Energy storage device

Abstract

This invention provides a switch fault diagnosis technology for an energy storage device that includes a current circuit breaker composed of multiple semiconductor switches connected in parallel. [Solution] The energy storage device comprises a battery pack having a positive electrode, a positive electrode external terminal 11, a discharge circuit breaker 13A included in a current interruption unit 30, a control unit, and a voltage sensor. The discharge circuit breaker 13A has a plurality of N-channel type MOSFETs 35A, a discharge interruption gate drive circuit 34A connected to the source terminal of each N-channel type MOSFET 35A, and a P-channel type MOSFET 36A provided between the discharge interruption gate drive circuit 34A and the gate terminal of each N-channel type MOSFET 35A. The control unit is connected to the discharge interruption gate drive circuit 34A and the gate terminal of each P-channel type MOSFET 36A. The voltage sensor measures the common-source voltage or common-drain voltage of the N-channel type MOSFET 35A.

Description

Technical Field

[0001] The technology disclosed in this specification relates to a power storage device.

Background Art

[0002] Conventionally, a power storage device including a power storage element, a current breaker connected between the positive electrode of the power storage element and an external terminal, a management unit, and a voltage sensor has been known (see, for example, Patent Document 1). Specifically, the battery pack described in Patent Document 1 includes a power storage element, a connection terminal for externally connecting the power storage element, a switch element provided in a current path through which a charging current and a discharging current flow to the power storage element between the power storage element and the connection terminal, a switch voltage detection unit that outputs a value corresponding to the potential difference between the input and output of the switch element, and a control unit.

[0003] The control unit described in the same document executes a switch-off process for giving an off command signal to the switch element while maintaining a state in which current is flowing through the current path, and a switch failure diagnosis process for diagnosing a failure when the value output from the switch voltage detection unit is smaller than a first reference value when an off command signal is given to the switch element by the switch-off process.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In some cases, to reduce costs and simplify wiring, a current circuit breaker is constructed using multiple semiconductor switches connected in parallel, with common gate wiring for these switches. In such a current circuit breaker, if some of the semiconductor switches experience an open fault, it becomes difficult to detect the open fault, and current concentrates on the healthy semiconductor switches, causing them to overheat. Furthermore, because the gate wiring is common, it is not possible to individually switch off the semiconductor switches to diagnose a closed fault, and if the parallel-connected semiconductor switches are switched off simultaneously, the power supply to the load will be interrupted. One aspect of the present invention provides a switch fault diagnosis technique for an energy storage device equipped with a current circuit breaker composed of a plurality of semiconductor switches connected in parallel. [Means for solving the problem]

[0006] The energy storage device of this disclosure comprises an energy storage element having a positive electrode, an external terminal, a current circuit breaker provided in the current path between the positive electrode and the external terminal, a control unit, and a voltage sensor, wherein the current circuit breaker has a plurality of N-channel MOSFETs connected in parallel, a gate drive circuit connected to the source terminal of each N-channel MOSFET, and a P-channel MOSFET provided between the gate drive circuit and the gate terminal of each N-channel MOSFET, the control unit is connected to the gate drive circuit and is also individually connected to the gate terminal of each P-channel MOSFET, and the voltage sensor measures the common-source voltage or common-drain voltage of the plurality of N-channel MOSFETs connected in parallel. [Effects of the Invention]

[0007] The above configuration provides a switch fault diagnosis technique for an energy storage device equipped with a current circuit breaker composed of multiple semiconductor switches connected in parallel. [Brief explanation of the drawing]

[0008] [Figure 1] Block diagram of the energy storage device according to Embodiment 1 [Figure 2] Block diagram of the current interruption unit. [Figure 3] Schematic diagram illustrating the open fault diagnosis process for a discharge circuit breaker (normal operation). [Figure 4] Schematic diagram illustrating the open fault diagnosis process for a discharge circuit breaker (in the case of an open fault). [Figure 5] Schematic diagram illustrating the open fault diagnosis process for a charge circuit breaker (normal operation). [Figure 6] Schematic diagram illustrating the open fault diagnosis process for a charge circuit breaker (in the case of an open fault). [Figure 7] Flowchart for open fault diagnosis process [Figure 8] Schematic diagram illustrating the closed fault diagnosis process (normal operation) [Figure 9] Schematic diagram illustrating the closed fault diagnosis process (in the case of a closed fault) [Figure 10] Schematic diagram illustrating the closed fault diagnosis process (in the case of a closed fault) [Figure 11] Flowchart for closed fault diagnosis process [Figure 12] Block diagram of the energy storage device related to the comparative example. [Modes for carrying out the invention]

[0009] [Summary of the Embodiment] An overview of the embodiments of this disclosure will be described below.

[0010] (1) The energy storage device according to the embodiment comprises an energy storage element having a positive electrode, an external terminal, a current circuit breaker provided in the current path between the positive electrode and the external terminal, a control unit, and a voltage sensor, wherein the current circuit breaker has a plurality of N-channel type MOSFETs connected in parallel, a gate drive circuit connected to the source terminal of each N-channel type MOSFET, and a P-channel type MOSFET provided between the gate drive circuit and the gate terminal of each N-channel type MOSFET, the control unit is connected to the gate drive circuit and is also individually connected to the gate terminal of each P-channel type MOSFET, and the voltage sensor measures the common-source voltage or common-drain voltage of the plurality of N-channel type MOSFETs connected in parallel.

[0011] Here, "multiple N-channel MOSFETs connected in parallel" may each have a pair of N-channel MOSFETs connected back-to-back. The "gate drive circuit" may have a gate drive circuit for discharge interruption and a gate drive circuit for charge interruption.

[0012] First, with reference to Figure 12, the energy storage device 100 relating to the comparative example will be described. The energy storage device 100 shown in Figure 12 includes an energy storage element 101, a current circuit breaker 102 that interrupts the discharge current of the energy storage element 101, a control unit (not shown), and a voltage sensor (not shown). The current circuit breaker 102 is a discharge circuit breaker that interrupts the discharge current of the energy storage element 101, and comprises a plurality of N-channel MOSFETs 103 connected in parallel, the drain terminal D of which is connected to the positive electrode of the energy storage element 101 and the source terminal S of which is connected to the positive electrode external terminal 104, and a gate drive circuit 105 which is connected to the source terminal S of each N-channel MOSFET 103 and also to the gate terminal G of each N-channel MOSFET 103. The control unit is connected to the gate drive circuit 105. The voltage sensor measures the common source voltage (for example, the voltage at point P106) applied to the source terminal S of each N-channel MOSFET 103.

