Ground fault protection system

Abstract

This ground fault protection system comprises: an external low-voltage terminal to which a low-voltage terminal of an external device outside the ground fault protection system is connected; an external high-voltage terminal to which a high-voltage terminal of the external device is connected; a non-isolated DC / DC converter; a first cut-off unit; a second cut-off unit; a non-linear protection element; and a control unit. The external low-voltage terminal is connected to a low-voltage terminal of a battery via the first cut-off unit and the non-isolated DC / DC converter, and the external high-voltage terminal is connected to a high-voltage terminal of the battery via the second cut-off unit and the non-isolated DC / DC converter. The non-linear protection element is connected in parallel with the second cut-off unit. The first cut-off unit is a semiconductor element including a diode or a thyristor, and the second cut-off unit includes a self arc-extinguishing element.

Description

Ground Fault Protection System

[0001] The present disclosure relates to a ground fault protection system that protects a battery from a ground fault current generated by a ground fault between a high voltage terminal of the battery and a ground conductor.

[0002] Patent Document 1 discloses a charging system for an electric vehicle that suppresses battery discharge and short-circuit current by connecting a diode to at least one of the positive and negative paths between a DC power supply and a battery.

[0003] Patent No. 5399439

[0004] If a ground fault occurs in the charging system disclosed in Patent Document 1, the ground fault current flowing in the negative path can be suppressed by a diode, but it is difficult to suppress the ground fault current flowing in the positive path, which may compromise safety.

[0005] The ground fault protection system according to the present disclosure is configured to protect a battery from a ground fault current generated by a ground fault between a high-voltage terminal of a battery and a ground conductor, and includes: an external low-voltage terminal configured to be connected to a low-voltage terminal of an external device outside the ground fault protection system; an external high-voltage terminal configured to be connected to a high-voltage terminal of the external device; a non-isolated DC / DC converter; a first circuit breaker; a second circuit breaker; a non-linear protection element; and a control unit configured to control the non-isolated DC / DC converter and the second circuit breaker, wherein the external low-voltage terminal is configured to be connected to the low-voltage terminal of the battery via the first circuit breaker and the non-isolated DC / DC converter, and the external high-voltage terminal is configured to be connected to the high-voltage terminal of the battery via the second circuit breaker and the non-isolated DC / DC converter, the non-linear protection element is connected in parallel with the second circuit breaker, the first circuit breaker is a semiconductor element including a diode or a thyristor, and the second circuit breaker includes a self-extinguishing element.

[0006] These comprehensive or specific aspects may be realized as a system, a method, an integrated circuit, a computer program, or a computer-readable recording medium such as a CD-ROM, or may be realized as any combination of a system, a method, an integrated circuit, a computer program, and a recording medium.

[0007] According to the ground fault protection system according to one aspect of the present disclosure, when a ground fault occurs, the ground fault current can be suppressed in both the positive side path and the negative side path.

[0008] FIG. 1 is a circuit diagram showing a first example of a ground fault protection system according to an embodiment. FIG. 2 is a circuit diagram showing an example of a DC / DC converter according to an embodiment. FIG. 3 is a circuit diagram showing a second example of a ground fault protection system according to an embodiment. FIG. 4 is a circuit diagram showing a third example of a ground fault protection system according to an embodiment. FIG. 5 is a circuit diagram showing a fourth example of a ground fault protection system according to an embodiment. FIG. 6 is a circuit diagram showing a fifth example of a ground fault protection system according to an embodiment. FIG. 7 is a circuit diagram showing a modified example of the fourth example of the ground fault protection system according to an embodiment. FIG. 8 is a circuit diagram showing a modified example of the fifth example of the ground fault protection system according to an embodiment. FIG. 9 is a flowchart showing an example of the operation of the ground fault protection system according to the embodiment during charging. FIG. 10 is a diagram for explaining a threshold value for gate-blocking a first circuit breaker (self-extinguishing element) according to an embodiment. FIG. 11A is a diagram for explaining the flow of operation of the ground fault protection system when a ground fault occurs, when a second circuit breaker is not provided in the DC / DC converter. FIG. 11B is a diagram illustrating the flow of operation of a ground fault protection system when a ground fault occurs when a second circuit breaker is not provided in the DC / DC converter. FIG. 11C is a diagram illustrating the flow of operation of a ground fault protection system when a ground fault occurs when a second circuit breaker is not provided in the DC / DC converter. FIG. 11D is a diagram illustrating the flow of operation of a ground fault protection system when a ground fault occurs when a second circuit breaker is not provided in the DC / DC converter. FIG. 11E is a diagram illustrating the flow of operation of a ground fault protection system when a ground fault occurs when a second circuit breaker is not provided in the DC / DC converter. FIG. 11F is a diagram illustrating the flow of operation of a ground fault protection system when a ground fault occurs when a second circuit breaker is not provided in the DC / DC converter. FIG. 12A is a diagram illustrating the flow of operation of a ground fault protection system when a ground fault occurs when a second circuit breaker is provided in the DC / DC converter. FIG. 12B is a diagram illustrating the flow of operation of a ground fault protection system when a ground fault occurs when a second circuit breaker is provided in the DC / DC converter. FIG. 12C is a diagram for explaining the flow of operations when a ground fault occurs in a ground fault protection system in which the second circuit breaker is provided in the DC / DC converter.Fig. 12D is a diagram for explaining the flow of operation of the ground fault protection system when a ground fault occurs when the second circuit breaker is provided in the DC / DC converter. Fig. 12E is a diagram for explaining the flow of operation of the ground fault protection system when a ground fault occurs when the second circuit breaker is provided in the DC / DC converter. Fig. 12F is a diagram for explaining the flow of operation of the ground fault protection system when a ground fault occurs when the second circuit breaker is provided in the DC / DC converter. Fig. 13 is a flowchart for explaining an example of the operation of the ground fault protection system during discharge according to an embodiment.

[0009] Hereinafter, the embodiments will be specifically described with reference to the drawings.

[0010] The embodiments described below are all comprehensive or specific examples, and the numerical values, shapes, materials, components, arrangement and connection of the components, steps, and order of steps shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0011] (Embodiment) Hereinafter, a ground fault protection system according to an embodiment will be described.

[0012] 1 is a circuit diagram showing a first example of a ground fault protection system 1 according to an embodiment. For example, the ground fault protection system 1 is used in a vehicle equipped with a battery 100, for example, an electric vehicle such as a battery electric vehicle (BEV) or a hybrid electric vehicle (HEV). In addition to the ground fault protection system 1, FIG. 1 also shows the battery 100, a housing 200, and a DC charging stand 300.

[0013] The battery 100 is a battery capable of applying a high voltage of, for example, several hundred volts to loads such as a motor and an inverter, etc. For example, the battery 100 is a main battery (for example, a lithium-ion battery) in an electric vehicle.

