DC microgrid, DC microgrid system, control method, and program

Abstract

To provide a direct current micro grid capable of facilitating cut-off of a fuse for connecting direct current micro grids in a case where short-circuit occurs in the direct current micro grids even when the rating of the fuse is increased.SOLUTION: A direct current micro grid comprises: a first fuse whose first terminal is connected with positive electrode wiring of a bus that is connected with the other direct current micro grid and whose second terminal is connected with positive electrode wiring that is connected with a plurality of power converters via a plurality of fuses; a second fuse whose first terminal is connected with negative electrode wiring of the bus that is connected with the other direct current micro grid and whose second terminal is connected with negative electrode wiring connected with the plurality of power converters via a plurality of fuses; and a first capacitor whose first terminal is connected with the positive electrode wiring connected with the other direct current micro grid and whose second terminal is connected with the negative electrode wiring connected with the other direct current micro grid, the first capacitor having such an electrostatic capacitance value that at least one of the first and second fuses can be cut off.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a DC microgrid, a DC microgrid system, a control method, and a program.

Background Art

[0002] As one form of supplying power to a plurality of loads, a DC microgrid system in which DC microgrids cooperate has attracted attention in various fields. In Patent Documents 1 and 2, technologies related to power supply are disclosed as related technologies.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, in limited spaces such as ships, a large amount of power exchange between DC microgrids is desirable. On the other hand, when DC microgrids are connected and linked together, fuses are sometimes used to disconnect the DC microgrid experiencing a short circuit or other malfunction. From the perspective of efficiently linking DC microgrids together, a fuse with a rating capable of withstanding large currents is desirable. On the other hand, from the perspective of immediately disconnecting the DC microgrid experiencing a short circuit or other malfunction, a fuse with a rating that can cut (melt) even with a small current is desirable. In other words, when DC microgrids are linked together via fuses, there is a trade-off between efficiently linking the DC microgrids together and immediately disconnecting the DC microgrid experiencing a malfunction, and it is generally difficult to achieve both. Therefore, in DC microgrid systems that link DC microgrids together via fuses, there is a need for a technology that allows for a high rating of the fuse while still making it easy to cut the fuse when a short circuit occurs in the DC microgrid.

[0005] This disclosure was made to solve the above problems and aims to provide a DC microgrid, a DC microgrid system, a control method, and a program that, in a DC microgrid system in which DC microgrids are connected to each other via fuses, makes it easier to blow the fuse when a short circuit occurs in the DC microgrid, even if the rating of the fuse is increased. [Means for solving the problem]

[0006] To solve the above problems, the DC microgrid described herein is A first fuse is connected to the positive terminal of a bus to which another DC microgrid is connected, and to the second terminal of a first fuse, to which a plurality of power converters are connected via a plurality of fuses; a second fuse is connected to the negative terminal of the bus to which the other DC microgrid is connected, and to the second terminal of a second fuse, to which a plurality of power converters are connected via a plurality of fuses; a first capacitor is connected to the positive terminal of the bus to which the other DC microgrid is connected, and to the negative terminal of the bus to which the other DC microgrid is connected, and has a capacitance capable of disconnecting at least one of the first fuse and the second fuse; and the plurality of power converters Each includes: a bridge circuit that generates AC power from DC power supplied by the positive terminal wiring of the bus to which the plurality of power converters are connected and the negative terminal wiring of the bus to which the plurality of power converters are connected; a second capacitor provided in parallel with the input terminal of the bridge circuit and smoothing the DC power; a current sensor that detects the current flowing from the second capacitor to the bus when the charge stored in the second capacitor toward the bus is discharged; a first switching element provided between the current sensor and the bus; and a control device that determines whether the current detected by the current sensor exceeds a predetermined threshold, and controls the first switching element to an off state if it is determined that the current detected by the current sensor exceeds the predetermined threshold. .

[0007] The DC microgrid system according to this disclosure comprises the DC microgrid and another DC microgrid that operates in conjunction with the DC microgrid.

[0008] The control method according to this disclosure comprises: a first fuse to which the positive terminal of a bus to which another DC microgrid is connected is connected, and to which the positive terminal of the bus to which a plurality of power converters are connected via a plurality of fuses is connected; a second fuse to which the negative terminal of the bus to which the other DC microgrid is connected is connected, and to which the negative terminal of the bus to which a plurality of power converters are connected via a plurality of fuses is connected; a first capacitor to which the first terminal is connected, and to which the negative terminal of the bus to which the other DC microgrid is connected is connected, and which has a capacitance capable of disconnecting at least one of the first fuse and the second fuse; and the plurality of power converters Each of the devices is a DC microgrid comprising: a bridge circuit that generates AC power from DC power supplied by the positive terminal wiring of the bus to which the plurality of power converters are connected and the negative terminal wiring of the bus to which the plurality of power converters are connected; a second capacitor provided in parallel with the input terminal of the bridge circuit and smoothing the DC power; a current sensor that detects the current flowing from the second capacitor to the bus when the charge stored in the second capacitor toward the bus is discharged; and a first switching element provided between the current sensor and the bus. The DC microgrid determines whether the current detected by the current sensor exceeds a predetermined threshold, and if it determines that the current detected by the current sensor exceeds the predetermined threshold, it controls the first switching element to an off state.

[0009] The program relating to this disclosure comprises: a first fuse to which the positive terminal of a bus to which another interconnected DC microgrid is connected is connected, and to which the positive terminal of the bus to which a plurality of power converters are connected via a plurality of fuses is connected is connected; a second fuse to which the negative terminal of the bus to which the other DC microgrid is connected is connected, and to which the negative terminal of the bus to which a plurality of power converters are connected via a plurality of fuses is connected is connected; a first capacitor to which the first terminal is connected is connected to the positive terminal of the bus to which the other DC microgrid is connected, and to which the second terminal is connected is connected to the negative terminal of the bus to which the other DC microgrid is connected, and which has a capacitance capable of disconnecting at least one of the first fuse and the second fuse; and each of the plurality of power converters is A computer for a DC microgrid comprising: a bridge circuit that generates AC power from DC power supplied by the positive terminal wiring of the bus to which the plurality of power converters are connected and the negative terminal wiring of the bus to which the plurality of power converters are connected; a second capacitor provided in parallel with the input terminal of the bridge circuit for smoothing the DC power; a current sensor that detects the current flowing from the second capacitor to the bus when the second capacitor discharges the charge it has stored toward the bus; and a first switching element provided between the current sensor and the bus, is instructed to determine whether the current detected by the current sensor exceeds a predetermined threshold, and if it is determined that the current detected by the current sensor exceeds the predetermined threshold, to control the first switching element to an OFF state. [Effects of the Invention]

