Energy storage system

Abstract

In an energy storage system in which multiple batteries are connected in series, and each battery is provided with a bypass section and a contact state detection section, unintended charging and discharging of capacitors used for oxide film removal, etc., is prevented. [Solution] The energy storage system 1 comprises a power line PL connecting a plurality of battery modules M1 to Mn in series, a plurality of bypass units B1 to Bn provided for each battery module M1 to Mn, a smoothing capacitor C connecting the positive and negative sides of the power line PL, a plurality of contact state detection units provided for each battery module M1 to Mn, and a first FET switch and a second FET switch that connect or disconnect the charge / discharge circuit of the smoothing capacitor C formed through a first contact state detection circuit DC1 and a second contact state detection circuit DC2.

Description

Technical Field

[0001] The present invention relates to a power storage system.

Background Art

[0002] As a power storage system in which a plurality of storage batteries are connected in series, there is known one in which a bypass section for switching the storage battery between a connected state and a bypass state is provided for each storage battery (see, for example, Patent Document 1). In the power storage system described in Patent Document 1, a first switch connected in series with the storage battery and a second switch connected in parallel with the storage battery and the first switch are provided in the bypass section. In this power storage system, when there is a storage battery that cannot discharge the required current, bypass control is executed in which the first switch corresponding to the storage battery is in an open state and the second switch corresponding to the storage battery is in a closed state, and discharge is performed from other storage batteries in the connected state.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the power storage system described in Patent Document 1, at the time of bypass control, it is necessary to prevent a large fluctuation in the input / output power of the power storage system due to a rapid change in the current of the power storage string (hereinafter, string current). Therefore, it is necessary to execute bypass control after reducing the string current to a predetermined value. On the other hand, when the first switch and the second switch are mechanical relays, in order to remove the oxide film formed on the contact portions of the first switch and the second switch over time, a voltage of a certain level or more is applied between the contacts of the first switch and the second switch, and it is necessary to operate the first switch and the second switch to generate arc discharge with a current value of a certain level or more at the contact portions.

[0005] If bypass control is performed after reducing the string current, a voltage above a certain level may not be applied to the contact points of the first and second switches, preventing the generation of an arc discharge with a current above a certain level, potentially resulting in insufficient removal of the oxide film. Therefore, a means is needed that allows both reducing the string current before operating the first and second switches, and operating the first and second switches while applying a voltage sufficient to remove the oxide film.

[0006] One possible method involves connecting a CR circuit to a battery storage string and switching the first switch from open to closed while charging the capacitor of the CR circuit with the power of any battery, or switching the second switch from open to closed while the capacitor is discharging. However, in this method, the contact state of the first and second switches is not checked before the bypass control is executed, or before the connection control is executed in which the first switch is closed and the second switch is open. Therefore, there is a possibility that the first and second switches may close simultaneously due to a malfunction of the control system, causing a short circuit in the battery.

[0007] To check the contact state of the first and second switches, it is conceivable to provide a contact state detection circuit that detects the potential difference across either the first or second switch. However, if batteries other than the battery to be treated for oxide film removal are in a bypass or connected state, the capacitor used for oxide film removal is connected to the battery via the contact state detection circuit, and the capacitor is charged and discharged. Therefore, when the oxide film removal process is performed, the potential difference between the contacts of the first or second switch disappears, making it impossible to generate an arc discharge with a current value above a certain level at the contact portion of the first or second switch.

[0008] In view of the above circumstances, the present invention aims to prevent unintended charging and discharging of capacitors used for oxide film removal and the like in an energy storage system in which a plurality of storage batteries are connected in series and each storage battery is provided with a bypass section and a contact state detection section. [Means for solving the problem]

[0009] The present invention provides an energy storage system comprising: a power line connecting a plurality of batteries in series; a first switch connected in series with the batteries via the power line; a second switch connected in parallel with the batteries and the first switch; a plurality of bypass sections provided for each battery; a capacitor connecting the positive and negative sides of the power line; a circuit section connected to the power line so as to straddle one of the first and second switches, during which current flows from the power line side or not depending on the state of the contact of one of the first and second switches; a detection section that detects the state of the contact of one of the first and second switches depending on whether or not current flows through the circuit section; a plurality of contact state detection sections provided for each battery; and a third switch that connects or disconnects the charging and discharging circuit of the capacitor formed through the circuit section. [Effects of the Invention]

[0010] According to the present invention, in an energy storage system in which a bypass section and a contact state detection section are provided for each battery, unintended charging and discharging of capacitors used for oxide film removal and the like can be prevented. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a schematic circuit diagram showing an energy storage system according to one embodiment of the present invention. [Figure 2] Figure 2 is a circuit diagram showing the first contact state detection circuit and the second contact state detection circuit of the energy storage system shown in Figure 1. [Figure 3] Figure 3 is a circuit diagram illustrating the first oxide film removal process. [Figure 4] Figure 4 is a circuit diagram illustrating the process of removing the second oxide film. [Figure 5] Figure 5 is a circuit diagram illustrating the pre-charge process. [Figure 6]FIG. 6 is a circuit diagram for explaining the operation of the power storage system according to the comparative example. [Figure 7] FIG. 7 is a circuit diagram for explaining the contact state detection process. [Figure 8] FIG. 8 is a circuit diagram for explaining the contact state detection process. [Figure 9] FIG. 9 is a circuit diagram for explaining the contact state detection process. [Figure 10] FIG. 10 is a circuit diagram for explaining the contact state detection process. [Figure 11] FIG. 11 is a circuit diagram for explaining the contact state detection process. [Figure 12] FIG. 12 is a circuit diagram for explaining the contact state detection process. [Figure 13] FIG. 13 is a circuit diagram for explaining the contact state detection process. [Figure 14] FIG. 14 is a flowchart for explaining the process of switching the power storage battery module to be bypass - controlled from the connected state to the bypass state. [Figure 15] FIG. 15 is a flowchart for explaining the process of switching the power storage battery module to be bypass - controlled from the connected state to the bypass state. [Figure 16] FIG. 16 is a circuit diagram showing the outline of the power storage system according to another embodiment of the present invention. [Figure 17] FIG. 17 is a circuit diagram showing the outline of the power storage system according to another embodiment of the present invention. [Figure 18] FIG. 18 is a circuit diagram showing the outline of the power storage system according to another embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in accordance with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and the embodiments can be appropriately changed without departing from the gist of the present invention. Also, in the embodiments shown below, there are some places where the illustration and description of some configurations are omitted. For the details of the omitted technologies, well-known or widely-known technologies are appropriately applied within the range where there is no contradiction with the content described below.

[0013] FIG. 1 is a circuit diagram showing an outline of a power storage system 1 according to an embodiment of the present invention. As shown in this figure, the power storage system 1 includes a power storage string STR, a power converter PCS, a string bus 2, and a battery control device 100. Although not shown in the figure, the power storage system 1 includes a plurality of power storage strings STR, and these plurality of power storage strings STR are connected in parallel to each other via the string bus 2 and are also connected to an external system (not shown). The power storage system 1 is a stationary or in-vehicle power source.

[0014] The power storage string STR includes n (n is an integer of 2 or more) battery modules M1 to Mn connected in series. Although not particularly limited, the battery modules M1 to Mn in this embodiment are those obtained by regenerating used batteries, and there are differences in the degree of deterioration of each of the battery modules M1 to Mn. The battery modules M1 to Mn are, for example, those in which a plurality of cells of a secondary battery such as a lithium-ion battery, a lithium-ion capacitor, or a nickel-metal hydride battery are connected.

[0015] The battery modules M1 to Mn are charged by being supplied with power from an external system through the string bus 2 and the power converter PCS. Also, the battery modules M1 to Mn supply power to an external system through the power converter PCS and the string bus 2.

[0016] The external system includes loads and generators. If the energy storage system 1 is stationary, the commercial power grid and facilities that consume electricity become the loads, and solar power generation systems become the generators. On the other hand, if the energy storage system 1 is vehicle-mounted, the drive motor, air conditioner, and various vehicle-mounted electrical components become the loads. Note that the drive motor can act as both a load and a generator.

[0017] The energy storage string STR may also consist of n battery cells or battery packs connected in series, instead of n battery modules M1 to Mn connected in series. In this case, the energy storage string STR may include a bypass section that bypasses each battery cell or battery pack.

[0018] The power converter PCS is either a DC / DC converter or a DC / AC converter and is connected to string bus 2. The power converter PCS is also connected to the positive terminal of the starting battery module M1 (hereinafter referred to as the total + of the energy storage string STR) and the negative terminal of the ending battery module Mn (hereinafter referred to as the total - of the energy storage string STR).

[0019] The power converter PCS converts the voltage input from string bus 2 to the battery storage string STR according to the specified charging power (or current) value and outputs it to multiple battery storage modules M1 to Mn during charging. Here, the voltage on the battery storage string STR side changes depending on the bypass state of battery storage modules M1 to Mn (the number of battery storage modules M1 to Mn that are bypassed) and the charging state of battery storage modules M1 to Mn. Therefore, the power converter PCS converts the voltage input from string bus 2 to the voltage on the battery storage string STR side and outputs it to multiple battery storage modules M1 to Mn during charging.

[0020] During the discharge of the energy storage string STR, the power converter PCS converts the voltages input from multiple battery modules M1 to Mn according to the indicated discharge power (or current) value and outputs it to the string bus 2. Here, the input voltage of the power converter PCS during discharge changes depending on the bypass state and charge state of the battery modules M1 to Mn. As a result, variations occur in the input voltages of the multiple power converter PCS during the discharge of the energy storage string STR. Therefore, during the discharge of the energy storage string STR, each power converter PCS converts its input voltage to an output voltage that matches that of the other power converter PCS.