[0014] The housing 200 is a grounded metal that surrounds the battery 100, such as a vehicle chassis. For example, the housing 200 is connected to the earth 400 via the terminal t3. The housing 200 is an example of a ground conductor.

[0015] The DC charging stand 300 is a charging device installed in a public facility, a home, or the like for charging an electric vehicle, and includes a charger 301. A low-voltage terminal p32 of the charger 301 is connected to earth 400 via a ground circuit 302. The DC charging stand 300 is an example of an external device outside the ground fault protection system 1.

[0016] The application of the ground fault protection system 1 is not limited to vehicles, and the ground fault protection system 1 can be applied to any system that includes a battery 100 and has a ground conductor such as a metal housing around the battery 100.

[0017] The ground fault protection system 1 is a system for charging and discharging the battery 100. The ground fault protection system 1 also has a function of protecting the battery 100 and the like from a ground fault current generated by a ground fault between the high voltage terminal p11 of the battery 100 and the housing 200.

[0018] The ground fault protection system 1 includes terminals t1 and t2. A low-voltage terminal p32 of the DC charging stand 300 is connected to the terminal t1. The terminal t1 is an example of an external low-voltage terminal. A high-voltage terminal p31 of the DC charging stand 300 is connected to the terminal t2. The terminal t2 is an example of an external high-voltage terminal. For example, when the connector at the end of the charging cable of the DC charging stand 300 is inserted into a charging port provided in the housing 200, the high-voltage terminal p31 and the low-voltage terminal p32 of the DC charging stand 300 (charger 301) are connected to the terminals t1 and t2, respectively. At this time, the terminal t3 of the housing 200 is connected to the earth 400 via the DC charging stand 300, and the housing 200 is grounded.

[0019] The path connecting the high voltage terminal p11 of the battery 100 and the terminal t2 is called the positive side path, and the path connecting the low voltage terminal p12 of the battery 100 and the terminal t1 is called the negative side path.

[0020] The ground fault protection system 1 includes a DC / DC converter 10 , a first circuit breaker 20 , a second circuit breaker 30 , a varistor 40 , a mechanical relay 50 , a diode 60 and a control unit 70 .

[0021] The DC / DC converter 10 is a non-insulated DC / DC converter, and is a bidirectional DC / DC converter capable of bidirectional voltage step-up and step-down. The DC / DC converter 10 has input / output high-voltage terminals p51 and p61, and is configured to step up or step down a voltage input to the input / output high-voltage terminal p51 and output it from the input / output high-voltage terminal p61, and to step up or step down a voltage input to the input / output high-voltage terminal p61 and output it from the input / output high-voltage terminal p51. The DC / DC converter 10 is an example of a non-insulated DC / DC converter. The DC / DC converter 10 is connected between terminals t1 and t2 and a battery 100. The DC / DC converter 10 is inserted in the positive-side path and connected to the negative-side path.

[0022] The first blocking unit 20 is a semiconductor element including a diode or a thyristor. In a first example, the first blocking unit 20 is a diode 21. The anode of the diode 21 is connected to the DC / DC converter 10, and the cathode of the diode 21 is connected to the terminal t1. Note that in this specification, the word "diode 21" can be replaced with the word "thyristor."

[0023] The second circuit breaker 30 includes a self-extinguishing element. The self-extinguishing element is, for example, a field effect transistor (FET) or an insulated gate bipolar transistor (IGBT). An example in which the self-extinguishing element is a FET will be described below. In a first example, the second circuit breaker 30 is provided in the DC / DC converter 10. An example circuit of the DC / DC converter 10 will now be described with reference to FIG. 2 .

[0024] FIG. 2 is a circuit diagram showing an example of the DC / DC converter 10 according to the embodiment.

[0025] The DC / DC converter 10 includes switches M1, M2, M3 and M4, an inductor L1, and capacitors C1 and C2.

[0026] The switch M1 is, for example, an N-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor). The drain of the switch M1 is connected to the terminal t2 via the mechanical relay 50, and the source of the switch M1 is connected to the drain of the switch M2. The switch M2 is, for example, an N-channel MOSFET. The drain of the switch M2 is connected to the source of the switch M1, and the source of the switch M2 is connected to the negative path.

[0027] The switch M4 is, for example, an N-channel MOSFET. The drain of the switch M4 is connected to the high-voltage terminal p11 of the battery 100, and the source of the switch M4 is connected to the drain of the switch M3. The switch M3 is, for example, an N-channel MOSFET. The drain of the switch M3 is connected to the source of the switch M4, and the source of the switch M3 is connected to the negative path.

[0028] 2 shows an anti-parallel diode (e.g., a body diode) connected to each of the switches M1, M2, M3, and M4, and each anti-parallel diode is connected in parallel with the corresponding switch. Specifically, the anode of each anti-parallel diode is connected to the source of the corresponding switch, and the cathode is connected to the drain of the corresponding switch.

[0029] Inductor L1 is connected between a node between switches M1 and M2 and a node between switches M3 and M4. Capacitor C1 is connected between the drain of switch M1 and the negative path. That is, capacitor C1 is connected between the positive path and the negative path on the terminals t1 and t2 sides of the DC / DC converter 10. Capacitor C2 is connected between the drain of switch M4 and the negative path. That is, capacitor C2 is connected between the positive path and the negative path on the battery 100 side of the DC / DC converter 10.

[0030] In the first example, the self-extinguishing element of the second circuit breaker unit 30 is the switch M1. Note that the second circuit breaker unit 30 may include a switch M4 in addition to the switch M1, and may further include switches M2 and M3.

[0031] Returning to the explanation in Fig. 1 , the varistor 40 is connected in parallel with the second cutoff unit 30. The varistor 40 is an example of a non-linear protection element. In a first example, the varistor 40 is connected between the input / output high-voltage terminals p51 and p61 of the DC / DC converter 10, as shown in Fig. 1 . The varistor 40 may also be connected in parallel with the switch M1. Furthermore, instead of the varistor 40, a Zener diode or a TVS diode (Transient Voltage Suppressor Diode) may be provided as the non-linear protection element.

[0032] The mechanical relay 50 is connected between the terminal t2 and the second cutoff unit 30 (in the first example, the DC / DC converter 10).

[0033] The diode 60 is a semiconductor element connected in series with the varistor 40. Note that a self-extinguishing element may be provided as the semiconductor element instead of the diode 60. The diode 60 prevents the potential difference between the input and output high-voltage terminals p51, p61 of the DC / DC converter 10 from being applied to the varistor 40, thereby suppressing leakage current from the varistor 40. The diode 60 is not a component necessary for the cut-off principle, and need not necessarily be provided if the effect of leakage current can be ignored.

[0034] As shown in FIG. 1, terminal t1 is connected to a low-voltage terminal p12 of battery 100 via a first circuit breaker 20 and a DC / DC converter 10, and terminal t2 is connected to a high-voltage terminal p11 of battery 100 via a second circuit breaker 30 and a DC / DC converter 10.