[0010] According to the DC microgrid, DC microgrid system, control method, and program described herein, in a DC microgrid system in which DC microgrids are interconnected via fuses, even if the rating of the fuse is increased, it is possible to make it easier to blow the fuse when a short circuit occurs in the DC microgrid. [Brief explanation of the drawing]

[0011] [Figure 1] This figure shows an example of the configuration of a DC microgrid system according to one embodiment of the present disclosure. [Figure 2] This figure shows an example of a DC microgrid system 1 that illustrates a specific example of the configuration of a power converter according to the first embodiment of this disclosure. [Figure 3] This figure shows an example of a first processing flow of a DC microgrid system according to one embodiment of the present disclosure. [Figure 4] This figure shows an example of a busbar short circuit in one embodiment of the present disclosure. [Figure 5] This figure shows an example of a short circuit in a bridge circuit according to one embodiment of the present disclosure. [Figure 6] This figure shows an example of a short circuit at the connection point between DC microgrids according to one embodiment of the present disclosure. [Figure 7] This figure shows an example of a second processing flow of a DC microgrid system according to one embodiment of the present disclosure. [Figure 8] This is the first figure showing an example of a state transition of a switching element in one embodiment of the present disclosure. [Figure 9] This is a second figure showing an example of the state transition of a switching element in one embodiment of the present disclosure. [Figure 10] This is a third figure showing an example of the state transition of a switching element in one embodiment of the present disclosure. [Figure 11] Figure 4 shows an example of the state transition of a switching element in one embodiment of the present disclosure. [Figure 12] Figure 5 shows an example of the state transition of a switching element in one embodiment of the present disclosure. [Figure 13] Figure 6 shows an example of the state transition of a switching element in one embodiment of the present disclosure. [Figure 14] Figure 7 shows an example of the state transition of a switching element in one embodiment of the present disclosure. [Figure 15]It is a schematic block diagram showing the configuration of a computer according to at least one embodiment.

Mode for Carrying Out the Invention

[0012] <Embodiment> Hereinafter, embodiments will be described in detail with reference to the drawings. A DC microgrid system according to an embodiment of the present disclosure will be described.

[0013] (Configuration of DC Microgrid System) FIG. 1 is a diagram showing an example of the configuration of a DC microgrid system 1 according to an embodiment of the present disclosure. As shown in FIG. 1, the DC microgrid system 1 includes DC microgrids 10a, 10b, and loads 20a, 20b. The DC microgrid system 1 is, for example, a system used in a ship. The DC microgrid system 1 has the DC microgrids 10a and 10b cooperate with each other. When a short circuit occurs at any location in the DC microgrid system 1 (for example, between the positive electrode wiring P and the negative electrode wiring N of the bus or any one of the plurality of power converters 103) where the DC microgrids 10a and 10b cooperate, the DC microgrid system 1 is a system that can disconnect the system in which the short circuit has occurred.

[0014] As shown in FIG. 1, the DC microgrid 10a includes bus ties 101p (an example of a first fuse), 101n (an example of a second fuse), a plurality of fuses 102p, 102n, a plurality of power converters 103, a control device 104, an initial charging sequence 105, a capacitor 106 (an example of a first capacitor), and a voltage sensor 107 (however, the voltage sensor 107 is shown in FIG. 2 described later). The number of each of the fuses 102p and 102n is the same as the number of the power converters 103, and in the example shown in FIG. 1, it is six.

[0015] Bus tie fuse 101p is a fuse installed in the positive terminal wiring P of the busbar in the DC microgrid system 1. Bus tie fuse 101n is a fuse installed in the negative terminal wiring N of the busbar in the DC microgrid system 1.

[0016] Each of the multiple fuses 102p is provided between the positive terminal wiring P and one of the multiple power converters 103, as shown in Figure 1. Similarly, each of the multiple fuses 102n is provided between the negative terminal wiring N and one of the multiple power converters 103, as shown in Figure 1.

[0017] Each of the multiple power converters 103 is connected to the positive terminal wiring P via a fuse 102p, as shown in Figure 1. Each of the multiple power converters 103 is also connected to the negative terminal wiring N via a fuse 102n, as shown in Figure 1. Furthermore, each of the multiple power converters 103 is connected to the load 20a, as shown in Figure 1.

[0018] Figure 2 is a diagram showing an example of a DC microgrid system 1 that illustrates a specific configuration of the power converter 103 according to the first embodiment of this disclosure. In the DC microgrid system 1 shown in Figure 2, a voltage sensor 107 is also shown.

[0019] Each of the multiple power converters 103 includes a bridge circuit 103a, a capacitor 103b (an example of a second capacitor), a cutoff circuit 103c (an example of a first switching element), an energy absorption circuit 103d, a charging circuit 103e, a current sensor 103f, a voltage sensor 103g, a protection diode 103h, a damping circuit 103i, and a control circuit 103j, as shown in Figure 2 (however, the protection diode 103h and the damping circuit 103i are shown in Figures 8 to 14 described later).

[0020] The bridge circuit 103a is a circuit that generates three-phase AC power from DC power. The bridge circuit 103a is constructed using switching elements such as transistors. Examples of transistors include power semiconductor elements such as SiC MOSFETs (Silicon Carbide Metal Oxide Semiconductor Field Effect Transistors) and IGBTs (Insulated Gate Bipolar Transistors).

[0021] Capacitor 103b smooths the DC voltage input to bridge circuit 103a. When current sensor 103f detects a current exceeding a predetermined threshold, the cutoff circuit 103c disconnects the power converter 103 from the bus based on control by control circuit 103j. Examples of cutoff circuits 103c include power semiconductor elements such as SiC MOSFETs and IGBTs, and physical switches.

[0022] The energy absorption circuit 103d absorbs the energy generated when regenerative power is generated at the load of the power converter 103 and a short circuit occurs inside the bus or the power converter 103, causing current to flow from the load to the power converter 103. As shown in Figure 2, the energy absorption circuit 103d comprises a switching element 103d1, a resistor 103d2, and a capacitor 103d3. When regenerative power is generated at the load of the power converter 103 and a short circuit occurs inside the bus or the power converter 103, the switching element 103d1 turns on based on the control circuit 103j, and the energy absorption circuit 103d prevents the rise in the DC voltage of the power converter 103 due to regenerative power at the load of the power converter 103 (i.e., overvoltage) by allowing current to flow according to the time constant determined by the resistor 103d2 and the capacitor 103d3. Examples of the switching element 103d1 include power semiconductor elements such as SiC MOSFETs and IGBTs, and physical switches.