[0013] The N-channel MOSFET 103 may have an open fault (in other words, a fault that remains in the open state) that does not turn into a closed state. Therefore, conventionally, the open fault of the N-channel MOSFET 103 has been diagnosed. However, the inventor of the present application has found that in the case of the current breaker 102 according to the comparative example, it is impossible to determine whether all the N-channel MOSFETs 103 are normal or whether an open fault has occurred in any of the N-channel MOSFETs 103.

[0014] Specifically, in the case of the current breaker 102 according to the comparative example, when diagnosing the open fault of the N-channel MOSFET 103, a close signal is output to the gate terminal G of each N-channel MOSFET 103 from the gate drive circuit 105 at once, and the common source voltage applied to the source terminal S of each N-channel MOSFET 103 is measured. If all the N-channel MOSFETs 103 are normal, all the N-channel MOSFETs 103 will be in the closed state, so the measured voltage will be greater than 0V (volt). However, even when an open fault has occurred in any of the N-channel MOSFETs 103 and no open fault has occurred in the other N-channel MOSFETs 103, the voltage will also be greater than 0V. Therefore, it is impossible to determine whether all the N-channel MOSFETs 103 are normal or whether an open fault has occurred in any of the N-channel MOSFETs 103. This results in a latent fault, which is disadvantageous in terms of functional safety.

[0015] According to the energy storage device described in (1) above, a P-channel MOSFET is connected between the gate drive circuit and the gate terminals of each N-channel MOSFET, and the management unit is individually connected to the gate terminals of each P-channel MOSFET. Therefore, even if a close signal is output from the gate drive circuit to each N-channel MOSFET simultaneously, by outputting the close signal only to the P-channel MOSFET connected to one N-channel MOSFET to be diagnosed by the management unit, as a result, the close signal can be output only to one N-channel MOSFET to be diagnosed. This makes it possible to diagnose open faults individually for each N-channel MOSFET, improving functional safety.

[0016] By the way, as a method of outputting a close signal only to one N-channel MOSFET to be diagnosed, a method of providing a gate drive circuit for each N-channel MOSFET and outputting a close signal only from the gate drive circuit connected to the N-channel MOSFET to be diagnosed can also be considered. For example, in the case of the current breaker 102 according to the comparative example, since one gate drive circuit 105 is originally provided, if the number of N-channel MOSFETs 103 is n, then n - 1 gate drive circuits will be added.

[0017] However, generally, the gate drive circuit is large and expensive, so the cost and footprint (the area required for installing components) increase. The inventor of the present application, who has studied this, has found that adding n P-channel MOSFETs can suppress the increase in cost and footprint more than adding n - 1 gate drive circuits. Specifically, since the P-channel MOSFET can be put into a closed state by stepping down the voltage applied to the gate terminal (gate voltage) with respect to the voltage applied to the source terminal (source voltage), a gate drive circuit is not required. The P-channel MOSFET is smaller and cheaper than the gate drive circuit, so adding n P-channel MOSFETs can suppress the increase in cost and footprint.

[0018] Therefore, according to the energy storage device described in (1) above, it is possible to provide a switch fault diagnosis technology for an energy storage device equipped with a current circuit breaker composed of multiple semiconductor switches connected in parallel.

[0019] (2) In the energy storage device described in (1) above, the control unit may perform a first diagnostic process for diagnosing an open fault in which the N-channel MOSFET does not enter a closed state, instructing the gate drive circuit to output a close signal, and outputting a close signal to the gate terminal of the P-channel MOSFET connected to any one of the N-channel MOSFETs to be diagnosed, while not outputting a close signal to the gate terminal of the other P-channel MOSFETs, and in that state, diagnosing an open fault based on the common source voltage or common drain voltage measured by the voltage sensor.

[0020] According to the energy storage device described in (2) above, in an energy storage device equipped with a current circuit breaker in which multiple N-channel MOSFETs are connected in parallel, open faults in each N-channel MOSFET can be diagnosed individually while suppressing increases in cost and footprint.

[0021] (3) The energy storage device described in (2) above comprises two current circuit breakers connected in series and a bypass current circuit breaker provided in a bypass path connected in parallel with the two current circuit breakers, wherein one of the current circuit breakers is a discharge circuit breaker in which the forward direction of the parasitic diode of each N-channel MOSFET is the charging direction of the energy storage element, and the other current circuit breaker is a charge circuit breaker in which the forward direction of the parasitic diode of each N-channel MOSFET is the discharge direction of the energy storage element, and the discharge circuit breaker and the charge circuit breaker may be back-to-back connected by connecting the source terminal of each N-channel MOSFET of the discharge circuit breaker to the source terminal of each N-channel MOSFET of the charge circuit breaker.

[0022] According to the energy storage device described in (3) above, the discharge circuit breaker and the charge circuit breaker are connected back-to-back. Therefore, when the discharge circuit breaker is opened, the discharge current is interrupted, but the charge current is not. In other words, the discharge current can be interrupted while maintaining a state in which the energy storage device can be charged. Conversely, when the charge circuit breaker is opened, the charge current is interrupted, but the discharge current is not. In other words, the charge current can be interrupted while maintaining a state in which power can be supplied to external devices.

[0023] Incidentally, when diagnosing a failure in an N-channel MOSFET, there is a possibility that all N-channel MOSFETs may become open. When all N-channel MOSFETs become open, a power fail occurs, which means that power is no longer supplied to external devices. For example, in the case of an energy storage device installed in a vehicle, a power fail could impair the safe operation of the vehicle, so countermeasures against power fails are required.

[0024] According to the energy storage device described in (3) above, a bypass current circuit breaker is provided in the bypass path connected in parallel with the two current circuit breakers (discharge circuit breaker and charge circuit breaker). Therefore, if there is a possibility of power failure occurring when diagnosing a fault, the occurrence of power failure can be suppressed by closing the bypass current circuit breaker and performing the diagnosis.

[0025] (4) In the energy storage device described in (3) above, when the control unit performs the first diagnostic process on the discharge circuit breaker, it may perform the process with the charge circuit breaker in an open state and the bypass current circuit breaker in a closed state.

[0026] In the case of a discharge circuit breaker, when the first diagnostic process is performed, if an open fault occurs in the N-channel MOSFET being diagnosed, all N-channel MOSFETs in the discharge circuit breaker will be in an open state. According to the energy storage device described in (4) above, when the first diagnostic process is performed on the discharge circuit breaker, the bypass current circuit breaker is closed, so that even if all N-channel MOSFETs of the discharge circuit breaker become open, power supply is maintained through the bypass path. This suppresses the occurrence of power failures.