[0035] The control unit 70 controls the DC / DC converter 10 and at least the second circuit breaker 30 of the first circuit breaker 20 and the second circuit breaker 30. In a first example, the control unit 70 controls the DC / DC converter 10 (switch M1 (second circuit breaker 30) and switches M2, M3, and M4) and the mechanical relay 50. For example, the control unit 70 controls the on and off of the switches M1, M2, M3, and M4 via gate drive circuits connected to the gates of the switches M1, M2, M3, and M4. The control unit 70 is a computer including a processor (microprocessor), memory, and the like. The memory is a read-only memory (ROM) or a random access memory (RAM), and can store programs executed by the processor. Note that, although an example has been described in which one control unit 70 controls the DC / DC converter 10 and at least the second circuit breaker 30 of the first circuit breaker 20 and the second circuit breaker 30, this is not limiting. For example, the components that control the DC / DC converter 10 of the control unit 70 and the components that control at least the second circuit breaker 30 of the first circuit breaker 20 and the second circuit breaker 30 may be provided separately.

[0036] The circuit configuration of the ground fault protection system 1 is not limited to the first example shown in Fig. 1. Second to fifth examples of the ground fault protection system 1 will be described below.

[0037] FIG. 3 is a circuit configuration diagram showing a second example of the ground fault protection system 1 according to the embodiment.

[0038] In a second example, the first cutoff unit 20 is a self-extinguishing element including an anti-parallel diode, such as an FET 22. The FET 22 is, for example, an N-channel MOSFET, and the drain of the FET 22 is connected to the terminal t1, and the source of the FET 22 is connected to the DC / DC converter 10. The anti-parallel diode of the FET 22 has an anode connected to the source of the corresponding FET 22 and a cathode connected to the drain of the FET 22. Note that the anti-parallel diode may be a body diode, and a separate diode element may not be provided.

[0039] In the second example, the control unit 70 controls the DC / DC converter 10 (switch M1 (second circuit breaker 30) and switches M2, M3, and M4), the first circuit breaker 20 (FET 22), and the mechanical relay 50. For example, the control unit 70 controls the on and off of the switches M1, M2, M3, and M4 and the FET 22 via a gate drive circuit connected to the gates of the switches M1, M2, M3, and M4 and the FET 22, or the like.

[0040] Other points in the second example are the same as those in the first example, and therefore a description thereof will be omitted.

[0041] FIG. 4 is a circuit configuration diagram showing a third example of the ground fault protection system 1 according to the embodiment.

[0042] In the third example, the mechanical relay 50 is connected between the varistor 40 and a node on the path connecting the terminal t2 and the DC / DC converter 10 (i.e., the positive path).

[0043] Other points in the third example are the same as those in the first example, and therefore description thereof will be omitted. Note that in the second example as well, the mechanical relay 50 may be provided as shown in FIG.

[0044] FIG. 5 is a circuit configuration diagram showing a fourth example of the ground fault protection system 1 according to the embodiment.

[0045] In the fourth example, the second circuit breaker 30 is a self-extinguishing element, such as an FET 31, connected between the terminal t2 and the DC / DC converter 10. As in the fourth example, the second circuit breaker 30 does not have to be provided in the DC / DC converter 10. The FET 31 is, for example, an N-channel MOSFET, and the drain of the FET 31 is connected to the terminal t2 via the mechanical relay 50, and the source of the FET 31 is connected to the DC / DC converter 10. Note that FIG. 5 shows an anti-parallel diode (for example, a body diode) connected to the FET 31, and the anti-parallel diode is connected in parallel with the FET 31. Specifically, the anode of the anti-parallel diode is connected to the source of the FET 31, and the cathode is connected to the drain of the FET 31.

[0046] In the fourth example, the varistor 40 is connected in parallel with the FET 31. Furthermore, in the fourth example, the diode (diode 60) in the first, second and third examples shown in Figures 1, 3 and 4, respectively, is not connected in series with the varistor 40. This is because the varistor 40 is not connected in parallel with the DC / DC converter 10, and the potential difference between the input and output high-voltage terminals p51 and p61 is not applied to the varistor 40.

[0047] In the fourth example, the control unit 70 controls the DC / DC converter 10 (switches M1, M2, M3, and M4), the second cutoff unit 30 (FET 31), and the mechanical relay 50. For example, the control unit 70 controls the on and off of the switches M1, M2, M3, and M4 and the FET 31 via a gate drive circuit connected to the gate of the switches M1, M2, M3, and M4 and the FET 31.

[0048] Other points in the fourth example are the same as those in the first example, and therefore a description thereof will be omitted.

[0049] FIG. 6 is a circuit configuration diagram showing a fifth example of the ground fault protection system 1 according to the embodiment.

[0050] In the fifth example, the first cutoff unit 20 is a self-extinguishing element including an anti-parallel diode, such as an FET 22. The FET 22 is the same as that described in the second example.

[0051] In the fifth example, the control unit 70 controls the DC / DC converter 10 (switches M1, M2, M3, and M4), the first circuit breaker 20, the second circuit breaker 30, and the mechanical relay 50. For example, the control unit 70 controls the on and off of the switches M1, M2, M3, and M4 and the FETs 22 and 31 via gate drive circuits connected to the gates of the switches M1, M2, M3, and M4 and the FETs 22 and 31.

[0052] Other points in the fifth example are the same as those in the fourth example, and therefore a description thereof will be omitted.

[0053] In the fourth and fifth examples, the position at which the mechanical relay 50 is provided is not limited to that shown in Figures 5 and 6. This will be described with reference to Figures 7 and 8.

[0054] FIG. 7 is a circuit configuration diagram showing a modification of the fourth example of the ground fault protection system 1 according to the embodiment.

[0055] FIG. 8 is a circuit configuration diagram showing a modification of the fifth example of the ground fault protection system 1 according to the embodiment.

[0056] 7 and 8, in the fourth and fifth examples as well, the mechanical relay 50 may be provided between the varistor 40 and a node on the path connecting the terminal t2 and the DC / DC converter 10 (i.e., the positive path). Note that although Fig. 7 and Fig. 8 show an example in which the mechanical relay 50 is provided between the varistor 40 and a node on the positive path between the terminal t2 and the second circuit breaker 30, the mechanical relay 50 may also be provided between the varistor 40 and a node on the positive path between the second circuit breaker 30 and the DC / DC converter 10.

[0057] Next, the operation of the ground fault protection system 1 (controller 70) will be described in detail. First, the operation of the ground fault protection system 1 during charging will be described in detail.