[0023] The charging circuit 103e absorbs the difference between the voltage on the bus side that may occur during restart (i.e., the potential difference between the positive terminal wiring P and the negative terminal wiring N) and the voltage at the input of the bridge circuit 103a (i.e., the potential difference across the capacitor 103b), and limits the current that flows until that potential difference becomes zero. The charging circuit 103e includes, for example, a resistor 103e1 and a switching element 103e2 (an example of a third switching element).

[0024] The current sensor 103f detects the current flowing from the bridge circuit 103a to the busbar. For example, if the positive terminal wiring P and the negative terminal wiring N of the busbar are short-circuited, current will flow from the capacitor 103b towards the busbar. The current sensor 103f detects this current.

[0025] The voltage sensor 103g detects the voltage at the input of the bridge circuit 103a, i.e., the potential difference across the capacitor 103b. The protection diode 103h allows a return current to flow when regenerative power is generated in the load of the power converter 103 and a short circuit occurs in the bus or inside the power converter 103.

[0026] The braking circuit 103i uses the DC microgrid system 1, for example, to apply the brakes to a ship (i.e., to slow down or stop the ship). The braking circuit 103i comprises a switching element 103i1 and a resistor 103i2.

[0027] Examples of switching elements 103i1 include power semiconductor elements such as SiC MOSFETs and IGBTs, and physical switches (Note that IGBTs are shown as an example in Figures 8 to 14, which will be described later). When deceleration or stopping is not performed, the switching element 103i1 is in the off state, and is controlled to the on state when deceleration or stopping is performed. The resistor 103i2 sets the braking effect (i.e., the degree of deceleration) according to the resistance value.

[0028] The control circuit 103j controls the power converter 103. For example, if the load of the power converter 103 is a three-phase AC motor, the control circuit 103j controls the switching of the transistors in the bridge circuit 103a to generate AC power from DC power to drive the three-phase AC motor. Also, for example, the control circuit 103j controls the switching elements 103c, 103d1, 103e2, and 103i1 to be on or off. Specifically, the control circuit 103j controls the switching element 103c to be on when the current sensor 103f detects a current below a predetermined threshold, and controls the switching element 103c to be off when the current sensor 103f detects a current exceeding a predetermined threshold. Furthermore, when the control circuit 103j controls the switching element 103c to the OFF state, it will not control the switching element 103c to the ON state until it is confirmed that the short circuit has been resolved (for example, until the potential difference between the positive terminal wiring P and the negative terminal wiring N of the busbar is the desired potential difference and the potential difference across both ends of the capacitor 103b falls within a predetermined threshold relative to the desired potential difference). Also, for example, if regenerative power is generated in the load of the power converter 103 and a short circuit occurs inside the busbar or the power converter 103, the control circuit 103j controls the switching elements 103c, 103d1, 103e2, and 103i1 to either the ON or OFF state. Details of the control by the control circuit 103j to turn the switching elements 103c, 103d1, 103e2, and 103i1 to either the ON or OFF state will be described later. Note that the control circuit 103j is omitted in Figures 8 to 14, which will be described later.

[0029] The initial charging sequence 105 controls the charge state during the initial operation of the generator G under load 20a. Capacitor 106 stores a charge that can break the bus tie fuses 101p and 101n. That is, the capacitance of capacitor 106 is selected to be such that it can store a charge that can break the bus tie fuses 101p and 101n. For example, the capacitance is determined such that the square-time product of the short-circuit current, which is determined by the impedance of the short-circuit path and the resistance value inside capacitor 106, exceeds the square-time product of the current that blows the bus tie fuses 101p and 101n. Voltage sensor 107 detects the potential difference between the positive terminal wiring P and the negative terminal wiring N of the busbar, i.e., the potential difference across the capacitor 106 via the bus tie fuses 101p and 101n.

[0030] Load 20a consists of loads connected to each of the power converters 103 of the DC microgrid 10a. These loads include motors that propel ships, and these motors generate regenerative power.

[0031] The DC microgrid 10b has the same configuration as the DC microgrid 10a. The loads 20b are loads connected to each of the power converters 103 of the DC microgrid 10b. Although Figure 1 shows an example where load 20b has the same configuration as load 20a, the configurations of load 20b and load 20a may be different.

[0032] (Processing performed by a DC microgrid system) Next, the processes performed by the DC microgrid system 1 will be explained with reference to Figures 3 to 14.

[0033] (Handling of a short circuit in the busbar) First, the processing performed by the DC microgrid system 1 when the positive terminal wiring P and negative terminal wiring N of the busbar are short-circuited will be explained with reference to Figures 3 and 4. Figure 3 is a diagram showing an example of the first processing flow of the DC microgrid system 1 according to one embodiment of the present disclosure. Figure 4 is a diagram showing an example of the image of a busbar short circuit in one embodiment of the present disclosure. Here, it is assumed that the control circuit 103j controls each switching element 103c to the ON state and each switching element 103d1, 103e2, and 103i1 to the OFF state. Then, in this state, it is assumed that a short circuit occurs in the busbar of the DC microgrid 10a, as shown in Figure 4.

[0034] In this case, as shown in part (a) of Figure 4, the charge stored in the capacitors 103b of each of the multiple power converters 103 of the DC microgrids 10a and 10b, and the charge stored in the capacitors 106 of the DC microgrids 10a and 10b, flow into the short circuit as current.

[0035] Each of the multiple power converters 103 has a current sensor 103f that detects the current flowing from the capacitor 103b to the short circuit point. The current sensor 103f outputs the detected current value to the control circuit 103j. The control circuit 103j compares the current value detected by the current sensor 103f with a predetermined threshold value. The control circuit 103j determines whether the current value detected by the current sensor 103f exceeds the threshold value (step S1). Specifically, the threshold value is set to a current smaller than the current flowing to the short circuit point as the charge stored in the capacitor 103b. In this case, the control circuit 103j determines that all of the currents detected by each current sensor 103f have exceeded the threshold value.

[0036] Then, if the control circuit 103j determines that the current detected by the current sensor 103f exceeds a threshold value, it controls the switching element 103c connected to the current sensor 103f that detected the current exceeding the threshold value to an off state (step S2). This control disconnects all power converters 103 from the busbar.