[0021] The power converter PCS is a bidirectional converter. Furthermore, when the current flowing through string bus 2 is alternating current, the power converter PCS is equipped with synchronization means to track changes in instantaneous values.

[0022] The energy storage string STR comprises n bypass units B1 to Bn, a system main relay S3, a smoothing capacitor C, a pre-charge circuit 10, a current sensor 11, and various sensors (not shown). Bypass units B1 to Bn are provided for each battery module M1 to Mn.

[0023] Each energy storage string STR includes a rectifier circuit RFC, a first contact state detection circuit DC1, a second contact state detection circuit DC2, and a microcontroller MCU for each bypass unit B1 to Bn. The current sensor 11 is installed at any position on the power line PL that is always energized, and detects the string current and transmits a detection signal to the string controller StC.

[0024] Each bypass unit B1 to Bn is equipped with a trip switch S1, a bypass line BL, and a bypass switch S2. The trip switch S1 is a mechanical relay connected in series with each battery module M1 to Mn by a power line PL. The trip switch S1 is located on the positive side of the energy string STR relative to each battery module M1 to Mn and is connected to the positive terminal of each battery module M1 to Mn.

[0025] Bypass line BL is a power line that bypasses each battery module M1 to Mn and the circuit breaker switch S1. One end of bypass line BL is connected to the circuit breaker switch S1, and the other end of bypass line BL is connected to the negative terminal of each battery module M1 to Mn. Bypass line BL is equipped with a mechanical relay, the bypass switch S2. That is, the bypass switch S2 is connected in parallel with each battery module M1 to Mn and the circuit breaker switch S1.

[0026] The starting battery module M1 and the ending battery module Mn are connected to the external system via the power converter PCS and string bus 2. When the bypass switch S2 is open and the circuit breaker switch S1 is closed in any of the bypass units B1 to Bn, the battery modules M1 to Mn corresponding to that bypass unit B1 to Bn are connected in series to the external system. On the other hand, when the circuit breaker switch S1 is open and the bypass switch S2 is closed in any of the bypass units B1 to Bn, the battery modules M1 to Mn corresponding to that bypass unit B1 to Bn are bypassed. Note that when it is not necessary to distinguish each bypass unit B1 to Bn from other bypass units B1 to Bn, they will be referred to as bypass unit Bx. Similarly, when it is not necessary to distinguish each battery module M1 to Mn from other battery modules M1 to Mn, they will be referred to as battery module Mx.

[0027] The system main relay S3 is located in a position on the power line PL that is always energized. Specifically, the system main relay S3 is located between the total positive terminal of the energy storage string STR and the trip switch S1 of the bypass unit B1 at the starting end. The system main relay S3 can be a mechanical relay, a semiconductor switch, or the like.

[0028] The smoothing capacitor C is connected between the total positive terminal of the energy storage string STR and the system main relay S3, and between the total negative terminal of the energy storage string STR and the terminal battery module Mn. The smoothing capacitor C is an element that stores electric charge, such as an electrolytic capacitor, film capacitor, or other capacitor, and smooths the voltage input from the power converter PCS to the energy storage string STR.

[0029] The precharge circuit 10 comprises a precharge resistor Rp and a precharge relay S4. The precharge relay S4 is a mechanical relay, a semiconductor switch, etc. The precharge resistor Rp and the precharge relay S4 are connected in series and are connected in parallel with the system main relay S3. The precharge circuit 10 is a circuit for charging (precharging) the smoothing capacitor C when the energy storage string STR is started up. In this embodiment, in addition to the precharge process for charging the smoothing capacitor C, the precharge circuit 10 is used for a first oxide film removal process to remove the oxide film from the contact portion of the cutoff switch S1 and a second oxide film removal process to remove the oxide film from the contact portion of the bypass switch S2.

[0030] The rectifier circuit RFC, the first contact state detection circuit DC1, the second contact state detection circuit DC2, and the microcontroller MCU constitute a contact state detection unit that detects the state (Open or Close) of the contacts of the corresponding bypass unit Bx's cutoff switch S1 and bypass switch S2. The configuration of this contact state detection unit will be described later.

[0031] The battery control device 100 comprises a string controller StC, module controllers MC1 to MCn, and a system controller SyC. A system controller SyC is provided for each energy storage system 1. Although not shown in the diagram, the battery control device 100 comprises multiple string controllers StC, and each string controller StC is provided for each energy storage string STR. Module controllers MC1 to MCn are provided for each battery storage module Mx.

[0032] Module controllers MC1 to MCn each consist of a microcontroller (MCU) and a relay driver (RD). When it is not necessary to distinguish each module controller MC1 to MCn from others, they will be referred to as module controller MCx.

[0033] The microcontroller (MCU) is a control device that performs control and status monitoring of the battery module Mx and the bypass unit Bx, and transmits status information of the corresponding battery module Mx to the string controller (StC). Status information of the battery module Mx includes the voltage, temperature, and cell voltage of the battery module Mx.

[0034] Furthermore, the microcontroller MCU determines whether it is necessary to switch the cutoff switch S1 and bypass switch S2 of the corresponding bypass unit Bx based on the voltage and SOC (State of Charge) of the corresponding battery module Mx. For example, when the energy storage string STR is discharging, if the voltage and SOC of the corresponding battery module Mx fall below a threshold, the microcontroller MCU determines that it is necessary to switch the cutoff switch S1 from Close to Open and the bypass switch S2 from Open to Close (hereinafter referred to as bypass control) for the corresponding bypass unit Bx. Also, for example, when the energy storage string STR is charging, if the voltage and SOC of the corresponding battery module Mx rise above a threshold, the microcontroller MCU determines that it is necessary to switch the bypass unit Bx. Note that the determination of whether it is necessary to switch the cutoff switch S1 and bypass switch S2 of the bypass unit Bx may be performed by the string controller StC. Furthermore, when the voltage or SOC of the battery module Mx is below or below a threshold, bypass control and control to release the bypass state (hereinafter referred to as connection control) may be performed.

[0035] When the microcontroller MCU determines that switching of the cutoff switch S1 and bypass switch S2 is necessary for the corresponding bypass unit Bx, it sends a signal to the string controller StC requesting the switching of the cutoff switch S1 and bypass switch S2 (hereinafter referred to as the switch switching request signal). The microcontroller MCU also sends a detection signal to the string controller StC indicating the state of the contacts of the cutoff switch S1 and bypass switch S2.

[0036] The string controller StC transmits the switch switching request signal received from the module controller MCx's microcontroller MCU to the system controller SyC. However, if the string controller StC determines whether to allow or deny the switching of the disconnect switch S1 and bypass switch S2, it is not necessary for the string controller StC to transmit the switch switching request signal to the system controller SyC.

[0037] When the system controller SyC receives a switch switching request signal from the string controller StC, it determines whether to allow or deny the switching of the cutoff switch S1 and the bypass switch S2. If the system controller SyC allows the switching of the cutoff switch S1 and the bypass switch S2, it sends a signal instructing the switch to switch (hereinafter referred to as the switch switching signal) to the string controller StC. The string controller StC then sends the switch switching signal received from the system controller SyC to the target module controller MCx.

[0038] When performing bypass control and connection control, the microcontroller MCU transmits the switch switching signal received from the string controller StC to the relay driver RD. The relay driver RD switches the open / close state of the corresponding disconnect switch S1 and bypass switch S2 according to the switch switching signal received from the microcontroller MCU.

[0039] The string controller StC transmits control signals to the relay driver RDp and the power converter PCS. The relay driver RDp controls the system main relay S3 and the precharge relay S4 according to the control signals transmitted from the string controller StC. The power converter PCS converts the charge and discharge power of the energy storage string STR according to the control signals transmitted from the string controller StC. The power converter PCS also controls the string current of the energy storage string STR according to the control signals from the string controller StC.

[0040] The string controller StC performs detection and estimation of the state of the energy storage string STR. Detection of the state of the energy storage string STR includes detecting the string current of the energy storage string STR based on the detection signal of the current sensor 11, detecting the total voltage of the energy storage string STR based on the detection signal of the voltage sensor (not shown), detecting the voltage of the battery module Mx based on the detection signal of the voltage sensor, detecting the temperature of the battery module Mx based on the detection signal of the temperature sensor (not shown), and detecting the voltage of the battery cells based on the detection signal of the cell voltage sensor (not shown). Furthermore, estimation of the state of the energy storage string STR includes estimating the SOC and SOH (State of Health) of the battery module Mx, and estimating the SOC and SOH of the energy storage string STR.

[0041] Methods for estimating SOH include charge-discharge testing, current integration, open-circuit voltage measurement, terminal voltage measurement, model-based methods (all of which use the time-dependent change in SOC), AC impedance measurement, model-based methods using adaptive digital filters, linear regression from IV characteristics (current-voltage characteristics) (slope of the straight line of the IV characteristics), and step response methods (all of which are methods that estimate using the time-dependent increase in internal resistance).

[0042] Various known methods for estimating the State of Charge (SOC) include the current integration method, the method of determining it from the Open Circuit Voltage (OCV) (voltage method), and a method that combines the current integration method and the voltage method. Furthermore, the OCV can be estimated using various known methods that utilize the change in terminal voltage over time or the increase in internal resistance over time.

[0043] The system controller SyC monitors the status of the energy storage strings STR, determines whether to grant or deny control requests from the string controller StC, and notifies the string controller StC of the authorization of the control requests. The system controller SyC also sets the indicative value for the charge / discharge power (or current) of each energy storage string STR and transmits the indicative value of that charge / discharge power (or current) to the string controller StC.

