Energy storage system

Abstract

A contact state detection circuit (DCx) comprises a signal insulator (IS), a first resistor (R1), a second resistor (R2), a first transistor (T1), a third resistor (R3), a second transistor (T2), and a first diode (D1). The resistance values of the second resistor (R2) and the third resistor (R3) are set such that, when the first transistor (T1) is on and the second transistor (T2) is off, the potential difference between a second input terminal (IN2) and the ground terminal (GND) is not more than a low-level threshold value.

Description

Power storage system

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

[0002] As a power storage system in which a plurality of storage batteries are connected in series, a bypass unit that switches 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 unit. 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 (Open) and the second switch corresponding to the storage battery is in a closed state (Close), and discharge is performed from other storage batteries in the connected state.

[0003] There is known a power storage system in which two sets of battery packs are connected in series via a main switch, and each cell of one battery pack and each cell of the other battery pack are connected in parallel via a parallel connection switch (see, for example, Patent Document 2). In the power storage system described in Patent Document 2, after the main switch is opened, the control of the parallel connection switch is started after confirming that all the parallel connection switches are in the open state, in order to prevent an overcurrent caused by sticking of the parallel connection switch. In this power storage system, by opening the main switch and confirming that the voltage between the terminals for extracting the power of the power storage system is 0V, it is confirmed that all the parallel connection switches are in the open state.

[0004] Japanese Patent Application Laid-Open No. 2013-31247, Japanese Patent Application Laid-Open No. 2002-42901

[0005] In the power storage system described in Patent Document 1, when a failure such as sticking occurs in the first switch or the second switch, the first switch or the second switch does not operate according to the command of the control system. At this time, the state of the contacts of the first switch and the second switch is not detected. Therefore, there is a possibility that the first switch and the second switch may be closed at the same time, causing a short circuit of the storage battery. Therefore, a contact state detection circuit for detecting the state of the contacts of the first switch and the second switch is required.

[0006] Here, we consider a case in which a contact state detection circuit is provided in the energy storage system described in Patent Document 1, and a capacitor is provided to connect the positive and negative sides of the energy storage system for the purpose of smoothing current and voltage and removing ripple voltage. In this case, it is necessary to control the charge state of the capacitor, but it is conceivable that controlling the charge state of the capacitor becomes difficult because the capacitor charges and discharges through the contact state detection circuit.

[0007] In the energy storage system described in Patent Document 2, the main switch must be in the open state in order to detect the state of the contacts of the parallel connection switch, and the state of the contacts of the parallel connection switch cannot be detected when the main switch is in the closed state.

[0008] In view of the above circumstances, the present invention aims to provide an energy storage system in which a plurality of storage batteries are connected in series by a power line, a bypass section is provided for each storage battery, and a capacitor is provided to connect the positive and negative terminals of the power line, in which the state of the switch contacts of the bypass section corresponding to any storage battery can be detected regardless of the connection state of the other storage batteries, and unnecessary charging and discharging of the capacitor can be suppressed.

[0009] The present invention provides an energy storage system comprising: a power line connecting a plurality of batteries in series; a first switch connected to the positive terminal of the batteries; 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 third switch provided between the capacitor and the batteries; a precharge switch and a precharge resistor connected in series; a precharge circuit connected in parallel with the third switch; and a plurality of contact state detection circuits provided for each battery for detecting the state of the contacts between the first switch and the second switch, wherein the contact state detection circuit comprises a first input terminal, a second input terminal, and a ground terminal connected to the first switch and the second switch; a signal output section that outputs a first signal corresponding to the potential difference between the first input terminal and the ground terminal, and a second signal corresponding to the potential difference between the second input terminal and the ground terminal; and the first switch and the batteries The device comprises a first resistor connected to the positive terminal of the battery and the first input terminal, a second resistor connected to the second switch and the negative terminal of the battery, a first transistor whose emitter is connected to the second resistor and whose base is connected to the first switch, the second switch and the ground terminal, a third resistor connected to the collector of the first transistor, the power supply voltage and the second input terminal, a second transistor whose base is connected to the second resistor and the emitter of the first transistor, whose collector is connected to the collector of the first transistor, the third resistor and the second input terminal, and whose emitter is connected to the first switch, the second switch and the ground terminal, and a first diode whose cathode is connected to the third resistor and the power supply voltage and whose anode is connected to the first resistor and the first input terminal, wherein the resistance values ​​of the second resistor and the third resistor are set such that the potential difference between the second input terminal and the ground terminal is less than or equal to a Low level threshold when the first transistor is ON and the second transistor is OFF.

[0010] According to the present invention, in an energy storage system in which a plurality of storage batteries are connected in series by a power line, a bypass section is provided for each storage battery, and a capacitor is provided to connect the positive and negative terminals of the power line, the state of the switch contacts of the bypass section corresponding to any storage battery can be detected regardless of the connection state of the other storage batteries, and unnecessary charging and discharging of the capacitor can be suppressed.

[0011] Figure 1 is a schematic circuit diagram showing an outline of an energy storage system according to one embodiment of the present invention. Figure 2 is a circuit diagram showing the contact state detection circuit, etc., of the energy storage system shown in Figure 1. Figure 3 is a circuit diagram showing the operation of the contact state detection circuit shown in Figure 2. Figure 4 is a circuit diagram showing the operation of the contact state detection circuit shown in Figure 2. Figure 5 is a circuit diagram showing the operation of the contact state detection circuit shown in Figure 2. Figure 6 is a circuit diagram showing the operation of the contact state detection circuit shown in Figure 2. Figure 7 is a circuit diagram showing the operation of the contact state detection circuit shown in Figure 2. Figure 8 is a circuit diagram showing the operation of the contact state detection circuit shown in Figure 2. Figure 9 is a circuit diagram for explaining the first oxide film removal process of the energy storage system shown in Figure 1. Figure 10 is a circuit diagram for explaining the second oxide film removal process of the energy storage system shown in Figure 1. Figure 11 is a flowchart for explaining the process of switching the battery module targeted for bypass control from a connected state to a bypass state in the energy storage system shown in Figure 1. Figure 12 is a flowchart illustrating the process of switching the battery module targeted for bypass control from a connected state to a bypass state in the energy storage system shown in Figure 1.

[0012] The present invention will be described below in accordance with preferred embodiments. However, the present invention is not limited to the embodiments shown below, and embodiments can be modified as appropriate without departing from the spirit of the invention. Furthermore, in the embodiments shown below, some components are not illustrated or described; however, details of the omitted technologies can be appropriately referred to from publicly known or well-known technologies, to the extent that they do not contradict the content described below.

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

[0014] The energy storage string STR comprises a power line PL and n (where n is an integer of 2 or more) battery modules M1 to Mn connected in series by the power line PL. Although not particularly limited, the battery modules M1 to Mn in this embodiment are refurbished used batteries, and there are differences in the degree of degradation of each battery module M1 to Mn. The battery modules M1 to Mn are, for example, composed of multiple cells of secondary batteries such as lithium-ion batteries, lithium-ion capacitors, and nickel-metal hydride batteries connected together.

[0015] Battery modules M1 to Mn are charged by power supplied from the external grid via the string bus 2 and the power converter PCS. Furthermore, battery modules M1 to Mn supply power to the external grid via 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 an AC / DC converter and is connected to the 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 the string bus 2 to the battery storage string STR according to the specified value of the charging power (or current) 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 the battery storage modules M1 to Mn (the number of battery storage modules M1 to Mn that are bypassed) and the charge state of the battery storage modules M1 to Mn. Therefore, the power converter PCS converts the voltage input from the 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] The power converter PCS converts the voltages input from multiple battery modules M1 to Mn during the discharge of the energy storage string STR, according to the indicated discharge power (or current), and outputs them 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 the string bus 2 is alternating current, the power converter PCS is equipped with a synchronization means to track changes in instantaneous values.

[0022] The energy storage string STR comprises n bypass units BU1 to BUn, n contact state detection circuits DC1 to DCn, a system main relay SMR, a smoothing capacitor C, a precharge circuit 10, a current sensor 11, and various sensors (not shown). The bypass units BU1 to BUn and the contact state detection circuits DC1 to DCn are provided for each battery module M1 to Mn.

[0023] Each bypass unit BU1 to BUn is equipped with a circuit breaker switch S1, a bypass line BL, and a bypass switch S2. The circuit breaker switch S1 is a mechanical relay connected in series with each battery module M1 to Mn via a power line PL. The circuit breaker switch S1 is located on the total positive side of the energy storage string STR, more so than each battery module M1 to Mn, and is connected to the positive terminal of each battery module M1 to Mn via the power line PL.

[0024] The bypass line BL is a power line that bypasses each battery module M1 to Mn and the trip switch S1. One end of the bypass line BL is connected to the power line PL at node P1 (see Figure 2), and via the power line PL it is connected to the positive terminal of the trip switch S1. The other end of the bypass line BL is connected to the power line PL at node P2 (see Figure 2), and via the power line PL it is connected to the negative terminals of each battery module M1 to Mn. The 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 trip switch S1.

[0025] The starting battery module M1 and the ending battery module Mn are connected to the external system via the power line PL, power converter PCS, and string bus 2. When the bypass switch S2 is opened and the circuit breaker switch S1 is closed in any of the bypass units BU1 to BUn, the battery modules M1 to Mn corresponding to those bypass units BU1 to BUn are connected in series to the external system. On the other hand, when the circuit breaker switch S1 is opened and the bypass switch S2 is closed in any of the bypass units BU1 to BUn, the battery modules M1 to Mn corresponding to those bypass units BU1 to BUn are bypassed. When it is not necessary to distinguish each bypass unit BU1 to BUn from other bypass units BU1 to BUn, it will be referred to as bypass unit BUx. Similarly, when it is not necessary to distinguish each battery module M1 to Mn from other battery modules M1 to Mn, it will be referred to as battery module Mx.