[0037] Even after all power converters 103 have been disconnected from the busbar, current flows from capacitor 106 towards the short circuit until the charge stored in capacitor 106 is discharged. This current flows through bus tie fuse 101p. Since capacitor 106 has stored enough charge to disconnect bus tie fuses 101p and 101n, the current flowing from capacitor 106 towards the short circuit disconnects bus tie fuse 101p. This allows the short-circuited DC microgrid 10a to be isolated from the normal DC microgrid 10b, as shown in part (b) of Figure 4.

[0038] (Handling of short circuits in power converters) Next, the processes performed by the DC microgrid system 1 when a short circuit occurs in the bridge circuit 103a of the power converter 103 will be described with reference to Figures 3 and 5. Figure 5 is a diagram showing an example of a short circuit in the bridge circuit 103a according to one embodiment of the present disclosure. Here, the control circuit 103j is assumed to control each switching element 103c to the ON state and each switching element 103d1, 103e2, and 103i1 to the OFF state. Then, in this state, a short circuit occurs in one of the bridge circuits 103a of the DC microgrid 10a, as shown in Figure 5.

[0039] In this case, as shown in part (a) of Figure 5, the charge stored in the capacitors 103b of each of the multiple power converters 103 of the DC microgrids 10a and 10b, and the charge stored in the capacitors 106 of the DC microgrids 10a and 10b, flow into the short circuit as an electric current.

[0040] Of the multiple power converters 103, the current sensor 103f of each power converter 103, excluding the one experiencing the short circuit, detects the current flowing from capacitor 103b to the short circuit point. Furthermore, since current flows from the bus side to the bridge circuit 103a through the current sensor 103f of the power converter 103 experiencing the short circuit, (in reality, current is detected within the range of errors due to noise and measurement accuracy, but this can be ignored) the current detected by the current sensor 103f of the power converter 103 experiencing the short circuit is the current flowing into the power converter 103. If the current detected by the current sensor 103f is the current flowing into the power converter 103, the control circuit 103j does not change its processing.

[0041] Each current sensor 103f outputs the detected current value to the control circuit 103j. The control circuit 103j compares the current value detected by the current sensor 103f with a predetermined threshold value. The control circuit 103j determines whether the current value detected by the current sensor 103f exceeds the threshold value (step S1). Specifically, the threshold value is set to a current smaller than the current that flows through the short-circuit point as the charge stored in the capacitor 103b. In this case, the control circuit 103j determines that all currents detected by current sensors 103f other than the current sensor 103f of the power converter 103 where the short circuit occurred have exceeded the threshold value.

[0042] Then, if the control circuit 103j determines that the current detected by the current sensor 103f exceeds a threshold value, it controls the switching element 103c connected to the current sensor 103f that detected the current exceeding the threshold value to the OFF state (step S2). This control disconnects all power converters 103 except for the power converter 103 where the short circuit occurred from the bus.

[0043] Even after all power converters 103 except for the one experiencing the short circuit have been disconnected from the bus, current continues to flow from capacitor 106 towards the short circuit until the charge stored in capacitor 106 is discharged. This current flows through the bus tie fuse 101p and the fuses 102p and 102n connected to the power converter 103 experiencing the short circuit. Since fuses 102p and 102n have smaller capacities than the bus tie fuses 101p (and 101n), in this case, at least one of fuses 102p and 102n will be blown (blown) before the bus tie fuse 101p is blown (blown). Because capacitor 106 has stored enough charge to blow the bus tie fuses 101p and 101n, the current flowing from capacitor 106 towards the short circuit causes at least one of the bus tie fuses 101p and 101n to blow. This allows the DC microgrid 10a experiencing the short circuit to be isolated from the normal DC microgrid 10b.

[0044] (Handling of short circuits that occur at connections between DC microgrids) Next, the processes performed by the DC microgrid system 1 when a short circuit occurs at the connection between DC microgrids 10a and 10b will be described with reference to Figures 3 and 6. Figure 6 is a diagram showing an example of a short circuit at the connection between two DC microgrids (10a and 10b) according to one embodiment of the present disclosure. Here, the control circuit 103j is assumed to control each switching element 103c to the ON state and each switching element 103d1, 103e2, and 103i1 to the OFF state. Then, in this state, a short circuit occurs at the connection between DC microgrids 10a and 10b, as shown in Figure 6.

[0045] In this case, as shown in part (a) of Figure 6, the charge stored in the capacitors 103b of each of the multiple power converters 103 of the DC microgrids 10a and 10b, and the charge stored in the capacitors 106 of the DC microgrids 10a and 10b, flow into the short circuit as an electric current.

[0046] Each of the multiple power converters 103 has a current sensor 103f that detects the current flowing from the capacitor 103b to the short-circuit point.

[0047] Each current sensor 103f outputs the detected current value to the control circuit 103j. The control circuit 103j compares the current value detected by the current sensor 103f with a predetermined threshold value. The control circuit 103j determines whether the current value detected by the current sensor 103f exceeds the threshold value (step S1). Specifically, the threshold value is set to a current smaller than the current that flows through the short-circuit point as the charge stored in the capacitor 103b. In this case, the control circuit 103j determines that all currents detected by current sensors 103f other than the current sensor 103f of the power converter 103 where the short circuit occurred have exceeded the threshold value.

[0048] Then, if the control circuit 103j determines that the current detected by the current sensor 103f exceeds a threshold value, it controls the switching element 103c connected to the current sensor 103f that detected the current exceeding the threshold value to an off state (step S2). This control disconnects the entire power converter 103 from the bus.

[0049] Even after all the power converters 103 have been disconnected from the busbar, current flows from capacitor 106 towards the short circuit until the charge stored in capacitor 106 is discharged. This current flows through the bus tie fuse 101n. In this case, the bus tie fuse 101n is blown (blown). This disconnects DC microgrids 10a and 10b.