[0058] 9 is a flowchart showing an example of the operation of the ground fault protection system 1 during charging according to the embodiment. When the battery 100 is charged by the charger 301 of the DC charging stand 300, the battery 100 is charged by the charger 301 via the DC / DC converter 10, and a charging current flows through a positive path from the charger 301, the DC / DC converter 10, and the battery 100, and through a negative path from the battery 100, the DC / DC converter 10, and the charger 301. Note that steps S11 to S13 shown in FIG. 9 are performed when the first circuit breaker 20 is a self-extinguishing element. That is, steps S11 to S13 are performed in the second and fifth examples of the ground fault protection system 1, but steps S11 to S13 are not performed in the first, third, and fourth examples of the ground fault protection system 1.

[0059] The control unit 70 determines whether the value of the charging current flowing from the DC / DC converter 10 to the terminal t1 via the first circuit breaker 20 is equal to or greater than a threshold value (step S11). For example, a current detection sensor is provided in the negative-side path, and the control unit 70 can make this determination by acquiring the detection result from the current detection sensor.

[0060] If the current value of the charging current is equal to or greater than the threshold value (Yes in step S11), the control unit 70 controls the first cutoff unit 20 (FET 22) to be in the ON state (step S12), and if the current value of the charging current is less than the threshold value (No in step S11), the control unit 70 gate blocks (GB) the first cutoff unit 20 (FET 22), i.e., stops switching and keeps it OFF (step S13). Here, the threshold value will be described with reference to FIG. 10.

[0061] FIG. 10 is a diagram for explaining a threshold value when the first blocking unit 20 (FET 22) according to the embodiment is gate-blocked.

[0062] As shown in FIG. 10 , when the battery 100 is charged with a large amount of power, the charging current increases. When the battery 100 is charged with a small amount of power, the charging current decreases. When a ground fault occurs, a ground fault current begins to flow from the battery 100 through the housing 200. Because the direction of the ground fault current flowing through the negative path is opposite to the direction of the charging current flowing through the negative path, the current in the negative path decreases rapidly, as shown in FIG. 10 . Even if the FET 22 is gate-blocked after detecting a ground fault, the current in the negative path becomes negative before the FET 22 is turned off, taking into account the detection delay and the delay until the gate voltage decreases. In other words, the battery 100 may discharge before the negative path is blocked, causing a ground fault current exceeding the charging current to flow through the housing 200. In particular, when a ground fault occurs when the charging current is small, the charging current is close to zero, and it takes a short time for the current polarity in the negative path to become negative.

[0063] Therefore, a threshold is set, and even if a ground fault does not occur, if the current value of the charging current is less than the threshold, the gate of FET 22 is blocked in advance in preparation for a ground fault. This prevents negative current from flowing through the negative path in the event of a ground fault. It also prevents the battery 100 from discharging, and as a result, the ground fault current can be limited to the same level as the charging current.

[0064] For example, the threshold value is set according to the voltage of the battery 100, the inductance of the path through which the charging current flows, and the cut-off delay time of the FET 22. The cut-off delay time of the FET 22 is the time from when the FET 22 receives a signal to cut off the FET 22 until it cuts off. The higher the voltage of the battery 100, the faster the rate at which the current in the negative path decreases (the amount of decrease per unit time) when a ground fault occurs. The smaller the inductance of the path, the faster the rate at which the current in the negative path decreases. The longer the cut-off delay time of the FET 22, the longer the time until the FET 22 is turned off (i.e., the time during which the current in the negative path continues to decrease). Therefore, an appropriate threshold value can be set in advance according to these values. Specifically, the threshold value is set to Ith≧V ｂａｔ ×T ｆｅｔｏｆｆ / L ｌｏｏｐ where Ith is a threshold value and V ｂａｔ is the voltage of the battery 100, and T ｆｅｔｏｆｆ is a delay time from when the FET 22 is short-circuited until it is cut off, and is stored in advance in the control unit 70. L, which varies depending on the grounding circuit 302 and the earth wire connected to the terminal t3 ｌｏｏｐ is the inductance of the path, and the expected minimum value may be stored in advance in the control unit 70. The control unit 70 also determines whether the charger 301 and other peripheral devices are in a low ｌｏｏｐ If the control unit 70 has the information, it may receive it through communication. ｌｏｏｐ The value of L ｌｏｏｐ The device may receive a signal that identifies a pattern.

[0065] As shown in FIG. 10, when the battery 100 is charged with a large amount of power, the charging current is equal to or greater than the threshold value (Ith), and the time Tｏｆｆ２ is the shut-off delay time T of the FET 22 ｆｅｔｏｆｆ Therefore, in this case, after the occurrence of a ground fault, the FET 22 can be turned off before a negative current flows in the negative path. On the other hand, when the battery 100 is charged with a small amount of power, the charging current is less than the threshold (Ith), and the time T until the current value in the negative path becomes zero after the occurrence of a ground fault is ｏｆｆ１ is the shut-off delay time T of the FET 22 ｆｅｔｏｆｆ It can be seen that the time is shorter than the time t1. Therefore, in this case, after a ground fault occurs, FET 22 cannot be turned off before a ground fault current flows in the negative path. Therefore, if the charging current is less than the threshold, the gate of FET 22 is blocked in advance. Note that even if the gate of FET 22 is blocked, charging current can flow in the negative path via the anti-parallel diode of FET 22.

[0066] Thus, in the second and fifth examples of the ground fault protection system 1, when charging the battery 100 from the DC charging stand 300, the control unit 70 gate-blocks the first circuit breaker 20 before the charging current flowing from the DC / DC converter 10 to the terminal t1 via the first circuit breaker 20 falls below zero.

[0067] When a ground fault occurs, first circuit breaker 20 is gate-blocked to cut off the negative path before the ground fault current flows into the negative path, i.e., before the charging current falls below zero, thereby preventing the ground fault current from flowing into the negative path. Furthermore, because the ground fault current does not flow into the negative path, a large current does not flow into the negative path when first circuit breaker 20 is gate-blocked. Therefore, it is not necessary to provide a nonlinear protection element such as a varistor in the negative path, or a mechanical relay for cutting off leakage current from the varistor, making it possible to miniaturize the circuit.

[0068] Furthermore, the first cutoff unit 20 is an element capable of synchronous rectification. That is, the FET 22 is an element that can be turned on when a current flows from the source to the drain of the FET 22. When the charging current of the battery 100 is equal to or higher than the threshold value (Ith) when no ground fault occurs, turning on the first cutoff unit 20 (FET 22) allows the current to be diverted to the FET 22 and the anti-parallel diode, thereby reducing conduction loss.

[0069] Returning to the description of FIG. 9 , the control unit 70 determines whether a ground fault has been detected (step S14). For example, the control unit 70 detects a ground fault by comparing the current value of the current flowing in the path (positive path) connecting the terminal t2 and the DC / DC converter 10 with the current value of the current flowing in the path (negative path) connecting the terminal t1 and the DC / DC converter 10. For example, current detection sensors are provided in the positive path and the negative path, and the control unit 70 can perform the comparison by acquiring detection results from these current detection sensors. When a ground fault occurs, a difference occurs between the current value of the current flowing in the positive path and the current value of the current flowing in the negative path due to current leakage into the housing 200. Therefore, a ground fault can be detected by comparing these values.

