in the example of Figure 6 is steeper than in the example of Figure 5. in More specifically, in the example of FIG. 6, a sharp pulse-like dI in A / dt waveform is generated.

[0078] Therefore, in the example of Figure 6, dI in As a result of the occurrence of the waveform of I / dt, Vg drops from Vg1 to Vg2. As mentioned above, during the period when Vg=Vg2, the semiconductor switch SW operates in the active region. Therefore, I in The maximum value of I clamp In this way, during the period when Vg=Vg2, I in Therefore, the state of the DC circuit breaker 1A during this period may be referred to as a current clamp state.

[0079] As described above, the example of FIG. 6 shows a case where the above-mentioned formula (1) is not satisfied, but the formula (2) is satisfied. In addition, the example of FIG. 6 shows a case where the above-mentioned formula (3) is satisfied. In FIG. 6, after Vg2 is supplied to the gate terminal GT, Q This illustrates a case where it is determined that the above formula (3) is satisfied after a certain period of time has elapsed. Therefore, at this point in time, Vg decreases from Vg2 to Vg0.

[0080] [Software implementation example] The functions of DC circuit breakers 1 to 1A (hereinafter referred to as "devices" for convenience) can be realized by a program that causes a computer to function as the device, and a program that causes a computer to function as each control block of the device (particularly each part included in control units 20 to 20A).

[0081] In this case, the device includes a computer having at least one control device (e.g., a processor) and at least one storage device (e.g., a memory) as hardware for executing the program. The control device and storage device execute the program to realize the functions described in each of the above embodiments.

[0082] The program may be non-transitory and may be recorded on one or more computer-readable recording media. The recording media may or may not be included in the device. In the latter case, the program may be supplied to the device via any wired or wireless transmission medium.

[0083] Some or all of the functions of the control blocks can be realized by logic circuits. For example, an integrated circuit in which a logic circuit that functions as each of the control blocks is formed is also included in the scope of one aspect of the present disclosure. In addition, the functions of the control blocks can also be realized by, for example, a quantum computer.

[0084] The processes described in the above embodiments may be executed by AI (Artificial Intelligence). In this case, the AI may run on the control device or on another device (for example, an edge computer or a cloud server).

[0085] 〔summary〕 A DC circuit breaker according to a first aspect of the present disclosure is a DC circuit breaker arranged upstream of a load in a DC power transmission system, and includes: a semiconductor switch connected to a DC transmission line in the DC power transmission system and having a gate terminal; a current sensor that detects a current value of a current flowing through the semiconductor switch and a current change rate that is a time rate of change of the current value; and a control unit that controls the semiconductor switch by supplying a gate voltage to the gate terminal, wherein the control unit reduces the current flowing through the semiconductor switch when the semiconductor switch is in a conductive state by changing the gate voltage based on the current change rate detected by the current sensor.

[0086] In the DC circuit breaker according to aspect 2 of the present disclosure, in aspect 1, the control unit may make the semiconductor switch conductive by supplying a first gate voltage to the gate terminal as the gate voltage, and when the current change rate detected by the current sensor is equal to or greater than a current change rate threshold, may supply a second gate voltage lower than the first gate voltage to the gate terminal as the gate voltage, thereby reducing the current flowing through the semiconductor switch while maintaining the conductive state of the semiconductor switch.

[0087] In the DC circuit breaker according to the third aspect of the present disclosure, in the second aspect, the semiconductor switch may operate in an active region when the second gate voltage is supplied to the gate terminal.

[0088] In the DC circuit breaker according to aspect 4 of the present disclosure, in aspect 2 or 3, the control unit may calculate the Joule heat generated in the semiconductor switch during the period in which the second gate voltage is supplied to the gate terminal based on the current value detected by the current sensor, and may determine whether to switch the semiconductor switch from a conducting state to a blocking state based on the Joule heat.