[0050] (Handling of cases where regenerative power is generated by the load and a short circuit occurs in the busbar) Next, the processing performed by the DC microgrid system 1 when regenerative power is generated in the load of the power converter 103 and a short circuit occurs in the busbar will be described with reference to Figures 7 to 14. An example of a load in this case is a three-phase AC motor. Figure 7 is a diagram showing an example of a second processing flow of the DC microgrid system 1 according to one embodiment of the present disclosure. Figure 8 is a first diagram showing an example of a state transition of a switching element in one embodiment of the present disclosure. Figure 9 is a second diagram showing an example of a state transition of a switching element in one embodiment of the present disclosure. Figure 10 is a third diagram showing an example of a state transition of a switching element in one embodiment of the present disclosure. Figure 11 is a fourth diagram showing an example of a state transition of a switching element in one embodiment of the present disclosure. Figure 12 is a fifth diagram showing an example of a state transition of a switching element in one embodiment of the present disclosure. Figure 13 is a sixth diagram showing an example of a state transition of a switching element in one embodiment of the present disclosure. Figure 14 is a seventh diagram showing an example of a state transition of a switching element in one embodiment of the present disclosure. Here, the control circuit 103j controls the switching element 103c in the power converter 103 that drives the load generating regenerative power to be in the ON state, and the switching elements 103d1, 103e2, and 103i1 to be in the OFF state. Note that the switching element 103i1 in the power converter 103 that drives the load generating regenerative power is always in the OFF state in the following explanation.

[0051] When the control circuit 103j controls the switching element 103c of the power converter 103 that generates regenerative power to be in the ON state, and the switching elements 103d1 and 103e2 to be in the OFF state (step S11), as shown in Figure 8, the current flowing due to the generated regenerative power flows from the output side to the input side inside the bridge circuit 103a, and further flows to the bus via the current sensor 103f, the switching element 103c, and the fuse 102p, and returns from the bus to the bridge circuit 103a as a return current via the fuse 102n. The current flowing due to the generated regenerative power is smaller than the current discharged from the capacitor 103b during a short circuit, and is a current value that is sufficiently smaller than the threshold value used by the control circuit 103j to determine whether the current detected by the current sensor 103f exceeds the threshold value.

[0052] In this state, assume that a short circuit occurs in the busbar, as shown in Figure 9. In this case, the current flowing due to the generated regenerative power flows toward the short circuit point, as shown in Figure 9, and the charges stored in capacitors 103b and 106 also flow toward the short circuit point as current. As the charge stored in capacitor 103b flows toward the short circuit point as current, the control circuit 103j determines that the current detected by the current sensor 103f has exceeded a threshold and controls the switching element 103c to the off state (step S12).

[0053] When the switching element 103c is turned off, a return current flows through the protection diode 103h, as shown in Figure 10. Also, because the switching element 103c is turned off, the current generated by the regenerative power that was flowing from the bridge circuit 103a to the bus through the switching element 103c and fuse 102p stops flowing.

[0054] However, when the load is a motor, the energy stored in the inductor of the motor causes a current to flow that charges the capacitor 103b, as shown in Figure 11. Since this current has no other path to flow besides the capacitor 103b, it continues to charge the capacitor 103b until the energy stored in the inductor of the motor is depleted. As a result, the voltage of the capacitor 103b rises. That is, the potential difference across the capacitor 103b increases. The voltage sensor 103g detects the potential difference across the capacitor 103b and outputs the detected potential difference to the control circuit 103j. The control circuit 103j compares the potential difference detected by the voltage sensor 103g with a predetermined threshold. The control circuit 103j determines whether the potential difference detected by the voltage sensor 103g exceeds the threshold. For example, the threshold in this case is set so as not to exceed the rated voltage of the switching elements constituting the bridge circuit 103a. The control circuit 103j controls the switching element 103d1 to the off state when the voltage sensor 103g detects a potential difference below the threshold, and controls the switching element 103d1 to the on state when the voltage sensor 103g detects a potential difference above the threshold.

[0055] When the voltage sensor 103g detects a potential difference exceeding a threshold and the control circuit 103j controls the switching element 103d1 to the ON state (step S13), as shown in Figure 12, the charge stored in capacitor 103b flows as current through the energy absorption circuit 103d. As current flows through the energy absorption circuit 103d, the potential difference across the ends of capacitor 103b decreases. Note that this current is determined by the resistance value of resistor 103d2, so the maximum current is suppressed. Also, in this state, since capacitor 103b and capacitor 103d3 are connected in parallel, the maximum amount of charge that can move from capacitor 103b to capacitor 103d3 is determined according to the ratio of the capacitance of capacitor 103b to the capacitance of capacitor 103d3.

[0056] Voltage sensors 103g and 107 each output their detection results to the control circuit 103j. Therefore, the control circuit 103j knows the detection results of both voltage sensors 103g and 107. When the potential difference across the terminals of capacitor 103b falls below a predetermined potential difference, the control circuit 103j controls the switching element 103d1 to the off state, as shown in Figure 13 (step S14). Note that the processing in step S14 may also be performed by the control device 104, after the voltage sensors 103g and 107 each output their detection results to the control device 104. When the processing in step S14 is performed, the potential difference between the positive terminal wiring P and the negative terminal wiring N of the busbar (i.e., the potential difference across the terminals of capacitor 106) and the potential difference across the terminals of capacitor 103b may be deviating by more than a predetermined threshold.

[0057] Therefore, the control circuit 103j turns on the switching element 103e2 (step S15). As a result, a resistor 103e1 is placed in the path between capacitor 106 and capacitor 103b, and the resistor 103e1 absorbs the difference between the voltage on the bus side (i.e., the potential difference between the positive terminal wiring P and the negative terminal wiring N) and the voltage at the input of the bridge circuit 103a (i.e., the potential difference across the ends of capacitor 103b).

[0058] The control circuit 103j compares the detection results of the voltage sensors 103g and 107 and determines whether the difference shown in the comparison results falls within a predetermined threshold (step S16). If the control circuit 103j determines that the difference shown in the comparison results does not fall within the predetermined threshold (NO in step S16), it returns to the process in step S16. If the control circuit 103j determines that the difference shown in the comparison results falls within the predetermined threshold (YES in step S16), it controls the switching element 103c to the ON state and the switching element 103e2 to the OFF state, as shown in Figure 14 (step S17).

[0059] In addition, in a DC microgrid system 1 according to another embodiment of this disclosure, the process in step S17 may be performed after a predetermined time has elapsed without performing the process in step S16.

[0060] Furthermore, in one embodiment of the present disclosure described above, the current is detected using the current sensor 103f, but in another embodiment of the present disclosure, the switching element 103c may be a semiconductor element and the increase in current may be detected using a non-saturation detection (so-called DESAT detection) technique.