[0070] If the control unit 70 does not detect a ground fault (No in step S14), the control unit 70 performs the process from step S11. That is, the process from step S11 to step S14 is repeated until a ground fault is detected. Note that if the first interrupter 20 is the diode 21, that is, in the first, third, and fourth examples of the ground fault protection system 1, if the control unit 70 does not detect a ground fault, the process in step S14 is performed again. That is, the process in step S14 is repeated until a ground fault is detected.

[0071] When the control unit 70 detects a ground fault (Yes in step S14), it gate-blocks the first circuit breaker 20 (FET 22) and the second circuit breaker 30 (switch M1 or FET 31) (step S15). Note that if the first circuit breaker 20 is the diode 21, the control unit 70 gate-blocks the second circuit breaker 30. Note that if the first circuit breaker 20 is the FET 22 and the first circuit breaker 20 has already been gate-blocked, the control unit 70 gate-blocks the second circuit breaker 30 while maintaining the gate-blocking of the first circuit breaker 20. Note that the control unit 70 may first gate-block the first circuit breaker 20 upon detecting a ground fault, and then gate-block the second circuit breaker 30.

[0072] Next, a specific operation flow of the ground fault protection system 1 (controller 70) will be described with reference to FIGS. 11A to 11F and FIGS. 12A to 12F.

[0073] Figures 11A to 11F are diagrams for explaining the flow of operation of the ground fault protection system 1 when a ground fault occurs when the second circuit breaker 30 is not provided in the DC / DC converter 10 (fourth and fifth examples).

[0074] As shown in Fig. 11A, it is assumed that the battery 100 is being charged by the charger 301 with no ground fault occurring. At this time, a charging current flows, as indicated by the dashed arrow. Note that in Figs. 11A to 11C, the second circuit breaker 30 (FET 31) is in the on state, and therefore the second circuit breaker 30 and the varistor 40 are not shown. In Figs. 11A to 11E, the mechanical relay 50 is in the on state, and therefore the mechanical relay 50 is not shown.

[0075] 11B, when a ground fault occurs, the high-voltage terminal p11 of the battery 100 and the housing 200 become conductive at the ground fault point, and the high voltage of the battery 100 is applied to the ground circuit 302, causing a ground fault current to begin flowing through the ground circuit 302. Immediately after the ground fault occurs, the charging current is greater than the ground fault current, so the charging current flows through the negative path.

[0076] After a ground fault occurs, the ground fault current increases, and as shown in FIG. 11C, after a certain time has elapsed since the occurrence of the ground fault, the charging current equals the ground fault current. At this time, if the first interrupter 20 is a diode 21 (fourth example), the diode 21 cuts off the current in the negative path simultaneously with the formation of a current zero point. Also, if the first interrupter 20 is an FET 22 (fifth example), the gate of the FET 22 is blocked when a ground fault is detected or when the charging current falls below the threshold Ith. Therefore, the anti-parallel diode of the FET 22 cuts off the current in the negative path simultaneously with the formation of a current zero point. This prevents the battery 100 from discharging. FIGS. 11C to 11F show the first interrupter 20 as a diode 21 or an anti-parallel diode of the FET 22.

[0077] 11D, the gate of the second circuit breaker 30 (FET 31) is blocked when or after a ground fault is detected. By blocking the gate of the second circuit breaker 30 when a ground fault occurs, the ground fault current can be interrupted in the positive path. At this time, the charging current (ground fault current) tends to continue to flow, generating a back electromotive force. However, because the varistor 40 is connected in parallel to the second circuit breaker 30, the current can be commutated to the varistor 40, and it is possible to prevent the second circuit breaker 30 from being destroyed by overvoltage or element heat generation during circuit breaker operation.

[0078] 11E, magnetic energy is recovered by the varistor 40, and the charging current = earth fault current can be reduced to almost zero. However, a minute leakage current flows through the varistor 40.

[0079] Therefore, as shown in Fig. 11F, the contacts of the mechanical relay 50 are opened. Even after the positive side path is cut off by the second cutoff unit 30, a small leakage current may still flow via the varistor 40, but by opening the contacts of the mechanical relay 50, even this small leakage current can be cut off. Note that the second cutoff unit 30 and the varistor 40 are not shown in Fig. 11F.

[0080] Figures 12A to 12F are diagrams for explaining the flow of operation of the ground fault protection system 1 when a ground fault occurs when the second circuit breaker 30 is provided in the DC / DC converter 10 (first to third examples).

[0081] As shown in Fig. 12A, it is assumed that the battery 100 is being charged by the charger 301 with no ground fault occurring. At this time, a charging current flows, as indicated by the dashed arrow. Note that in Figs. 12A to 12C, the second circuit breaker 30 (switch M1) is in the on state, and therefore the second circuit breaker 30 and the varistor 40 are not shown. In Figs. 12A to 12E, the mechanical relay 50 is in the on state, and therefore the mechanical relay 50 is not shown.

[0082] 12B, when a ground fault occurs, the high-voltage terminal p11 of the battery 100 and the housing 200 become conductive at the ground fault point, and the high voltage of the battery 100 is applied to the ground circuit 302, causing a ground fault current to begin flowing through the ground circuit 302. Immediately after the ground fault occurs, the charging current is greater than the ground fault current, so the charging current flows through the negative path.

[0083] After a ground fault occurs, the ground fault current increases, and as shown in FIG. 12C , after a certain time has elapsed since the occurrence of the ground fault, the charging current equals the ground fault current. At this time, if the first interrupter 20 is a diode 21 (first and third examples), the diode 21 cuts off the current in the negative path simultaneously with the formation of a current zero point. Also, if the first interrupter 20 is an FET 22 (second example), the gate of the FET 22 is blocked when a ground fault is detected or when the charging current falls below the threshold Ith. Therefore, the anti-parallel diode of the FET 22 cuts off the current in the negative path simultaneously with the formation of a current zero point. This prevents the battery 100 from discharging. FIGS. 12C to 12F show the first interrupter 20 as a diode 21 or an anti-parallel diode of the FET 22.

[0084] 12D , the second circuit breaker 30 (switch M1) is gate-blocked at the timing when or after a ground fault is detected. Switches M2, M3, and M4 may also be gate-blocked simultaneously. By gate-blocking the second circuit breaker 30 when a ground fault occurs, the ground fault current can be interrupted in the positive path. At this time, the charging current (ground fault current) continues to flow, generating a back electromotive force. However, because the varistor 40 is connected between the input / output high-voltage terminals p51 and p61 of the DC / DC converter 10, the current can be commutated to the varistor 40, preventing the second circuit breaker 30 from being damaged by overvoltage or element heat generation during interruption.

