Protection circuit and power storage system

Abstract

To protect at least one of a first switch and a second switch from overvoltage and rush current.SOLUTION: The protection circuit 10 includes a plurality of storage battery modules M1 to Mn connected in series, a plurality of cut-off switches S1 each provided for each of the storage battery modules M1 to Mn, a storage battery string STR including a plurality of bypass switches S2 each provided for each of the storage battery modules M1 to Mn, and a protection circuit 10 having the cut-off switches S1 and the bypass switches S2 as switches to be protected, the protection circuit 10 including zener diodes M1 and ZD1 connected in parallel with the switches to be protected and having cathodes connected between the switches to be protected and the storage battery modules to Mn, and resistors and connected in series with the zener diodes and. ZD2 R2 ZD1 R1 ZD2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a protection circuit and a power storage system. [Background technology]

[0002] There is known an energy storage system that includes a plurality of storage batteries connected in series, and a first switch and a second switch that are provided for each storage battery and switch the corresponding storage battery between a connected state and a bypass state (see, for example, Patent Document 1). The first switch connects the storage batteries together, and the second switch is connected to a bypass line. In the energy storage system described in Patent Document 1, the first switch corresponding to a storage battery that cannot discharge the required current is opened, and the second switch corresponding to that storage battery is closed, thereby bypassing the storage battery that cannot discharge the required current and discharging from another storage battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-31247 Summary of the Invention [Problem to be solved by the invention]

[0004] In the energy storage system described in Patent Document 1, when a first switch changes from a closed state to an open state, the sum of the voltages of the connected storage batteries and the storage batteries cut off by the first switch is applied across the contacts of the first switch. Also, in the energy storage system described in Patent Document 1, when a second switch changes from a closed state to an open state, the voltage of the connected storage batteries is applied across the contacts of the second switch. The greater the number of storage batteries connected in series, the higher the voltage applied to the first switch and the second switch. Therefore, it is necessary to use switches with a high withstand voltage or to provide protection circuits for the first switch and the second switch to limit the voltage applied to the first switch and the second switch.

[0005] If the first switch and the second switch are made to have a high withstand voltage, the cost of the first switch and the second switch will increase. In particular, the increase in cost of the first switch and the second switch will be more significant as the number of storage batteries connected in series increases. In contrast, if a protection circuit is provided in the first switch and the second switch, the withstand voltage required for the first switch and the second switch will decrease, so the cost of the first switch and the second switch can be reduced.

[0006] However, when the energy storage system described in Patent Document 1 is connected to a load via a power converter such as a DC / DC converter, a situation may arise in which the potential difference between the output capacitor of the power converter and the energy storage system side becomes large when the storage battery is bypassed. In such a situation, a rush current (inrush current) may flow into the protection circuit, and excessive arc discharge may occur at the contacts of the first switch and the second switch.

[0007] In view of the above circumstances, an object of the present invention is to provide a protection circuit and a power storage system that can protect at least one of a first switch and a second switch from an overvoltage and a rush current. [Means for solving the problem]

[0008] The protection circuit of the present invention is for a power storage system including a plurality of storage batteries connected in series, a storage battery string including a plurality of first switches provided for each of the storage batteries, each connected in series to the storage battery, a plurality of second switches provided for each of the storage batteries, each connected in parallel to the storage battery and the first switch, and capacitors connected to the positive and negative sides of the storage battery string, and the protection circuit is configured to protect at least one of the first switches and the second switches, and includes a Zener diode connected in parallel to the switch to be protected, the cathode of which is connected between the switch to be protected and the storage battery, and a resistor connected in series or parallel to the Zener diode.

[0009] The energy storage system of the present invention comprises a storage battery string including a plurality of storage batteries connected in series, a plurality of first switches provided for each of the storage batteries and each connected in series with the storage battery, a plurality of second switches provided for each of the storage batteries and each connected in parallel with the storage battery and the first switch, and a protection circuit for protecting at least one of the first switch and the second switch, and capacitors connected to the positive and negative sides of the storage battery string, and the protection circuit comprises a Zener diode connected in parallel with the switch to be protected and having a cathode connected between the switch to be protected and the storage battery, and a resistor connected in series or parallel to the Zener diode. [Effects of the Invention]