[0044] The system controller SyC monitors the state of the energy storage strings STR based on the detection and estimation results of the state of the energy storage strings STR transmitted from the string controller StC. Then, the system controller SyC calculates the instructed charge / discharge power (or current) to be allocated to each energy storage string STR, based on the input / output power (or current) instruction for the entire energy storage system 1 received from a higher-level system (not shown) and the state of the energy storage strings STR.

[0045] Each string controller StC executes bypass control of a bypass unit Bx if a request for switching the Open / Close switches S1 and S2 of the bypass unit Bx for any of the battery modules Mx is permitted by the system controller SyC (hereinafter referred to as a bypass control request). Here, when executing bypass control, the string controller StC performs a first oxide film removal process and a second oxide film removal process.

[0046] Before bypass control is performed, a string current reduction process, a first oxide film removal process, and a second oxide film removal process are performed. After bypass control is performed, a precharge process is performed. The string current reduction process reduces the string current to a predetermined value. The predetermined value is set to a low value such that fluctuations in the input and output power of the entire energy storage system 1 are kept within an acceptable range when bypass control of the energy storage string STR is performed.

[0047] Here, the string controller StC gradually and continuously reduces the indicated value of the string current from its current value to a predetermined value during the string current reduction process. Specifically, the string controller StC repeatedly updates the indicated value of the string current by a predetermined amount ΔP1, which is an equal division of the difference between the indicated value of the string current and the predetermined value. In this process, the rate of change of the indicated value of the string current (amount of change per unit time) is set to such an extent that fluctuations in the input and output power of the entire energy storage system 1 are kept within an acceptable range. As a result, the power converter PCS gradually and continuously reduces the string current from its current value to a predetermined value in order to keep fluctuations in the input and output power of the entire energy storage system 1 within an acceptable range.

[0048] Furthermore, when bypass control and connection control are performed, the module controller MCx executes a process to detect the contact state of the disconnect switch S1 and bypass switch S2 (hereinafter referred to as the contact state detection process). The contact state detection process will be described later.

[0049] Figure 2 is a circuit diagram showing the first contact state detection circuit DC1 and the second contact state detection circuit DC2 of the energy storage system 1 shown in Figure 1. As shown in this figure, the first contact state detection circuit DC1 is a circuit that introduces or does not introduce current from the power line PL side depending on the state of the contacts of the cutoff switch S1. The first contact state detection circuit DC1 comprises a first resistor R1, a first Zener diode ZD1, a second resistor R2, a third resistor R3, a first signal isolator IS1, and a first FET switch S5. The second contact state detection circuit DC2 is a circuit that introduces or does not introduce current from the power line PL side depending on the state of the contacts of the bypass switch S2. The second contact state detection circuit DC2 comprises a fourth resistor R4, a fifth resistor R5, a second Zener diode ZD2, a sixth resistor R6, a seventh resistor R7, and a second FET switch S6.

[0050] One end of the first resistor R1 is connected to the cutoff switch S1 and the positive terminal of the battery module Mx, and the other end of the first resistor R1 is connected to the input terminal IN1H of the first signal isolator IS1. The cathode of the first Zener diode ZD1 is connected to the other end of the first resistor R1 and the input terminal IN1H of the first signal isolator IS1. The connection point P1 between one end of the bypass line BL and the power line PL and the ground terminal GND1H of the first signal isolator IS1 are connected by the first ground line GL1. The anode of the first Zener diode ZD1 is connected to the first ground line GL1 via the first FET switch S5.

[0051] The first FET switch S5 is a field-effect transistor (FET), specifically an N-channel MOSFET (Metal Oxide Semiconductor FET). The gate of the first FET switch S5 is connected to the output terminal OUT1H of the first signal isolator IS1 via a third resistor R3. The drain of the first FET switch S5 is connected to the anode of the first Zener diode ZD1, and the source of the first FET switch S5 is connected to the first ground line GL1.

[0052] One end of the second resistor R2 is connected to the gate of the first FET switch S5 and one end of the third resistor R3, and the other end of the second resistor R2 is connected to the first ground line GL1. The anode of the first Zener diode ZD1 is connected to the ground terminal GND1H of the first signal isolator IS1 via the first FET switch S5, the second resistor R2, and the first ground line GL1. The second resistor R2 is a pull-down resistor.

[0053] One end of the third resistor R3 is connected to the gate of the first FET switch S5 and one end of the second resistor R2, and the other end of the third resistor R3 is connected to the output terminal OUT1H of the first signal isolator IS1. The third resistor R3 is a damping resistor that suppresses and converges the oscillations of the voltage waveform applied between the gate and source of the first FET switch S5.

[0054] The rectifier circuit RFC comprises a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4, which are configured as a bridge circuit. The cathode of the first diode D1 is connected to the cathode of the second diode D2, and the anode of the first diode D1 is connected to the cathode of the third diode D3. In addition, the anode of the second diode D2 is connected to the cathode of the fourth diode D4, and the anode of the third diode D3 is connected to the anode of the fourth diode D4.

[0055] The connection point between the anode of the first diode D1 and the cathode of the third diode D3 (hereinafter referred to as the first output section o1 of the rectifier circuit RFC) is connected to the connection point P2 between the other end of the bypass line BL and the power line PL. The negative terminal of the battery module Mx and the bypass switch S2 are connected to the connection point P2 between the other end of the bypass line BL and the power line PL. In other words, the first output section o1 of the rectifier circuit RFC is connected to the negative terminal of the battery module Mx and the bypass switch S2.

[0056] The connection point between the cathode of the first diode D1 and the cathode of the second diode D2 (hereinafter referred to as the second output section o2 of the rectifier circuit RFC) is connected to the input terminal IN2H of the second signal isolator IS2 via the fourth resistor R4. The connection point between the anode of the third diode D3 and the anode of the fourth diode D4 (hereinafter referred to as the second input section i2 of the rectifier circuit RFC) is connected to the ground terminal GND2H of the second signal isolator IS2 via the second ground line GL2.

[0057] The connection point between the anode of the second diode D2 and the cathode of the fourth diode D4 (hereinafter referred to as the first input i1 of the rectifier circuit RFC) is connected to the first ground line GL1. The connection point P3 between the first input i1 of the rectifier circuit RFC and the first ground line GL1 is located between the connection point P4 between the source of the first FET switch S5 and the first ground line GL1 and the connection point P1.

[0058] The first output section o1 and the first input section i1 of the rectifier circuit RFC are connected via a bypass switch S2. Furthermore, the first output section o1 and the first input section i1 of the rectifier circuit RFC are connected to the battery module Mx via a cutoff switch S1.

[0059] One end of the fourth resistor R4 is connected to the second output section o2 of the rectifier circuit RFC, and the other end of the fourth resistor R4 is connected to one end of the fifth resistor R5, the cathode of the second Zener diode ZD2, and the input terminal IN2H of the second signal isolator IS2.

[0060] One end of the fifth resistor R5 is connected to the other end of the fourth resistor R4, the cathode of the second Zener diode ZD2, and the input terminal IN2H of the second signal isolator IS2. The other end of the fifth resistor R5 is connected to the anode of the second Zener diode ZD2 and the drain of the second FET switch S6. The cathode of the second Zener diode ZD2 is connected to the other end of the fourth resistor R4, one end of the fifth resistor R5, and the input terminal IN2H of the second signal isolator IS2, and the anode of the second Zener diode ZD2 is connected to the second ground line GL2 via the second FET switch S6. The second Zener diode ZD2 and the fifth resistor R5 are connected in parallel.

[0061] The second output section o2 and the second input section i2 of the rectifier circuit RFC are connected via the fourth resistor R4, the second Zener diode ZD2, and the second FET switch S6. Here, the fifth resistor R5 is a pull-down resistor that connects the input terminal IN2H of the second signal isolator IS2 to ground via the second FET switch S6.

[0062] The second FET switch S6 is a field-effect transistor, specifically an N-channel MOSFET. The gate of the second FET switch S6 is connected to the output terminal OUT2H of the second signal isolator IS2 via the seventh resistor R7. The drain of the second FET switch S6 is connected to the anode of the second Zener diode ZD2, and the source of the second FET switch S6 is connected to the second ground line GL2.

[0063] One end of the sixth resistor R6 is connected to the gate of the second FET switch S6 and one end of the seventh resistor R7, and the other end of the sixth resistor R6 is connected to the second ground line GL2. The anode of the second Zener diode ZD2 is connected to the ground terminal GND2H of the second signal isolator IS2 via the second FET switch S6, the sixth resistor R6, and the second ground line GL2. The sixth resistor R6 is a pull-down resistor.

[0064] One end of the seventh resistor R7 is connected to the gate of the second FET switch S6 and one end of the sixth resistor R6, and the other end of the seventh resistor R7 is connected to the output terminal OUT2H of the second signal isolator IS2. The seventh resistor R7 is a damping resistor that suppresses and converges the oscillations of the voltage waveform applied between the gate and source of the second FET switch S6.

[0065] The first signal isolator IS1 is an element that transmits signals between the high-voltage and low-voltage sides while isolating the high-voltage side from the low-voltage side, such as a digital isolator or photocoupler. The input terminal IN1H is the high-voltage side input terminal of the first signal isolator IS1, the output terminal OUT1H is the high-voltage side output terminal of the first signal isolator IS1, and the ground terminal GND1H is the high-voltage side ground terminal of the first signal isolator IS1. The output terminal OUT1L is the low-voltage side output terminal of the first signal isolator IS1, the input terminal IN1L is the low-voltage side input terminal of the first signal isolator IS1, and the ground terminal GND1L is the low-voltage side ground terminal of the first signal isolator IS1.