[0027] However, if the charge circuit breaker is in a closed state, even if all N-channel MOSFETs in the discharge circuit breaker become open, the rated voltage of the energy storage element will be applied to the source terminals of the N-channel MOSFETs in the discharge circuit breaker via the bypass path and the charge circuit breaker. Therefore, even if an open fault occurs, it will be mistakenly judged as not having occurred.

[0028] According to the energy storage device described in (4) above, when the first diagnostic process is performed on the discharge circuit breaker, the charge circuit breaker is opened. If all N-channel MOSFETs of the discharge circuit breaker are open, the common-source voltage will be 0 volts (or close to it), and it can be determined that an open fault has occurred. Conversely, if the common-source voltage is the rated voltage (or close to it), it means that there is no voltage applied through the bypass path and the charge circuit breaker, and therefore the voltage is applied through the N-channel MOSFETs of the discharge circuit breaker, and it can be determined that no open fault has occurred.

[0029] (5) In the energy storage device described in (3) above, when the control unit performs the first diagnostic process with respect to the charging circuit breaker, it may perform the process with the discharge circuit breaker in a closed state and the bypass current circuit breaker in an open state.

[0030] In the first diagnostic process for the charge circuit breaker, the common drain voltage of the N-channel MOSFET of the charge circuit breaker is measured. If the bypass current breaker is closed, the rated voltage will always be applied to the drain terminal of the N-channel MOSFET of the charge circuit breaker via the bypass current breaker, making it impossible to determine an open fault.

[0031] In contrast, if the bypass current circuit breaker is left open, the rated voltage will not be applied to the drain terminal of the charging circuit breaker via the bypass current circuit breaker. Therefore, if the common source voltage is the rated voltage, the voltage is applied through the N-channel MOSFET of the charging circuit breaker, and it can be determined that no open fault has occurred. Even if an open fault has occurred, the common drain voltage will not be 0V because a voltage is applied to the drain terminal via the parasitic diode, but the common source voltage will be lower than the rated voltage due to the voltage division by the parasitic diode. Therefore, if the common source voltage is lower than the rated voltage, it can be determined that an open fault has occurred.

[0032] In the first diagnostic process for the charge circuit breaker, the bypass path is opened. However, since the forward direction of the parasitic diode in the charge circuit breaker is the discharge direction, power supply is maintained via the parasitic diode even if all N-channel MOSFETs in the charge circuit breaker are open. Therefore, power failure can be suppressed even when the bypass path is opened.

[0033] (6) In the energy storage device described in any one of (3) to (5) above, the control unit may perform a second diagnostic process for diagnosing a closed fault in which the N-channel MOSFET does not become open, wherein the bypass current circuit breaker is closed, the output of a closed signal from the gate drive circuit to each of the N-channel MOSFETs is stopped, and the closed fault is diagnosed based on the common source voltage measured by the voltage sensor in that state.

[0034] When diagnosing a closed fault in which an N-channel MOSFET does not become open, the output of the closed signal to all N-channel MOSFETs is stopped. If the output of the closed signal is stopped, and no closed fault has occurred in any of the N-channel MOSFETs, then all N-channel MOSFETs will become open, and the voltage between the two current breakers (i.e., the common-source voltage) will become 0V. Therefore, if the common-source voltage is 0V, it can be determined that no closed fault has occurred in any of the N-channel MOSFETs.

[0035] However, if all N-channel MOSFETs in the discharge circuit breaker become open, a power fail will occur, resulting in a loss of power supply to external devices. According to the energy storage device described in (6) above, by first closing the bypass current circuit breaker before performing the diagnosis, power supply to external devices is maintained via the bypass path even if all N-channel MOSFETs in the discharge circuit breaker become open. This suppresses the occurrence of power failures during diagnosis.

[0036] (7) In the energy storage device described in any one of (3) to (6) above, the bypass current circuit breaker may be two P-channel MOSFETs connected back-to-back.

[0037] While mechanical relays can be used as bypass current circuit breakers, P-channel MOSFETs are smaller, quieter, and offer superior responsiveness (controllability) compared to mechanical relays. However, because P-channel MOSFETs have parasitic diodes (so-called body diodes), if only one P-channel MOSFET is used, there is a risk that discharge or charge current may unintentionally flow to the energy storage element due to the parasitic diode even when the circuit is open.

[0038] According to the energy storage device described in (7) above, the two P-channel MOSFETs are connected back-to-back, which suppresses the unintended flow of discharge current and charge current when the bypass current circuit breaker is open. While it is possible to use N-channel MOSFETs instead of P-channel MOSFETs, this requires the addition of a gate drive circuit that outputs a closed signal to them. Since P-channel MOSFETs do not require a gate drive circuit, the cost and footprint increase can be kept down compared to using N-channel MOSFETs.

[0039] [Details of the embodiment] Details of embodiments of this disclosure are described below. This disclosure is not limited to these examples and is intended to include all modifications within the meaning and scope equivalent to the claims, as indicated by the claims. Embodiments of the present disclosure can be implemented in various forms, such as apparatus, methods, computer programs for realizing the functions of such apparatus or methods, and recording media on which such computer programs are stored.

[0040] <Embodiment 1> Embodiment 1 will be described with reference to Figures 1 to 11. In the following description, reference numerals in the drawings may be omitted for identical components, with some exceptions.

[0041] [1] Electrical configuration of the energy storage device Referring to Figure 1, the electrical configuration of the energy storage device 1 according to Embodiment 1 will be described. The energy storage device 1 is an on-board energy storage device that is mounted on a vehicle such as a four-wheeled automobile or a motorcycle and supplies power to a vehicle load 2 (see Figure 2). Four-wheeled automobiles include gasoline automobiles, electric automobiles, hybrid automobiles, plug-in hybrid automobiles, etc. The vehicle load 2 is an example of an external device.

[0042] The energy storage device 1 includes a battery pack 10, a positive external terminal 11 (an example of an external terminal), a negative external terminal 12, a current interruption unit 30, a BMU 14 (Battery Management Unit), a current sensor 15, a voltage sensor 16, and a communication connector 17. The BMU 14 is an example of a management unit.

[0043] The battery pack 10 has multiple energy storage elements 10A. In the battery pack 10 according to Embodiment 1, 12 energy storage elements 10A are connected in 3 parallel and 4 series. In Figure 1, the three energy storage elements 10A connected in parallel are shown as a single battery symbol. The energy storage elements 10A are rechargeable secondary batteries, specifically lithium-ion secondary batteries. The battery pack 10 according to Embodiment 1 is assumed to have a rating of 12V.