[0026] Each contact state detection circuit DC1 to DCn is a circuit that detects the contact state (Open or Close) of the cutoff switch S1 and bypass switch S2 of the corresponding bypass unit BUx. When it is not necessary to distinguish each contact state detection circuit DC1 to DCn from other contact state detection circuits DC1 to DCn, they will be referred to as contact state detection circuit DCx. The configuration of each contact state detection circuit DCx will be described later.

[0027] The system main relay SMR is installed in a location on the power line PL that is always energized. Specifically, the system main relay SMR is installed between the total + of the energy storage string STR and the trip switch S1 of the bypass unit BU1 at the starting end. The system main relay SMR can be a mechanical relay, a semiconductor switch, etc.

[0028] The smoothing capacitor C connects the total positive and total negative terminals of the energy storage string STR. Specifically, the smoothing capacitor C connects the system main relay SMR and the power converter PCS on the positive side of the power line PL, and the battery module Mn and the power converter PCS on the negative side of the power line PL. The smoothing capacitor C is an element that stores electric charge, such as an electrolytic capacitor, film capacitor, or 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 switch Sp. The precharge switch Sp is a mechanical relay, a semiconductor switch, etc. The precharge resistor Rp and the precharge switch Sp are connected in series and are connected in parallel with the system main relay SMR. 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 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.

[0031] 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 the others, they will be referred to as module controller MCx.

[0032] The microcontroller MCU is a control device that performs control and status monitoring of the battery module Mx and the bypass unit BUx, and transmits status information of the corresponding battery module Mx and bypass unit BUx to the string controller StC. Status information of the battery module Mx includes the voltage, temperature, and cell voltage of the battery module Mx. Status information of the bypass unit BUx includes the contact status of the cutoff switch S1 and the bypass switch S2.

[0033] Furthermore, the microcontroller MCU determines whether it is necessary to switch the cutoff switch S1 and bypass switch S2 of the corresponding bypass unit BUx 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 BUx. 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 perform bypass control for the corresponding bypass unit BUx. Note that the determination of whether it is necessary to switch the cutoff switch S1 and bypass switch S2 of the bypass unit BUx 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.

[0034] When the microcontroller MCU determines that switching of the cutoff switch S1 and bypass switch S2 is necessary for the corresponding bypass unit BUx, 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 signal to the string controller StC according to the state of the contact state detection circuit DCx.

[0035] 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 the bypass switch S2, it is not necessary to transmit the switch switching request signal from the string controller StC to the system controller SyC.

[0036] 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.

[0037] The microcontroller MCU sends a switch switching signal to the relay driver RD when performing bypass control and connection control. 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.

[0038] Here, the microcontroller MCU executes a process to detect the state of the contacts of the disconnect switch S1 and the bypass switch S2 (hereinafter referred to as the contact state detection process) when bypass control and connection control are performed. The contact state detection process will be described later.

[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 SMR and the precharge switch Sp 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 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 energy storage string STR includes detecting the 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). 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] 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, according to 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.

[0042] Each string controller StC executes bypass control of the bypass unit BUx for any one of the battery modules Mx when a request for switching the open / close of the cutoff switch S1 and the bypass switch S2 of the bypass unit BUx (hereinafter referred to as a bypass control request) is permitted by the system controller SyC. Here, when executing the bypass control, the string controller StC executes a first oxide film removal process and a second oxide film removal process.

[0043] Before executing the bypass control, a string current reduction process is executed. When executing the bypass control, a first oxide film removal process and a second oxide film removal process are executed. After executing the bypass control, a precharge process is executed. The string current reduction process is a process of reducing the string current to a predetermined value. The predetermined value is set to a low value such that the fluctuation of the input / output power of the entire power storage system 1 is suppressed within an allowable range when the bypass control of the power storage string STR is executed.

[0044] Here, in the string current reduction process, the string controller StC gradually and continuously reduces the commanded value of the string current from the current value to the predetermined value. Specifically, the string controller StC repeatedly updates the commanded value of the string current by a predetermined amount ΔP1 obtained by equally dividing the difference between the current value and the predetermined value of the commanded value of the string current. At this time, the change rate (amount of change per unit time) of the commanded value of the string current is set such that the fluctuation of the input / output power of the entire power storage system 1 is suppressed within an allowable range. Thereby, the power converter PCS gradually and continuously reduces the string current from the current value to the predetermined value so as to suppress the fluctuation of the input / output power of the entire power storage system 1 within an allowable range.

[0045] FIG. 2 is a circuit diagram showing a contact state detection circuit DCx and the like of the power storage system 1 shown in FIG. 1. As shown in this figure, the contact state detection circuit DCx includes a first resistor R1, a second resistor R2, a first transistor T1, a third resistor R3, a second transistor T2, a first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, a Zener diode ZD1, and a signal isolator IS.

[0046] The signal isolator IS is an element that transmits signals between the high-voltage side and the low-voltage side while insulating the high-voltage side and the low-voltage side, such as a digital isolator or a photocoupler. The signal isolator IS incorporates a power supply. Note that it is not essential for the signal isolator IS to incorporate a power supply, and a voltage may be applied to the power supply terminal +V from an external isolated DC / DC converter.

[0047] The first input terminal IN1 and the second input terminal IN2 are input terminals provided on the high-voltage side of the signal isolator IS. The power supply terminal +V is provided on the high-voltage side of the signal isolator IS and is a power supply terminal for connecting to the built-in power supply. The ground terminal GND is a ground terminal provided on the high-voltage side of the signal isolator IS and is connected to the node P1 via the ground wire GL. The first output terminal OUT1 and the second output terminal OUT2 are output terminals provided on the low-voltage side of the signal isolator IS. The first output terminal OUT1 is connected to the first input terminal IN1' of the microcontroller MCU, and the second output terminal OUT2 is connected to the second input terminal IN2' of the microcontroller MCU. Here, the signal isolator IS insulates the high-voltage circuit including the battery module Mx, etc. and the low-voltage circuit including the microcontroller MCU, etc.

[0048] One end of the first resistor R1 is connected to the power line PL at the node P3 between the cutoff switch S1 and the positive electrode of the battery module Mx. The other end of the first resistor R1 is connected to the first input terminal IN1 of the signal isolator IS.

[0049] One end of the second resistor R2 is connected to node P2. The first transistor T1 is a bipolar transistor. The emitter e1 of the first transistor T1 is connected to the other end of the second resistor R2. The base b1 of the first transistor T1 is connected to the ground line GL, and via the ground line GL, it is connected to node P1 and the ground terminal GND. The first transistor T1 turns ON when a positive voltage is applied between the base b1 and the emitter e1, and turns OFF when the potential difference between the base b1 and the emitter e1 is 0, or when a negative voltage is applied between the base b1 and the emitter e1. Here, a bipolar transistor has a lower voltage threshold between the base b1 and the emitter e1 than a MOSFET (metal-oxide-semiconductor field-effect transistor), and can be turned ON with a smaller potential difference than a MOSFET. In this embodiment, since the voltage between the base b1 and the emitter e1 is low, a bipolar transistor is more suitable than a MOSFET as the first transistor T1.

[0050] One end of the third resistor R3 is connected to the collector c1 of the first transistor T1, and the other end of the third resistor R3 is connected to the power supply terminal +V. That is, the emitter e1 of the first transistor T1 is connected to node P2 via the second resistor R2, and the collector c1 of the first transistor T1 is connected to the power supply terminal +V via the third resistor R3.

[0051] The second transistor T2 is a bipolar transistor. The base b2 of the second transistor T2 is connected to the other end of the second resistor R2 and to the emitter e1 of the first transistor T1. The collector c2 of the second transistor T2 is connected to the collector c1 of the first transistor T1, one end of the third resistor R3 and to the second input terminal IN2. The emitter e2 of the second transistor T2 is connected to the ground line GL, and via the ground line GL, it is connected to node P1 and the ground terminal GND. The second transistor T2 turns ON when a positive voltage is applied between the base b2 and the emitter e2, and turns OFF when the potential difference between the base b2 and the emitter e2 is 0, or when a negative voltage is applied between the base b2 and the emitter e2. Here, a bipolar transistor has a lower voltage threshold between the base b2 and the emitter e2 than a MOSFET, and can be turned ON with a smaller potential difference than a MOSFET. In this embodiment, since the voltage between the base b2 and the emitter e2 is low, a bipolar transistor is more suitable than a MOSFET as the second transistor T2. The node P4 between the other end of the second resistor R2 and the emitter e1 of the first transistor T1 is connected to the ground terminal GND via the second transistor T2 and the ground line GL.

[0052] The first diode D1 is a rectifier element that causes the first input terminal IN1 to conduct to the power supply terminal +V when the potential of the first input terminal IN1 is higher than the sum of the potential of the power supply terminal +V and the forward voltage of the first diode D1. The cathode of the first diode D1 is connected to the other end of the third resistor R3 and to the power supply terminal +V, and the anode of the first diode D1 is connected to the other end of the first resistor R1 and to the first input terminal IN1.

[0053] The resistance values ​​of the second resistor R2 and the third resistor R3 are set so that the potential difference between the second input terminal IN2 and the ground terminal GND is below the Low level threshold when the first transistor T1 is ON and the second transistor T2 is OFF. Furthermore, the resistance value of the second resistor R2 is set considering the time constant (τ = CR2) so that the discharge rate of the smoothing capacitor C is sufficiently slow. In the time constant formula, C and R2 are the capacitance of the smoothing capacitor C and the resistance value of the second resistor R2, respectively.

[0054] The second input terminal IN2 is connected to the power supply terminal +V via the third resistor R3. In other words, the third resistor R3 is a pull-up resistor that raises the input voltage of the second input terminal IN2 to the power supply voltage Vcc when the first transistor T1 and the second transistor T2 are OFF.