[0066] The output terminal OUT1L of the first signal isolator IS1 is connected to the input terminal IN1' of the microcontroller MCU. The input terminal IN1L of the first signal isolator IS1 is connected to the output terminal OUT1' of the microcontroller MCU. The ground terminal GND1L of the first signal isolator IS1 is connected to the ground terminal GND' of the microcontroller MCU. Here, the first signal isolator IS1 isolates the high-voltage circuit, including the battery module Mx, etc., from the low-voltage circuit, including the microcontroller MCU, etc.

[0067] The second signal isolator IS2 is an element that transmits signals between the high-voltage and low-voltage sides while insulating the high-voltage side from the low-voltage side of a digital isolator, photocoupler, etc. The input terminal IN2H is the high-voltage side input terminal of the second signal isolator IS2, the output terminal OUT2H is the high-voltage side output terminal of the second signal isolator IS2, and the ground terminal GND2H is the high-voltage side ground terminal of the second signal isolator IS2. The output terminal OUT2L is the low-voltage side output terminal of the second signal isolator IS2, the input terminal IN2L is the low-voltage side input terminal of the second signal isolator IS2, and the ground terminal GND2L is the low-voltage side ground terminal of the second signal isolator IS2.

[0068] The output terminal OUT2L of the second signal isolator IS2 is connected to the input terminal IN2' of the microcontroller MCU. The input terminal IN2L of the second signal isolator IS2 is connected to the output terminal OUT2' of the microcontroller MCU. The ground terminal GND2L of the second signal isolator IS2 is connected to the ground terminal GND' of the microcontroller MCU. Here, the second signal isolator IS2 isolates the high-voltage circuit, including the battery module Mx, etc., from the low-voltage circuit, including the microcontroller MCU, etc.

[0069] The microcontroller MCU outputs a gate drive signal to turn on the first FET switch S5 from its output terminal OUT1' to the input terminal IN1L of the first signal isolator IS1. The gate drive signal input to the input terminal IN1L of the first signal isolator IS1 is output to the gate of the first FET switch S5 from the output terminal OUT1H of the first signal isolator IS1. When the first FET switch S5 is ON, the first contact state detection circuit DC1 is connected to the power line PL. Conversely, when the first FET switch S5 is OFF, the first contact state detection circuit DC1 is disconnected from the power line PL.

[0070] The microcontroller (MCU) outputs a gate drive signal to turn on the second FET switch S6 from its output terminal OUT2' to the input terminal IN2L of the second signal isolator IS2. The gate drive signal input to the input terminal IN2L of the second signal isolator IS2 is output to the gate of the second FET switch S6 from the output terminal OUT2H of the second signal isolator IS2. When the second FET switch S6 is ON, the second contact state detection circuit DC2 is connected to the power line PL. Conversely, when the second FET switch S6 is OFF, the second contact state detection circuit DC2 is disconnected from the power line PL.

[0071] Figure 3 is a circuit diagram illustrating the first oxide film removal process. As shown in this figure, in the first oxide film removal process, when the potential of the smoothing capacitor C is lower than the potential of the battery module M' that is subject to bypass control, the cutoff switch S1 of the bypass unit B' corresponding to the battery module M' is switched from Open to Close. At this time, the system main relay S3 is Open, the precharge relay S4 is Close, and the bypass switch S2 of the bypass unit B' is Open. In the bypass units Bx other than bypass unit B', the cutoff switch S1 is Open and the bypass switch S2 is Close.

[0072] Here, before the start of the first oxide film removal process, a contact state detection process is performed to confirm that both the cutoff switch S1 and the bypass switch S2 are open in bypass unit B', and that in the bypass units Bx other than bypass unit B', the cutoff switch S1 is open and the bypass switch S2 is closed. When this contact state detection process is performed, the first FET switch S5 is turned ON in all first contact state detection circuits DC1, and the second FET switch S6 is turned ON in all second contact state detection circuits DC2.

[0073] In contrast, when the first oxide film removal process is performed, the first FET switch S5 is turned OFF in all first contact state detection circuits DC1, and the second FET switch S6 is turned OFF in all second contact state detection circuits DC2. As a result, current flows from the battery module M' through the bypass switch S1, precharge relay S4, precharge resistor Rp, smoothing capacitor C of the bypass unit B', and the bypass switch S2 of the other bypass units Bx, and the smoothing capacitor C is charged.

[0074] Here, the potential difference between the battery module M' and the smoothing capacitor C is set to a magnitude sufficient to generate an arc discharge with a current value sufficient to remove the oxide film on the contact portion of the bypass switch S1 when the bypass switch S1 of the bypass unit B' is switched. In this embodiment, the charge of the smoothing capacitor C is removed by the operation of the power converter PCS before the execution of the first oxide film removal process. Note that the potential of the smoothing capacitor C does not need to be 0 at the start of the first oxide film removal process; it is sufficient that the potential is low enough to remove the oxide film on the contact portion of the bypass switch S1 when the bypass switch S1 is switched.

[0075] Furthermore, the charging time of the smoothing capacitor C is set considering the time constant (τ=CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the pre-charge resistor Rp, so that a sufficient amount of charge flows from the battery module M' to the smoothing capacitor C to remove the oxide film on the contact portion of the cutoff switch S1.

[0076] Therefore, in the first oxide film removal process, the cutoff switch S1 of the bypass unit B' is switched from Open to Close when a voltage sufficient to remove the oxide film from the contact portion is applied, thereby removing the oxide film from the contact portion of the cutoff switch S1.

[0077] Figure 4 is a circuit diagram illustrating the second oxide film removal process. As shown in this figure, during the second oxide film removal process, with the smoothing capacitor C charged, the bypass switch S2 of bypass unit B' is switched from Open to Close. At this time, the system main relay S3 and the cutoff switch S1 of bypass unit B' are Open, and the precharge relay S4 is Close. In bypass units Bx other than bypass unit B', the cutoff switch S1 is Open and the bypass switch S2 is Close.

[0078] Here, before the start of the second oxide film removal process, a contact state detection process is performed to confirm that both the cutoff switch S1 and the bypass switch S2 are open in bypass unit B', and that in bypass units Bx other than bypass unit B', the cutoff switch S1 is open and the bypass switch S2 is closed. When this contact state detection process is performed, the first FET switch S5 is turned ON in all first contact state detection circuits DC1, and the second FET switch S6 is turned ON in all second contact state detection circuits DC2.

[0079] In contrast, when the second oxide film removal process is performed, the first FET switch S5 is turned OFF in all first contact state detection circuits DC1, and the second FET switch S6 is turned OFF in all second contact state detection circuits DC2. As a result, the smoothing capacitor C discharges, and current flows from the smoothing capacitor C through the precharge resistor Rp, precharge relay S4, bypass switch S2 of bypass unit B', and bypass switch S2 of other bypass units Bx.

[0080] Here, the potential of the smoothing capacitor C is set to a height sufficient to generate an arc discharge with a current value sufficient to remove the oxide film at the contact portion of the bypass switch S2 of the bypass unit B' when the bypass switch S2 is switched. In this embodiment, the charging time of the smoothing capacitor C during the execution of the first oxide film removal process is set considering the time constant (τ=CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the precharge resistor Rp.

[0081] Furthermore, the discharge time of the smoothing capacitor C is set considering the time constant (τ=CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the precharge resistor Rp, so that a sufficient amount of charge flows from the smoothing capacitor C to the bypass switch S2 to remove the oxide film on the contact portion of the bypass switch S2 of the bypass unit B'.

[0082] Therefore, in the second oxide film removal process, the bypass switch S2 of the bypass unit B' is switched from Open to Close when a voltage sufficient to remove the oxide film from the contact portion is applied, thereby removing the oxide film from the contact portion of the bypass switch S2.

[0083] Figure 5 is a circuit diagram illustrating the pre-charge process. As shown in this figure, the pre-charge process is a process in which the smoothing capacitor C is charged from the connected battery module Mx via the pre-charge circuit 10. In this embodiment, the process is performed after the smoothing capacitor C is discharged during the second oxide film removal process, and with one or more battery modules Mx other than the battery module M' connected.

[0084] During the pre-charge process, the bypass switch S1 and system main relay S3 of bypass unit B' are open, and the bypass switch S2 and pre-charge relay S4 of bypass unit B' are closed. Battery modules Mx other than battery module M' are either connected or bypassed depending on their charge status.

[0085] Here, the potential difference between the decharged smoothing capacitor C and the entire connected battery module M1~Mn becomes large. However, during the pre-charge process, the inrush current to the smoothing capacitor C is suppressed by the pre-charge resistor Rp of the pre-charge circuit 10. Also, during the pre-charge process, the current flowing from the connected battery module Mx to the smoothing capacitor C passes through the pre-charge circuit 10 without going through the system main relay S3.

[0086] Here, before the pre-charge process begins, a contact state detection process is performed to confirm that in bypass unit B', the cutoff switch S1 is open and the bypass switch S2 is closed, and in bypass units B other than bypass unit B', one of the cutoff switch S1 and the bypass switch S2 is open and the other is closed. When this contact state detection process is performed, the first FET switch S5 is turned ON in all first contact state detection circuits DC1, and the second FET switch S6 is turned ON in all second contact state detection circuits DC2.

[0087] In contrast, when the pre-charge process is executed, the first FET switch S5 is turned OFF in all first contact state detection circuits DC1, and the second FET switch S6 is turned OFF in all second contact state detection circuits DC2. As a result, current flows from the connected battery module Mx through the pre-charge relay S4, pre-charge resistor Rp, etc., to the smoothing capacitor C, and the smoothing capacitor C is charged.