[0044] The current interruption unit 30 is provided in the current path 22 between the positive electrode of the energy storage element 10A and the positive electrode external terminal 11. The current interruption unit 30 will be described later. The BMU14 includes a microcomputer 18 with a CPU and RAM integrated into a single chip, a memory unit 19, a communication unit 20, and other components. The memory unit 19 stores various programs and data executed by the microcomputer 18. The microcomputer 18 controls the various parts of the energy storage device 1 by executing the programs stored in the memory unit 19. The communication unit 20 is a communication circuit for the BMU14 to communicate with the vehicle's ECU (Electronic Control Unit).

[0045] The current sensor 15 measures the charging current and discharging current of the battery pack 10 and outputs them to the BMU 14. The voltage sensor 16 measures the voltage of each energy storage element 10A and outputs it to the BMU 14. As will be described in more detail later, the voltage sensor 16 also measures the common source voltage of the discharge circuit breaker 13A (see Figure 2) and the common drain voltage of the charge circuit breaker 13B (see Figure 2). The communication connector 17 is a connector to which a communication cable is connected for the BMU 14 to communicate with the vehicle's ECU.

[0046] [2] Current interruption section As shown in Figure 2, the current interruption unit 30 comprises two current circuit breakers 13 (discharge circuit breaker 13A and charge circuit breaker 13B) connected in series, a bypass path 50 connected in parallel with the two current circuit breakers 13, and a bypass current circuit breaker 33 provided in the bypass path 50.

[0047] The discharge circuit breaker 13A comprises one gate drive circuit 34A (hereinafter referred to as the discharge circuit breaker gate drive circuit 34A), three (an example of multiple) N-channel MOSFETs 35A connected in parallel, and three P-channel MOSFETs 36A.

[0048] The discharge-cutting gate drive circuit 34A is connected to the source terminal S of each N-channel MOSFET 35A via the power line 39, and also to the gate terminal G of each N-channel MOSFET 35A via the common signal line 40 and branch line 41. The discharge-cutting gate drive circuit 34A is also connected to the BMU 14 via signal lines (not shown).

[0049] The drain terminal D of each of the three N-channel MOSFETs 35A is connected to the positive terminal of the energy storage element 10A. The source terminal S of each N-channel MOSFET 35A is connected to the discharge interruption gate drive circuit 34A via the power line 39 and also to the positive external terminal 11 via the charge circuit breaker 13B. Each N-channel MOSFET 35A has a parasitic diode 38. The cathode of the parasitic diode 38 is connected to the energy storage element 10A, and the anode is connected to the positive external terminal 11 via the charge circuit breaker 13B. In other words, the forward direction of the parasitic diode 38 of the N-channel MOSFET 35A is the direction that charges the energy storage element 10A (charging direction).

[0050] Each P-channel MOSFET 36A is located between the discharge-cutting gate drive circuit 34A and the gate terminal G of each N-channel MOSFET 35A. Specifically, each P-channel MOSFET 36A is located on a branch line 41 that branches off from a common signal line 40 connected to the discharge-cutting gate drive circuit 34A and is connected to the gate terminal G of each N-channel MOSFET 35A. Each P-channel MOSFET 36A has its drain terminal D connected to the discharge-cutting gate drive circuit 34A and its source terminal S connected to the gate terminal G of the N-channel MOSFET 35A.

[0051] The charge circuit breaker 13B is located between the discharge circuit breaker 13A and the positive external terminal 11. The charge circuit breaker 13B comprises one gate drive circuit 34B (hereinafter referred to as the charge circuit breaker gate drive circuit 34B), three N-channel MOSFETs 35B connected in parallel, and three P-channel MOSFETs 36B.

[0052] The charge interruption gate drive circuit 34B is connected to the source terminal S of each N-channel MOSFET 35B via the power line 39, and is also connected to the gate terminal G of each N-channel MOSFET 35A via a common signal line 42 and branch line 43. The charge interruption gate drive circuit 34B is also connected to the BMU 14 via a signal line (not shown).

[0053] The drain terminal D of each of the three N-channel MOSFETs 35B is connected to the positive external terminal 11. The source terminal S of each N-channel MOSFET 35B is connected to the charge interruption gate drive circuit 34B via the power line 39, and is also connected to the positive terminal of the energy storage element 10A via the discharge circuit breaker 13A. Each N-channel MOSFET 35B has a parasitic diode 38. The anode of the parasitic diode 38 is connected to the energy storage element 10A via the discharge circuit breaker 13A, and the cathode is connected to the positive external terminal 11. That is, the forward direction of the parasitic diode 38 of the N-channel MOSFET 35B is the direction that discharges the energy storage element 10A (discharge direction).

[0054] The P-channel MOSFET 36B is located between the charge interruption gate drive circuit 34B and the gate terminal G of each N-channel MOSFET 35B. Specifically, each P-channel MOSFET 36B is located on a branch line 43 that branches off from a common signal line 42 connected to the charge interruption gate drive circuit 34B and is connected to the gate terminal G of each N-channel MOSFET 35B. Each P-channel MOSFET 36B has its drain terminal D connected to the charge interruption gate drive circuit 34B and its source terminal S connected to the gate terminal G of the N-channel MOSFET 35B.

[0055] The P-channel MOSFET 36A may have its source terminal S connected to the gate drive circuit 34A and its drain terminal D connected to the gate terminal G of the N-channel MOSFET 35A. Similarly, the P-channel MOSFET 36B may have its source terminal S connected to the gate drive circuit 34B and its drain terminal D connected to the gate terminal G of the N-channel MOSFET 35B.

[0056] The discharge circuit breaker 13A and the charge circuit breaker 13B are connected back-to-back by connecting the source terminal S of the N-channel MOSFET 35A to the source terminal S of the N-channel MOSFET 35B. When the discharge current is interrupted, all three N-channel MOSFET 35B of the charge circuit breaker 13B are closed, and all three N-channel MOSFET 35A of the discharge circuit breaker 13A are opened. In this way, the discharge current is interrupted, but the charge current is not.

[0057] When interrupting the charging current, the opposite occurs: all three N-channel MOSFETs 35A of the discharge circuit breaker 13A are closed, and all three N-channel MOSFETs 35B of the charging circuit breaker 13B are open. In this way, the charging current is interrupted, but the discharge current is not.

[0058] In the following explanation, when the gate drive circuit 34A for discharge interruption and the gate drive circuit 34B for charge interruption are not distinguished, they will simply be referred to as gate drive circuit 34. Similarly, when the N-channel MOSFET 35A and N-channel MOSFET 35B are not distinguished, they will simply be referred to as N-channel MOSFET 35, and when the P-channel MOSFET 36A and P-channel MOSFET 36B are not distinguished, they will simply be referred to as P-channel MOSFET 36.