[0010] According to the present invention, at least one of the first switch and the second switch can be protected from an overvoltage and a rush current. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a circuit diagram showing an outline of a power storage system including a protection circuit according to one embodiment of the present invention. [Figure 2] FIG. 2 is a diagram for explaining the operation of the power storage system shown in FIG. [Figure 3] FIG. 3 is a diagram for explaining the operation of the power storage system shown in FIG. [Figure 4] FIG. 4 is a diagram for explaining the operation of the power storage system shown in FIG. [Figure 5] FIG. 5 is a diagram for explaining the operation of the power storage system shown in FIG. [Figure 6] FIG. 6 is a circuit diagram showing an outline of a power storage system including a protection circuit according to another embodiment of the present invention. [Figure 7] FIG. 7 is a circuit diagram showing an outline of a power storage system including a protection circuit according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described below in accordance with preferred embodiments. Note that the present invention is not limited to the embodiments described below, and the embodiments can be modified as appropriate without departing from the spirit of the present invention. In addition, in the embodiments described below, some components are omitted from illustration and description, but for the details of the omitted technologies, publicly known or well-known technologies are applied as appropriate within the scope of not causing any contradictions with the content described below.

[0013] Fig. 1 is a circuit diagram showing an outline of a power storage system 1 including a protection circuit 10 according to one embodiment of the present invention. The power storage system 1 shown in this figure is a stationary or vehicle-mounted power supply, and includes a plurality of storage battery strings STR, a plurality of power converters PCS, a string bus 2, and a storage battery control device 100. The storage battery strings STR are connected to an external system (not shown) via the power converters PCS and the string bus 2. The plurality of storage battery strings STR are also connected in parallel with each other.

[0014] The storage battery string STR includes n (n is an integer of 2 or greater) storage battery modules M1 to Mn connected in series. Although not particularly limited, the storage battery modules M1 to Mn in this embodiment are refurbished second-hand storage batteries, and the storage battery modules M1 to Mn have different degrees of deterioration. The storage battery modules M1 to Mn are, for example, a plurality of connected cells of secondary batteries such as lithium-ion batteries, nickel-metal hydride batteries, and lithium-ion capacitors.

[0015] The storage battery modules M1 to Mn are charged by receiving power from an external system via the string bus 2 and the power converter PCS. The storage battery modules M1 to Mn also supply power to the external system via the power converter PCS and the string bus 2.

[0016] The external system includes a load, a generator, etc. When the power storage system 1 is for stationary use, the loads are the commercial power supply system and facilities that consume power, and the generator is a solar power generation system, etc. On the other hand, when the power storage system 1 is for vehicle use, the loads are the drive motor, air conditioner, various vehicle electrical components, etc. Note that the drive motor can be both a load and a generator.

[0017] The battery string STR may include n series-connected battery cells or battery packs instead of n series-connected battery modules M1 to Mn. The battery string STR may also include a bypass circuit that bypasses each battery cell or each battery pack.

[0018] The power converter PCS is 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 positive terminal of the battery string STR) and the negative terminal of the terminal battery module Mn (hereinafter referred to as the negative terminal of the battery string STR).

[0019] When charging the battery string STR, the power converter PCS converts the voltage input from the string bus 2 according to the charging power (or current) instruction value from the higher-level controller and outputs the converted voltage to the multiple battery modules M1-Mn. Here, the voltage on the battery string STR side changes according to the bypass state of the battery modules M1-Mn (the number of bypassed battery modules M1-Mn) and the charging state of the battery modules M1-Mn. Therefore, when charging the battery string STR, the power converter PCS converts the voltage input from the string bus 2 to the voltage on the battery string STR side and outputs the converted voltage to the multiple battery modules M1-Mn.

[0020] When a storage battery string STR is discharged, the power converter PCS converts the voltage input from the multiple storage battery modules M1 to Mn according to the discharge power (or current) instruction value from the higher-level controller and outputs the converted voltage to the string bus 2. Here, the input voltage of the power converter PCS during discharge varies according to the bypass state of the storage battery modules M1 to Mn and the charge state of the storage battery modules M1 to Mn. This causes variations in the input voltage of the power converter PCS between the storage battery strings STR during discharge. Therefore, when a storage battery string STR is discharged, the power converter PCS converts the input voltage to a voltage that is consistent with the other storage battery strings STR and outputs the converted voltage to the string bus 2.

[0021] The power converter PCS is a bidirectional converter. When the current flowing through the string bus 2 is an AC current, the power converter PCS includes a synchronization means for tracking changes in instantaneous values.

[0022] The power converter PCS includes an output capacitor C and an inductor (not shown). The output capacitor C and the inductor form an LC filter that smoothes the output voltage and reduces ripple noise in the output voltage. The output capacitor C is provided to connect the positive and negative sides of the storage battery string STR.

