Power storage system

Abstract

To suppress fluctuation of input / output power between a power storage string and an external system, and remove an oxide coating from a contact portion of a switch of a bypass part or the like with a reduced cost.SOLUTION: A storage battery control device 100 executes a first oxide film removing process of operating cutoff switches S1 corresponding to arbitrary storage battery modules M1 to Mn in a state where bypass switches S2 corresponding to the arbitrary storage battery modules M1 to Mn and a first system main relay S3A are opened and in a state where a pre-charge relay S4 is closed, and a second oxide film removing process of operating the bypass switches S2 corresponding to the arbitrary storage battery modules M1 to Mn in a state where the cutoff switches S1 corresponding to the arbitrary storage battery modules M1 to Mn and the first system main relay S3A are opened and in a state where the pre-charge relay S4 is closed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electricity storage system. [Background technology]

[0002] As a power storage system having a power storage string in which a plurality of storage batteries are connected in series, one in which a bypass unit that switches the storage batteries between a connected state and a bypass state is provided for each storage battery is known (see, for example, Patent Document 1). In the power storage system described in Patent Document 1, a cutoff switch that cuts off / connects the storage battery and a bypass switch connected in parallel to the storage battery and the cutoff switch are provided in the bypass unit. In this power storage system, bypass control is executed in which the cutoff switch corresponding to a storage battery that cannot discharge the required current is set to the cutoff state and the bypass switch corresponding to that storage battery is set to the connected state, and discharge is performed 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, it is necessary to prevent large fluctuations in the input / output power between the energy storage string and an external system due to sudden changes in the current of the energy storage string (hereinafter referred to as the string current) during bypass control. Therefore, it is necessary to reduce the string current to a predetermined value before executing bypass control. On the other hand, if the cutoff switch and bypass switch are mechanical relays, it is necessary to operate the cutoff switch and bypass switch while a voltage above a certain level is applied between the contacts of the cutoff switch and bypass switch to remove the oxide film that forms on the contact parts of the cutoff switch and bypass switch over time, thereby generating an arc discharge at the contact parts with a current value above a certain level.

[0005] If bypass control is performed after reducing the string current to suppress fluctuations in input / output power between the energy storage string and an external system, a voltage above a certain level may not be applied to the contact points of the cutoff switch and bypass switch, preventing arc discharge of a current above a certain level and resulting in insufficient removal of the oxide film. Therefore, a means is needed that enables both operating the cutoff switch and bypass switch after reducing the string current and operating the cutoff switch and bypass switch while applying a voltage sufficient to remove the oxide film.

[0006] One possible method for achieving this is to connect a CR circuit to a power storage string, and switch the cutoff switch from open to close while charging the capacitor of the CR circuit with power from a storage battery, or switch the bypass switch from open to close while discharging the capacitor. However, this method requires the implementation of a new CR circuit, which increases costs.

[0007] In view of the above circumstances, the present invention aims to suppress fluctuations in input / output power between the storage string and an external system and remove oxide coatings from contact portions of switches such as the bypass section in a storage system having a storage string in which multiple storage batteries are connected in series, with each storage battery being provided with a bypass section that switches the storage batteries between a connected state and a bypass state, while keeping costs down. [Means for solving the problem]

[0008] The power storage system of the present invention is a power storage system including a power storage string in which a plurality of storage batteries are connected in series, and a power converter that converts input and output power of the power storage string, wherein the power storage string includes a first switch provided for each of the storage batteries, a second switch connected in parallel to the first switch and the storage batteries, a plurality of bypass units that switch the storage batteries between a connected state and a bypass state, a smoothing capacitor that connects the positive side and negative side of the power storage string, a third switch provided between the storage battery on the most positive side or the storage battery on the most negative side and the smoothing capacitor, a pre-charge circuit connected in parallel to the third switch and that suppresses inrush current to the smoothing capacitor, a fourth switch provided in the pre-charge circuit, and a power converter that converts input and output power of the power storage string. and a control unit that controls the above-mentioned storage battery, and the control unit executes at least one of a first oxide film removal process of removing an oxide film on a contact portion of the first switch by operating the first switch corresponding to any of the storage batteries with the second switch and the third switch corresponding to the any of the storage batteries in an open state and the fourth switch in a closed state; a second oxide film removal process of removing an oxide film on a contact portion of the second switch by operating the second switch corresponding to any of the storage batteries in an open state and the third switch corresponding to the any of the storage batteries in a closed state; and a third oxide film removal process of removing an oxide film on a contact portion of the third switch by operating the third switch in a state in which a charging current or a discharging current of the smoothing capacitor is flowing through the third switch. [Effects of the Invention]