[0088] Figure 6 is a circuit diagram illustrating the operation of a comparative example energy storage system 1C. The energy storage system 1C shown in this figure differs from the energy storage system 1 according to the described embodiment in that the first contact state detection circuit DC1 does not have a first FET switch S5, and the second contact state detection circuit DC2 does not have a second FET switch S6.

[0089] Figure 6 shows the state before the execution of the first or second oxide film removal treatment. Specifically, the battery module M' targeted for bypass control (target of oxide film removal treatment) is in the shut-off state, the other battery modules Mx are in the bypass state, the system main relay S3 is open, and the pre-charge relay S4 is closed.

[0090] In the comparative example energy storage system 1C, as shown in Figure 6, the smoothing capacitor C is connected to the battery module M' via the first contact state detection circuit DC1 and the second contact state detection circuit DC2, which correspond to the battery module M', and via the power line PL and the bypass line BL. Therefore, before the start of the first oxide film removal process, current flows from the battery module M' to the smoothing capacitor C via the first contact state detection circuit DC1, the precharge relay S4, and the precharge resistor Rp, and the smoothing capacitor C is charged. As a result, the potential difference between the battery module M' and the smoothing capacitor C is not large enough to generate an arc discharge with a current value sufficient to remove the oxide film at the contact portion of the cutoff switch S1 of the bypass unit B' when the cutoff switch S1 is switched.

[0091] Furthermore, before the start of the second oxide film removal process, current flows from the smoothing capacitor C to the battery module M' via the second contact state detection circuit DC2 and the rectifier circuit RFC, etc. (the smoothing capacitor C discharges). As a result, the potential of the smoothing capacitor C does not reach a level high enough to generate an arc discharge with a current value sufficient to remove the oxide film at the contact portion of the bypass switch S2 of the bypass unit B' when the bypass switch S2 is switched.

[0092] In contrast, in the energy storage system 1 according to this embodiment, the first FET switch S5 is turned OFF in all first contact state detection circuits DC1 and the second FET switch S6 is turned OFF in all second contact state detection circuits DC2, except when the contact state detection process is executed. As a result, when the first oxide film removal process is executed, the potential difference between the battery module M' and the smoothing capacitor C can be set to a size that generates an arc discharge with a current value sufficient to remove the oxide film from the contact portion of the cutoff switch S1 of the bypass unit B' when the cutoff switch S1 is switched. Also, when the second oxide film removal process is executed, the potential of the smoothing capacitor C can be set to a height that generates an arc discharge with a current value sufficient to remove the oxide film from the contact portion of the bypass switch S2 of the bypass unit B' when the bypass switch S2 is switched.

[0093] Figures 7 to 13 are circuit diagrams illustrating the contact state detection process. In the states shown in Figures 7 to 13, the first FET switch S5 is ON in the first contact state detection circuit DC1, and the second FET switch S6 is ON in the second contact state detection circuit DC2.

[0094] In the state shown in Figure 7, both the cutoff switch S1 and the bypass switch S2 are open in the bypass unit Bx corresponding to the battery module Mx that is the target of the contact state detection process, while the other battery module Mx is connected.

[0095] In the state shown in Figure 7, current flows in the following order: battery module Mx, first resistor R1, first Zener diode ZD1, first FET switch S5, second diode D2, fourth resistor R4, second Zener diode ZD2, second FET switch S6, third diode D3, and battery module Mx. A reverse current flows through the first Zener diode ZD1, and the potential difference between the input terminal IN1H of the first signal isolator IS1 and the ground terminal GND1H becomes equal to the Zener voltage of the first Zener diode ZD1. As a result, the logic value of the input signal at the input terminal IN1H of the first signal isolator IS1 becomes High. The first signal isolator IS1 outputs a High voltage from its output terminal OUT1L to the input terminal IN1' of the microcontroller MCU.

[0096] Furthermore, a reverse current flows through the second Zener diode ZD2, causing the potential difference between the input terminal IN2H and the ground terminal GND2H of the second signal isolator IS2 to become equal to the Zener voltage of the second Zener diode ZD2. As a result, the logic value of the input signal at the input terminal IN2H of the second signal isolator IS2 becomes High. The second signal isolator IS2 outputs a High voltage from its output terminal OUT2L to the input terminal IN2' of the microcontroller MCU.

[0097] In the state shown in Figure 8, both the cutoff switch S1 and the bypass switch S2 are open in the bypass unit Bx corresponding to the battery module Mx that is the target of the contact state detection process, and the other battery module Mx is in a bypass state.

[0098] In the state shown in Figure 8, current flows in the same order as in the state shown in Figure 7: battery module Mx, first resistor R1, first Zener diode ZD1, first FET switch S5, second diode D2, fourth resistor R4, second Zener diode ZD2, second FET switch S6, third diode D3, and battery module Mx. A reverse current flows through the first Zener diode ZD1, and the potential difference between the input terminal IN1H of the first signal isolator IS1 and the ground terminal GND1H becomes equal to the Zener voltage of the first Zener diode ZD1. As a result, the logic value of the input signal at the input terminal IN1H of the first signal isolator IS1 becomes High. The first signal isolator IS1 outputs a High voltage from its output terminal OUT1L to the input terminal IN1' of the microcontroller MCU.

[0099] Furthermore, when the potential difference between the input terminal IN2H and the ground terminal GND2H of the second signal isolator IS2 becomes equal to the Zener voltage of the second Zener diode ZD2, the logic value of the input signal at the input terminal IN2H of the second signal isolator IS2 becomes High. The second signal isolator IS2 outputs a High voltage from its output terminal OUT2L to the input terminal IN2' of the microcontroller MCU.

[0100] In the state shown in Figure 9, both the disconnect switch S1 and the bypass switch S2 are open in the bypass unit Bx corresponding to the battery module Mx that is the target of the contact state detection process, and the other battery module Mx is in a disconnected state.

[0101] In the state shown in Figure 9, current flows in the same order as in the states shown in Figures 7 and 8: battery module Mx, first resistor R1, first Zener diode ZD1, first FET switch S5, second diode D2, fourth resistor R4, second Zener diode ZD2, second FET switch S6, third diode D3, and battery module Mx. A reverse current flows through the first Zener diode ZD1, and the potential difference between the input terminal IN1H of the first signal isolator IS1 and the ground terminal GND1H becomes equal to the Zener voltage of the first Zener diode ZD1. As a result, the logic value of the input signal at the input terminal IN1H of the first signal isolator IS1 becomes High. The first signal isolator IS1 outputs a High voltage from its output terminal OUT1L to the input terminal IN1' of the microcontroller MCU.

[0102] Furthermore, when the potential difference between the input terminal IN2H and the ground terminal GND2H of the second signal isolator IS2 becomes equal to the Zener voltage of the second Zener diode ZD2, the logic value of the input signal at the input terminal IN2H of the second signal isolator IS2 becomes High. The second signal isolator IS2 outputs a High voltage from its output terminal OUT2L to the input terminal IN2' of the microcontroller MCU.

[0103] In the state shown in Figure 10, the bypass unit Bx corresponding to the battery module Mx targeted by the contact state detection process has the cutoff switch S1 open and the bypass switch S2 closed, while the other battery module Mx is connected. The operation is the same even if the other battery module Mx is in a bypass state.

[0104] In the state shown in Figure 10, current flows in the following order: battery module Mx, first resistor R1, first Zener diode ZD1, first FET switch S5, bypass switch S2, and battery module Mx. A reverse current flows through the first Zener diode ZD1, and the potential difference between the input terminal IN1H of the first signal isolator IS1 and the ground terminal GND1H becomes equal to the Zener voltage of the first Zener diode ZD1. As a result, the logic value of the input signal at the input terminal IN1H of the first signal isolator IS1 becomes High. The first signal isolator IS1 outputs a High voltage from its output terminal OUT1L to the input terminal IN1' of the microcontroller MCU.

[0105] In contrast, no current flows through the second Zener diode ZD2, so the potential difference between the input terminal IN2H and the ground terminal GND2H of the second signal isolator IS2 becomes 0. As a result, the logic value of the input signal at the input terminal IN2H of the second signal isolator IS2 becomes Low. The second signal isolator IS2 outputs a Low voltage from its output terminal OUT2L to the input terminal IN2' of the microcontroller MCU.

[0106] Here, the fifth resistor R5, which is a pull-down resistor, connects the input terminal IN2H of the second signal isolator IS2 to ground via the second FET switch S6. As a result, the potential difference between the input terminal IN2H and the ground terminal GND2H is maintained at 0 when no reverse current flows through the second Zener diode ZD2, preventing high impedance between the input terminal IN2H and the ground terminal GND2H of the second signal isolator IS2.

[0107] In the state shown in Figure 11, the bypass unit Bx corresponding to the battery module Mx targeted for contact state detection processing has the cutoff switch S1 open and the bypass switch S2 closed, while the other battery module Mx is in a cutoff state.

[0108] In the state shown in Figure 11, as in the state shown in Figure 10, current flows in the following order: battery module Mx, first resistor R1, first Zener diode ZD1, first FET switch S5, bypass switch S2, and battery module Mx. A reverse current flows through the first Zener diode ZD1, and the potential difference between the input terminal IN1H of the first signal isolator IS1 and the ground terminal GND1H becomes equal to the Zener voltage of the first Zener diode ZD1. As a result, the logic value of the input signal at the input terminal IN1H of the first signal isolator IS1 becomes High. The first signal isolator IS1 outputs a High voltage from its output terminal OUT1L to the input terminal IN1' of the microcontroller MCU.