[0085] Furthermore, by connecting the diode 60 in series with the varistor 40, the potential difference between the input / output high-voltage terminals p51 and p61 of the DC / DC converter 10 is prevented from being applied to the varistor 40. As a result, the leakage current of the varistor 40 can be suppressed.

[0086] 12E, magnetic energy is recovered by the varistor 40, and the charging current = earth fault current can be reduced to almost zero. However, a minute leakage current flows through the varistor 40.

[0087] 12F, the contacts of the mechanical relay 50 are opened. Even after the positive side path is cut off by the second cutoff unit 30, a small leakage current may still flow via the varistor 40, but by opening the contacts of the mechanical relay 50, even this small leakage current can be cut off.

[0088] Next, the operation of the ground fault protection system 1 during discharge will be described in detail.

[0089] 13 is a flowchart showing an example of the operation of the ground fault protection system 1 during discharge according to the embodiment. For example, the battery 100 may be used for a V2H (Vehicle to Home) system, and a V2H stand may be connected to the terminals t1 and t2 as an external device, allowing discharge from the battery 100 to the V2H stand. However, if the first circuit breaker 20 is a diode 21, discharge from the battery 100 to the V2H stand is not possible. Therefore, the operation of the ground fault protection system 1 during discharge described below is performed when the first circuit breaker 20 is a self-extinguishing element (i.e., in the second and fifth examples).

[0090] When discharging from the battery 100 to the V2H stand, the battery 100 is discharged via the DC / DC converter 10, and the discharge current flows through the positive path from the battery 100, the DC / DC converter 10, and the V2H stand, and through the negative path from the V2H stand, the DC / DC converter 10, and the battery 100.

[0091] The control unit 70 controls the first circuit breaker 20 to the ON state (step S21). When discharging the battery 100 to the V2H stand, the control unit 70 basically controls the first circuit breaker 20 to the ON state. This is because if the first circuit breaker 20 is not controlled to the ON state, a discharge current cannot flow through the negative side path, and the battery 100 cannot be discharged to the V2H stand.

[0092] Next, the control unit 70 determines whether or not a ground fault has been detected (step S22). If the control unit 70 has not detected a ground fault (No in step S22), the control unit 70 performs the process from step S21. In other words, the processes in steps S21 and S22 are repeated until a ground fault is detected, and the first circuit breaker 20 is maintained in the ON state.

[0093] When the control unit 70 detects a ground fault (Yes in step S22), the control unit 70 blocks the gates of the first cutoff unit 20 (FET 22) and the second cutoff unit 30 (switch M1 or FET 31) (step S23).

[0094] In this way, when discharging from battery 100 to a V2H stand (external device), control unit 70 controls first circuit breaker 20 to the ON state and gate-blocks first circuit breaker 20 after detecting a ground fault. When discharging from battery 100, first circuit breaker 20 is kept in the ON state to allow a discharge current to flow, and when a ground fault occurs, first circuit breaker 20 is gate-blocked, thereby cutting off the current in the negative path. For example, when a ground fault occurs, a difference occurs between the current value of the current flowing in the positive path and the current value of the current flowing in the negative path due to current leakage into housing 200. By comparing these values, a ground fault can be detected and a circuit-breaking operation can be initiated before the ground fault current becomes a large current.

[0095] Note that ground fault protection system 1 does not necessarily have to have a function for discharging from battery 100 to an external device. In other words, ground fault protection system 1 does not necessarily have to have a function for performing the operation described in Fig. 13. In this case, switches M2 and M4 included in DC / DC converter 10 can each be replaced with a diode.

[0096] As described above, when a ground fault occurs, the first circuit breaker 20 provided in the negative path connecting the terminal t1 and the DC / DC converter 10 can cut off the negative path. Furthermore, a ground fault current (charging current) from the DC charging stand 300 (charger 301) flows in the positive path connecting the terminal t2 and the DC / DC converter 10. However, the first circuit breaker 20 cuts off the discharge current from the battery 100 in the negative path, thereby suppressing the current from the DC charging stand 300 in the positive path. Furthermore, the second circuit breaker 30 can immediately cut off the ground fault current flowing in the positive path after the ground fault occurs. Therefore, when a ground fault occurs, the ground fault current can be suppressed in both the positive path and the negative path.

[0097] Note that, although a back electromotive force is generated when the second circuit breaker 30 interrupts the ground fault current, the current is commutated to the varistor 40 connected in parallel to the second circuit breaker 30, allowing the varistor 40 to recover magnetic energy. Also, as described above, the negative side path is cut off by the gate block of the first circuit breaker 20 after detecting a ground fault, thereby cutting off the discharge current of the battery 100 and reducing the generated magnetic energy. Therefore, the energy recovery performance required for the varistor 40 can be reduced, making it possible to miniaturize the varistor 40 and, ultimately, the circuit.

[0098] (Other Embodiments) As described above, the embodiments have been described as examples of the technology according to the present disclosure. However, the technology according to the present disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. For example, the following modifications are also included in one embodiment of the present disclosure.

[0099] For example, in the above embodiment, an example has been described in which the ground fault protection system 1 includes the mechanical relay 50 , but the ground fault protection system 1 does not necessarily have to include the mechanical relay 50 .

[0100] For example, in the above embodiment, an example has been described in which the ground fault protection system 1 includes the diode 60 , but the ground fault protection system 1 does not necessarily have to include the diode 60 .

[0101] In the above-described embodiment, each component included in the ground fault protection system 1 may be configured with dedicated hardware, or may be realized by executing a software program suitable for each component. Each component may be realized by a program execution unit such as a CPU or processor reading and executing a software program recorded on a recording medium such as a hard disk or semiconductor memory.

[0102] Some or all of the functions of the ground fault protection system 1 according to the above-described embodiment are typically realized as an LSI, which is an integrated circuit. These functions may be individually integrated into single chips, or some or all of them may be integrated into a single chip. Furthermore, the integrated circuit is not limited to an LSI, and may be realized using a dedicated circuit or a general-purpose processor. It is also possible to use an FPGA (Field Programmable Gate Array), which can be programmed after LSI manufacturing, or a reconfigurable processor, which can reconfigure the connections and settings of circuit cells within an LSI.

[0103] Furthermore, if an integrated circuit technology that can replace LSI emerges due to advances in semiconductor technology or other derived technologies, it is natural that each component included in the ground fault protection system 1 can be integrated into an integrated circuit using that technology.

[0104] In addition, this disclosure also includes forms obtained by making various modifications to the embodiments that a person skilled in the art would think of, and forms realized by arbitrarily combining the components and functions in each embodiment within the scope that does not deviate from the intent of this disclosure.

[0105] (Additional Notes) The above description of the embodiments discloses the following techniques.