[0059] The N-channel MOSFET 35 and P-channel MOSFET 36 are normally off; they become closed (on) when a close signal is input to the gate terminal G, and open (off) when the input of the close signal stops. The P-channel MOSFET 46, which will be described later, behaves similarly.

[0060] The BMU14 is connected to the discharge interruption gate drive circuit 34A and the charge interruption gate drive circuit 34B via separate signal lines, and is also connected to the gate terminal G of each P-channel type MOSFET 36A and 36B via separate signal lines.

[0061] In the following explanation, the common voltage across the source terminal S of each N-channel MOSFET 35A of the discharge circuit breaker 13A (for example, the voltage at point P1 shown in Figure 2) will be referred to as the common source voltage, and the common voltage across the drain terminal D of each N-channel MOSFET 35B of the charge circuit breaker 13B (for example, the voltage at point P2 shown in Figure 2) will be referred to as the common drain voltage. As mentioned above, the voltage sensor 16 also measures the common source voltage and the common drain voltage.

[0062] The bypass current circuit breaker 33 is provided to suppress the interruption of the discharge current during open fault diagnosis processing and closed fault diagnosis processing, which will be described later. The bypass current circuit breaker 33 according to Embodiment 1 is equipped with two P-channel type MOSFETs 46. The two P-channel type MOSFETs 46 are connected back-to-back by connecting their source terminals S to each other. The BMU14 is connected to the gate terminals G of the two P-channel MOSFETs 46 via a common signal line. The BMU14 may also be connected to the two P-channel MOSFETs 46 via separate signal lines.

[0063] [3] Fault diagnosis of N-channel MOSFETs The BMU14 performs two types of fault diagnosis processes: an open fault diagnosis process (an example of the first diagnostic process) to diagnose an open fault (in other words, a fault that remains in an open state) in which the N-channel MOSFET 35 does not enter a closed state, and a closed fault diagnosis process (an example of the second diagnostic process) to diagnose a closed fault (in other words, a fault that remains in a closed state) in which the N-channel MOSFET 35 does not enter an open state. The following describes each fault diagnosis process.

[0064] [3-1] Open fault diagnosis process Open fault diagnosis processing is performed for both the discharge circuit breaker 13A and the charge circuit breaker 13B. The open fault diagnosis processing for the discharge circuit breaker 13A and the open fault diagnosis processing for the charge circuit breaker 13B are described below.

[0065] [3-1-1] Open fault diagnosis process for discharge circuit breakers The open fault diagnosis process for the discharge circuit breaker 13A is performed with the bypass current circuit breaker 33 in a closed state and the charge circuit breaker 13B in an open state. The reason for this will be explained later. The open fault diagnosis process for the discharge circuit breaker 13A is performed individually for each N-channel MOSFET 35A. The BMU 14 selects one N-channel MOSFET 35A as the target for diagnosis and outputs a close signal to the gate terminal G of the P-channel MOSFET 36A connected to the selected N-channel MOSFET 35A. At this time, the BMU 14 does not output a close signal to the other P-channel MOSFET 36A. Therefore, the P-channel MOSFET 36A connected to the N-channel MOSFET 35A that was not selected as the target for diagnosis will be in an open state.

[0066] The BMU14 then instructs the discharge-cutting gate drive circuit 34A to output a close signal. The discharge-cutting gate drive circuit 34A, instructed to output a close signal, simultaneously outputs a close signal to the gate terminal G of each N-channel MOSFET 35A. However, since the P-channel MOSFET 36A connected to the N-channel MOSFET 35A that is not selected as the diagnostic target is in an open state, as a result, the close signal is output only to the gate terminal G of the N-channel MOSFET 35A that is selected as the diagnostic target. Then, the BMU14 diagnoses an open fault based on the common-source voltage measured by the voltage sensor 16 in that state. This will be explained in detail below.

[0067] Figure 3 shows an example where the N-channel MOSFET 35A selected for diagnosis is functioning normally. In Figure 3, the three N-channel MOSFETs 35A in the discharge circuit breaker 13A are labeled 35A_1, 35A_2, and 35A_3 to distinguish them. Similarly, the three N-channel MOSFETs 35B are labeled 35B_1, 35B_2, and 35B_3. For ease of understanding, Figure 3 omits the P-channel MOSFET 36, bypass path 50, and bypass current circuit breaker 33 for each current circuit breaker 13.

[0068] This explanation assumes that N-channel MOSFET 35A_1 is selected as the diagnostic target, and that no closed-loop faults have occurred in the other N-channel MOSFETs, 35A_2 and 35A_3. In other words, it assumes that the other N-channel MOSFETs, 35A_2 and 35A_3, are in an open-loop state.

[0069] In the open fault diagnosis of N-channel MOSFET 35A_1, a closed signal is output only to N-channel MOSFET 35A_1 among the three N-channel MOSFETs 35A of the discharge circuit breaker 13A. If an open fault does not occur in N-channel MOSFET 35A_1, then N-channel MOSFET 35A_1 will be in a closed state, and the common-source voltage will be 12V. In other words, the common-source voltage will be greater than 0V. In this case, of the three N-channel MOSFETs 35A in the discharge circuit breaker 13A, only N-channel MOSFET 35A_1 is in a closed state, so it is determined that N-channel MOSFET 35A_1 does not have an open fault.

[0070] Figure 4 shows an example of an open fault occurring in the N-channel MOSFET 35A_1. When an open fault occurs in the N-channel MOSFET 35A_1, it cannot enter a closed state, so the common-source voltage becomes 0V (or a voltage close to 0V). In the following explanation, voltages close to 0V will also be referred to as 0V. When the common-source voltage is 0V, it is determined that an open fault has occurred in the N-channel MOSFET 35A_1.

[0071] The reason for closing the bypass current circuit breaker 33 and opening the charge circuit breaker 13B will be explained. The reason for closing the bypass current circuit breaker 33 is that if an open fault occurs in the N-channel MOSFET 35A selected as the diagnostic target, all N-channel MOSFETs 35A in the discharge circuit breaker 13A will become open, resulting in a power fail where power is not supplied to the vehicle load 2. By keeping the bypass current circuit breaker 33 closed, even if all N-channel MOSFETs 35A in the discharge circuit breaker 13A become open, power supply to the vehicle load 2 is maintained via the bypass path 50, thus suppressing the occurrence of a power fail.

[0072] The reason for opening the charge circuit breaker 13B is that it closes the bypass current circuit breaker 33. If the bypass current circuit breaker 33 is closed, and assuming the charge circuit breaker 13B is also closed, even if an open fault occurs in the N-channel MOSFET 35A selected as the diagnostic target and all N-channel MOSFETs 35A of the discharge circuit breaker 13A are open, voltage will still be applied to point P1 via the bypass current circuit breaker 33 and the charge circuit breaker 13B. As a result, the voltage at point P1 becomes 12V, leading to the incorrect conclusion that no open fault has occurred.