[0023] The battery string STR includes n bypass units B1 to Bn, one string cutoff switch S3, and various sensors (not shown). The string cutoff switch S3 is provided on the power line PL of the battery string STR and connects or disconnects the battery string STR from the power converter PCS. Note that it is not essential to provide the string cutoff switch S3 in the battery string STR.

[0024] The current sensor 3 is provided on the power line PL of the storage battery string STR, detects the current of the storage battery string STR (hereinafter referred to as string current), and transmits the detected values ​​to a controller 101, which will be described later. The other various sensors transmit various detected values ​​to the controller 101. The other various sensors include a voltage sensor that detects the total voltage of the storage battery string STR, a voltage sensor that detects the voltage between the positive and negative terminals of each storage battery module M1 to Mn, a temperature sensor that detects the temperature of each storage battery module M1 to Mn, and a cell voltage sensor that detects the voltage of a storage battery cell in each storage battery module M1 to Mn.

[0025] Each bypass unit B1 to Bn provided for each storage battery module M1 to Mn includes a bypass line BL, a cutoff switch S1, a bypass switch S2, and a protection circuit 10. The bypass line BL is a power line that bypasses each storage battery module M1 to Mn and the cutoff switch S1. The cutoff switch S1 is provided between the positive electrode of each storage battery module M1 to Mn and one end of the bypass line BL. The bypass switch S2 is provided on the bypass line BL. The cutoff switch S1 and the bypass switch S2 are mechanical relays. The cutoff switch S1 and the bypass switch S2 may be semiconductor switches or the like.

[0026] The starting battery module M1 and the ending battery module Mn are connected to an external system via a power converter PCS and a string bus 2. The battery modules M1 to Mn corresponding to the bypass units B1 to Bn whose cutoff switch S1 is closed and whose bypass switch S2 is open are connected in series to the external system. On the other hand, the battery modules M1 to Mn corresponding to the bypass units B1 to Bn whose cutoff switch S1 is open and whose bypass switch S2 is closed are bypassed.

[0027] A protection circuit 10 is provided for each of the bypass units B1 to Bn to protect the cutoff switch S1 and the bypass switch S2 from overvoltage and to suppress rush current flowing through the bypass units B1 to Bn. The protection circuit 10 includes a Zener diode ZD1, a diode D1, and a resistor R1 provided for the cutoff switch S1, and a Zener diode ZD2, a diode D2, and a resistor R2 provided for the bypass switch S2.

[0028] The Zener diode ZD1 and the diode D1 are connected in series. The anode of the Zener diode ZD1 and the anode of the diode D1 are connected together. The Zener diode ZD1 and the diode D1 are connected in parallel with the cutoff switch S1. The cathode of the Zener diode ZD1 is connected between the cutoff switch S1 and the positive electrodes of the storage battery modules M1 to Mn. The cathode of the diode D1 is connected between the cutoff switch S1 and the resistor R1.

[0029] One end of the resistor R1 is connected between the anode of the Zener diode ZD1 and the anode of the diode D1, and the other end of the resistor R1 is connected between the cathode of the diode D1 and the bypass switch S2. That is, the resistor R1 and the diode D1 are connected in parallel, and the resistor R1 and the Zener diode ZD1 are connected in series.

[0030] The Zener diode ZD1 passes a forward current, but passes a reverse current (Zener current) when a Zener voltage is applied. The diode D1 passes a forward current, but hardly passes a reverse current. The forward current of the Zener diode ZD1 is a current that flows from the diode D1 side to the storage battery modules M1 to Mn side, and the reverse current of the Zener diode ZD1 is a current that flows from the storage battery modules M1 to Mn side to the diode D1 side. The forward current of the diode D1 is a current that flows from the Zener diode ZD1 side to the positive electrode side of the storage battery string STR, and the reverse current of the diode D1 is a current that flows from the positive electrode side of the storage battery string STR to the Zener diode ZD1 side.

[0031] If the Zener diode ZD1 and the diode D1 are not provided corresponding to the cutoff switch S1, when the cutoff switch S1 is switched from a state in which the cutoff switch S1 is closed and the bypass switch S2 is open to a state in which the cutoff switch S1 is open, a high voltage is applied to the cutoff switch S1. For example, in the bypass unit B1, when the cutoff switch S1 is switched from a state in which the cutoff switch S1 is closed and the bypass switch S2 is open to a state in which the cutoff switch S1 is open, a voltage V all and the voltage of the disconnected storage battery module M1, V all Therefore, the cutoff switch S1 is turned on by the voltage V all It is necessary to use a high-cost product with a withstand voltage equal to or greater than the maximum value of '.