[0106] (Technology 1) A ground fault protection system configured to protect a battery from a ground fault current generated by a ground fault between a high-voltage terminal of a battery and a ground conductor, the ground fault protection system comprising: an external low-voltage terminal configured to be connected to a low-voltage terminal of an external device outside the ground fault protection system; an external high-voltage terminal configured to be connected to a high-voltage terminal of the external device; a non-isolated DC / DC converter; a first circuit breaker; a second circuit breaker; a non-linear protection element; and a control unit configured to control the non-isolated DC / DC converter and the second circuit breaker, wherein the external low-voltage terminal is configured to be connected to the low-voltage terminal of the battery via the first circuit breaker and the non-isolated DC / DC converter, and the external high-voltage terminal is configured to be connected to the high-voltage terminal of the battery via the second circuit breaker and the non-isolated DC / DC converter, the non-linear protection element is connected in parallel with the second circuit breaker, the first circuit breaker is a semiconductor element including a diode or a thyristor, and the second circuit breaker includes a self-extinguishing element.

[0107] According to this configuration, when a ground fault occurs, the negative path can be shut off by a first shutoff unit provided in the negative path connecting the external low-voltage terminal and the non-isolated DC / DC converter. Furthermore, a ground fault current (charging current) from an external device (e.g., a charger for charging a battery) flows through the positive path connecting the external high-voltage terminal and the non-isolated DC / DC converter. However, the first shutoff unit shuts off the discharge current from the battery in the negative path, thereby suppressing the current from the external device in the positive path. Furthermore, the second shutoff unit can immediately shut off the ground fault current flowing through the positive path after the ground fault occurs. Therefore, when a ground fault occurs, the ground fault current can be suppressed in both the positive path and the negative path.

[0108] Although a back electromotive force is generated when the second circuit breaker interrupts the ground fault current, the current is commutated to a nonlinear protection element, such as a varistor, connected in parallel to the second circuit breaker, allowing the nonlinear protection element to recover magnetic energy. Furthermore, as described above, the negative side path is interrupted by the gate block of the first circuit breaker after detecting a ground fault, thereby interrupting the battery discharge current and reducing the generated magnetic energy. This reduces the energy recovery performance required of the nonlinear protection element, enabling the nonlinear protection element to be made smaller, thereby enabling the circuit to be more compact.

[0109] (Technology 2) A ground fault protection system according to Technology 1, wherein the first circuit breaker is a self-extinguishing element including an anti-parallel diode, and the control unit is configured to control the non-isolated DC / DC converter, the first circuit breaker, and the second circuit breaker.

[0110] In this way, the first interrupter may be a self-extinguishing element such as an FET or an IGBT.

[0111] (Technology 3) The ground fault protection system according to Technology 2, wherein the anti-parallel diode is a body diode.

[0112] In this way, the anti-parallel diode may be a body diode, and there is no need to provide a separate diode element.

[0113] (Technology 4) The ground fault protection system according to Technology 2 or 3, wherein the first interrupter is an element capable of synchronous rectification.

[0114] According to this, when charging the battery when no ground fault has occurred, the first circuit breaker (self-extinguishing element) can be turned on to shunt the current to the self-extinguishing element and the anti-parallel diode, thereby reducing conduction loss.

[0115] (Technology 5) A ground fault protection system according to any one of technologies 1 to 4, wherein the second circuit breaker is a self-extinguishing element connected between the external high-voltage terminal and the non-insulated DC / DC converter.

[0116] In this way, the second cutoff unit may be provided between the external high voltage terminal and the non-insulated DC / DC converter in the positive side path.

[0117] (Technology 6) A ground fault protection system according to any one of Technologies 1 to 4, wherein the second circuit breaker is provided in the non-insulated DC / DC converter.

[0118] In this way, the second cutoff unit may be provided within the non-insulated DC / DC converter.

[0119] (Technology 7) A ground fault protection system according to Technology 5 or 6, wherein the nonlinear protection element is connected in parallel with the self-extinguishing element of the second circuit breaker.

[0120] In this manner, the non-linear protection element may be connected in parallel with the self-extinguishing element.

[0121] (Technology 8) The ground fault protection system according to Technology 6, wherein the nonlinear protection element is connected between the input and output high voltage terminals of the non-isolated DC / DC converter.

[0122] In this way, when the second cutoff unit is provided in the non-insulated DC / DC converter, the non-linear protection element may be connected between the input and output high voltage terminals of the non-insulated DC / DC converter.

[0123] (Technology 9) A ground fault protection system according to any one of technologies 1 to 8, further comprising a mechanical relay connected between the external high voltage terminal and the second circuit breaker.

[0124] With this, even after the positive side path is cut off by the second cut-off section, a small leakage current may flow through the nonlinear protection element, but by opening the contacts of the mechanical relay, even this small leakage current can be cut off.

[0125] (Technology 10) The ground fault protection system described in Technology 8 further comprises a mechanical relay connected between a node on a path connecting the external high voltage terminal and the non-isolated DC / DC converter and the non-linear protection element.

[0126] With this, even after the positive side path is cut off by the second cut-off section, a small leakage current may flow through the nonlinear protection element, but by opening the contacts of the mechanical relay, even this small leakage current can be cut off.

[0127] (Technology 11) The ground fault protection system according to Technology 6, 8 or 10, further comprising a semiconductor element connected in series with the nonlinear protection element.

[0128] According to this, by connecting the semiconductor element in series with the nonlinear protection element, it is possible to prevent a high voltage from being applied to the nonlinear protection element.

[0129] (Technology 12) A ground fault protection system according to Technology 11, wherein the semiconductor element connected in series with the nonlinear protection element is a diode.

[0130] Thus, the semiconductor element may be a diode.

[0131] (Technology 13) A ground fault protection system according to any one of Technologies 2 to 4, wherein the control unit is configured to gate-block the first circuit breaker before the charging current flowing from the non-insulated DC / DC converter to the external low-voltage terminal via the first circuit breaker becomes zero or less when the battery is charged from the external device.

[0132] According to this, when a ground fault occurs, the first circuit breaker is gate-blocked and the negative path is cut off before the ground fault current flows into the negative path, i.e., before the charging current falls below zero, so the ground fault current can be prevented from flowing into the negative path. Furthermore, because the ground fault current does not flow into the negative path, a large current does not flow into the negative path when the first circuit breaker is gate-blocked. Therefore, it is not necessary to provide a nonlinear protection element such as a varistor or a mechanical relay in the negative path, and the circuit can be made smaller.

[0133] (Technology 14) A ground fault protection system as described in Technology 13, wherein the control unit is configured to control the first circuit breaker to an on state when the current value of the charging current is greater than or equal to a threshold when the battery is charged from the external device, and the control unit is configured to gate-block the first circuit breaker when the current value of the charging current is less than the threshold.