[0073] In contrast, the forward direction of the parasitic diode 38 of the charge circuit breaker 13B is the discharge direction, so if the charge circuit breaker 13B is left open, no voltage is applied to point P1 via the bypass current circuit breaker 33 and the charge circuit breaker 13B. For this reason, if an open fault occurs, the voltage at point P1 will be 0V, and it can be correctly determined that an open fault has occurred. If no open fault occurs, the voltage at point P1 will be 12V, but since no voltage is applied to point P1 via the charge circuit breaker 13B, the voltage is applied via the discharge circuit breaker 13A, and it can be correctly determined that no open fault has occurred.

[0074] [3-1-2] Open fault diagnosis procedure for charge circuit breakers The open fault diagnosis process for the charging circuit breaker 13B is performed with the discharge circuit breaker 13A in the closed state and the bypass current circuit breaker 33 in the open state. The reason for opening the bypass current circuit breaker 33 will be explained later.

[0075] Figure 5 shows an example where the N-channel MOSFET 35B selected for diagnosis is functioning normally. Here, we assume that N-channel MOSFET 35B_1 is selected for diagnosis, and that no closed-loop faults have occurred in the other N-channel MOSFETs 35B_2 and 35B_3. In other words, we assume that the other N-channel MOSFETs 35B_2 and 35B_3 are in an open state.

[0076] In the open fault diagnosis of N-channel MOSFET 35B_1, a close signal is output only to N-channel MOSFET 35B_1 among the three N-channel MOSFETs 35B of the charge circuit breaker 13B. If an open fault does not occur in N-channel MOSFET 35B_1, it will be in a closed state and the common drain voltage will be 12V. If the common drain voltage is 12V, it is determined that no open fault has occurred in N-channel MOSFET 35B_1.

[0077] Figure 6 shows an example of an open fault occurring in the N-channel MOSFET 35B_1. When an open fault occurs in the N-channel MOSFET 35B_1, it does not enter a closed state, but the parasitic diode 38 prevents the common drain voltage from becoming 0V. However, due to the voltage division by the parasitic diode 38, the common drain voltage will be lower than 12V. Figure 6 shows the case where the common drain voltage is 11.4V. Therefore, if the common drain voltage is less than 12V, it is determined that an open fault has occurred in the N-channel MOSFET 35B_1.

[0078] Let me explain why the bypass current circuit breaker 33 is left open. As mentioned earlier, in the open fault diagnosis process for the charge circuit breaker 13B, the common drain voltage at point P2 is measured. If the bypass current circuit breaker 33 were closed, a voltage of 12V would be applied to point P2 via the bypass current circuit breaker 33, making it impossible to determine whether or not an open fault has occurred.

[0079] In contrast, if the bypass circuit breaker 33 is left open, a voltage of 12V will not be applied to point P2 via the bypass circuit breaker 33. Therefore, if an open fault occurs, the voltage at point P2 will be lower than 12V, and it can be determined that an open fault has occurred. As described above, the open fault diagnosis process for the charging circuit breaker 13B opens the bypass current circuit breaker 33, but this does not cause a power failure. This is because the forward direction of the parasitic diode 38 of the charging circuit breaker 13B is the discharge direction, so even if all N-channel MOSFETs 35B of the charging circuit breaker 13B are open, power supply to the vehicle load 2 is maintained via the parasitic diode 38.

[0080] [3-1-3] Flowchart of Open Fault Diagnosis Process Referring to Figure 7, the flow of the open fault diagnosis process performed by the BMU14 will be explained. Here, the open fault diagnosis process for the discharge circuit breaker 13A will be used as an example.

[0081] In S101, the BMU14 closes the bypass current circuit breaker 33 and opens the charge circuit breaker 13B. In S102, the BMU14 selects one N-channel MOSFET 35A to be diagnosed. If the S102 process is being performed for the second time or later, the BMU14 will select an N-channel MOSFET 35A that has not yet been selected. In S103, the BMU14 outputs a close signal to the P-channel MOSFET 36A connected to the N-channel MOSFET 35A, which has been selected as the diagnostic target.

[0082] In S104, the BMU14 instructs the discharge interruption gate drive circuit 34A to output a close signal. In S105, the BMU14 measures the common-source voltage using the voltage sensor 16. In S106, the BMU14 determines whether the measured common-source voltage is greater than 0V. If it is greater than 0V, the process proceeds to S107; otherwise, it proceeds to S108.

[0083] In S107, the BMU14 determines that no open fault has occurred in the N-channel MOSFET 35A selected as the diagnostic target. In S108, the BMU14 determines that an open fault has occurred in the N-channel MOSFET 35A, which was selected as the target for diagnosis. In S109, the BMU14 determines whether all N-channel MOSFETs 35A of the discharge circuit breaker 13A have been selected. If all N-channel MOSFETs 35A have been selected, the process ends. If there are still N-channel MOSFETs 35A that have not been selected, the process returns to S102 and is repeated.

[0084] [3-2] Closed fault diagnosis process Referring to Figure 2, the closed fault diagnosis process will be explained. As mentioned above, the closed fault diagnosis process is a process that diagnoses closed faults in which the N-channel MOSFET 35 does not become open. In the closed fault diagnosis process, the BMU 14 stops the output of the closed signal from the discharge interruption gate drive circuit 34A to each N-channel MOSFET 35A, and also stops the output of the closed signal from the charge interruption gate drive circuit 34B to each N-channel MOSFET 35B. In this state, it diagnoses a closed fault based on the voltage between the two current circuit breakers 13 (i.e., common source voltage) measured by the voltage sensor 16.

[0085] Figure 8 shows an example where no closed-loop failures have occurred in any of the N-channel MOSFETs 35. For ease of understanding, the P-channel MOSFETs 36 of each current circuit breaker 13 are omitted in Figure 8. If no closed fault has occurred in any of the N-channel MOSFETs 35, stopping the output of the closed signal to each N-channel MOSFET 35 will cause all N-channel MOSFETs 35 to become open. In this case, since the discharge circuit breaker 13A and the charge circuit breaker 13B are connected back-to-back, no voltage is applied to point P1 via the parasitic diode 38, and the common-source voltage becomes 0V. Therefore, if the common-source voltage is 0V, it is determined that no closed fault has occurred in any of the N-channel MOSFETs 35.