[0032] In contrast, in this embodiment, in which the Zener diode ZD1 and the diode D1 are provided corresponding to the cutoff switch S1, when the cutoff switch S1 is switched from a state in which the cutoff switch S1 is closed and the bypass switch S2 is open to a state in which the cutoff switch S1 is open, the voltage applied to the cutoff switch S1 is limited to the Zener voltage of the Zener diode ZD1. Note that if only the Zener diode ZD1 and the resistor R1 are provided without the diode D1, the voltage applied to the cutoff switch S1 is the sum of the Zener voltage of the Zener diode ZD1 and the voltage applied to the resistor R1.

[0033] The resistor R1 connects the output capacitor C and the Zener diode ZD1 via the string cutoff switch S3, etc., and limits the forward current flowing through the Zener diode ZD1. The resistance value of the resistor R1 is set so that the current flowing through the Zener diode ZD1 through the resistor R1 when the cutoff switch S1 is open is limited to an allowable value, and the potential V C and voltage V all The time required to equalize the ' and ' is set to satisfy the condition that the time required to equalize them is kept within an acceptable value.

[0034] The Zener diode ZD2 and the diode D2 are connected in series with each other. The anode of the Zener diode ZD2 and the anode of the diode D2 are connected together. The Zener diode ZD2 and the diode D2 are connected in parallel with the bypass switch S2. The cathode of the Zener diode ZD2 is connected between the bypass switch S2 and the negative electrodes of the storage battery modules M1 to Mn. The cathode of the diode D2 is connected between the bypass switch S2 and the other end of the resistor R1.

[0035] One end of the resistor R2 is connected between the anode of the Zener diode ZD2 and the anode of the diode D2, and the other end of the resistor R2 is connected between the cathode of the diode D2 and the bypass switch S2. That is, the resistor R2 and the diode D2 are connected in parallel, and the resistor R2 and the Zener diode ZD2 are connected in series.

[0036] The Zener diode ZD2 passes a forward current but passes a reverse current when a Zener voltage is applied. The diode D2 passes a forward current but hardly passes a reverse current. The forward current of the Zener diode ZD2 is a current that flows from the diode D2 side to the subsequent storage battery modules M1 to Mn side, and the reverse current of the Zener diode ZD2 is a current that flows from the subsequent storage battery modules M1 to Mn side to the diode D2 side. The forward current of the diode D2 is a current that flows from the Zener diode ZD2 side to the positive electrode side of the storage battery string STR, and the reverse current of the diode D1 is a current that flows from the positive electrode side of the storage battery string STR to the Zener diode ZD2 side.

[0037] If the Zener diode ZD2 and the diode D2 are not provided corresponding to the bypass switch S2, when the bypass switch S2 is switched from a state in which the bypass switch S2 is closed and the cutoff switch S1 is open to a state in which the bypass switch S2 is open, a high voltage is applied to the bypass switch S2. For example, in the bypass unit B1, when the bypass switch S2 is switched from a state in which the bypass switch S2 is closed and the cutoff switch S1 is open to a state in which the bypass switch S2 is open, a voltage V all Therefore, the bypass switch S2 is connected to the power supply 1 through the power supply 2 through the power supply 3 through the power supply 4 through the power supply 5 through the power supply 6 through the power supply 7 through the power supply 8 through the power supply 9 through the power supply 10 through the power supply 11 through the power supply 12 through the power supply 13 through the power supply 14 through the power supply 15 through the power supply 16 through the power supply 17 through the power supply 18 through all Therefore, it is necessary to use a high-cost product with a withstand voltage equal to or greater than the maximum value of the above.

[0038] In contrast, in this embodiment, in which the Zener diode ZD2 and the diode D2 are provided corresponding to the bypass switch S2, when the bypass switch S2 is switched from a state in which the bypass switch S2 is closed and the cutoff switch S1 is open to a state in which the bypass switch S2 is open, the voltage applied to the bypass switch S2 is suppressed to the Zener voltage of the Zener diode ZD2. Note that if the diode D2 is not provided and only the Zener diode ZD2 and the resistor R2 are provided, the voltage applied to the bypass switch S2 is the sum of the Zener voltage of the Zener diode ZD2 and the voltage applied to the resistor R2.