[0009] According to the present invention, in a storage system having a storage string in which a plurality of storage batteries are connected in series, and a bypass unit that switches the storage batteries between a connected state and a bypass state is provided for each storage battery, it is possible to suppress fluctuations in input / output power between the storage string and an external system, and to remove oxide coatings from the contact parts of switches such as the bypass unit, all while keeping costs down. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a circuit diagram showing an outline of a power storage system according to one embodiment of the present invention. [Figure 2] FIG. 2 is a circuit diagram for explaining the first oxide layer removal process. [Figure 3] FIG. 3 is a circuit diagram for explaining the second oxide film removal process. [Figure 4] FIG. 4 is a circuit diagram for explaining the precharge process. [Figure 5] FIG. 5 is a flowchart illustrating a process of switching a storage battery module that is the target of a bypass control request from a connected state to a bypass state. [Figure 6] FIG. 6 is a circuit diagram showing an outline of a power storage string according to another embodiment of the present invention. [Figure 7] FIG. 7 is a circuit diagram for explaining the third oxide film removal process performed in the power storage string of FIG. [Figure 8] FIG. 8 is a flowchart for explaining the process of switching the storage battery module that is the target of the bypass control request in the power storage string of FIG. 6 from the connected state to the bypass state. [Figure 9] FIG. 9 is a circuit diagram showing an outline of a power storage string according to another embodiment of the present invention. [Figure 10] FIG. 10 is a circuit diagram for explaining the third oxide film removal process performed in the power storage string of FIG. [Figure 11] FIG. 11 is a flowchart for explaining the process of switching the storage battery module that is the target of the bypass control request in the power storage string of FIG. 9 from the connected state to the bypass state. [Figure 12] FIG. 12 is a circuit diagram showing an outline of a power storage string according to another embodiment of the present invention. [Figure 13] FIG. 13 is a circuit diagram showing an outline of a power storage string according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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.

[0012] Fig. 1 is a circuit diagram showing an outline of a power storage system 1 according to one embodiment of the present invention. As shown in this diagram, the power storage system 1 includes a plurality of power storage strings STR, a plurality of power converters PCS, a string bus 4, and a storage battery control device 100. The plurality of power storage strings STR are connected in parallel to each other and also to an external system (an external system, not shown) via the string bus 4. The power storage system 1 is a stationary or vehicle-mounted power supply.

[0013] The power storage 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 or lithium-ion capacitors.

[0014] The storage battery modules M1 to Mn are charged by receiving power from an external system via the string bus 4 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 4.

[0015] The external system includes a load, a generator, etc. When the power storage system 1 is for stationary use, household appliances, commercial power systems, etc. are the loads, and the solar power generation system, commercial power systems, etc. are the generators. On the other hand, when the power storage system 1 is for vehicle use, the drive motor, air conditioner, various vehicle electrical components, etc. are the loads. The drive motor is both a load and a generator.

[0016] The power storage string STR may include n series-connected storage battery cells or storage battery packs instead of n series-connected storage battery modules M1 to Mn. The power storage string STR may also include a bypass unit that bypasses each storage battery cell or each storage battery pack.

[0017] The power converter PCS is a DC / DC converter or a DC / AC converter, and is connected to the string bus 4. The power converter PCS is also connected to the positive terminal of the starting storage battery module M1 (total + of the storage string STR) and the negative terminal of the terminal storage battery module Mn (total − of the storage string STR).

[0018] When charging the storage string STR, the power converter PCS converts the voltage input from the string bus 4 according to the indicated value of the charging power (or current) and outputs it to the multiple storage battery modules M1 to Mn. Here, the voltage on the side of the storage string STR changes depending on the bypass state of the storage battery modules M1 to Mn (the number of bypassed storage battery modules M1 to Mn) and the charging state of the storage battery modules M1 to Mn. Therefore, when charging the storage string STR, the power converter PCS converts the voltage input from the string bus 4 to the voltage on the side of the storage string STR and outputs it to the multiple storage battery modules M1 to Mn.