[0055] The second diode D2 is a rectifier element that causes the first input terminal IN1 to conduct to the ground terminal GND when the potential of the first input terminal IN1 is less than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the second diode D2. The cathode of the second diode D2 is connected to the other end of the first resistor R1, the first input terminal IN1, and the anode of the first diode D1. The anode of the second diode D2 is connected to the ground line GL. In other words, the first input terminal IN1 is connected to the ground terminal GND via the second diode D2 and the ground line GL.

[0056] The third diode D3 is a rectifier element that causes the second input terminal IN2 to conduct to the power supply voltage Vcc when the potential of the second input terminal IN2 is higher than the sum of the potential of the power supply terminal +V and the forward voltage of the third diode D3. The cathode of the third diode D3 is connected to the other end of the third resistor R3, the power supply terminal +V, and the cathode of the first diode D1. The anode of the third diode D3 is connected to the collector c2 of the second transistor T2, the collector c1 of the first transistor T1, one end of the third resistor R3, and the second input terminal IN2. That is, the second input terminal IN2 is connected to the power supply voltage Vcc via the third diode D3.

[0057] The fourth diode D4 is a rectifier element that connects the second input terminal IN2 to the ground terminal GND when the potential of the second input terminal IN2 is less than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4. The cathode of the fourth diode D4 is connected to the collector c2 of the second transistor T2, the second input terminal IN2, and the anode of the third diode D3. The anode of the fourth diode D4 is connected to the ground line GL. In other words, the second input terminal IN2 is connected to the ground terminal GND via the fourth diode D4.

[0058] The fifth diode D5 and the Zener diode ZD1 are rectifier elements provided to protect the cutoff switch S1 from overvoltage, with the purpose of keeping the voltage applied to the cutoff switch S1 below the rated voltage of the cutoff switch S1. The anode of the fifth diode D5 is connected to node P3 and one end of the first resistor R1. The cathode of the Zener diode ZD1 is connected to the cathode of the fifth diode D5. The anode of the Zener diode ZD1 is connected to the ground line GL. In other words, both ends of the cutoff switch S1 are connected by the fifth diode D5 and the Zener diode ZD1. The sum of the forward voltage of the fifth diode D5 and the Zener voltage of the Zener diode ZD1 is set to be below the rated voltage of the cutoff switch S1.

[0059] Figure 3 is a circuit diagram showing the operation of the contact state detection circuit DCx shown in Figure 2. In the state shown in Figure 3, in the bypass unit BUx corresponding to the battery module Mx that is the target of bypass control or connection control, the cutoff switch S1 is Open and the bypass switch S2 is Closed. That is, the battery module Mx is in a bypass state. Note that the other battery modules M1 to Mn may be in a connected state, a bypass state, or a cutoff state. Also, the energy storage string STR may be in the middle of charging / discharging or in the middle of stopped charging / discharging, and the operation will be the same in either case.

[0060] As shown in Figure 3, in the contact state detection circuit DCx corresponding to the bypassed battery module Mx, the potential difference between the base b1 and emitter e1 of the first transistor T1 becomes 0, and the first transistor T1 turns OFF. Also in the same contact state detection circuit DCx, the potential difference between the base b2 and emitter e2 of the second transistor T2 becomes 0, and the second transistor T2 turns OFF. When the first transistor T1 and the second transistor T2 are OFF, the input voltage of the second input terminal IN2 is raised to the power supply voltage Vcc by the third resistor R3. As a result, the potential difference between the second input terminal IN2 and the ground terminal GND becomes greater than or equal to the High level threshold, and the logic value of the second input terminal IN2 becomes High. The signal isolator IS outputs a signal with a logic value of High from the second output terminal OUT2 to the second input terminal IN2' of the microcontroller MCU.

[0061] On the other hand, in the contact state detection circuit DCx corresponding to the bypassed battery module Mx, the potential of the first input terminal IN1 becomes higher than the potential of the power supply terminal +V, causing the first diode D1 to conduct in the forward direction. As a result, the first input terminal IN1 conducts to the power supply terminal +V via the first diode D1, and the potential difference between the first input terminal IN1 and the ground terminal GND becomes greater than or equal to the High level threshold, and the logic value of the first input terminal IN1 becomes High. The signal isolator IS outputs a signal with a logic value of High from the first output terminal OUT1 to the first input terminal IN1' of the microcontroller MCU.

[0062] Figure 4 is a circuit diagram showing the operation of the contact state detection circuit DCx shown in Figure 2. In the state shown in Figure 4, the bypass switch S1 is closed and the bypass switch S2 is open in the bypass unit BUx corresponding to the battery module Mx that is the target of bypass control or connection control. That is, the battery module Mx is in a connected state. Note that the other battery modules M1 to Mn may be in a connected state, a bypass state, or a disconnected state. Also, the energy storage string STR may be in the middle of charging / discharging or in the middle of stopped charging / discharging, and the operation will be the same in either case.

[0063] As shown in Figure 4, in the contact state detection circuit DCx corresponding to the connected battery module Mx, a positive voltage is applied between the base b1 and emitter e1 of the first transistor T1. As a result, the first transistor T1 turns ON. Conversely, a negative voltage is applied between the base b2 and emitter e2 of the second transistor T2. As a result, the second transistor T2 turns OFF.

[0064] With the first transistor T1 ON and the second transistor T2 OFF, the voltage obtained by subtracting the voltage of the battery module Mx from the power supply voltage Vcc is divided by the second resistor R2 and the third resistor R3. As a result, the potential difference between the second input terminal IN2 and the ground terminal GND becomes less than or equal to the Low level threshold, and the logic value of the second input terminal IN2 becomes Low. The signal isolator IS outputs a signal with a logic value of Low from its second output terminal OUT2 to the second input terminal IN2' of the microcontroller MCU.

[0065] Here, in the contact state detection circuit DCx corresponding to the connected battery module Mx, if the potential of the second input terminal IN2 is less than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4, the fourth diode D4 conducts in the forward direction, and the second input terminal IN2 conducts to the ground terminal GND. As a result, the lower limit of the potential of the second input terminal IN2 is limited to being greater than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4.

[0066] On the other hand, in the contact state detection circuit DCx corresponding to the connected battery module Mx, the first input terminal IN1 is connected to the ground terminal GND via the cutoff switch S1. As a result, the potential of the first input terminal IN1 becomes the same as the potential of the ground terminal GND, and the logic value of the first input terminal IN1 becomes Low. The signal isolator IS outputs a signal with a logic value of Low from the first output terminal OUT1 to the first input terminal IN1' of the microcontroller MCU.

[0067] Figure 5 is a circuit diagram showing the operation of the contact state detection circuit DCx shown in Figure 2. In the state shown in Figure 5, both the disconnect switch S1 and the bypass switch S2 are open in the bypass unit BUx corresponding to the battery module Mx that is the target of bypass control or connection control. That is, the battery module Mx is in a disconnected state. Also in the state shown in Figure 5, the impedance of the power converter PCS is sufficiently high. Also in the state shown in Figure 5, charging and discharging of the energy storage string STR has stopped. Note that the battery modules M1 to Mn other than the battery module Mx may be in a connected state, a bypass state, or a disconnected state.

[0068] As shown in Figure 5, in the contact state detection circuit DCx corresponding to the shut-off battery module Mx when the impedance of the power converter PCS is sufficiently high, a positive voltage is applied between the base b1 and emitter e1 of the first transistor T1. As a result, the first transistor T1 turns ON. On the other hand, a negative voltage is applied between the base b2 and emitter e2 of the second transistor T2. As a result, the second transistor T2 turns OFF.

[0069] With the first transistor T1 ON and the second transistor T2 OFF, the voltage obtained by subtracting the voltage of the battery module Mx from the power supply voltage Vcc is divided by the second resistor R2 and the third resistor R3. As a result, the potential difference between the second input terminal IN2 and the ground terminal GND becomes less than or equal to the Low level threshold, and the logic value of the second input terminal IN2 becomes Low. The signal isolator IS outputs a signal with a logic value of Low from the second output terminal OUT2 to the second input terminal IN2' of the microcontroller MCU.

[0070] Here, if the potential of the second input terminal IN2 is less than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4, the fourth diode D4 conducts in the forward direction, and the second input terminal IN2 conducts to the ground terminal GND via the fourth diode D4. As a result, the lower limit of the potential of the second input terminal IN2 is limited to being greater than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4.

[0071] On the other hand, in the contact state detection circuit DCx corresponding to the disconnected battery module Mx when the impedance of the power converter PCS is sufficiently high, the potential of the first input terminal IN1 becomes higher than the sum of the potential of the power supply terminal +V and the forward voltage of the first diode D1, causing the first diode D1 to conduct in the forward direction. As a result, the first input terminal IN1 conducts with the power supply voltage Vcc via the first diode D1, the potential difference between the first input terminal IN1 and the ground terminal GND becomes greater than or equal to the High level threshold, and the logic value of the first input terminal IN1 becomes High. The signal isolator IS outputs a signal with a logic value of High from the first output terminal OUT1 to the first input terminal IN1' of the microcontroller MCU.

[0072] Figure 6 is a circuit diagram showing the operation of the contact state detection circuit DCx shown in Figure 2. In the state shown in Figure 6, both the disconnect switch S1 and the bypass switch S2 are open in the bypass unit BUx corresponding to the battery module Mx that is the target of bypass control or connection control. That is, the battery module Mx is in a disconnected state. Also, in the state shown in Figure 6, the impedance of the power converter PCS is not sufficiently high. Also, in the state shown in Figure 6, charging and discharging of the energy storage string STR has stopped. Note that the battery modules M1 to Mn other than the battery module Mx may be in a connected state, a bypass state, or a disconnected state.