[0039] The resistor R2 connects the output capacitor C and the Zener diode ZD2 via the string cutoff switch S3, etc., and limits the forward current flowing through the Zener diode ZD2. The resistance value of the resistor R2 is set so that the current flowing through the Zener diode ZD2 through the resistor R2 when the bypass switch S2 is open is limited to an allowable value, and the potential V C and voltage V all The time required to equalize the two is set to an acceptable value.

[0040] The battery control device 100 includes a controller 101 and a relay driver 102 provided for each battery string STR. The controller 101 transmits control signals to the relay driver 102 and the power converter PCS. The relay driver 102 controls the cutoff switch S1 and bypass switch S2 of the bypass units B1 to Bn and the string cutoff switch S3 in accordance with the control signal transmitted from the controller 101. The power converter PCS converts the charging / discharging power of the battery string STR in accordance with the control signal transmitted from the controller 101. The power converter PCS controls the string current of the battery string STR in accordance with the control signal transmitted from the controller 101.

[0041] The controller 101 detects and estimates the state of the battery string STR, and sends device control requests to a system controller (not shown) that controls the entire energy storage system 1. Examples of detecting the state of the battery string STR include detecting the string current of the battery string STR based on the detection signal of the current sensor 3, detecting the total voltage of the battery string STR based on the detection signal of the voltage sensor, detecting the voltage of the battery modules M1 to Mn based on the detection signal of the voltage sensor, detecting the temperature of the battery modules M1 to Mn based on the detection signal of the temperature sensor, and detecting the voltage of the battery cells based on the detection signal of the cell voltage sensor. Examples of estimating the state of the battery string STR include estimating the SOC (State of Charge) and SOH (State of Health) of the battery modules M1 to Mn and estimating the SOC and SOH of the battery string STR. Examples of sending device control requests to the system controller include requests for open / close switching control of the cutoff switch S1, bypass switch S2, and string cutoff switch S3, and requests for control of the power converter PCS.

[0042] When a request for open / close switching control of the cutoff switch S1 and bypass switch S2 for any of the storage battery modules M1 to Mn is permitted by the system controller, the controller 101 executes open / close switching control of the cutoff switch S1 and bypass switch S2. At this time, the controller 101 reduces the string current of the storage battery string STR to 0 before executing open / close switching control of the cutoff switch S1 and bypass switch S2. Note that the controller 101 may open the string cutoff switch S3 after reducing the string current of the storage battery string STR to 0.

[0043] 2 to 5 are diagrams for explaining the operation of the power storage system 1 shown in FIG. 2. In FIG. 2, a potential V due to the charge accumulated in the output capacitor C in the power converter PCS is C The voltage of the bypass target battery module M1 and the voltage V of the connected battery module Mx all and the total voltage V all 'Higher State (V C >V all 2 does not show the connected storage battery modules Mx, the connected storage battery modules Mx may be included among the storage battery modules M3 to Mn-1 (not shown), there may be no connected storage battery modules Mx, or the storage battery modules M2 and Mn may be connected storage battery modules Mx.

[0044] 2 also shows the operation of the battery string STR when the battery module M1 is switched from the connected state to the bypass state. When the battery module M1 is switched from the connected state to the bypass state, first, the cutoff switch S1 of the bypass unit B1 is switched from Close to Open, and then the bypass switch S2 of the bypass unit B1 is switched from Open to Close.

[0045] As shown in Figure 2, when the cutoff switch S1 of the bypass unit B1 is switched from Close to Open, the Zener voltage of the Zener diode ZD1 is applied across the contacts of the cutoff switch S1. If the protection circuit 10 is not provided, the voltage V all ' is applied.

[0046] When the cutoff switch S1 is switched from Close to Open, current flows from the output capacitor C to the storage battery module M1 etc. via the resistor R1 and the Zener diode ZD1. At this time, a voltage drops across the resistor R1, and the potential V of the output capacitor C C and voltage V all The difference between the output capacitor C and the output capacitor C is reduced, and finally the potential V C and voltage V all As a result, the potential V C and voltage V all This sufficiently suppresses rush current that may occur until the voltages ' and ' are equalized, and prevents excessive arc discharge from occurring at the contacts of the cutoff switch S1.

[0047] Figure 3 shows the potential V of the output capacitor C. C The voltage V of the connected battery module Mx all Higher state (V C >V all 3 does not show the connected storage battery modules Mx, the connected storage battery modules Mx may be included among the unillustrated storage battery modules M3 to Mn-1, there may be no connected storage battery modules Mx, or the connected storage battery modules M2 and Mn may be the connected storage battery modules Mx.