[0086] Figure 9 shows an example where a closed fault occurs in the N-channel MOSFET 35A_1 of the discharge circuit breaker 13A. When a closed fault occurs in the N-channel MOSFET 35A_1, the common-source voltage becomes 12V. Therefore, if the common-source voltage is 12V, it is determined that a closed fault has occurred in one of the N-channel MOSFETs 35.

[0087] Incidentally, if all N-channel MOSFETs 35 of the discharge circuit breaker 13A become open, a power fail occurs as the discharge current is interrupted, resulting in no power being supplied to the vehicle load 2. For this reason, when the BMU 14 performs a closed fault diagnosis process, it first outputs a closed signal to the two P-channel MOSFETs 46 of the bypass current circuit breaker 33 to close the bypass current circuit breaker 33. In this way, even if all N-channel MOSFETs 35A of the discharge circuit breaker 13A become open, power supply to the vehicle load 2 is maintained via the bypass path 50, thus suppressing the occurrence of a power fail.

[0088] However, when power is supplied via the bypass route 50, the current supply performance is reduced compared to when power is supplied via the charging circuit breaker 13B. Nevertheless, if the closed fault diagnosis process is performed when no large current is flowing, such as when the vehicle is parked, the reduced current supply performance will not be a problem.

[0089] Figure 10 shows an example where a closed fault occurs in the N-channel MOSFET 35B_1 of the charge circuit breaker 13B. In the example shown in Figure 10, no closed faults occur in the three N-channel MOSFETs 35A of the discharge circuit breaker 13A, so they are all open. Therefore, no voltage is applied to point P1 via the discharge circuit breaker 13A. However, a voltage is applied to point P1 via the bypass path 50 and the N-channel MOSFET 35B_1 of the charge circuit breaker 13B, so the common-source voltage becomes greater than 0V. Therefore, when diagnosing a closed fault with the bypass path 50 closed, it can be determined that a closed fault has occurred even if a closed fault has occurred in the N-channel MOSFET 35B of the charge circuit breaker 13B.

[0090] Refer to Figure 11 to describe the flow of the closed fault diagnosis process performed by the BMU14.

[0091] In S201, the BMU14 closes the bypass current circuit breaker 33. In S202, the BMU14 instructs the discharge interruption gate drive circuit 34A and the charge interruption gate drive circuit 34B to stop outputting the close signal.

[0092] In S203, the BMU14 measures the common-source voltage. In S204, the BMU14 determines whether the measured common-source voltage is 0V or not. If it is 0V, proceed to S205; otherwise, proceed to S206.

[0093] In S205, BMU14 determines that no closed-loop failure has occurred in any of the N-channel MOSFETs 35. In S206, the BMU14 determines that a closed fault has occurred in one of the N-channel MOSFETs 35.

[0094] [4] Effects of the embodiment Referring to Figure 2, the effects of Embodiment 1 will be explained. Here, the discharge circuit breaker 13A will be used as an example. In the energy storage device 1 according to Embodiment 1, a P-channel MOSFET 36A is connected between the discharge circuit breaker gate drive circuit 34A and the gate terminal G of each N-channel MOSFET 35A, and the BMU 14 is individually connected to the gate terminal G of each P-channel MOSFET 36A. Therefore, even if a close signal is output simultaneously from the discharge circuit breaker gate drive circuit 34A to each N-channel MOSFET 35A, the BMU 14 outputs the close signal only to the P-channel MOSFET 36A connected to the one N-channel MOSFET 35A to be diagnosed, and as a result, the close signal can be output only to the one N-channel MOSFET 35A to be diagnosed. This makes it possible to individually diagnose open faults for each N-channel MOSFET 35A, improving functional safety.

[0095] The P-channel MOSFET 36A can be closed by stepping down the voltage applied to the gate terminal G (gate voltage) relative to the voltage applied to the source terminal S (source voltage), thus eliminating the need for a gate drive circuit. Since the P-channel MOSFET 36A is smaller and less expensive than a gate drive circuit, adding three P-channel MOSFET 36A units results in a lower cost and footprint increase than adding two discharge-cutting gate drive circuits 34A.

[0096] Therefore, the energy storage device 1 provides a switch fault diagnosis technology for an energy storage device 1 that includes a current circuit breaker 13 composed of multiple semiconductor switches (N-channel type MOSFET 35) connected in parallel. Although the explanation here uses the discharge circuit breaker 13A as an example, the same applies to the charge circuit breaker 13B.

[0097] In the energy storage device 1, the two current circuit breakers 13 (discharge circuit breaker 13 and charge circuit breaker 13B) are connected back-to-back. Therefore, when the discharge circuit breaker 13 is opened, the discharge current is interrupted, but the charge current is not. In other words, the discharge current can be interrupted while maintaining a state in which the energy storage device 1 can be charged. Conversely, when the charge circuit breaker 13B is opened, the charge current is interrupted, but the discharge current is not. In other words, the charge current can be interrupted while maintaining a state in which power can be supplied to the vehicle load 2.

[0098] According to the energy storage device 1, when performing an open fault diagnosis process for the discharge circuit breaker, the charge circuit breaker 13B is opened and the bypass current circuit breaker 33 is closed, so that an open fault can be diagnosed while suppressing the occurrence of power failures.

[0099] According to the energy storage device 1, when performing an open fault diagnosis process for the charging circuit breaker 13B, the discharge circuit breaker is closed and the bypass current circuit breaker 33 is opened, so that an open fault can be diagnosed while suppressing the occurrence of power failures.

[0100] According to the energy storage device 1, when performing a closed fault diagnosis process, the bypass current circuit breaker 33 is closed first before the diagnosis is performed. This ensures that even if all N-channel MOSFETs 35 become open, power supply to the vehicle load 2 is maintained via the bypass path 50. This suppresses the occurrence of power failures during diagnosis.

[0101] According to the energy storage device 1, the two P-channel type MOSFETs 46 of the bypass current circuit breaker 33 are connected back-to-back, which suppresses the unintended flow of discharge current and charging current when the bypass current circuit breaker 33 is open. While it is possible to use N-channel MOSFETs instead of P-channel MOSFETs, this requires the addition of a gate drive circuit that outputs a closed signal to them. Since P-channel MOSFETs do not require a gate drive circuit, the cost and footprint increase can be kept down compared to using N-channel MOSFETs.

[0102] <Other Embodiments> The technology disclosed herein is not limited to the embodiments described above in the description and drawings, and the following embodiments, for example, are also included in the technical scope disclosed herein.