[0109] In contrast, no current flows through the second Zener diode ZD2, so the potential difference between the input terminal IN2H and the ground terminal GND2H of the second signal isolator IS2 becomes 0. As a result, the logic value of the input signal at the input terminal IN2H of the second signal isolator IS2 becomes Low. The second signal isolator IS2 outputs a Low voltage from its output terminal OUT2L to the input terminal IN2' of the microcontroller MCU.

[0110] Even in the state shown in Figure 11, the fifth resistor R5, which is a pull-down resistor, connects the input terminal IN2H of the second signal isolator IS2 to ground via the second FET switch S6, thereby maintaining a potential difference of 0 between the input terminal IN2H and the ground terminal GND2H when no reverse current flows through the second Zener diode ZD2.

[0111] In the state shown in Figure 12, the bypass unit Bx corresponding to the battery module Mx targeted by the contact state detection process has the cutoff switch S1 closed and the bypass switch S2 open, while the other battery module Mx is connected. The operation is the same even if the other battery module Mx is in a bypass state.

[0112] In the state shown in Figure 12, current flows in the following order: battery module Mx, cutoff switch S1, second diode D2, fourth resistor R4, second Zener diode ZD2, second FET switch S6, third diode D3, and battery module Mx. A reverse current flows through the second Zener diode ZD2, and the potential difference between the input terminal IN2H and the ground terminal GND2H of the second signal isolator IS2 becomes equal to the Zener voltage of the second Zener diode ZD2. As a result, the logic value of the input signal at the input terminal IN2H of the second signal isolator IS2 becomes High. The second signal isolator IS2 outputs a High voltage from its output terminal OUT2L to the input terminal IN2' of the microcontroller MCU.

[0113] In contrast, no current flows through the first Zener diode ZD1, so the potential difference between the input terminal IN1H and the ground terminal GND1H of the first signal isolator IS1 becomes 0. As a result, the logic value of the input signal at the input terminal IN1H of the first signal isolator IS1 becomes Low. The first signal isolator IS1 outputs a Low voltage from its output terminal OUT1L to the input terminal IN1' of the microcontroller MCU.

[0114] In the state shown in Figure 13, the bypass unit Bx corresponding to the battery module Mx targeted for contact state detection processing has the cutoff switch S1 in the closed position and the bypass switch S2 in the open position, while the other battery module Mx is in the cutoff state.

[0115] In the state shown in Figure 13, as in the state shown in Figure 12, current flows in the following order: battery module Mx, cutoff switch S1, second diode D2, fourth resistor R4, second Zener diode ZD2, second FET switch S6, third diode D3, and battery module Mx. A reverse current flows through the second Zener diode ZD2, and the potential difference between the input terminal IN2H of the second signal isolator IS2 and the ground terminal GND2H becomes equal to the Zener voltage of the second Zener diode ZD2. As a result, the logic value of the input signal at the input terminal IN2H of the second signal isolator IS2 becomes High. The second signal isolator IS2 outputs a High voltage from its output terminal OUT2L to the input terminal IN2' of the microcontroller MCU.

[0116] In contrast, no current flows through the first Zener diode ZD1, so the potential difference between the input terminal IN1H and the ground terminal GND1H of the first signal isolator IS1 becomes 0. As a result, the logic value of the input signal at the input terminal IN1H of the first signal isolator IS1 becomes Low. The first signal isolator IS1 outputs a Low voltage from its output terminal OUT1L to the input terminal IN1' of the microcontroller MCU.

[0117] Figures 14 and 15 are flowcharts illustrating the process of switching the battery module M' targeted for bypass control from a connected state to a bypass state. First, in step S01, the string controller StC monitors the battery module Mx of the energy storage string STR and determines whether or not there is a battery module M' that requires bypass control. If the determination in step S01 is positive, the process proceeds to step S02; if the determination in step S01 is negative, the process ends.

[0118] At the start of the process shown in the flowcharts of Figures 14 and 15, the pre-charge relay S4 is open and the system main relay S3 is closed. Also, the first FET switch S5 and the second FET switch S6 are OFF. Furthermore, the smoothing capacitor C is in a charged state (post-pre-charge state).

[0119] In step S02, the string controller StC records the current connection or bypass status of the battery module Mx of the energy storage string STR in its built-in memory (not shown). Next, the string controller StC repeatedly executes the loop processing of steps S03 to S05 until the indicated value of the string current reaches a predetermined value (string current reduction processing). Here, in steps S03 to S05, the string controller StC gradually and continuously reduces the indicated value of the string current by a predetermined amount ΔP1 from the current value to the predetermined value.

[0120] First, in step S03, the string controller StC updates the indicated value of the string current to a value reduced by a predetermined amount ΔP1. This predetermined amount ΔP1 is set to a small amount to suit the purpose of preventing abrupt changes in the input and output power of the energy storage system 1. If the difference between the current value of the string current and the predetermined value is small, this predetermined amount ΔP1 may be equal to the difference between the current value of the string current and the predetermined value. On the other hand, if the difference between the current value of the string current and the predetermined value is relatively large, this predetermined amount ΔP1 may be less than the difference between the current value of the string current and the predetermined value. If this predetermined amount ΔP1 is less than the difference between the current value of the string current and the predetermined value, the string current update is repeated multiple times.

[0121] Next, in step S04, the string controller StC waits for a predetermined time T1 after transmitting the string current instruction value to the power converter PCS. This predetermined time T1 is set considering the time required for the string controller StC to control the power converter PCS and the rate of change of the string current.

[0122] Next, in step S05, the string controller StC determines whether the string current has reached a predetermined value (i.e., whether the decrease in string current has been completed). If the determination in step S05 is positive, the process proceeds to step S06; if the determination in step S05 is negative, the process proceeds to step S03.

[0123] Next, in step S06, the string controller StC sends a control signal to the relay driver RDp to switch the system main relay S3 from Close to Open. This disconnects the energy storage string STR from the power converter PCS.

[0124] Next, in step S07, the string controller StC sends a control signal to all module controllers MCx to open the disconnect switch S1 and bypass switch S2 of all bypass units Bx. In all module controllers MCx, the microcontroller MCU sends a control signal to the relay driver RD to open the disconnect switch S1 and bypass switch S2. The relay driver RD opens the corresponding disconnect switch S1 and bypass switch S2.

[0125] Next, in steps S08 to S11, all module controllers MCx perform contact state detection processing. First, in step S08, the microcontroller MCU of each module controller MCx outputs a gate drive signal from output terminal OUT1' to turn on the first FET switch S5, and outputs a gate drive signal from output terminal OUT2' to turn on the second FET switch S6. As a result, the first FET switch S5 turns ON (FET1: ON), and the second FET switch S6 turns ON (FET2: ON).

[0126] Next, in step S09, the microcontroller MCU of each module controller MCx determines whether the logic value of input terminal IN1' is High and the logic value of input terminal IN2' is High. If the determination in step S09 is positive, the process proceeds to step S10; if the determination in step S09 is negative, the process proceeds to step S11.

[0127] In this case, if both the cutoff switch S1 and the bypass switch S2 are open (the battery module Mx is in the cutoff state), the logic values ​​of the input signals at input terminals IN1' and IN2' will both be High.

[0128] In step S10, the microcontroller MCU of each module controller MCx stops the gate drive signals that were outputting from output terminals OUT1' and OUT2'. As a result, the first FET switch S5 turns OFF (FET1: OFF) and the second FET switch S6 turns OFF (FET2: OFF). In response, in step S11, the microcontroller MCU of each module controller MCx outputs a signal to the string controller StC indicating a switch malfunction.

[0129] Next, in step S12, the string controller StC sends a control signal to the power converter PCS to discharge the smoothing capacitor C. In this step, the charge of the smoothing capacitor C is removed so that the oxide film on the contact portion of the cutoff switch S1 can be removed in the first oxide film removal process (steps S18, S19). Note that the potential of the smoothing capacitor C does not need to be 0.

[0130] Next, in step S13, the string controller StC sends a control signal to the corresponding module controller MCx to switch the bypass switch S2 of the bypass unit Bx corresponding to the battery module Mx other than the battery module M' from Open to Close. Upon receiving this control signal, the microcontroller MCU of the module controller MCx sends a control signal to the relay driver RD to switch the bypass switch S2 from Open to Close.

[0131] Next, in steps S14 to S16, the module controller MCx corresponding to the battery module Mx other than battery module M' performs contact state detection processing. First, in step S14, the microcontroller MCU of each module controller MCx outputs a gate drive signal from output terminal OUT1' to turn on the first FET switch S5, and outputs a gate drive signal from output terminal OUT2' to turn on the second FET switch S6. As a result, the first FET switch S5 and the second FET switch S6 are turned on.

[0132] Next, in step S15, the microcontroller MCU of each module controller MCx determines whether the logic value of input terminal IN1' is High and the logic value of input terminal IN2' is Low. If the determination in step S15 is positive, the process proceeds to step S16; if the determination in step S15 is negative, the process proceeds to step S11.

[0133] Here, when the cutoff switch S1 is open and the bypass switch S2 is closed (the battery module Mx is in bypass mode), the logic value of input terminal IN1' becomes High, and the logic value of the input signal at input terminal IN2' becomes Low.

[0134] In step S16, the microcontroller MCU of each module controller MCx stops the gate drive signals that were outputting from output terminals OUT1' and OUT2'. As a result, the first FET switch S5 and the second FET switch S6 are turned OFF. In response to this, in step S11, the microcontroller MCU of each module controller MCx outputs a signal to the string controller StC indicating a switch malfunction.

[0135] Next, in step S17, the string controller StC sends a control signal to the relay driver RDp to switch the precharge relay S4 from open to closed. This connects the precharge circuit 10 to the power line PL, bypassing the system main relay S3.