[0061] (Effects and Benefits) The DC microgrid system 1 according to one embodiment of the present disclosure has been described above. In the DC microgrid system 1, the DC microgrid 10a includes a first fuse 101p, a second fuse 101n, and a first capacitor 106. The first fuse 101p has a first terminal connected to the positive terminal wiring P of a bus to which another DC microgrid 10b is connected, and a second terminal connected to the positive terminal wiring P of the bus to which a plurality of power converters 103 are connected via a plurality of fuses 102p. The second fuse 101n has a first terminal connected to the negative terminal wiring N of the bus to which the other DC microgrid 10b is connected, and a second terminal connected to the negative terminal wiring N of the bus to which a plurality of power converters 103 are connected via a plurality of fuses 102n. The first capacitor 106 has a first terminal connected to the positive terminal wiring P of the bus to which the other DC microgrid 10b is connected, and a second terminal connected to the negative terminal wiring N of the bus to which the other DC microgrid 10b is connected, and has a capacitance capable of disconnecting at least one of the first fuse 101p and the second fuse 101n.

[0062] As a result, in the DC microgrid system 1, when the charge stored in the first capacitor 106 flows as a current toward the short circuit point, that current flows from the first capacitor 106 to the short circuit point via the first fuse 101p and the second fuse 101n. The first capacitor 106 has a capacitance that can disconnect at least one of the first fuse 101p and the second fuse 101n. Therefore, when current flows from the first capacitor 106 to the short circuit point via the first fuse 101p and the second fuse 101n, at least one of the first fuse 101p and the second fuse 101n can be disconnected. As a result, the DC microgrid 10a can be disconnected from another DC microgrid 10b.

[0063] In addition, the order of processing in the embodiments of this disclosure may be changed, as long as appropriate processing is performed.

[0064] Each of the storage units and memory devices (including registers and latches) in the embodiments of this disclosure may be located anywhere within the scope of appropriate information transmission and reception. Furthermore, each of the storage units and memory devices may be multiple in number, storing data in a distributed manner within the scope of appropriate information transmission and reception.

[0065] While embodiments of this disclosure have been described, the control circuit 103j and other control devices described above may have a computer system internally. The process described above is stored in program form on a computer-readable recording medium, and the process is performed when the computer reads and executes this program. A specific example of a computer is shown below.

[0066] Figure 15 is a schematic block diagram showing the configuration of a computer according to at least one embodiment. As shown in Figure 15, the computer 5 includes a CPU 6, main memory 7, storage 8, and interface 9. For example, the control circuit 103j and other control devices described above are each implemented in the computer 5. The operation of each processing unit described above is stored in the storage 8 in the form of a program. The CPU 6 reads the program from the storage 8 and loads it into the main memory 7, and executes the above processing according to the program. The CPU 6 also allocates storage areas in the main memory 7 corresponding to each of the storage units described above according to the program.

[0067] Examples of storage 8 include HDDs (Hard Disk Drives), SSDs (Solid State Drives), magnetic disks, magneto-optical disks, CD-ROMs (Compact Disc Read Only Memory), DVD-ROMs (Digital Versatile Disc Read Only Memory), and semiconductor memory such as Flash memory. Storage 8 may be an internal medium directly connected to the bus of computer 5, or an external medium connected to computer 5 via interface 9 or a communication line. Furthermore, if this program is distributed to computer 5 via a communication line, computer 5, upon receiving the program, may expand it into main memory 7 and execute the above processing. In at least one embodiment, storage 8 is a tangible storage medium that is not temporary.

[0068] Furthermore, the above program may implement some of the functions described above. Moreover, the above program may be a file that can implement the above functions in combination with a program already recorded in the computer system, a so-called differential file (differential program).

[0069] While several embodiments of this disclosure have been described, these embodiments are illustrative and do not limit the scope of the disclosure. These embodiments may be modified in various ways, including additions, omissions, substitutions, and changes, without departing from the gist of the disclosure.

[0070] <Note> The DC microgrid 10a, DC microgrid system 1, control method, and program described in each embodiment of this disclosure can be understood, for example, as follows.

[0071] (1) The DC microgrid (10a) according to the first embodiment is The first terminal is connected to the positive terminal wiring (P) of the bus to which another DC microgrid (10b) is connected, and the second terminal is connected to the first fuse (101p) to which the positive terminal wiring (P) of the bus to which multiple power converters (103) are connected via multiple fuses (102p), The first terminal is connected to the negative terminal wiring (N) of the bus to which the other DC microgrid (10b) is connected, and the second terminal is connected to the negative terminal wiring (N) of the bus to which the multiple power converters (103) are connected via multiple fuses (102n), and the second fuse (101n) is connected. A first capacitor (106) has a capacitance capable of discharging at least one of the first fuse (101p) and the second fuse (101n), with a first terminal connected to the positive terminal wiring (P) of the bus to which the other DC microgrid (10b) is connected, and a second terminal connected to the negative terminal wiring (N) of the bus to which the other DC microgrid (10b) is connected. It is equipped with.

[0072] The DC microgrid (10a) comprises a first capacitor (106) having capacitance capable of discharging at least one of the first fuse (101p) and the second fuse (101n). This makes it possible to easily discharge the fuses (101p, 101n) in the event of a short circuit in the DC microgrid (10a) in a DC microgrid system in which DC microgrids (10a, 10b) are connected to each other via fuses (101p, 101n), even if the ratings of the fuses (101p, 101n) are increased.

[0073] (2) The DC microgrid (10a) relating to the second embodiment is the DC microgrid (10a) of (1), The first terminal and the second terminal of the first capacitor (106) are It may also be connected via the second fuse (101n).

[0074] This allows the DC microgrid (10a) to cut the fuse 101n in the event of a short circuit at the connection point between two DC microgrids (10a and 10b).

[0075] (3) The DC microgrid (10a) relating to the third aspect is the DC microgrid (10a) of (1) or (2), Each of the aforementioned multiple power converters (103) A bridge circuit (103a) that generates AC power from DC power supplied by the positive terminal wiring (P) of the bus to which the plurality of power converters (103) are connected, and the negative terminal wiring (N) of the bus to which the plurality of power converters (103) are connected, A second capacitor (103b) is provided in parallel with the input terminal of the bridge circuit (103a) to smooth the DC power, A current sensor (103f) detects the current flowing from the second capacitor (103b) to the bus when the charge stored in the second capacitor (103b) is discharged toward the bus, A first switching element (103c) is provided between the current sensor (103f) and the busbar, A control device (104) determines whether the current detected by the current sensor (103f) exceeds a predetermined threshold, and if it is determined that the current detected by the current sensor (103f) exceeds the predetermined threshold, controls the first switching element (103c) to the off state. It may also be equipped with

[0076] This allows the DC microgrid (10a) to disconnect the power converter (103) where a short circuit has occurred from the busbar.