[0019] When the storage string STR is discharging, the power converter PCS converts the voltage input from the multiple storage battery modules M1 to Mn according to the indicated value of the discharge power (or current) and outputs the converted voltage to the string bus 4. Here, the input voltage of the power converter PCS during discharging varies depending on 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 strings STR during discharging. Therefore, when the storage string STR is discharging, the power converter PCS converts the input voltage to a voltage that is consistent with the other storage strings STR and outputs the converted voltage to the string bus 4.

[0020] The power converter PCS is a bidirectional converter. When the current flowing through the string bus 4 is an AC current, the power converter PCS includes a synchronization means for tracking changes in instantaneous values.

[0021] The energy storage string STR includes n bypass units B1 to Bn, a first system main relay S3A, a second system main relay S3B, a smoothing capacitor C, a precharge circuit 10, a current sensor 11, and various sensors (not shown). The current sensor 11 is provided at an arbitrary position on the power line PL where current is always applied, and detects the string current and transmits a detection signal to the string controller 102.

[0022] The bypass units B1 to Bn are provided for the respective storage battery modules M1 to Mn, and each of the bypass units B1 to Bn includes a cutoff switch S1, a bypass line BL, and a bypass switch S2.

[0023] The cutoff switch S1 is a mechanical relay connected in series with each of the storage battery modules M1 to Mn, and is provided on the positive side of the power storage string STR relative to each of the storage battery modules M1 to Mn.

[0024] The bypass line BL is a power line that bypasses each of the storage battery modules M1 to Mn and the cutoff switch S1. The bypass line BL is provided with a bypass switch S2, which is a mechanical relay. That is, the bypass switch S2 is connected in parallel with each of the storage battery modules M1 to Mn and the cutoff switch S1.

[0025] 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 4. When the bypass switch S2 is open and the cutoff switch S1 is closed in all of the bypass units B1 to Bn, all of the battery modules M1 to Mn are connected in series to the external system. On the other hand, when the cutoff switch S1 is open and the bypass switch S2 is closed in any of the bypass units B1 to Bn, the battery module M1 to Mn corresponding to that bypass unit B1 to Bn is bypassed.

[0026] The first system main relay S3A and the second system main relay S3B are provided at positions on the power line PL where current is always applied. Specifically, the first system main relay S3A is provided between the positive terminal of the power storage string STR and the cutoff switch S1 of the bypass unit B1 at the start end. The second system main relay S3B is provided between the negative terminal of the power storage string STR and the storage battery module Mn at the end. The first system main relay S3A and the second system main relay S3B are mechanical relays, semiconductor switches, or the like.

[0027] The smoothing capacitor C is connected between the positive terminal of the power storage string STR and the first system main relay S3A, and between the negative terminal of the power storage string STR and the second system main relay S3B. The smoothing capacitor C is an element that stores electric charge, such as an electrolytic capacitor, a film capacitor, or a capacitor, and smoothes the voltage input from the power converter PCS to the power storage string STR.

[0028] The precharge circuit 10 includes a resistor R and a precharge relay S4. The precharge relay S4 is a mechanical relay, a semiconductor switch, or the like. The resistor R and the precharge relay S4 are connected in series and in parallel with the first system main relay S3A. The precharge circuit 10 is a circuit for charging (precharging) the smoothing capacitor C when the power storage string STR is started up, etc. In this embodiment, the precharge circuit 10 is used not only for the precharge process of charging the smoothing capacitor C, but also for a first oxide film removal process of removing an oxide film from the contact portion of the cutoff switch S1 and a second oxide film removal process of removing an oxide film from the contact portion of the bypass switch S2.

[0029] The battery control device 100 includes a plurality of string controllers 102, a plurality of relay drivers 103, and one system controller 101. The string controller 102 and the relay driver 103 are provided for each power storage string STR.

[0030] The string controller 102 transmits control signals to the relay driver 103 and power converter PCS of the corresponding power storage string STR. The relay driver 103 controls the cutoff switch S1 and bypass switch S2 of the bypass units B1 to Bn, the first system main relay S3A and the second system main relay S3B, and the pre-charge relay S4 in accordance with the control signal transmitted from the string controller 102. The power converter PCS converts the charging / discharging power of the power storage string STR in accordance with the control signal transmitted from the string controller 102. The power converter PCS controls the string current of the power storage string STR in accordance with the control signal from the string controller 102.