[0073] In the contact state detection circuit DCx shown in Figure 6, the voltage applied to the cutoff switch S1 is limited to less than or equal to the sum of the Zener voltage of Zener diode ZD1 and the forward voltage of the fifth diode D5 due to the action of Zener diode ZD1 and fifth diode D5. Also, a positive voltage is applied between the base b2 and emitter e2 of the second transistor T2, and the second transistor T2 turns ON. On the other hand, a negative voltage is applied between the base b1 and emitter e1 of the first transistor T1, and the first transistor T1 turns OFF.

[0074] With the first transistor T1 OFF and the second transistor T2 ON, the second input terminal IN2 conducts to the ground terminal GND via the second transistor T2. As a result, the potential difference between the second input terminal IN2 and the ground terminal GND becomes less than or equal to the Low level threshold, and the logic value of the second input terminal IN2 becomes Low. The signal isolator IS outputs a signal with a logic value of Low from the second output terminal OUT2 to the second input terminal IN2' of the microcontroller MCU. On the other hand, the potential of the first input terminal IN1 becomes higher than the sum of the potential of the power supply terminal +V and the forward voltage of the first diode D1, causing the first diode D1 to conduct in the forward direction, and the first input terminal IN1 conducts to the power supply terminal +V via the first diode D1. As a result, the potential difference between the first input terminal IN1 and the ground terminal GND becomes greater than or equal to the High level threshold, and the logic value of the first input terminal IN1 becomes High. The signal isolator IS outputs a signal with a logic value of High from its first output terminal OUT1 to the first input terminal IN1' of the microcontroller MCU.

[0075] Figure 7 is a circuit diagram showing the operation of the contact state detection circuit DCx shown in Figure 2. Figure 7 shows the transient state from when the charging battery module Mx switches from the connected state to the disconnected state until charging stops. Note that the battery modules M1 to Mn other than the battery module Mx may be in the connected state, bypass state, or disconnected state.

[0076] During the transient state from when the charging battery module Mx switches from the connected state to the disconnected state until charging stops, a positive voltage is applied between the base b1 and emitter e1 of the first transistor T1. As a result, the first transistor T1 turns ON. Also during this transient state, a negative voltage is applied between the base b2 and emitter e2 of the second transistor T2. As a result, the second transistor T2 turns OFF.

[0077] With the first transistor T1 ON and the second transistor T2 OFF, the voltage obtained by subtracting the voltage of the battery module Mx from the power supply voltage Vcc is divided by the second resistor R2 and the third resistor R3. As a result, the potential difference between the second input terminal IN2 and the ground terminal GND becomes less than or equal to the Low level threshold, and the logic value of the second input terminal IN2 becomes Low.

[0078] Here, if the potential of the second input terminal IN2 is less than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4, the fourth diode D4 conducts in the forward direction, and the second input terminal IN2 conducts to the ground terminal GND via the fourth diode D4. As a result, the lower limit of the potential of the second input terminal IN2 is limited to being greater than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4.

[0079] On the other hand, during this transient state, a negative voltage equivalent to the potential difference between the charging voltage and the total voltage of the connected battery modules M1 to Mn is applied between the first input terminal IN1 and the ground terminal GND. As a result, the second diode D2 conducts in the forward direction, and the first input terminal IN1 conducts to the ground terminal GND via the second diode D2. Consequently, the potential difference between the first input terminal IN1 and the ground terminal GND becomes less than or equal to the Low level threshold, and the logic value of the first input terminal IN1 becomes Low.

[0080] Figure 8 is a circuit diagram showing the operation of the contact state detection circuit DCx shown in Figure 2. Figure 8 shows the transient state from when the discharged battery module Mx switches from the connected state to the disconnected state until the discharge stops. Note that the battery modules M1 to Mn other than the battery module Mx may be in the connected state, bypass state, or disconnected state.

[0081] During the transient state from when the discharged battery module Mx switches from the connected state to the disconnected state until the discharge stops, a positive voltage is applied between the base b1 and emitter e1 of the first transistor T1, similar to the case when charging stops. As a result, the first transistor T1 turns ON. Also, during this transient state, a negative voltage is applied between the base b2 and emitter e2 of the second transistor T2. As a result, the second transistor T2 turns OFF.

[0082] Similar to the case when charging is stopped, with the first transistor T1 ON and the second transistor T2 OFF, the voltage obtained by subtracting the voltage of the battery module Mx from the power supply voltage Vcc is divided by the second resistor R2 and the third resistor R3. As a result, the potential difference between the second input terminal IN2 and the ground terminal GND becomes less than or equal to the Low level threshold, and the logic value of the second input terminal IN2 becomes Low.

[0083] Similar to the case of charging stoppage, if the potential of the second input terminal IN2 is less than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4, the fourth diode D4 conducts in the forward direction, and the second input terminal IN2 conducts to the ground terminal GND via the fourth diode D4. As a result, the lower limit of the potential of the second input terminal IN2 is limited to being greater than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4.

[0084] On the other hand, during this transient state, a voltage equivalent to the potential difference between the discharge voltage and the total voltage of the connected battery modules M1 to Mn is applied between the first input terminal IN1 and the ground terminal GND. As a result, the first diode D1 conducts in the forward direction, and the first input terminal IN1 conducts to the power supply terminal +V via the first diode D1. Consequently, the potential difference between the first input terminal IN1 and the ground terminal GND becomes greater than or equal to the High level threshold, and the logic value of the first input terminal IN1 becomes High.

[0085] In this transient state, from when the battery module Mx is switched from a connected state to a disconnected state until charging and discharging stops, the logical value of the first input terminal IN1 differs between charging and discharging. Therefore, in this transient state, the state of the contacts of the disconnect switch S1 corresponding to the battery module Mx that is switched from a connected state to a disconnected state cannot be correctly detected.

[0086] Therefore, during the transient state from when the battery module Mx, which is being charged or discharged, switches from the connected state to the disconnected state until charging or discharging stops, the microcontroller MCU waits without determining the state of the contacts of the disconnect switch S1, and determines the state of the contacts of the disconnect switch S1 after the charging or discharging has stopped.

[0087] Figure 9 is a circuit diagram illustrating the first oxide film removal process of the energy storage system 1 shown in Figure 1. 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 Mx that is subject to bypass control or connection control, the cutoff switch S1 of the bypass unit BUx corresponding to the battery module Mx is switched from Open to Close. At this time, the system main relay SMR is Open, the precharge switch Sp is Close, and the bypass switch S2 of the bypass unit BUx is Open. In addition, for bypass units BU1 to BUn other than the bypass unit BUx, the cutoff switch S1 is Open and the bypass switch S2 is Close.

[0088] In this embodiment, the charge of the smoothing capacitor C is discharged by the operation of the power converter PCS before the first oxide film removal process is performed. The potential of the smoothing capacitor C at the start of the first oxide film removal process only needs to be low enough to allow a sufficient amount of charge to flow in to remove the oxide film on the contact portion of the cutoff switch S1; it does not need to be zero relative to ground.

[0089] The charging time of the smoothing capacitor C during the first oxide film removal process is set considering the time constant (τ = CRp) so that a sufficient amount of charge flows from the battery module Mx to the smoothing capacitor C via the cutoff switch S1 to remove the oxide film on the contact portion of the cutoff switch S1. Here, C is the capacitance of the smoothing capacitor C, and Rp is the resistance value of the pre-charge resistor Rp.

[0090] In the first oxide film removal process, current flows from the battery module Mx through the first resistor R1, the first diode D1, the power supply terminal +V, the ground terminal GND, the precharge switch Sp, the precharge resistor Rp, and the smoothing capacitor C in that order. To suppress the charging of the smoothing capacitor C by the current flowing from the battery module Mx through the first resistor R1, the resistance value (R1) of the first resistor R1 is set so that the time constant (τ = CR1) is sufficiently long. In other words, the resistance value of the first resistor R1 is set to sufficiently increase the potential difference between the battery module Mx and the smoothing capacitor C in order to generate an arc discharge with a current value sufficient to remove the oxide film on the contact portion of the cutoff switch S1 when the cutoff switch S1 is switched.

[0091] Therefore, in the first oxide film removal process, the cutoff switch S1 of the bypass unit BUx is switched from Open to Close when a voltage sufficient to remove the oxide film from the contact portion is applied.

[0092] Figure 10 is a circuit diagram illustrating the second oxide film removal process of the energy storage system 1 shown in Figure 1. As shown in this figure, in the second oxide film removal process, when the smoothing capacitor C is charged to a potential similar to that of the battery module Mx, the bypass switch S2 of the bypass unit BUx, which is the target of bypass control or connection control, is switched from Open to Close. At this time, the system main relay SMR is Open, the precharge switch Sp is Close, and the cutoff switch S1 of the bypass unit BUx is Open. In addition, for bypass units BU1 to BUn other than the bypass unit BUx, the cutoff switch S1 is Open and the bypass switch S2 is Close.

[0093] The discharge time of the smoothing capacitor C during the execution of the second oxide film removal process is set considering the time constant (τ = CRp) so that a sufficient amount of charge flows from the smoothing capacitor C to the negative electrode side via the bypass switch S2 to remove the oxide film on the contact portion of the bypass switch S2.

[0094] In the second oxide film removal process, current flows from the smoothing capacitor C to the precharge resistor Rp, then to the precharge switch Sp, the first transistor T1, and finally to the second resistor R2. To suppress discharge from the smoothing capacitor C to the second resistor R2, etc., when the bypass switch S2 is switched, the resistance value of the second resistor R2 (R2) is set so that the time constant (τ = CR2) is sufficiently long. In other words, the resistance value of the second resistor R2 is set to sufficiently raise the potential of the smoothing capacitor C in order to generate an arc discharge with a current value sufficient to remove the oxide film on the contact portion of the bypass switch S2 when the bypass switch S2 is switched.