[0136] Next, in step S18, the string controller StC sends a control signal to the module controller MCx corresponding to the battery module M' to switch the disconnect switch S1 from Open to Close. Upon receiving this control signal, the microcontroller MCU of the module controller MCx sends a control signal to the relay driver RD to switch the disconnect switch S1 from Open to Close.

[0137] Next, in step S19, the string controller StC waits for a predetermined time T2 after switching the cutoff switch S1 from Open to Close. This predetermined time T2 is the time required to charge the smoothing capacitor C and is set considering the time constant (τ=CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the resistor R. As a result, the first oxide film removal process is performed and the oxide film on the contact portion of the cutoff switch S1 is removed.

[0138] Next, in step S20, the string controller StC sends a control signal to the module controller MCx corresponding to the battery module M' to switch the disconnect switch S1 from Close to Open. Upon receiving this control signal, the microcontroller MCU of the module controller MCx sends a control signal to the relay driver RD to switch the disconnect switch S1 from Open to Close.

[0139] Next, in steps S21 to S23, the module controller MCx corresponding to the battery module M' performs contact state detection processing. First, in step S21, the microcontroller MCU of the module controller MCx outputs a gate drive signal from output terminal OUT1' to turn on the first FET switch S5, and outputs a gate drive signal from output terminal OUT2' to turn on the second FET switch S6. As a result, the first FET switch S5 and the second FET switch S6 are turned on.

[0140] Next, in step S22, the microcontroller MCU of the module controller MCx determines whether the logic value of input terminal IN1' is High and the logic value of input terminal IN2' is High. If the determination in step S22 is positive, the process proceeds to step S23; if the determination in step S22 is negative, the process proceeds to step S11.

[0141] Here, if both the cutoff switch S1 and the bypass switch S2 are open (the battery module M' is in the cutoff state), the logic values ​​of the input signals at input terminals IN1' and IN2' will both be High.

[0142] In step S23, the microcontroller MCU of the module controller MCx corresponding to the battery module M' stops the gate drive signals that were outputting from output terminals OUT1' and OUT2'. In response, in step S11, the microcontroller MCU of the module controller MCx outputs a signal detecting a switch malfunction to the string controller StC.

[0143] Next, in step S24, the string controller StC sends a control signal to the module controller MCx corresponding to the battery module M' to switch the bypass switch S2 from Open to Close. Upon receiving this control signal, the microcontroller MCU of the module controller MCx sends a control signal to the relay driver RD to switch the bypass switch S2 from Open to Close.

[0144] Next, in step S25, the string controller StC waits for a predetermined time T3 after switching the bypass switch S2 from Open to Close. This predetermined time T3 is the time required for the smoothing capacitor C to discharge, and is set considering the time constant (τ=CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the resistor R. This allows the second oxide film removal process to be performed, and the oxide film on the contact portion of the bypass switch S2 is removed.

[0145] Next, in step S26, the string controller StC sends a control signal to the relay driver RDp to switch the pre-charge relay S4 from Close to Open. Next, in step S27, the string controller StC sends a control signal to the corresponding module controller MCx to switch the connected / bypass state of the battery module Mx to a state that reflects the bypass control. The state that reflects the bypass control is the state in which the battery module M' that was determined to require bypass control in step S01, based on the connected / bypass state of the battery module Mx stored in memory in step S02, is in the bypass state. Although not explained here, after the execution of step S27, all module controllers MCx perform contact state detection processing.

[0146] Next, in step S28, the string controller StC sends a control signal to the relay driver RDp to switch the pre-charge relay S4 from Open to Close. Then, in step S29, the string controller StC waits for a predetermined time T4 after switching the pre-charge relay S4 from Open to Close. This predetermined time T4 is the time required to charge the smoothing capacitor C, and is set considering the time constant (τ=CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the resistor R. As a result, the pre-charge process is performed and the smoothing capacitor C is charged.

[0147] Next, in step S30, the string controller StC sends a control signal to the relay driver RDp to switch the system main relay S3 from open to closed. This connects the energy storage string STR to the power converter PCS.

[0148] Next, in step S31, the string controller StC sends a control signal to the relay driver RDp to switch the precharge relay S4 from Close to Open. This completes the bypass control of the battery module M', the removal of the oxide film from the contacts of the disconnect switch S1 and bypass switch S2 corresponding to the battery module M', and the precharging of the smoothing capacitor C. This completes the process shown in the flowcharts of Figures 14 and 15.

[0149] As described above, in the energy storage system 1 according to this embodiment, the smoothing capacitor C is provided to connect the positive and negative sides of the power line PL that connects a plurality of battery modules Mx in series. On the other hand, the first contact state detection circuit DC1 is connected to the power line PL so as to straddle the cutoff switch S1, and the second contact state detection circuit DC2 is connected to the power line PL so as to straddle the bypass switch S2 via the rectifier circuit RFC. Thus, the first contact state detection circuit DC1, the second contact state detection circuit DC2, and the power line PL form a charging and discharging circuit for the smoothing capacitor C.

[0150] In response, the first FET switch S5 and the second FET switch S6 connect or disconnect the charging and discharging circuit of the smoothing capacitor C. By doing so, the charging and discharging circuit of the smoothing capacitor C is disconnected by the first FET switch S5 and the second FET switch S6, preventing unintended charging and discharging of the smoothing capacitor C that occurs through the first contact state detection circuit DC1 and the second contact state detection circuit DC2. Therefore, the contact state of the disconnect switch S1 and the bypass switch S2 can be detected, and the smoothing capacitor C can be controlled to a desired potential to remove the oxide film on the contact portions of the disconnect switch S1 and the bypass switch S2.

[0151] Furthermore, in the energy storage system 1 according to this embodiment, a first FET switch S5 is provided in the first contact state detection circuit DC1 to connect or disconnect the first contact state detection circuit DC1. Also, a second FET switch S6 is provided in the second contact state detection circuit DC2 to connect or disconnect the second contact state detection circuit DC2.

[0152] The microcontroller MCU of each module controller MCx turns on the first FET switch S5 and the second FET switch S6 when it detects the contact state of the cutoff switch S1 and the bypass switch S2. This enables detection of the contact state of the cutoff switch S1 and the bypass switch S2. Conversely, the microcontroller MCU of each module controller MCx turns off the first FET switch S5 and the second FET switch S6 except when it detects the contact state of the cutoff switch S1 and the bypass switch S2. This prevents unintended charging and discharging of the smoothing capacitor C that occurs through the first contact state detection circuit DC1 and the second contact state detection circuit DC2.

[0153] Here, since the first FET switch S5 is provided in the first contact state detection circuit DC1 and the second FET switch S6 is provided in the second contact state detection circuit DC2, the voltage withstand capability requirement is lower compared to when they are connected in series with the smoothing capacitor C. Therefore, it becomes possible to connect / disconnect the charging / discharging circuit of the smoothing capacitor C without using FET switches with high voltage withstand capability.

[0154] Furthermore, in the energy storage system 1 according to this embodiment, a first Zener diode ZD1 is provided in the first contact state detection circuit DC1, and current is introduced or not introduced from the power line PL side depending on the state of the cutoff switch S1. The microcontroller MCU has an input terminal IN1' and a ground terminal GND' connected to the first Zener diode ZD1 via a first signal isolator IS1, and detects the state of the contacts of the cutoff switch S1 based on the potential difference between the two terminals.

[0155] Furthermore, a second Zener diode ZD2 is provided in the second contact state detection circuit DC2, and depending on the state of the bypass switch S2, current is introduced or not introduced from the power line PL side. The microcontroller MCU has an input terminal IN2' and a ground terminal GND' connected to the second Zener diode ZD2 via a second signal isolator IS2, and detects the state of the contacts of the bypass switch S2 based on the potential difference between the two ends.

[0156] Here, a charging and discharging circuit for the smoothing capacitor C is formed through the first Zener diode ZD1 and the second Zener diode ZD2. The first FET switch S5 and the second FET switch S6 are provided to connect and disconnect this charging and discharging circuit for the smoothing capacitor C. Therefore, unintended charging and discharging of the smoothing capacitor C through the first Zener diode ZD1 and the second Zener diode ZD2 can be prevented.

[0157] Furthermore, in the energy storage system 1 according to this embodiment, the cutoff switch S1 and the bypass switch S2 are mechanical relays. Mechanical relays are operated when a voltage above a certain level is applied to the contact portion, and when an arc discharge with a current value above a certain level occurs at the contact portion, the oxide film formed on the contact portion is removed over time. However, in the energy storage system 1 according to this embodiment, bypass control is performed with the string current reduced, so the oxide film is not removed when bypass control is performed.

[0158] In contrast, the energy storage system 1 according to this embodiment performs a first oxide film removal process and a second oxide film removal process using the smoothing capacitor C. Specifically, the string controller StC performs a first oxide film removal process by operating the interruption switch S1 while keeping the bypass switch S2 in the open state during discharge of the smoothing capacitor C. This removes the oxide film formed on the contact portion of the interruption switch S1. Furthermore, the string controller StC performs a second oxide film removal process by operating the bypass switch S2 while keeping the interruption switch S1 in the open state during charge of the smoothing capacitor C. This removes the oxide film formed on the contact portion of the bypass switch S2.

[0159] Figure 16 is a circuit diagram showing a power storage system 1' according to another embodiment of the present invention. In the power storage system 1' shown in this figure, a first FET switch S5 is provided between a first resistor R1 and the input terminal IN1H of the first signal isolator IS1 (see Figure 2). In addition, a second FET switch S6 is provided between a fourth resistor R4 and the input terminal IN2H of the second signal isolator IS2 (see Figure 2).