[0031] The string controller 102 detects and estimates the state of the power storage string STR, notifies the system controller 101 of device control requests, etc. Examples of detecting the state of the power storage string STR include detecting the string current of the power storage string STR based on a detection signal from the current sensor 11, detecting the total voltage of the power storage string STR based on a detection signal from a voltage sensor (not shown), detecting the voltage of the storage battery modules M1 to Mn based on a detection signal from a voltage sensor, detecting the temperature of the storage battery modules M1 to Mn based on a detection signal from a temperature sensor (not shown), and detecting the voltage of the storage battery cells based on a detection signal from a cell voltage sensor (not shown). Examples of estimating the state of the power storage string STR include estimating the SOC (State of Charge) and SOH (State of Health) of the storage battery modules M1 to Mn, and estimating the SOC and SOH of the power storage string STR. Examples of notifying the system controller 101 of device control requests include a request for open / close switching control of the cutoff switch S1 and bypass switch S2 of the bypass units B1 to Bn, and a request for control of the power converter PCS.

[0032] Methods for estimating SOH include methods using charge / discharge tests, current integration methods, open circuit voltage measurements, terminal voltage measurements, model-based methods (all of which use changes in SOC over time), AC impedance measurements, model-based methods using an adaptive digital filter, linear regression from IV characteristics (current-voltage characteristics) (the slope of the straight line in the IV characteristics), and step response methods (all of which are methods of estimation using the increase in internal resistance over time).

[0033] There are various known methods for estimating the SOC, such as a current integration method, a method of determining the SOC from the OCV (Open Circuit Voltage) (voltage method), a method that combines the current integration method and the voltage method, etc. The OCV can also be estimated using various known methods that use the change in the terminal voltage over time or the increase in the internal resistance over time.

[0034] The system controller 101 is a controller that performs overall control of the entire power storage system 1, and executes 1:m communication with a plurality of string controllers 102. This system controller 101 monitors the state of the power storage strings STR, determines whether or not to grant a device control request from the string controllers 102, and notifies the string controllers 102 of permission for the device control request. In addition, the system controller 101 sets an instruction value for the charge / discharge power (or current) of each power storage string STR, and transmits the instruction value for the charge / discharge power (or current) to the string controllers 102.

[0035] The system controller 101 monitors the state of the power storage strings STR based on the detection results and estimation results of the state of the power storage strings STR transmitted from the string controller 102. Then, the system controller 101 calculates an instruction value of the charge / discharge power (or current) to be allocated to each power storage string STR according to an instruction of the input / output power (or current) of the entire power storage system 1 received from a higher-level system (not shown) and the state of the power storage string STR.

[0036] Here, each string controller 102 executes the open / close switching control (hereinafter referred to as bypass control) of the cutoff switch S1 and the bypass switch S2 of the bypass unit B1 to Bn (hereinafter referred to as B') for any of the storage battery modules M1 to Mn (hereinafter referred to as M') when a request (hereinafter referred to as bypass control request) for open / close switching control is permitted by the system controller 101. The string controller 102 executes the first oxide film removal process and the second oxide film removal process when executing the bypass control.

[0037] When the bypass control is executed, a string current reduction process, a first oxide film removal process, a second oxide film removal process, a bypass state switching process, and a precharge process are executed. The string current reduction process is a process for reducing the string current to a predetermined value. The predetermined value is set to a low value that keeps fluctuations in the input / output power of the entire power storage system 1 within an allowable range when the bypass control of the power storage string STR is executed.

[0038] Here, in the string current reduction process, the string controller 102 gradually and continuously reduces the command value of the string current from the current value to a predetermined value. Specifically, the string controller 102 repeatedly updates the command value of the string current by a predetermined amount ΔP1, which is equal to the difference between the current command value of the string current and the predetermined value. At this time, the rate of change of the command value of the string current (amount of change per time) is set to a level that keeps fluctuations in the input / output power of the entire power storage system 1 within an allowable range. As a result, the power converter PCS gradually and continuously reduces the string current from the current value to the predetermined value so as to keep fluctuations in the input / output power of the entire power storage system 1 within an allowable range.

[0039] 2 is a circuit diagram for explaining the first oxide film removal process. As shown in this diagram, in the first oxide film removal process, the cutoff switch S1 (hereinafter referred to as S1') of the bypass unit B' is switched from open to closed when the potential of the smoothing capacitor C is lower than the potential of the storage battery module M' that is the target of bypass control. At this time, the first system main relay S3A is open, the second system main relay S3B and the pre-charge relay S4 are closed, and the bypass switch S2 (hereinafter referred to as S2') of the bypass unit B' is open. In addition, in the other bypass units B1 to Bn, the cutoff switch S1 is open and the bypass switch S2 is closed. As a result, current flows from the storage battery module M' through the cutoff switch S1', pre-charge relay S4, resistor R, smoothing capacitor C, and bypass switch S2 of the other bypass units B1 to Bn, charging the smoothing capacitor C.