[0095] Therefore, in the second oxide film removal process, the bypass switch S2 of the bypass unit BUx is switched from Open to Close when a voltage sufficient to remove the oxide film from the contact portion is applied.

[0096] Figures 11 and 12 are flowcharts illustrating the process of switching the battery module Mx, which is the target of bypass control, from a connected state to a bypass state. In the following explanation, the battery module Mx, which is the target of bypass control, will be referred to as battery module M', and the bypass unit BUx, module controller MCx, and contact state detection circuit DCx corresponding to battery module M' will be referred to as bypass unit BU', module controller MC', and contact state detection circuit DC', respectively.

[0097] First, the string controller StC monitors the battery modules M1 to Mn of the energy storage string STR and determines whether or not there is a battery module M' that requires bypass control (step S01). If there is no battery module M' that requires bypass control (NO in step S01), the process is terminated.

[0098] At the start of the process shown in the flowcharts of Figures 11 and 12, the precharge switch Sp is Open and the system main relay SMR is Closed. Also, the smoothing capacitor C is in a charged state (post-precharge state).

[0099] If there is a battery module M' that requires bypass control (YES in step S01), the string controller StC records the current connection or bypass status of the battery modules M1 to Mn of the energy storage string STR in its built-in memory (not shown) (step S02). Next, the string controller StC repeatedly executes the loop processing in steps S03 to S05 until the indicated value of the string current reaches a predetermined value (string current reduction processing). 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.

[0100] First, the string controller StC updates the indicated value of the string current to a value reduced by a predetermined amount ΔP1 (step S03). 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.

[0101] Next, the string controller StC waits for a predetermined time t1 after transmitting the string current instruction value to the power converter PCS (step S04). 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.

[0102] Next, 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) (step S05). If the decrease in string current has been completed (YES in step S05), the string controller StC sends a control signal to the relay driver RDp to switch the system main relay SMR from Close to Open (step S06). As a result, the energy storage string STR is disconnected from the power converter PCS.

[0103] Next, the string controller StC sends a control signal to all module controllers MC1 to MCn to open the cutoff switch S1 and bypass switch S2 of all bypass units BU1 to Bun (step S07). In all module controllers MC1 to MCn, the microcontroller MCU sends a control signal to the relay driver RD to open the cutoff switch S1 and bypass switch S2. The relay driver RD opens the corresponding cutoff switch S1 and bypass switch S2.

[0104] Next, the microcontrollers MCU of all module controllers MC1 to MCn determine whether the logic value of the first input terminal IN1 is High and the logic value of the second input terminal IN2 is Low (step S08). If the logic value of the first input terminal IN1 is Low or the logic value of the second input terminal IN2 is High (NO in step S08), each microcontroller MCU outputs a switch malfunction detection signal to the string controller StC (step S09). In this case, the process ends.

[0105] On the other hand, each microcontroller MCU outputs a switch operation confirmation signal to the string controller StC (step S10) if the logic value of the first input terminal IN1 is High and the logic value of the second input terminal IN2 is Low (YES in step S08). Next, the string controller StC sends a control signal to the power converter PCS to discharge the smoothing capacitor C (step S11). 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 (step S16). Note that the potential of the smoothing capacitor C does not need to be 0 relative to ground.

[0106] Next, the string controller StC sends a control signal to the corresponding module controller MCx to switch the bypass switch S2 of the bypass unit BUx, which is not subject to bypass control, from Open to Close (step S12). Upon receiving this control signal, the microcontroller MCU of the module controller MCx outputs a control signal to the relay driver RD to switch the bypass switch S2 from Open to Close. As a result, the battery module Mx, which is not subject to bypass control, enters a bypass state.

[0107] Next, each microcontroller MCU determines whether the logic value of the first input terminal IN1 is High and the logic value of the second input terminal IN2 is High (step S13). If the logic value of the first input terminal IN1 is Low, or the logic value of the second input terminal IN2 is Low (NO in step S13), each microcontroller MCU outputs a switch malfunction detection signal to the string controller StC (step S09). In this case, the process ends.

[0108] On the other hand, if the logic value of the first input terminal IN1 is High and the logic value of the second input terminal IN2 is High (YES in step S13), each microcontroller MCU outputs a switch operation confirmation signal to the string controller StC (step S14).

[0109] Next, the string controller StC outputs a control signal to the relay driver RDp that switches the precharge switch Sp from Open to Close (step S15). As a result, the precharge circuit 10 is connected to the power line PL with the system main relay SMR bypassed.

[0110] Next, the string controller StC sends a control signal to the module controller MC' to switch the cutoff switch S1 from Open to Close (step S16). Upon receiving this control signal, the module controller MC's microcontroller MCU outputs a control signal to the relay driver RD to switch the cutoff switch S1 from Open to Close. This executes the first oxide film removal process, and the oxide film on the contact portion of the cutoff switch S1 is removed.

[0111] Next, the microcontroller MCU of the module controller MC' determines whether the logic value of the first input terminal IN1 is Low and the logic value of the second input terminal IN2 is Low (step S17). If the logic value of the first input terminal IN1 is High, or the logic value of the second input terminal IN2 is High (NO in step S17), the microcontroller MCU of the module controller MC' outputs a switch malfunction detection signal to the string controller StC (step S09). In this case, the process ends.

[0112] On the other hand, the microcontroller MCU of the module controller MC' outputs a switch operation confirmation signal to the string controller StC (step S18) if the logic value of the first input terminal IN1 is Low and the logic value of the second input terminal IN2 is Low (YES in step S17). Next, the string controller StC waits for a predetermined time t2 after switching the cutoff switch S1 from Open to Close (step S19). This predetermined time t2 is the time required for sufficient charge to flow to the smoothing capacitor C to remove the oxide film on the contact portion of the cutoff switch S1, and is set considering the time constant (τ = CRp).

[0113] Next, the string controller StC sends a control signal to the module controller MC' to switch the cutoff switch S1 from Close to Open (step S20). Upon receiving this control signal, the module controller MC' sends a control signal to the relay driver RD via the microcontroller MCU to switch the bypass switch S2 from Close to Open.

[0114] Next, the microcontroller MCU of the module controller MC' determines whether the logic value of the first input terminal IN1 is High and the logic value of the second input terminal IN2 is Low (step S21). If the logic value of the first input terminal IN1 is Low, or the logic value of the second input terminal IN2 is High (NO in step S21), the microcontroller MCU of the module controller MC' outputs a switch malfunction detection signal to the string controller StC (step S09). In this case, the process ends.

[0115] On the other hand, the microcontroller MCU of the module controller MC' outputs a switch operation confirmation signal to the string controller StC (step S22) if the logic value of the first input terminal IN1 is High and the logic value of the second input terminal IN2 is Low (YES in step S21).

[0116] Next, the string controller StC sends a control signal to the module controller MC' to switch the bypass switch S2 from Open to Close (step S23). Upon receiving this control signal, the module controller MC's microcontroller MCU sends a control signal to the relay driver RD to switch the bypass switch S2 from Open to Close. This executes the second oxide film removal process, and the oxide film on the contact portion of the bypass switch S2 is removed.

[0117] Next, the microcontroller MCU of the module controller MC' determines whether the logic value of the first input terminal IN1 is High and the logic value of the second input terminal IN2 is High (step S24). If the logic value of the first input terminal IN1 is Low, or the logic value of the second input terminal IN2 is Low (NO in step S24), the microcontroller MCU of the module controller MC' outputs a switch malfunction detection signal to the string controller StC (step S09). In this case, the process ends.

[0118] On the other hand, the microcontroller MCU of the module controller MC' outputs an operation confirmation signal to the string controller StC (step S25) if the logic value of the first input terminal IN1 is High and the logic value of the second input terminal IN2 is High (YES in step S24).

[0119] Next, the string controller StC waits for a predetermined time t3 after switching the bypass switch S2 from Open to Close (step S26). This predetermined time t3 is the time required for the charge necessary to remove the oxide film on the contact portion of the bypass switch S2 to be released from the smoothing capacitor C, and is set considering the time constant (τ = CRp).

[0120] Next, the string controller StC outputs a control signal to the relay driver RDp to switch the precharge switch Sp from Close to Open (step S27). Next, the string controller StC outputs control signals to the module controllers MC1 to MCn to set all battery modules M1 to Mn to reflect the bypass control of battery module M' (step S28). The state reflecting the bypass control of battery module M' is the state in which battery module M', which was determined to require bypass control in step S01 based on the connection / bypass state of battery module Mx recorded in memory in step S02, is in the bypass state.

[0121] Next, in all module controllers MC1 to MCn, the microcontroller MCU determines whether the logical values ​​of the first input terminal IN1 and the second input terminal IN2 correspond to the connected / bypassed state of the battery modules M1 to Mn (step S29). For example, in module controller MCx corresponding to a connected battery module Mx, the microcontroller MCU determines whether the logical value of the first input terminal IN1 is Low and the logical value of the second input terminal IN2 is Low. On the other hand, in module controller MCx corresponding to a bypassed battery module Mx, the microcontroller MCU determines whether the logical value of the first input terminal IN1 is High and the logical value of the second input terminal IN2 is High.

[0122] If the logical values ​​of the first input terminal IN1 and the second input terminal IN2 do not correspond to the connection / bypass status of the battery modules M1 to Mn (NO in step S29), the corresponding microcontroller MCU outputs a switch malfunction detection signal to the string controller StC (step S09). In this case, the process is terminated.

[0123] On the other hand, if the logic values ​​of the first input terminal IN1 and the second input terminal IN2 correspond to the connected / bypassed state of the battery module Mx (YES in step S29), the corresponding microcontroller MCU outputs a signal to the string controller StC to confirm the operation of the switch (step S30).