[0048] 3 also shows the operation of the battery string STR when the battery module M1 is switched from the bypass state to the connected state. When the battery module M1 is switched from the bypass state to the connected state, first, the bypass switch S2 of the bypass unit B1 is switched from Close to Open, and then the cutoff switch S1 of the bypass unit B1 is switched from Open to Close.

[0049] As shown in Fig. 3, when the bypass switch S2 of the bypass unit B1 is switched from Close to Open, the Zener voltage of the Zener diode ZD2 is applied across the contacts of the bypass switch S2. If the protection circuit 10 is not provided, the voltage V of the connected storage battery module Mx is applied across the contacts of the bypass switch S2. all is applied.

[0050] When the bypass switch S2 is switched from Close to Open, current flows from the output capacitor C to the storage battery module Mx via the resistor R2 and the Zener diode ZD2. At this time, a voltage drops across the resistor R2, and the potential V of the output capacitor C C and voltage V all The difference between the output capacitor C and the potential V C and voltage V all As a result, the potential V C and voltage V all This sufficiently suppresses rush current that may occur until the voltages are equalized, thereby preventing excessive arc discharge from occurring at the contacts of the bypass switch S2.

[0051] Figure 4 shows the potential V of the output capacitor C. C is the voltage V all 'Lower state (V C <V allThe storage battery string STR of 1′) is shown. Note that the storage battery modules M2 and Mn correspond to the storage battery module Mx in a connected state, but the storage battery modules M3 to Mn-1 (not shown) may also include a storage battery module Mx in a connected state.

[0052] 4 shows the behavior of the battery string STR when the battery module M1 is switched from the connected state to the bypass state. As shown in FIG. 4, when the cutoff switch S1 of the bypass unit B1 is switched from close to open, the Zener voltage of the Zener diode ZD1 is applied across the contacts of the cutoff switch S1. If the protection circuit 10 is not provided, the voltage V all ' is applied.

[0053] When the cutoff switch S1 is switched from Close to Open, current flows from the bypass target storage battery module M1 and the connected storage battery module Mx to the output capacitor C via the Zener diode ZD1, diode D1, and resistor R1. At this time, a voltage drops across resistor R1, and the potential V of the output capacitor C C and voltage V all The difference between the output capacitor C and the output capacitor C is reduced, and finally the potential V C and voltage V all The difference between the voltage V and the voltage V is reduced to the Zener voltage of the Zener diode ZD1. As a result, the current starts to flow from the storage battery module M1 to the output capacitor C. C and voltage V all This sufficiently suppresses the rush current that may occur until the difference between Vcc and Vdd' decreases to the Zener voltage of the Zener diode ZD1, thereby preventing excessive arc discharge from occurring at the contacts of the cutoff switch S1.

[0054] Figure 5 shows the potential V of the output capacitor C. C The voltage V of the connected battery module Mx all Lower state (V C <V all) is shown. Note that storage battery modules M2 and Mn correspond to storage battery modules Mx in a connected state, but storage battery modules Mx in a connected state may also exist among storage battery modules M3 to Mn-1 (not shown).

[0055] 5 shows the behavior of the battery string STR when the battery module M1 is switched from the bypass state to the connected state. As shown in FIG. 5, when the bypass switch S2 of the bypass unit B1 is switched from Close to Open, the Zener voltage of the Zener diode ZD2 is applied across the contacts of the bypass switch S2. If the protection circuit 10 is not provided, the voltage V of the battery module Mx in the connected state is applied across the contacts of the bypass switch S2. all is applied.

[0056] When the bypass switch S2 is switched from Close to Open, current flows from the connected storage battery module Mx to the output capacitor C via the Zener diode ZD2, diode D2, and resistor R2. At this time, a voltage drops across resistor R2, and the potential V of the output capacitor C C and voltage V all The difference between the output capacitor C and the potential V C and voltage V all The difference between the voltage V and the voltage V is reduced to the Zener voltage of the Zener diode ZD1. As a result, the voltage V C and voltage V all This sufficiently suppresses the rush current that may occur until the difference between the two voltages decreases to the Zener voltage of the Zener diode ZD2, thereby preventing excessive arc discharge from occurring at the contacts of the bypass switch S2.

[0057] As described above, the protection circuit 10 according to this embodiment protects the cutoff switch S1 and includes a Zener diode ZD1 and a resistor R1. The Zener diode ZD1 is connected in parallel with the cutoff switch S1, with its cathode connected between the cutoff switch S1 and the storage battery modules M1 to Mn. This limits the voltage applied to the cutoff switch S1 when the cutoff switch S1 is switched from closed to open.