[0160] The gate of the first FET switch S5 is connected to the output terminal OUT1H of the first signal isolator IS1 via the third resistor R3 (see Figure 2). The drain of the first FET switch S5 is connected to the other end of the first resistor R1, and the source of the first FET switch S5 is connected to the input terminal IN1H of the first signal isolator IS1 and the cathode of the first Zener diode ZD1.

[0161] The gate of the second FET switch S6 is connected to the output terminal OUT2H of the second signal isolator IS2 via the seventh resistor R7 (see Figure 2). The drain of the second FET switch S6 is connected to the other end of the fourth resistor R4, and the source of the second FET switch S6 is connected to the input terminal IN2H of the second signal isolator IS2 and the cathode of the second Zener diode ZD2.

[0162] The first FET switch S5 may be provided on the first ground line GL1. The second FET switch S6 may be provided on the second ground line GL2.

[0163] Figure 17 is a circuit diagram showing another embodiment of the present invention, energy storage system 1''. In this energy storage system 1'', the first FET switch S5 is connected in series with the smoothing capacitor C. The second FET switch S6 is not provided.

[0164] The gate of the first FET switch S5 is connected to the output terminal OUT1H of the first signal isolator IS1 via the third resistor R3 (see Figure 2). The drain of the first FET switch S5 is connected to one end of the smoothing capacitor C, and the source of the first FET switch S5 is connected to the power line PL.

[0165] Note that the first FET switch S5 can also be replaced with the system main relay S3 and the pre-charge relay S4. By opening the system main relay S3 and the pre-charge relay S4, the charging and discharging circuit of the smoothing capacitor C can be interrupted.

[0166] Figure 18 is a schematic circuit diagram showing another embodiment of the energy storage system 1X of the present invention. The energy storage system 1X shown in this figure differs from the embodiment described above in that it is equipped with a first FET switch S5X, which is a p-channel MOSFET, instead of the first FET switch S5, which is an n-channel MOSFET. The first FET switch S5X is connected in series with the smoothing capacitor C. The second FET switch S6 is not provided.

[0167] The gate of the first FET switch S5X is connected to the output terminal OUT1H of the first signal isolator IS1 (see Figure 2). Note that the third resistor R3 is unnecessary, simplifying the gate drive circuit.

[0168] The drain of the first FET switch S5X is connected to one end (positive terminal) of the smoothing capacitor C, and the source of the first FET switch S5X is connected to the total positive power line PL of the energy storage string STR. When a negative voltage is applied between the gate and source of the first FET switch S5X, the first FET switch S5X is turned ON, and the charging and discharging circuit of the smoothing capacitor C is connected.

[0169] Although the present invention has been described above based on the embodiments described above, the present invention is not limited to the embodiments described above, and modifications may be made, or publicly known or well-known technologies may be combined as appropriate, without departing from the spirit of the present invention.

[0170] For example, in the above embodiment, the switch that connects / disconnects the charging / discharging circuit of the smoothing capacitor C formed through the first contact state detection circuit DC1 and the second contact state detection circuit DC2 is an FET. However, this switch may be other switches such as a mechanical relay or a bipolar transistor.

[0171] Furthermore, in the above-described embodiment, a first Zener diode ZD1 is provided in the first contact state detection circuit DC1 and a second Zener diode ZD2 is provided in the second contact state detection circuit DC2. However, instead of the first Zener diode ZD1 and the second Zener diode ZD2, switching elements such as PNP or NPN transistors may be provided.

[0172] Furthermore, in the above-described embodiment, a first contact state detection circuit DC1 for detecting the contact state of the cutoff switch S1 and a second contact state detection circuit DC2 for detecting the contact state of the bypass switch S2 are provided. However, it is also possible to provide only one of the first contact state detection circuit DC1 and the second contact state detection circuit DC2.

[0173] Furthermore, in the above-described embodiment, the cutoff switch S1 and the bypass switch S2 are mechanical relays, but at least one of the cutoff switch S1 and the bypass switch S2 may be a semiconductor switch. In this case, the first oxide film removal treatment or the second oxide film removal treatment only needs to be performed on one of the mechanical relays, the cutoff switch S1 and the bypass switch S2.

[0174] Furthermore, the timing for executing the first oxide film removal process and the second oxide film removal process, as well as the battery modules M1 to Mn targeted by the first and second oxide film removal processes, can be set as appropriate.

[0175] Furthermore, in the first oxide film removal process, it is not essential to remove the oxide film from the contact portion of the cutoff switch S1 using the charging current of the smoothing capacitor C. In the first oxide film removal process, the cutoff switch S1 may be operated to form a circuit and discharge the smoothing capacitor C, thereby removing the oxide film from the contact portion of the cutoff switch S1 using the discharge current of the smoothing capacitor C.

[0176] Furthermore, in the second oxide film removal process, it is not essential to remove the oxide film from the contact portion of the bypass switch S2 using the discharge current of the smoothing capacitor C. In the second oxide film removal process, the oxide film from the contact portion of the bypass switch S2 may be removed by operating the bypass switch S2 to form a circuit and charge the smoothing capacitor C, thereby using the charging current of the smoothing capacitor C.

[0177] Furthermore, in the above-described embodiment, the indicated value of the string current is changed gradually and continuously over time by a predetermined amount ΔP1 until it reaches the target value. However, if, for example, the effect of the change in string current on the input and output power of the energy storage system 1,1',1'' is negligible, the indicated values ​​of the string current may be changed simultaneously.

[0178] Furthermore, in the above-described embodiment, a pre-charge circuit 10 was given as an example that includes a pre-charge resistor Rp and a pre-charge relay S4. However, the pre-charge circuit 10 only needs to have a function to suppress the inrush current to the smoothing capacitor C, and for example, a constant current diode or the like may be provided instead of the pre-charge resistor Rp.

[0179] Furthermore, in the above embodiment, the smoothing capacitor C is provided outside the power converter PCS, but the smoothing capacitor C may be replaced with a capacitor built into the power converter PCS that connects the total positive and total negative terminals of the energy storage string STR. [Explanation of Symbols]

[0180] 1: Energy storage system 1': Energy storage system 1”: Energy storage system 1X: Energy storage system 100: Battery control device (control unit) B1~Bn, Bx, B': Bypass unit (bypass section) C: Smoothing capacitor (capacitor) DC1: First contact state detection circuit (circuit section, contact state detection section) DC2: Second contact state detection circuit (circuit section, contact state detection section) GND': Ground terminal IN1', IN2': Input terminals M1~Mn, Mx, M': Battery module (battery) MCU: Microcontroller (detection unit, contact state detection unit) PL: Power line S1: Disconnection switch (first switch) S2: Bypass switch (second switch) S3: System main relay (3rd switch) S4: Pre-charge relay (3rd switch) S5: First FET switch (third switch) S5X: 1st FET switch (3rd switch) S6: Second FET switch (third switch) StC: String Controller (Control Unit) ZD1: First Zener diode (element) ZD2: Second Zener diode (element)

Claims

1. A power line connecting multiple storage batteries in series, The system comprises a first switch connected in series with the battery via the aforementioned power line, a second switch connected in parallel with the battery and the first switch, and a plurality of bypass sections provided for each battery, A capacitor connecting the positive and negative sides of the power line, The power line is connected to the power line so as to straddle one of the first switch and the second switch, and current flows from the power line side or not depending on the state of the contact of one of the first switch and the second switch; the power line is connected to the power line so as to straddle the first switch and the second switch, and the power line is connected to the power line so as to whether or not current flows from the power line side; the power line is connected to the power line, and current flows from the power line side or not depending on the state of the contact of one of the first switch and the second switch; and the power line is connected to the power line, and the power line is connected to the power line, and current flows from the power line side or not depending on the state of the contact of one of the first switch and the second switch; and the power line is connected to the power line, and the power line is connected to the power line, and current flows from the power line side or not depending on the state of the contact of one of the first switch and the second switch; and the power line is connected to the power line, and current flows from the power line side or not depending on the state of the contact of one of the first switch and the second switch; and the power line is connected to the power line, and current flows from the power line side or not depending on the state of the contact of one of the first switch and the second switch; and the power line is connected to the power line, and current flows from the power line, and current flows from the power line, and current flows from the power line, and current flows from the power line, and current flows from the power line, and current flows from the power line, and the power line is connected to the power line, and current flows from the power line, and current flows from the power line, and current flows from the power line, and the power line A third switch that connects or disconnects the charging and discharging circuit of the capacitor formed through the circuit section. A battery storage system equipped with the following features.

2. The third switch is provided in the circuit section and connects or disconnects the circuit section. The detection unit, except when detecting the state of one of the contacts of the first switch or the second switch, disconnects the circuit using the third switch, and when detecting the state of one of the contacts of the first switch or the second switch, connects the circuit using the third switch. The energy storage system according to claim 1.

3. The circuit section includes an element that introduces or does not introduce current from the power line side depending on the potential difference between the first switch and the second switch. The detection unit includes an input terminal and a ground terminal connected to the element, and detects the state of one of the contacts of the first switch and the second switch based on the potential difference between the input terminal and the ground terminal. The energy storage system according to claim 1 or 2.

4. The first switch and the second switch are mechanical relays, When the capacitor is discharged, the control unit maintains one of the first and second switches in the open position, and moves the other of the first and second switches from the open position to the closed position. The energy storage system according to claim 1 or 2, comprising:

5. The first switch and the second switch are mechanical relays, When the capacitor is being charged, the control unit operates the other of the first and second switches from the open state to the closed state while keeping one of the first and second switches in the open state. The energy storage system according to claim 1 or 2, comprising:

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