[0077] (4) The DC microgrid (10a) relating to the fourth aspect is the DC microgrid (10a) of (3), A first path provided in parallel with the second capacitor (103b) and having a second switching element (103d1), wherein the first path is energized when the second switching element (103d1) is in the ON state and disconnected when the second switching element (103d1) is in the OFF state. Equipped with, The control device (104) is The power converter (103) may also be configured to generate regenerative power in the load, control the first switching element (103c) to the off state, and then control the second switching element (103d1) to the on state if the current path through which the regenerative power flows is only through the second capacitor (103b).

[0078] This allows the DC microgrid (10a) to reduce the potential difference across the second capacitor (103b).

[0079] (5) The DC microgrid (10a) relating to the fifth aspect is the DC microgrid (10a) of (3) or (4), A second path is provided in parallel with the first switching element (103c) and includes a third switching element (103e2) and a resistor (103e1) connected in series with the third switching element (103e2). Equipped with, The control device (104) is If it is determined that the comparison result between the potential difference across the first capacitor (106) and the potential difference across the second capacitor (103b) falls within a predetermined threshold range, the first switching element (103c) may be controlled to the off state and the third switching element (103e2) may be controlled to the on state.

[0080] As a result, the DC microgrid (10a) can absorb the potential difference with the resistor (103e1) even if the potential difference between the positive terminal wiring (P) and the negative terminal wiring (N) of the busbar (i.e., the potential difference across the capacitor 106) and the potential difference across the capacitor (103b) are different. Furthermore, the DC microgrid (10a) can charge the first capacitor (106) via the second path. Consequently, the DC microgrid (10a) can set an appropriate potential when restarting.

[0081] (6) A DC microgrid system (1) according to the sixth embodiment comprises one DC microgrid (10a) from any of (1) to (5), The aforementioned DC microgrid (10a) is linked to another DC microgrid (10b), It is equipped with.

[0082] The DC microgrid system (1) includes a first capacitor (106) having capacitance capable of discharging at least one of the first fuse (101p) and the second fuse (101n). This allows the DC microgrid system (1), in which DC microgrids (10a, 10b) are interconnected via fuses (101p, 101n), to easily discharge the fuses (101p, 101n) in the event of a short circuit in the DC microgrid (10a), even if the ratings of the fuses (101p, 101n) are increased.

[0083] (7) The control method relating to the seventh aspect is: The first terminal is connected to the positive terminal wiring (P) of the bus to which another DC microgrid (10b) is connected, and the second terminal is connected to the first fuse (101p) to which the positive terminal wiring (P) of the bus to which multiple power converters (103) are connected via multiple fuses (102p), The first terminal is connected to the negative terminal wiring (N) of the bus to which the other DC microgrid (10b) is connected, and the second terminal is connected to the negative terminal wiring (N) of the bus to which the multiple power converters (103) are connected via multiple fuses (102n), and the second fuse (101n) is connected. A first capacitor (106) has a capacitance capable of discharging at least one of the first fuse (101p) and the second fuse (101n), with a first terminal connected to the positive terminal wiring (P) of the bus to which the other DC microgrid (10b) is connected, and a second terminal connected to the negative terminal wiring (N) of the bus to which the other DC microgrid (10b) is connected. Equipped with, Each of the aforementioned multiple power converters (103) A bridge circuit (103a) that generates AC power from DC power supplied by the positive terminal wiring (P) of the bus to which the plurality of power converters (103) are connected, and the negative terminal wiring (N) of the bus to which the plurality of power converters (103) are connected, A second capacitor (103b) is provided in parallel with the input terminal of the bridge circuit (103a) to smooth the DC power, A current sensor (103f) detects the current flowing from the second capacitor (103b) to the bus when the charge stored in the second capacitor (103b) is discharged toward the bus, A first switching element (103c) is provided between the current sensor (103f) and the busbar, A DC microgrid (10a) equipped with the following features: The system determines whether the current detected by the current sensor (103f) exceeds a predetermined threshold, and if it determines that the current detected by the current sensor (103f) exceeds the predetermined threshold, the system controls the first switching element (103c) to the off state.

[0084] This control method comprises a first capacitor (106) having capacitance capable of disconnecting at least one of the first fuse (101p) and the second fuse (101n). As a result, in a DC microgrid system (1) in which DC microgrids (10a, 10b) are interconnected via fuses (101p, 101n), the control method makes it easier to disconnect the fuses (101p, 101n) in the event of a short circuit in the DC microgrid (10a), even if the ratings of the fuses (101p, 101n) are increased.

[0085] (8) The program relating to the eighth aspect is The first terminal is connected to the positive terminal wiring (P) of the bus to which another DC microgrid (10b) is connected, and the second terminal is connected to the first fuse (101p) to which the positive terminal wiring (P) of the bus to which multiple power converters (103) are connected via multiple fuses (102p), The first terminal is connected to the negative terminal wiring (N) of the bus to which the other DC microgrid (10b) is connected, and the second terminal is connected to the negative terminal wiring (N) of the bus to which the multiple power converters (103) are connected via multiple fuses (102n), and the second fuse (101n) is connected. A first capacitor (106) has a capacitance capable of discharging at least one of the first fuse (101p) and the second fuse (101n), with a first terminal connected to the positive terminal wiring (P) of the bus to which the other DC microgrid (10b) is connected, and a second terminal connected to the negative terminal wiring (N) of the bus to which the other DC microgrid (10b) is connected. Equipped with, Each of the aforementioned multiple power converters (103) A bridge circuit (103a) that generates AC power from DC power supplied by the positive terminal wiring (P) of the bus to which the plurality of power converters (103) are connected, and the negative terminal wiring (N) of the bus to which the plurality of power converters (103) are connected, A second capacitor (103b) is provided in parallel with the input terminal of the bridge circuit (103a) to smooth the DC power, A current sensor (103f) detects the current flowing from the second capacitor (103b) to the bus when the charge stored in the second capacitor (103b) is discharged toward the bus, A first switching element (103c) is provided between the current sensor (103f) and the busbar, A computer (5) of a DC microgrid (10a) equipped with: The current sensor (103f) determines whether the detected current exceeds a predetermined threshold, and if it is determined that the detected current exceeds the predetermined threshold, the first switching element (103c) is controlled to be in the off state. Make it run.