[0058] Here, the resistor R1 is connected in series with the Zener diode ZD1. Therefore, when the isolation switch S1 is switched from Close to Open, the potential V of the output capacitor C C and voltage V all When there is a difference between the potential V of the output capacitor C and the storage battery modules M1 to Mn, the current flowing between the output capacitor C and the storage battery modules M1 to Mn passes through the resistor R1. As a result, when the cutoff switch S1 is switched from Close to Open, the potential V of the output capacitor C C and voltage V all This can mitigate the difference between the voltages of the cutoff switch S1 and the voltages of the cutoff switch S2, thereby protecting the cutoff switch S1 from rush current.

[0059] The protection circuit 10 according to this embodiment also includes a diode D1 connected in parallel with the Zener diode ZD1 and the cutoff switch S1. The anode of the diode D1 is connected to the anode of the Zener diode ZD1. This makes it possible to suppress the current flowing forward through the Zener diode ZD1 when the cutoff switch S1 is open.

[0060] If the diode D1 is not provided and the resistor R1 is connected in series or parallel to the Zener diode ZD1, a voltage exceeding the Zener voltage of the Zener diode ZD1 is applied to the cutoff switch S1 in the open state. In contrast, in the protection circuit 10 according to this embodiment, the resistor R1 is connected in series with the Zener diode ZD1 and in parallel with the diode D1, so that the voltage applied to the cutoff switch S1 in the open state can be limited to the Zener voltage of the Zener diode ZD1 or less.

[0061] The protection circuit 10 according to this embodiment protects the bypass switch S2 and includes a Zener diode ZD2 and a resistor R2. The Zener diode ZD2 is connected in parallel with the bypass switch S2, and its cathode is connected between the bypass switch S2 and the storage battery modules M1 to Mn. This makes it possible to limit the voltage applied to the bypass switch S2 when the bypass switch S2 is switched from closed to open.

[0062] Here, the resistor R2 is connected in series with the Zener diode ZD2. Therefore, when the bypass switch S2 is switched from Close to Open, the potential Vc of the output capacitor C and the voltage V all When there is a difference between the potential V of the output capacitor C and the connected storage battery module Mx, the current flows through the resistor R2. As a result, when the bypass switch S2 is switched from Close to Open, the potential V of the output capacitor C C and voltage V all This can mitigate the difference between the voltages and protect the bypass switch S2 from rush current.

[0063] The protection circuit 10 according to this embodiment also includes a diode D2 connected in parallel with the bypass switch S2 together with the Zener diode ZD2. The anode of this diode D2 is connected to the anode of the Zener diode ZD2. This makes it possible to suppress the current flowing forward through the Zener diode ZD2 when the bypass switch S2 is open.

[0064] If the diode D2 is not provided and the resistor R2 is connected in series or parallel to the Zener diode ZD2, a voltage exceeding the Zener voltage of the Zener diode ZD2 is applied to the bypass switch S2 in the open state. In contrast, in the protection circuit 10 according to this embodiment, the resistor R2 is connected in series with the Zener diode ZD2 and in parallel with the diode D2, so that the voltage applied to the bypass switch S2 in the open state can be limited to the Zener voltage of the Zener diode ZD2 or less.

[0065] 6 is a circuit diagram showing an outline of a power storage system 1' including a protection circuit 10' according to another embodiment of the present invention. As shown in this diagram, each of the bypass units B1 to Bn of the power storage system 1' according to this embodiment includes a protection circuit 10'.

[0066] In the protection circuit 10', a resistor R1 is connected in parallel with the Zener diode ZD1 and the diode D1, and a resistor R2 is connected in parallel with the Zener diode ZD2 and the diode D2.

[0067] In the energy storage system 1 according to the above embodiment, when the cutoff switch S1 is switched from Close to Open, the potential V C is the voltage V all If lower than (V C <V all '), potential V C and voltage V all On the other hand, in the energy storage system 1′ of this embodiment, when the cutoff switch S1 is switched from Close to Open, the difference between the potential V C is the voltage V all If it is lower than the potential V C and voltage V all The difference decreases until it becomes 0.

[0068] In the energy storage system 1 according to the above embodiment, when the bypass switch S2 is switched from Close to Open, the potential V C is the voltage V all If it is lower than the potential V C and voltage V all On the other hand, in the energy storage system 1′ of this embodiment, when the bypass switch S2 is switched from Close to Open, the difference between the potential V C is the voltage V all If it is lower than the potential V C and voltage V all The difference decreases until it becomes 0.