[0124] Next, the string controller StC outputs a control signal to the relay driver RDp to switch the precharge switch Sp from Open to Close (step S31). Then, the string controller StC waits for a predetermined time t4 after switching the precharge switch Sp from Open to Close (step S32). This predetermined time t4 is the time required to charge the smoothing capacitor C to suppress the inrush current, and is set considering the time constant (τ = CRp). As a result, the precharge process is executed and the smoothing capacitor C is charged.

[0125] Next, the string controller StC outputs a control signal to the relay driver RDp to switch the system main relay SMR from Open to Close (step S33). As a result, the energy storage string STR is connected to the power converter PCS.

[0126] Next, the string controller StC outputs a control signal to the relay driver RDp to switch the precharge switch Sp from Close to Open (step S34). This completes the bypass control of the battery module M', the removal of the oxide film from the contact portions of the cutoff 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 11 and 12.

[0127] As described above, in the energy storage system 1 according to this embodiment, the contact state detection circuit DCx comprises a signal isolator IS, a first resistor R1, a second resistor R2, a first transistor T1, a third resistor R3, a second transistor T2, and a first diode D1. The signal isolator IS comprises a first input terminal IN1, a second input terminal IN2, and a ground terminal GND. The ground terminal GND is connected to a cutoff switch S1 and a bypass switch S2. The signal isolator IS outputs a first signal corresponding to the potential difference between the first input terminal IN1 and the ground terminal GND, and a second signal corresponding to the potential difference between the second input terminal IN2 and the ground terminal GND, to the microcontroller MCU.

[0128] The first resistor R1 is connected to the cutoff switch S1, the positive terminal of the battery module Mx, and the first input terminal IN1. The second resistor R2 is connected to the bypass switch S2 and the negative terminal of the battery module Mx. The first transistor T1 is a bipolar transistor that turns ON when a positive voltage is applied between its base b1 and emitter e1, and allows current to flow from the collector c1 to the emitter e1. The emitter e1 of the first transistor T1 is connected to the second resistor R2, and the base b1 of the first transistor T1 is connected to the cutoff switch S1, the bypass switch S2, and the ground terminal GND.

[0129] The third resistor R3 is connected to the collector c1 of the first transistor T1, the power supply voltage Vcc, and the second input terminal IN2. The second transistor T2 is a bipolar transistor that turns ON when a positive voltage is applied between its base b2 and emitter e2, and allows current to flow from its collector c2 to its emitter e2. The base b2 of the second transistor T2 is connected to the second resistor R2 and the emitter e1 of the first transistor T1, the collector c2 of the second transistor T2 is connected to the collector c1 of the first transistor T1, the third resistor R3, and the second input terminal IN2, and the emitter e2 of the second transistor T2 is connected to the cutoff switch S1, the bypass switch S2, and the ground terminal GND.

[0130] The cathode of the first diode D1 is connected to the third resistor R3 and the power supply voltage Vcc, and the anode of the first diode D1 is connected to the first resistor R1 and the first input terminal IN1.

[0131] Here, since the second input terminal IN2 is connected to the power supply voltage Vcc via the third resistor R3, when both the first transistor T1 and the second transistor T2 are OFF, the potential difference between the second input terminal IN2 and the ground terminal GND is greater than or equal to the High level threshold. In contrast, the resistance values ​​of the second resistor R2 and the third resistor R3 are set so that when the first transistor T1 is ON and the second transistor T2 is OFF, the potential difference between the second input terminal IN2 and the ground terminal GND is less than or equal to the Low level threshold.

[0132] When the cutoff switch S1 is open and the bypass switch S2 is closed, the first transistor T1 turns OFF because the potential difference between its base b1 and emitter e1 becomes 0, and the second transistor T2 turns OFF because the potential difference between its base b2 and emitter e1 becomes 0 (see Figure 3). As a result, the potential difference between the second input terminal IN2 and the ground terminal GND becomes greater than or equal to the High level threshold. The signal isolator IS outputs a signal indicating that the potential difference between the second input terminal IN2 and the ground terminal GND is greater than or equal to the High level threshold as a second signal to the second input terminal IN2' of the microcontroller MCU. On the other hand, when the potential of the first input terminal IN1 becomes higher than the sum of the potential of the power supply terminal +V and the forward voltage of the first diode D1, the first input terminal IN1 is connected to the power supply voltage Vcc via the first diode D1, and the potential difference between the first input terminal IN1 and the ground terminal GND becomes greater than or equal to the High level threshold. The signal isolator IS outputs a signal as the first signal to the first input terminal IN1' of the microcontroller MCU, indicating that the potential difference between the first input terminal IN1 and the ground terminal GND is greater than or equal to a high level threshold.

[0133] When the cutoff switch S1 is closed and the bypass switch S2 is open, the first transistor T1 turns ON when a positive voltage is applied between its base b1 and emitter e1, and the second transistor T2 turns OFF when a negative voltage is applied between its base b2 and emitter e2 (see Figure 4). As a result, the potential difference between the second input terminal IN2 and the ground terminal GND becomes less than or equal to the Low level threshold. The signal isolator IS outputs a signal indicating that the potential difference between the second input terminal IN2 and the ground terminal GND is less than or equal to the Low level threshold as a second signal to the second input terminal IN2' of the microcontroller MCU. On the other hand, at the first input terminal IN1, the voltage obtained by subtracting the voltage of the battery module Mx from the power supply voltage Vcc is divided by the second resistor R2 and the third resistor R3, so that the potential difference between the first input terminal IN1 and the ground terminal GND becomes less than or equal to the Low level threshold. The signal isolator IS outputs a signal to the first input terminal IN1' of the microcontroller MCU as the first signal, indicating that the potential difference between the first input terminal IN1 and the ground terminal GND is below the Low level threshold.

[0134] When the cutoff switch S1 is open and the bypass switch S2 is open, the ON / OFF state of the first transistor T1 and the second transistor T2 changes depending on the impedance of the power converter PCS (see Figures 5 and 6). When the impedance of the power converter PCS is sufficiently high, the first transistor T1 turns ON when a positive voltage is applied between its base b1 and emitter e1, and the second transistor T2 turns OFF when a negative voltage is applied between its base b2 and emitter e2 (see Figure 5). Since the first transistor T1 is ON and the second transistor T2 is OFF, the potential difference between the second input terminal IN2 and the ground terminal GND becomes less than or equal to the Low level threshold. The signal isolator IS outputs a signal indicating that the potential difference between the second input terminal IN2 and the ground terminal GND is less than or equal to the Low level threshold as a second signal to the second input terminal IN2' of the microcontroller MCU. On the other hand, when the potential of the first input terminal IN1 becomes higher than the sum of the potential of the power supply terminal +V and the forward voltage of the first diode D1, the first input terminal IN1 is connected to the power supply voltage Vcc via the first diode D1, and the potential difference between the first input terminal IN1 and the ground terminal GND becomes greater than or equal to the High level threshold. The signal isolator IS outputs a signal indicating that the potential difference between the first input terminal IN1 and the ground terminal GND is greater than or equal to the High level threshold as the first signal to the first input terminal IN1' of the microcontroller MCU.

[0135] In contrast, if the impedance of the power converter PCS is not sufficiently high, the first transistor T1 is turned OFF when a negative voltage is applied between its base b1 and emitter e1, and the second transistor T2 is turned ON when a positive voltage is applied between its base b2 and emitter e2 (see Figure 6). The second input terminal IN2 is connected to the ground terminal GND via the second transistor T2, so that the potential difference between the second input terminal IN2 and the ground terminal GND is below the Low level threshold. The signal isolator IS outputs a signal indicating that the potential difference between the second input terminal IN2 and the ground terminal GND is below the Low level threshold as a second signal to the second input terminal IN2' of the microcontroller MCU. On the other hand, when the potential of the first input terminal IN1 becomes higher than the sum of the potential of the power supply terminal +V and the forward voltage of the first diode D1, the first input terminal IN1 is connected to the power supply voltage Vcc via the first diode D1, and the potential difference between the first input terminal IN1 and the ground terminal GND becomes greater than or equal to the High level threshold. The signal isolator IS outputs a signal indicating that the potential difference between the first input terminal IN1 and the ground terminal GND is greater than or equal to the High level threshold as the first signal to the first input terminal IN1' of the microcontroller MCU.

[0136] As a result, the microcontroller MCU can determine the state of the contacts between the disconnect switch S1 and the bypass switch S2 based on the first and second signals output from the signal isolator IS to the first input terminal IN1' and the second input terminal IN2'. In particular, in the energy storage system 1 according to this embodiment, the state of the contacts between the disconnect switch S1 and the bypass switch S2 corresponding to the battery module M' can be determined regardless of the state (connected / bypassed / disconnected) of the other battery modules M1 to Mn. Furthermore, in the energy storage system 1 according to this embodiment, the state of the contacts between the disconnect switch S1 and the bypass switch S2 corresponding to the battery module M' can be determined regardless of the impedance of the power converter PCS.

[0137] In the energy storage system 1 according to this embodiment, a first oxide film removal process is performed. In this first oxide film removal process, the cutoff switch S1 switches from the Open state to the Close state, and the charging current of the smoothing capacitor C flows to the cutoff switch S1 of the bypass unit BU' through the precharge circuit 10, thereby removing the oxide film on the contact portion of the cutoff switch S1. When this first oxide film removal process is performed, a charging current flows from the battery module M' to the smoothing capacitor C through the contact state detection circuit DC' and the precharge circuit 10. In contrast, the contact state detection circuit DC' is provided with a first resistor R1, and by setting the resistance value of the first resistor R1, the charging speed of the smoothing capacitor C can be sufficiently slowed down. As a result, the cutoff switch S1 can be operated when the potential difference across the cutoff switch S1 is sufficiently large, and the oxide film on the contact portion of the cutoff switch S1 can be removed.