[0086] This program comprises a first capacitor (106) having capacitance capable of disconnecting at least one of the first fuse (101p) and the second fuse (101n). This allows the program to make it easier to disconnect the fuses (101p, 101n) in the event of a short circuit in a DC microgrid (10a) in a DC microgrid system (1) where DC microgrids (10a, 10b) are connected to each other via fuses (101p, 101n), even if the ratings of the fuses (101p, 101n) are increased. [Explanation of symbols]

[0087] 1. DC microgrid system 5. Computers 6..CPU 7. Main Memory 8. Storage 9. Interface 10a, 10b... DC microgrids 20a, 20b...Load 101p, 101n, 102p, 102n... fuses 103... Power Converter 103a...Bridge circuit 103b, 103d3, 106... Capacitors 103c, 103d1, 103e2... Switching elements 103d... Energy absorption circuit 103d2, 103e1...resistance 103e...Charging circuit 103f...Current sensor 103g, 107... Voltage sensor 104...Control device 105...Initial charging sequence

Claims

1. The first terminal is connected to the positive terminal wiring of a bus to which another DC microgrid is connected, and the second terminal is connected to the positive terminal wiring of the bus to which multiple power converters are connected via multiple fuses, and a first fuse is connected to the positive terminal wiring of the bus to which multiple power converters are connected, The first terminal is connected to the negative terminal wiring of the bus to which the other DC microgrid is connected, and the second terminal is connected to the negative terminal wiring of the bus to which the multiple power converters are connected via multiple fuses, and a second fuse is connected to the negative terminal wiring of the bus to which the multiple power converters are connected, A first terminal is connected to the positive terminal wiring of the bus to which the other DC microgrid is connected, and a second terminal is connected to the negative terminal wiring of the bus to which the other DC microgrid is connected, and a first capacitor having capacitance capable of disconnecting at least one of the first fuse and the second fuse, Equipped with, Each of the aforementioned multiple power converters is A bridge circuit that generates AC power from DC power supplied by the positive terminal wiring of the bus to which the plurality of power converters are connected, and the negative terminal wiring of the bus to which the plurality of power converters are connected, A second capacitor is provided in parallel with the input terminal of the bridge circuit to smooth the DC power, A current sensor detects the current flowing from the second capacitor to the bus when the second capacitor discharges the charge it has stored toward the bus, A first switching element is provided between the current sensor and the busbar, A control device that determines whether the current detected by the current sensor exceeds a predetermined threshold, and controls the first switching element to an off state if it is determined that the current detected by the current sensor exceeds the predetermined threshold, A DC microgrid equipped with a

2. The first terminal and the second terminal of the first capacitor are Connected via the second fuse, The DC microgrid according to claim 1.

3. A first path provided in parallel with the second capacitor and having a second switching element, wherein the first path is energized when the second switching element is in the ON state and disconnected when the second switching element is in the OFF state. Equipped with, The control device is When regenerative power is generated in the load of the power converter, the first switching element is controlled to the off state, and when the current path through which the regenerative power flows is only that of the second capacitor, the second switching element is controlled to the on state. The DC microgrid according to claim 1.

4. A second path is provided in parallel with the first switching element and includes a third switching element and a resistor connected in series with the third switching element. Equipped with, The control device is If it is determined that the comparison result between the potential difference across the terminals of the first capacitor and the potential difference across the terminals of the second capacitor falls within a predetermined threshold range, the first switching element is controlled to the off state and the third switching element is controlled to the on state. A DC microgrid according to any one of claims 1 to 3.

5. A DC microgrid according to any one of claims 1 to 4, The aforementioned DC microgrid is linked to another DC microgrid, A DC microgrid system equipped with a DC microgrid.

6. The first terminal is connected to the positive terminal wiring of a bus to which another DC microgrid is connected, and the second terminal is connected to the positive terminal wiring of the bus to which multiple power converters are connected via multiple fuses, and a first fuse is connected to the positive terminal wiring of the bus to which multiple power converters are connected, The first terminal is connected to the negative terminal wiring of the bus to which the other DC microgrid is connected, and the second terminal is connected to the negative terminal wiring of the bus to which the multiple power converters are connected via multiple fuses, and a second fuse is connected to the negative terminal wiring of the bus to which the multiple power converters are connected, A first terminal is connected to the positive terminal wiring of the bus to which the other DC microgrid is connected, and a second terminal is connected to the negative terminal wiring of the bus to which the other DC microgrid is connected, and a first capacitor having capacitance capable of disconnecting at least one of the first fuse and the second fuse, Equipped with, Each of the aforementioned multiple power converters is A bridge circuit that generates AC power from DC power supplied by the positive terminal wiring of the bus to which the plurality of power converters are connected, and the negative terminal wiring of the bus to which the plurality of power converters are connected, A second capacitor is provided in parallel with the input terminal of the bridge circuit to smooth the DC power, A current sensor detects the current flowing from the second capacitor to the bus when the second capacitor discharges the charge it has stored toward the bus, A first switching element is provided between the current sensor and the busbar, A DC microgrid equipped with, The system determines whether the current detected by the current sensor exceeds a predetermined threshold, and if it determines that the current detected by the current sensor exceeds the predetermined threshold, it controls the first switching element to an off state. Control method.

7. The first terminal is connected to the positive terminal wiring of a bus to which another DC microgrid is connected, and the second terminal is connected to the positive terminal wiring of the bus to which multiple power converters are connected via multiple fuses, and a first fuse is connected to the positive terminal wiring of the bus to which multiple power converters are connected, The first terminal is connected to the negative terminal wiring of the bus to which the other DC microgrid is connected, and the second terminal is connected to the negative terminal wiring of the bus to which the multiple power converters are connected via multiple fuses, and a second fuse is connected to the negative terminal wiring of the bus to which the multiple power converters are connected, A first terminal is connected to the positive terminal wiring of the bus to which the other DC microgrid is connected, and a second terminal is connected to the negative terminal wiring of the bus to which the other DC microgrid is connected, and a first capacitor having capacitance capable of disconnecting at least one of the first fuse and the second fuse, Equipped with, Each of the aforementioned multiple power converters is A bridge circuit that generates AC power from DC power supplied by the positive terminal wiring of the bus to which the plurality of power converters are connected, and the negative terminal wiring of the bus to which the plurality of power converters are connected, A second capacitor is provided in parallel with the input terminal of the bridge circuit to smooth the DC power, A current sensor detects the current flowing from the second capacitor to the bus when the second capacitor discharges the charge it has stored toward the bus, A first switching element is provided between the current sensor and the busbar, A DC microgrid computer equipped with: The current sensor determines whether the detected current exceeds a predetermined threshold, and if it is determined that the detected current exceeds the predetermined threshold, the first switching element is controlled to an off state. A program that executes the command.

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