[0134] According to this, because the first interrupter has a certain interruption delay time, if a ground fault occurs when the charging current is small, the current in the negative path rapidly decreases and becomes negative before the interruption delay time has elapsed. In other words, the battery discharges before the negative path is interrupted, causing a ground fault current exceeding the charging current to flow into the housing. Therefore, even when a ground fault does not occur, if the charging current is below a threshold, the first interrupter is gate-blocked in advance in preparation for a ground fault. This further prevents negative current from flowing through the negative path in the event of a ground fault. Furthermore, battery discharge can be prevented, thereby limiting the ground fault current to approximately the charging current.

[0135] (Technology 15) A ground fault protection system according to Technology 14, wherein the threshold value is set according to the voltage of the battery, the inductance of the path through which the charging current flows, and the interruption delay time of the first interrupter.

[0136] According to this, the higher the battery voltage, the faster the rate of decrease (amount of decrease per unit time) of the current in the negative path when a ground fault occurs, the smaller the path inductance, the faster the rate of decrease of the current in the negative path, and the longer the interruption delay time of the first interrupter, the longer the time until the first interrupter is turned off (i.e., the time over which the current in the negative path continues to decrease). Therefore, appropriate thresholds can be preset according to these values.

[0137] (Technology 16) A ground fault protection system described in any one of Technologies 2 to 4 and 13 to 15, wherein the control unit is configured to control the first circuit breaker to an on state when discharging from the battery to the external device, and to gate block the first circuit breaker after detecting the ground fault.

[0138] According to this, when discharging from the battery, the first circuit breaker is kept in the on state to allow the discharge current to flow, and when a ground fault occurs, the first circuit breaker is gate-blocked, thereby cutting off the current in the negative path.

[0139] (Technology 17) A ground fault protection system according to any one of technologies 1 to 16, wherein the control unit is configured to gate-block the second circuit breaker after detecting the ground fault.

[0140] In this way, when a ground fault occurs, the second circuit breaker is gate-blocked, thereby suppressing the ground fault current in the positive path.

[0141] (Technology 18) A ground fault protection system according to any one of Technologies 1 to 17, wherein the control unit is configured to detect the ground fault by comparing the current value of a current flowing in a path connecting the external high-voltage terminal and the non-insulated DC / DC converter with the current value of a current flowing in a path connecting the external low-voltage terminal and the non-insulated DC / DC converter.

[0142] According to this, when a ground fault occurs, a difference occurs between the current value of the current flowing in the positive path and the current value of the current flowing in the negative path due to current leakage into the ground conductor, and the ground fault can be detected by comparing these.

[0143] The present disclosure is applicable to systems in which a grounded conductor such as a metal housing is present around the battery.

[0144] REFERENCE SIGNS LIST 1 Ground fault protection system 10 DC / DC converter 20 First interrupter 21, 60 Diode 22, 31 FET 30 Second interrupter 40 Varistor 50 Mechanical relay 70 Control unit 100 Battery 200 Housing 300 DC charging stand 301 Charger 302 Ground circuit C1, C2 Capacitor L1 Inductor M1, M2, M3, M4 Switch t1, t2 Terminal

Claims

1. A ground fault protection system configured to protect a battery from a ground fault current generated by a ground fault between a high voltage terminal of the battery and a ground conductor, comprising: an external low voltage terminal configured to be connected to a low voltage terminal of an external device outside the ground fault protection system; an external high voltage terminal configured to be connected to a high voltage terminal of the external device; a non-isolated DC / DC converter; a first circuit breaker; a second circuit breaker; a non-linear protection element; and a control unit configured to control the non-isolated DC / DC converter and the second circuit breaker, wherein the external low voltage terminal is configured to be connected to the low voltage terminal of the battery via the first circuit breaker and the non-isolated DC / DC converter, and the external high voltage terminal is configured to be connected to the high voltage terminal of the battery via the second circuit breaker and the non-isolated DC / DC converter, the non-linear protection element is connected in parallel with the second circuit breaker, the first circuit breaker is a semiconductor element including a diode or a thyristor, and the second circuit breaker includes a self-extinguishing element.

2. The ground fault protection system according to claim 1, wherein the first circuit breaker is a self-extinguishing element equipped with an anti-parallel diode, and the control unit controls the non-isolated DC / DC converter, the first circuit breaker, and the second circuit breaker.

3. The ground fault protection system of claim 2, wherein the anti-parallel diode is a body diode.

4. The ground fault protection system according to claim 2, wherein the first interrupter is a synchronously rectifying element.

5. A ground fault protection system according to any one of claims 1 to 4, wherein the second circuit breaker is a self-extinguishing element connected between the external high voltage terminal and the non-isolated DC / DC converter.

6. The ground fault protection system according to any one of claims 1 to 4, wherein the second circuit breaker is provided in the non-isolated DC / DC converter.

7. The ground fault protection system according to claim 5, wherein the non-linear protection element is connected in parallel with the self-extinguishing element of the second circuit breaker.

8. The ground fault protection system according to claim 6, wherein the non-linear protection element is connected between the input and output high voltage terminals of the non-isolated DC / DC converter.

9. The ground fault protection system according to any one of claims 1 to 4, further comprising a mechanical relay connected between the external high voltage terminal and the second circuit breaker.

10. The ground fault protection system according to claim 8, further comprising a mechanical relay connected between the non-linear protection element and a node on a path connecting the external high voltage terminal and the non-isolated DC / DC converter.

11. The ground fault protection system of claim 6, further comprising a semiconductor element connected in series with the nonlinear protection element.

12. The ground fault protection system according to claim 11, wherein the semiconductor element connected in series with the nonlinear protection element is a diode.

13. A ground fault protection system according to any one of claims 2 to 4, wherein the control unit is configured to gate-block the first circuit breaker before the charging current flowing from the non-isolated DC / DC converter to the external low-voltage terminal via the first circuit breaker becomes zero or less when the battery is being charged from the external device.

14. A ground fault protection system as described in claim 13, wherein the control unit is configured to, when charging the battery from the external device, control the first circuit breaker to an on state if the current value of the charging current is equal to or greater than a threshold, and gate-block the first circuit breaker if the current value of the charging current is less than the threshold.

15. The ground fault protection system according to claim 14, wherein the threshold value is set in accordance with the voltage of the battery, the inductance of a path through which the charging current flows, and the interruption delay time of the first interrupter.

16. A ground fault protection system according to any one of claims 2 to 4, wherein the control unit is configured to control the first circuit breaker to an ON state when discharging from the battery to the external device, and to gate-block the first circuit breaker after detecting the ground fault.

17. The ground fault protection system according to any one of claims 1 to 4, wherein the control unit is configured to gate-block the second circuit breaker unit after detecting the ground fault.

18. A ground fault protection system according to any one of claims 1 to 4, wherein the control unit is configured to detect the ground fault by comparing the current value of the current flowing in the path connecting the external high-voltage terminal and the non-insulated DC / DC converter with the current value of the current flowing in the path connecting the external low-voltage terminal and the non-insulated DC / DC converter.

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