[0138] Furthermore, in the energy storage system 1 according to this embodiment, a second oxide film removal process is performed. In this second oxide film removal process, the bypass switch S2 switches from the Open state to the Closed state, and the discharge current of the smoothing capacitor C flows through the precharge circuit 10 to the bypass switch S2 of the bypass unit BU', thereby removing the oxide film on the contact portion of the bypass switch S2. When this second oxide film removal process is performed, the discharge current of the smoothing capacitor C flows through the precharge circuit 10 and the contact state detection circuit DC'. In contrast, the contact state detection circuit DCx is provided with a second resistor R2, and by setting the resistance value of the second resistor R2, the discharge rate of the smoothing capacitor C can be sufficiently slowed down. As a result, the bypass switch S2 can be operated when the potential difference across the bypass switch S2 is sufficiently large, and the oxide film on the contact portion of the bypass switch S2 can be removed.

[0139] Furthermore, the contact state detection circuit DCx includes a second diode D2. The cathode of the second diode D2 is connected to the first resistor R1 and the first input terminal IN1, and the anode of the first diode D1 is connected to the ground terminal GND.

[0140] As a result, when the potential of the first input terminal IN1 is less than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the second diode D2, the first input terminal IN1 conducts to the ground terminal GND via the second diode D2. Therefore, the lower limit of the potential of the first input terminal IN1 is restricted to being greater than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the second diode D2, thus stabilizing the operation of the signal isolator IS.

[0141] Furthermore, the contact state detection circuit DCx includes a third diode D3. The cathode of the third diode D3 is connected to the third resistor R3 and the power supply voltage Vcc, and the anode of the third diode D3 is connected to the second input terminal IN2.

[0142] As a result, when the potential of the second input terminal IN2 is higher than the sum of the potential of the power supply terminal +V and the forward voltage of the third diode D3, the second input terminal IN2 is connected to the power supply voltage Vcc via the third diode D3. Therefore, the upper limit of the potential of the second input terminal IN2 is limited to less than or equal to the sum of the potential of the power supply terminal +V and the forward voltage of the third diode D3, thus stabilizing the operation of the signal isolator IS.

[0143] Furthermore, the contact state detection circuit DCx includes a fourth diode D4. The cathode of the fourth diode D4 is connected to the second input terminal IN2, and the anode of the fourth diode D4 is connected to the ground terminal GND.

[0144] As a result, when the potential of the second input terminal IN2 is less than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4, the second input terminal IN2 is connected to the ground terminal GND via the fourth diode D4. Therefore, the lower limit of the potential of the second input terminal IN2 is restricted to being greater than or equal to the difference between the potential of the ground terminal GND and the forward voltage of the fourth diode D4, and the operation of the signal isolator IS becomes stable.

[0145] Furthermore, the contact state detection circuit DCx includes a fifth diode D5 and a Zener diode ZD1. The anode of the fifth diode D5 is connected to the cutoff switch S1, the positive terminal of the battery module Mx, and the first resistor R1. The cathode of the Zener diode ZD1 is connected to the cathode of the fifth diode D5, and the anode of the Zener diode ZD1 is connected to the cutoff switch S1 and the ground terminal GND. As a result, the voltage applied to the cutoff switch S1 is limited to the sum of the forward voltage of the fifth diode D5 and the Zener voltage of the Zener diode ZD1, protecting the cutoff switch S1 from overvoltage.

[0146] Furthermore, the contact state detection circuit DCx includes a microcontroller MCU that controls the cutoff switch S1 and the bypass switch S2. The microcontroller MCU determines the state of the contacts between the cutoff switch S1 and the bypass switch S2 based on a first signal corresponding to the potential difference between the first input terminal IN1 output from the signal isolator IS and the ground terminal GND, and a second signal corresponding to the potential difference between the second input terminal IN2 and the ground terminal GND.

[0147] Specifically, the microcontroller MCU determines the state of the contacts of the cutoff switch S1 and the bypass switch S2 to Open when the first signal indicates that the potential difference between the first input terminal IN1 and the ground terminal GND is greater than or equal to the High level threshold, and the second signal indicates that the potential difference between the second input terminal IN2 and the ground terminal GND is less than or equal to the Low level threshold. Furthermore, the microcontroller MCU determines the state of the contacts of the cutoff switch S1 to Open and the state of the contacts of the bypass switch S2 to Close when the first signal indicates that the potential difference between the first input terminal IN1 and the ground terminal GND is greater than or equal to the High level threshold, and the second signal indicates that the potential difference between the second input terminal IN2 and the ground terminal GND is greater than or equal to the High level threshold. Furthermore, if the first signal indicates that the potential difference between the first input terminal IN1 and the ground terminal GND is less than or equal to the Low level threshold, and the second signal indicates that the potential difference between the second input terminal IN2 and the ground terminal GND is less than or equal to the Low level threshold, the state of the contacts of the cutoff switch S1 is determined to be Close, and the state of the contacts of the bypass switch S2 is determined to be Open.

[0148] This allows for accurate determination of the contact state between the disconnect switch S1 and bypass switch S2 corresponding to battery module M', regardless of the state of the other battery modules M1 to Mn. Furthermore, it allows for accurate determination of the contact state between the disconnect switch S1 and bypass switch S2 corresponding to battery module M', regardless of the impedance level of the power converter PCS.

[0149] In this transient state, from the time the charging battery module Mx is switched to the off state and charging stops, the potential difference between the first input terminal IN1 and the ground terminal GND becomes less than or equal to the Low level threshold. In contrast, from the time the discharging battery module Mx is switched to the off state and discharging stops, the potential difference between the first input terminal IN1 and the ground terminal GND becomes greater than or equal to the High level threshold.

[0150] Therefore, the microcontroller MCU remains in standby mode without determining the state of the contacts between the cutoff switch S1 and the bypass switch S2 while the battery module Mx is charging or discharging. When the charging or discharging of the battery module Mx stops, it determines the state of the contacts between the cutoff switch S1 and the bypass switch S2. This allows for accurate determination of the state of the contacts between the cutoff switch S1 and the bypass switch S2.

[0151] Furthermore, in the energy storage system 1 according to this embodiment, the cutoff switch S1 and the bypass switch S2 are mechanical relays. When a mechanical relay is operated with a voltage above a certain level applied to the contact portion, and 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.

[0152] 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 the bypass switch S2 is kept open when the smoothing capacitor C is discharged. This removes the oxide film formed on the contact portion of the interruption switch S1. The string controller StC also performs a second oxide film removal process by operating the bypass switch S2 while the interruption switch S1 is kept open when the smoothing capacitor C is charged. This removes the oxide film formed on the contact portion of the bypass switch S2.

[0153] 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.

[0154] For example, in the energy storage system 1 according to the above embodiment, a signal isolator IS is provided, which has two input terminals, a first input terminal IN1 and a second input terminal IN2, and two output terminals, a first output terminal OUT1 and a second output terminal OUT2. However, two signal isolators IS, each having one input terminal and one output terminal, may also be provided. Furthermore, it is not essential to provide a microcontroller MCU for each battery module M1 to Mn; one microcontroller MCU may be shared among multiple battery modules M1 to Mn.

[0155] 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. Moreover, performing the first oxide film removal treatment or the second oxide film removal treatment is not essential, and the above-described contact state detection circuit DCx may be provided in an energy storage system in which the first oxide film removal treatment and the second oxide film removal treatment are not performed.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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, for example, if the effect of the change in string current on the input and output power of the energy storage system 1 is minor, the indicated values ​​of the string current may be changed all at once.

[0160] 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 switch Sp. 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.

[0161] 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.

[0162] Here, the features of the embodiments of the energy storage system according to the present invention described above are briefly summarized and listed below in [1] to

[10] .