[0069] FIG. 7 is a circuit diagram showing an outline of a power storage system 1" including a protection circuit 10" according to another embodiment of the present invention. As shown in this figure, each of the bypass units B1 to Bn of the power storage system 1" according to this embodiment includes a protection circuit 10".

[0070] In the protection circuit 10'', diodes D1 and D2 are not provided, and a resistor R1 is connected in series with the Zener diode ZD1, and a resistor R2 is connected in series with the Zener diode ZD2. The resistor R1 limits the forward current of the Zener diode ZD1, and the resistor R2 limits the forward current of the Zener diode ZD2.

[0071] In the energy storage system 1″ according to this embodiment, when the cutoff switch S1 is switched from Close to Open, the potential V C and voltage V all When the difference between V and ZD1 is large, the current flowing between the output capacitor C and the Zener diode ZD1 passes through the resistor R1. As a result, when the isolation switch S1 is switched from Close to Open, the potential V of the output capacitor C C and voltage V all This can mitigate the difference between the voltages of the cutoff switch S1 and the voltages of the cutoff switch S2, thereby protecting the cutoff switch S1 from rush current.

[0072] When the bypass switch S2 is switched from Close to Open, the potential V of the output capacitor C C and voltage V all When the difference between the output capacitor C and the Zener diode ZD2 is large, the current flowing between the output capacitor C and the Zener diode ZD2 passes through the resistor R2. As a result, when the bypass switch S2 is switched from Close to Open, the potential V of the output capacitor C C and voltage V all This can mitigate the difference between the voltages and protect the bypass switch S2 from rush current.

[0073] The present invention has been described above based on the above-mentioned embodiment, but the present invention is not limited to the above-mentioned embodiment, and modifications may be made within the scope of the spirit of the present invention, and publicly known or well-known technologies may be combined as appropriate.

[0074] For example, in the above embodiment, the switches to be protected are the cutoff switch S1 and the bypass switch S2, but the switches to be protected may be only the cutoff switch S1 or only the bypass switch S2.

[0075] In addition, in the above embodiment, the capacitors connected to the positive and negative sides of the storage battery string STR are output capacitors C inside the power converter PCS, but they may also be capacitors outside the power converter PCS. [Explanation of symbols]

[0076] 1,1',1": Energy storage system 10,10',10” :Protection circuit C: Output capacitor (capacitor) D1, D2: Diodes M1 to Mn, Mx: Battery modules (batteries) PCS: Power converter S1: Isolation switch (first switch, switch to be protected) S2: Bypass switch (second switch, switch to be protected) STR: Battery string R1,R2:Resistance ZD1, ZD2: Zener diode

Claims

1. A protection circuit for protecting at least one of the first switches and the second switches in a power storage system including a plurality of storage batteries connected in series, a plurality of first switches provided for each of the storage batteries and each connected in series with the storage battery, and a plurality of second switches provided for each of the storage batteries and each connected in parallel with the storage battery and the first switch, and capacitors connected to positive and negative sides of the storage battery string, a Zener diode connected in parallel with the switch to be protected, the cathode of the Zener diode being connected between the switch to be protected and the storage battery; a resistor connected in series or in parallel with the Zener diode; A protection circuit comprising:

2. 2. The protection circuit according to claim 1, further comprising a diode having an anode connected to the anode of the Zener diode and connected in parallel with the switch to be protected together with the Zener diode.

3. 3. The protection circuit according to claim 2, wherein the resistor is connected in series with the Zener diode and in parallel with the diode.

4. the switch to be protected is the first switch, 3. The protection circuit according to claim 1, wherein the cathode of the Zener diode is connected between the positive electrode of the storage battery and the first switch.

5. the switch to be protected is the second switch, 3. The protection circuit according to claim 1, wherein the cathode of the Zener diode is connected between the negative electrode of the storage battery and the second switch.

6. 3. The protection circuit according to claim 1, wherein the capacitor is an output capacitor in a power converter to which the positive and negative terminals of the storage battery string are connected.

7. a battery string including: a plurality of storage batteries connected in series; a plurality of first switches provided for each of the storage batteries, each connected in series with the storage battery; a plurality of second switches provided for each of the storage batteries, each connected in parallel with the storage battery and the first switch; and a protection circuit that protects at least one of the first switch and the second switch; a capacitor connected to the positive and negative terminals of the battery string; Equipped with The protection circuit includes: a Zener diode connected in parallel with the switch to be protected, the cathode of the Zener diode being connected between the switch to be protected and the storage battery; a resistor connected in series or in parallel with the Zener diode; A power storage system comprising:

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