[0089] In the DC circuit breaker according to aspect 5 of the present disclosure, in aspect 4, when the Joule heat is equal to or greater than a Joule heat threshold, the control unit may switch the semiconductor switch from a conductive state to a cut-off state by supplying a cut-off gate voltage as the gate voltage to the gate terminal.

[0090] The DC circuit breaker according to aspect 6 of the present disclosure may further include a voltage sensor for detecting a voltage value of a predetermined inter-terminal voltage in the semiconductor switch in accordance with aspect 4 or 5, and the control unit may calculate the Joule heat based on the current value detected by the current sensor and the voltage value detected by the voltage sensor.

[0091] In the DC circuit breaker according to aspect 7 of the present disclosure, in any one of aspects 1 to 6, the semiconductor switch may be made conductive by supplying a first gate voltage to the gate terminal as the gate voltage, and when the current value is equal to or greater than a current threshold, the semiconductor switch may be switched from a conductive state to a cut-off state by supplying a cut-off gate voltage to the gate terminal as the gate voltage.

[0092] A DC power transmission system according to an eighth aspect of the present disclosure may include the DC circuit breaker according to any one of the first to seventh aspects, and the load located downstream of the DC circuit breaker.

[0093] [Additional Notes] One aspect of the present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of one aspect of the present disclosure. [Explanation of symbols]

[0094] 1.1A DC circuit breaker 11 Current Sensor 12 Voltage Sensor 20,20A control section 21 Switching control section 22 Current value comparison section 23 Current change rate comparison section 24 Joule heat calculation section 25 Joule heat comparator 81 DC power lines 100 DC power transmission system SW Semiconductor switch LD load

Claims

1. A DC circuit breaker arranged upstream of a load in a DC power transmission system, a semiconductor switch connected to a DC transmission line in the DC power transmission system and having a gate terminal; a current sensor that detects a current value of a current flowing through the semiconductor switch and a current change rate that is a time change rate of the current value; a control unit that controls the semiconductor switch by supplying a gate voltage to the gate terminal, the control unit reduces the current flowing through the semiconductor switch when the semiconductor switch is in a conductive state by changing the gate voltage based on the current change rate detected by the current sensor; The control unit supplying a first gate voltage as the gate voltage to the gate terminal to cause the semiconductor switch to conduct; when the current change rate detected by the current sensor is equal to or greater than a current change rate threshold, a second gate voltage lower than the first gate voltage is supplied to the gate terminal as the gate voltage, thereby reducing the current flowing through the semiconductor switch while maintaining a conductive state of the semiconductor switch; The control unit calculating Joule heat generated in the semiconductor switch during a period in which the second gate voltage is supplied to the gate terminal based on the current value detected by the current sensor; The DC circuit breaker determines whether or not to switch the semiconductor switch from a conductive state to a cut-off state based on the Joule heat.

2. 2. The DC circuit breaker according to claim 1, wherein the semiconductor switch operates in an active region when the second gate voltage is supplied to the gate terminal.

3. 2. The DC circuit breaker according to claim 1, wherein when the Joule heat is equal to or greater than a Joule heat threshold, the control unit switches the semiconductor switch from a conducting state to a blocking state by supplying a blocking gate voltage as the gate voltage to the gate terminal.

4. The DC circuit breaker further includes a voltage sensor that detects a voltage value of a predetermined voltage between terminals of the semiconductor switch, The DC circuit breaker according to claim 1 , wherein the control unit calculates the Joule heat based on the current value detected by the current sensor and the voltage value detected by the voltage sensor.

5. The control unit supplying a first gate voltage as the gate voltage to the gate terminal to cause the semiconductor switch to conduct; 2. The DC circuit breaker according to claim 1, wherein when the current value is equal to or greater than a current threshold, a cutoff gate voltage is supplied to the gate terminal as the gate voltage, thereby switching the semiconductor switch from a conducting state to a cutoff state.

6. The DC circuit breaker according to claim 1; the load being located downstream of the DC breaker.

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