[0163] [1] A power storage system (1) comprising: a power line (PL) connecting a plurality of storage batteries (M1 to Mn) in series; a first switch (S1) connected to the positive terminal of the storage batteries (M1 to Mn); a second switch (S2) connected in parallel with the storage batteries (M1 to Mn) and the first switch (S1); a plurality of bypass sections (BU1 to BUn) provided for each of the storage batteries (M1 to Mn); a capacitor (C) connecting the positive and negative terminals of the power line (PL); a third switch (SMR) provided between the capacitor (C) and the storage batteries (M1 to Mn); a precharge circuit (10) comprising a precharge switch (Sp) connected in parallel with the third switch (SMR); and a plurality of contact state detection circuits (DC1 to DCn) provided for each of the storage batteries (M1 to Mn) for detecting the state of the contacts between the first switch (S1) and the second switch (S2), wherein The contact state detection circuit (DC1 to DCn) includes a first input terminal (IN1), a second input terminal (IN2), and a ground terminal (GND) connected to the first switch (S1) and the second switch (S2), and a signal output unit (IS) that outputs a first signal corresponding to the potential difference between the first input terminal (IN1) and the ground terminal (GND), and a second signal corresponding to the potential difference between the second input terminal (IN2) and the ground terminal (GND), a first resistor (R1) connected to the first switch (S1), the positive terminal of the storage battery (M1 to Mn), and the first input terminal (IN1), and a second resistor (R2) connected to the second switch (S2) and the negative terminal of the storage battery (M1 to Mn), A first transistor (T1) whose emitter is connected to the second resistor (R2) and whose base is connected to the first switch (S1), the second switch (S2), and the ground terminal (GND), and a third resistor (R3) connected to the collector of the first transistor (T1), the power supply voltage, and the second input terminal (IN2),Energy storage system (1) comprising: a second transistor (T2) whose base is connected to the second resistor (R2) and the emitter of the first transistor (T1), whose collector is connected to the collector of the first transistor (T1), the third resistor (R3) and the second input terminal (IN2), and whose emitter is connected to the first switch (S1), the second switch (S2) and the ground terminal (GND); and a first diode (D1) whose cathode is connected to the third resistor (R3) and the power supply voltage, and whose anode is connected to the first resistor (R1) and the first input terminal (IN1), wherein the resistance values ​​of the second resistor (R2) and the third resistor (R3) are set such that when the first transistor (T1) is ON and the second transistor (T2) is OFF, the potential difference between the second input terminal (IN2) and the ground terminal (GND) is less than or equal to a Low level threshold. [2] The energy storage system (1) according to [1], wherein the contact state detection circuit (DC1 to DCn) comprises a second diode (D2) whose cathode is connected to the first resistor (R1) and the first input terminal (IN1) and whose anode is connected to the ground terminal (GND). [3] The energy storage system (1) according to [1] or [2], wherein the contact state detection circuit (DC1 to DCn) comprises a third diode (D3) whose cathode is connected to the third resistor (R3) and the power supply voltage and whose anode is connected to the second input terminal (IN2). [4] The energy storage system (1) according to [1] or [2], wherein the contact state detection circuit (DC1 to DCn) comprises a fourth diode (D4) whose cathode is connected to the second input terminal (IN2) and whose anode is connected to the ground terminal (GND). [5] The contact state detection circuit (DC1 to DCn) comprises a fifth diode (D5) whose anode is connected to the first switch (S1), the positive terminal of the storage battery (M1 to Mn), and the first resistor (R1), and a Zener diode (ZD1) whose cathode is connected to the cathode of the fifth diode (D5) and whose anode is connected to the first switch (S1) and the ground terminal (GND), as described in [1] or [2] (1). [6]The energy storage system (1) according to [1] or [2], comprising a control unit (100) that controls the first switch (S1), the second switch (S2), the third switch (SMR), and the precharge switch (Sp), and determines the state of the contacts between the first switch (S1) and the second switch (S2) based on the first signal and the second signal. [7] The control unit (100) determines the state of the contacts of the first switch (S1) and the second switch (S2) to be open when the first signal indicates that the potential difference between the first input terminal (IN1) and the ground terminal (GND) is greater than or equal to the High level threshold, and the second signal indicates that the potential difference between the second input terminal (IN2) and the ground terminal (GND) is less than or equal to the Low level threshold; and determines the state of the contacts of the first switch (S1) to be open and the state of the contacts of the second switch (S2) to be closed when the first signal indicates that the potential difference between the first input terminal (IN1) and the ground terminal (GND) is greater than or equal to the High level threshold, and the second signal indicates that the potential difference between the second input terminal (IN2) and the ground terminal (GND) is greater than or equal to the High level threshold. [6] The energy storage system (1) according to [6], wherein the state of the contacts of the first switch (S1) is determined to be closed and the state of the contacts of the second switch (S2) is determined to be open when the first signal indicates that the potential difference between the first input terminal (IN1) and the ground terminal (GND) is less than or equal to a Low level threshold, and the second signal indicates that the potential difference between the second input terminal (IN2) and the ground terminal (GND) is less than or equal to a Low level threshold. [8] The energy storage system (1) according to [6], wherein the control unit (100) does not determine the state of the contacts of the first switch (S1) and the second switch (S2) while the batteries (M1 to Mn) are being charged and discharged, and determines the state of the contacts of the first switch (S1) and the second switch (S2) when the charging and discharging of the batteries (M1 to Mn) is stopped. [9] The first switch (S1) and the second switch (S2) are mechanical relays,The energy storage system (1) according to [6], wherein the control unit (100) maintains one of the first switch (S1) and the second switch (S2) in an open state when the capacitor (C) is discharged, and operates the other of the first switch (S1) and the second switch (S2) from an open state to a closed state.

[10] The energy storage system (1) according to [6], wherein the first switch (S1) and the second switch (S2) are mechanical relays, and the control unit (100) maintains one of the first switch (S1) and the second switch (S2) in an open state when the capacitor (C) is charged, and operates the other of the first switch (S1) and the second switch (S2) from an open state to a closed state.

[0164] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

[0165] This application is based on Japanese Patent Application No. 2025-016594 filed on February 4, 2025, the contents of which are incorporated herein by reference.

[0166] According to the present invention, in an energy storage system in which multiple batteries are connected in series by power lines, a bypass section is provided for each battery, and a capacitor is provided to connect the positive and negative terminals of the power lines, it is possible to provide an energy storage system that can detect the state of the switch contacts of the bypass section corresponding to any battery, regardless of the connection state of the other batteries, and can suppress unnecessary charging and discharging of the capacitor. The present invention, which achieves this effect, is useful with respect to energy storage systems.

[0167] 1: Energy storage system 10: Pre-charge circuit 100: Battery control device (control unit) b1: Base b2: Base BU1 to Bun, BUx, BU': Bypass unit (bypass section) C: Smoothing capacitor (capacitor) c1: Collector c2: Collector D1: First diode D2: Second diode D3: Third diode D4: Fourth diode D5: Fifth diode DC1 to DCn, DCx, DC': Contact state detection circuit e1: Emitter e2: Emitter GND: Ground terminal IN1: First input terminal IN2: Second input terminal IS: Signal isolator (signal output section) M1 to Mn, Mx, M': Battery module (battery) MCU: Microcontroller (control unit) PL: Power line R1: First resistor R2 : Second resistor R3: Third resistor S1: Cut-off switch (first switch) S2: Bypass switch (second switch) SMR: System main relay (third switch) Sp: Precharge switch T1: First transistor T2: Second transistor Vcc: Power supply voltage ZD1: Zener diode

Claims

1. A power storage system comprising: a power line connecting a plurality of storage batteries in series; a first switch connected to the positive terminal of the storage batteries; a second switch connected in parallel with the storage batteries and the first switch, with a plurality of bypass sections provided for each storage battery; a capacitor connecting the positive and negative terminals of the power line; a third switch provided between the capacitor and the storage batteries; a precharge circuit comprising a precharge switch connected in parallel with the third switch; and a plurality of contact state detection circuits provided for each storage battery for detecting the state of the contacts between the first switch and the second switch, wherein the contact state detection circuit comprises: a first input terminal; a second input terminal; a ground terminal connected to the first switch and the second switch, and a signal output section that outputs a first signal corresponding to the potential difference between the first input terminal and the ground terminal, and a second signal corresponding to the potential difference between the second input terminal and the ground terminal; a first resistor connected to the first switch, the positive terminal of the storage battery and the first input terminal; and a second resistor connected to the second switch and the negative terminal of the storage battery. A power storage system comprising: a first transistor whose emitter is connected to the second resistor and whose base is connected to the first switch, the second switch and the ground terminal; a third resistor whose collector is connected to the power supply voltage and the second input terminal of the first transistor; a second transistor whose base is connected to the second resistor and the emitter of the first transistor, whose collector is connected to the collector of the first transistor, the third resistor and the second input terminal, and whose emitter is connected to the first switch, the second switch and the ground terminal; and a first diode whose cathode is connected to the third resistor and the power supply voltage and whose anode is connected to the first resistor and the first input terminal, wherein the resistance values ​​of the second resistor and the third resistor are set such that when the first transistor is ON and the second transistor is OFF, the potential difference between the second input terminal and the ground terminal is less than or equal to a Low level threshold.

2. The energy storage system according to claim 1, wherein the contact state detection circuit comprises a second diode whose cathode is connected to the first resistor and the first input terminal and whose anode is connected to the ground terminal.

3. The energy storage system according to claim 1 or 2, wherein the contact state detection circuit comprises a third diode whose cathode is connected to the third resistor and the power supply voltage and whose anode is connected to the second input terminal.

4. The energy storage system according to claim 1 or 2, wherein the contact state detection circuit comprises a fourth diode whose cathode is connected to the second input terminal and whose anode is connected to the ground terminal.

5. The energy storage system according to claim 1 or 2, wherein the contact state detection circuit comprises a fifth diode whose anode is connected to the first switch, the positive terminal of the battery, and the first resistor, and a Zener diode whose cathode is connected to the cathode of the fifth diode and whose anode is connected to the first switch and the ground terminal.

6. The energy storage system according to claim 1 or 2, further comprising a control unit that controls the first switch, the second switch, the third switch, and the precharge switch, and determines the state of the contacts between the first switch and the second switch based on the first signal and the second signal.

7. The energy storage system according to claim 6, wherein the control unit determines the state of the contacts of the first switch and the second switch to be open when the first signal indicates that the potential difference between the first input terminal and the ground terminal is greater than or equal to a High level threshold, and the second signal indicates that the potential difference between the second input terminal and the ground terminal is less than or equal to a Low level threshold; the control unit determines the state of the contacts of the first switch to be open and the contacts of the second switch to be closed when the first signal indicates that the potential difference between the first input terminal and the ground terminal is greater than or equal to a High level threshold, and the second signal indicates that the potential difference between the second input terminal and the ground terminal is greater than or equal to a High level threshold; and the control unit determines the state of the contacts of the first switch to be closed and the contacts of the second switch to be open when the first signal indicates that the potential difference between the first input terminal and the ground terminal is less than or equal to a Low level threshold, and the second signal indicates that the potential difference between the second input terminal and the ground terminal is less than or equal to a Low level threshold.

8. The energy storage system according to claim 6, wherein the control unit does not determine the state of the contacts between the first switch and the second switch while the battery is being charged or discharged, and determines the state of the contacts between the first switch and the second switch when the charging or discharging of the battery is stopped.

9. The energy storage system according to claim 6, wherein the first switch and the second switch are mechanical relays, and the control unit operates the other of the first switch and the second switch from the open state to the closed state while keeping one of the first switch and the second switch in the open state when the capacitor is discharged.

10. The energy storage system according to claim 6, wherein the first switch and the second switch are mechanical relays, and the control unit operates the other of the first switch and the second switch from the open state to the closed state while keeping one of the first switch and the second switch in the open state when the capacitor is being charged.

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