[0103] (1) In the above embodiment, the example given was that the bypass current circuit breaker 33 is closed when diagnosing a closed fault, but the bypass current circuit breaker 33 may be closed even when diagnosing a closed fault. For example, when the vehicle is parked, no large current flows from the energy storage device 1 to the vehicle. When no large current flows, there is no problem with the current carrying performance of the P-channel type MOSFET 46. For this reason, when the vehicle is parked, the bypass current circuit breaker 33 is closed and all N-channel type MOSFETs 35 of the two current circuit breakers 13 (discharge circuit breaker 13A and charge circuit breaker 13B) are opened, so the gate drive circuit 34 can be stopped, and the power consumed by the gate drive circuit 34 can be suppressed.

[0104] However, there is a possibility that a large current may flow if the vehicle load 2 suddenly activates while power is being supplied via the bypass route 50. However, since the N-channel MOSFET 35 has the characteristic of being able to switch between open and closed states instantly compared to mechanical relays, if the current sensor 15 detects that the current has increased, the N-channel MOSFET 35 can be immediately closed to cope with sudden large currents.

[0105] (2) In the above embodiment, the example was given in which the energy storage device 1 is equipped with two current circuit breakers 13 (discharge circuit breaker 13A and charge circuit breaker 13B), but the energy storage device 1 may be equipped with only one of the current circuit breakers 13.

[0106] (3) In the above embodiment, the bypass current circuit breaker 33 is shown as being composed of two P-channel type MOSFETs 46, but it may also be composed of two N-channel type MOSFETs connected back-to-back and one gate drive circuit, or one P-channel type MOSFET, or one N-channel type MOSFET and one gate drive circuit. Alternatively, the bypass current circuit breaker 33 may be a mechanical relay.

[0107] (4) In the above embodiment, an in-vehicle energy storage device 1 was used as an example of an energy storage device, but the energy storage device is not limited to in-vehicle use. For example, the energy storage device may be used in a stationary energy storage system, as a backup power supply for electronic equipment, or for other purposes.

[0108] (5) In the above embodiment, the example shown is that the energy storage device 1 is equipped with a bypass path 50 and a bypass current circuit breaker 33, but the energy storage device 1 does not need to be equipped with a bypass path 50 and a bypass current circuit breaker 33. For example, in the case of an in-vehicle energy storage device 1, if the vehicle is equipped with another backup energy storage device, a power failure will not occur because power is supplied from the backup energy storage device, so the energy storage device 1 does not need to be equipped with a bypass path 50 and a bypass current circuit breaker 33. Alternatively, if the energy storage device 1 is not for in-vehicle use, temporary power failure may not be a problem. In that case, it is not necessary to provide a bypass path 50 and a bypass current circuit breaker 33. If a bypass path 50 and a bypass current circuit breaker 33 are not provided, the charge circuit breaker 13B may be in a closed state when performing an open fault diagnosis process for the discharge circuit breaker 13A.

[0109] (6) In the above embodiment, a lithium-ion secondary battery was given as an example of the energy storage element 10A, but the energy storage element 10A is not limited to this. For example, the energy storage element 10A may be a secondary battery other than a lithium-ion secondary battery. The energy storage element 10A may also be a capacitor that undergoes an electrochemical reaction. [Explanation of Symbols]

[0110] 1: Energy storage device 10A: Energy storage element 11: Positive external terminal (an example of an external terminal) 13A: Discharge circuit breaker (an example of a current circuit breaker) 13B: Charge circuit breaker (an example of a current circuit breaker) 14: BMU (An example of a management department) 16: Voltage sensor 22: Current path 33: Bypass current circuit breaker 34A: Discharge interruption gate drive circuit (an example of a gate drive circuit) 34B: Gate drive circuit for interrupting charging (an example of a gate drive circuit) 35A: N-channel MOSFET 35B: N-channel MOSFET 36A: P-channel MOSFET 36B: P-channel MOSFET 46: P-channel MOSFET 50: Bypass Route D: Drain terminal G: Gate terminal S: Source terminal

Claims

1. It is an energy storage device, A storage element having a positive electrode, External terminals, A current circuit breaker is provided in the current path between the positive electrode and the external terminal, Management Department, Voltage sensor and, Equipped with, The current circuit breaker is, Multiple N-channel MOSFETs connected in parallel, A gate drive circuit connected to the source terminal of each of the aforementioned N-channel MOSFETs, A P-channel MOSFET is provided between the gate drive circuit and the gate terminal of each of the N-channel MOSFETs, It has, The control unit is connected to the gate drive circuit and is also individually connected to the gate terminal of each P-channel MOSFET. The voltage sensor is an energy storage device that measures the common-source voltage or common-drain voltage of the plurality of N-channel MOSFETs connected in parallel.

2. The energy storage device according to claim 1, The control unit performs a first diagnostic process for diagnosing an open fault in which the N-channel MOSFET does not enter a closed state, wherein the control unit instructs the gate drive circuit to output a close signal, and outputs the close signal to the gate terminal of the P-channel MOSFET connected to any one of the N-channel MOSFETs to be diagnosed, while not outputting a close signal to the gate terminal of the other P-channel MOSFETs, and in that state, performs the first diagnostic process for diagnosing an open fault based on the common source voltage or common drain voltage measured by the voltage sensor.

3. The energy storage device according to claim 2, Two of the aforementioned current circuit breakers connected in series, A bypass current circuit breaker is provided in a bypass path connected in parallel with the two aforementioned current circuit breakers, Equipped with, On the other hand, the current circuit breaker is a discharge circuit breaker in which the forward direction of the parasitic diode of each N-channel MOSFET is the charging direction of the energy storage element. The other current circuit breaker is a charge circuit breaker in which the forward direction of the parasitic diode of each N-channel MOSFET is the discharge direction of the energy storage element. An energy storage device in which the discharge circuit breaker and the charge circuit breaker are back-to-back connected by connecting the source terminal of each N-channel MOSFET of the discharge circuit breaker to the source terminal of each N-channel MOSFET of the charge circuit breaker.

4. The energy storage device according to claim 3, The energy storage device wherein, when the control unit performs the first diagnostic process on the discharge circuit breaker, it does so with the charge circuit breaker in an open state and the bypass current circuit breaker in a closed state.

5. The energy storage device according to claim 3, The energy storage device wherein, when the control unit performs the first diagnostic process on the charging circuit breaker, it closes the discharge circuit breaker and opens the bypass current circuit breaker.

6. The energy storage device according to claim 3, The control unit performs a second diagnostic process for diagnosing a closed fault in which the N-channel MOSFET does not become open, wherein the bypass current circuit breaker is closed, the output of a closed signal from the gate drive circuit to each of the N-channel MOSFETs is stopped, and the closed fault is diagnosed based on the common source voltage measured by the voltage sensor in that state.

7. The energy storage device according to claim 3, The aforementioned bypass current circuit breaker is a power storage device consisting of two P-channel MOSFETs connected back-to-back.

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