[0040] Here, the potential difference between the storage battery module M' and the smoothing capacitor C is set to a value large enough to generate an arc discharge sufficient to remove the oxide film from the contact portion of the cutoff switch S1' when the cutoff switch S1' is switched. In this embodiment, before the first oxide film removal process is performed, the power converter PCS operates to discharge the charge from the smoothing capacitor C. Note that the potential of the smoothing capacitor C at the start of the first oxide film removal process does not need to be zero; it only needs to be low enough to remove the oxide film from the contact portion of the cutoff switch S1' when the cutoff switch S1' is switched.

[0041] In addition, the charging time of the smoothing capacitor C is set taking into account the time constant (τ=CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor R so that a sufficient amount of charge flows from the storage battery module M' to the smoothing capacitor C to remove the oxide film on the contact portion of the cut-off switch S1'.

[0042] Therefore, in the first oxide film removal process, the cutoff switch S1' is switched from open to close while a voltage sufficient to remove the oxide film from the contact portion is applied, thereby removing the oxide film from the contact portion of the cutoff switch S1'.

[0043] 3 is a circuit diagram for explaining the second oxide film removal process. As shown in this diagram, in the second oxide film removal process, the bypass switch S2' is switched from open to closed while the smoothing capacitor C is charged. At this time, the first system main relay S3A and the cutoff switch S1' are open, and the second system main relay S3B and pre-charge relay S4 are closed. In the other bypass units B1 to Bn, the cutoff switch S1 is open and the bypass switch S2 is closed. As a result, the smoothing capacitor C discharges, and current flows from the smoothing capacitor C through the resistor R, the pre-charge relay S4, the bypass switch S2', the bypass switch S2 of the other bypass units B1 to Bn, and the second system main relay S3B.

[0044] Here, the potential of the smoothing capacitor C is set to a level sufficient to generate an arc discharge at the contact point of the bypass switch S2' when the bypass switch S2' is switched, which is sufficient to remove the oxide film. In this embodiment, the charging time of the smoothing capacitor C during the first oxide film removal process is set in consideration of the time constant (τ=CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor R.

[0045] In addition, the discharge time of the smoothing capacitor C is set taking into consideration the time constant (τ=CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor R so that a sufficient amount of charge flows from the smoothing capacitor C to the bypass switch S2' to remove the oxide film on the contact portion of the bypass switch S2'.

[0046] Therefore, in the second oxide film removal process, the bypass switch S2' is switched from open to close while a voltage sufficient to remove the oxide film from the contact portion is applied, thereby removing the oxide film from the contact portion of the bypass switch S2'.

[0047] 4 is a circuit diagram illustrating the precharge process. As shown in this diagram, the precharge process is a process in which the smoothing capacitor C is charged from the connected storage battery modules M1 to Mn via the precharge circuit 10. In this embodiment, the precharge process is performed in a state in which the storage battery modules M1 to Mn that are not subject to bypass control are connected or bypassed after the charge in the smoothing capacitor C is removed by discharging the smoothing capacitor C in the second oxide film removal process.

[0048] During the precharge process, the cutoff switch S1' and the first system main relay S3A of the bypass unit B' are open, and the second system main relay S3B and the precharge relay S4 are closed. The other storage battery modules M1 to Mn are in a connected state or a bypass state depending on their charge states.

[0049] Here, the potential difference between the smoothing capacitor C in a discharged state and all of the connected storage battery modules M1 to Mn becomes large, but in the precharge process, the resistance R of the precharge circuit 10 suppresses the inrush current to the smoothing capacitor C. Also, in the precharge process, the current flowing from the connected storage battery modules M1 to Mn to the smoothing capacitor C passes through the precharge circuit 10 without passing through the first system main relay S3A.

[0050] 5 is a flowchart for explaining the process of switching the storage battery module M' that is the target of a bypass control request from the connected state to the bypass state. First, in step S1, the string controller 102 monitors the storage battery modules M1 to Mn of the power storage string STR and determines whether or not there is a storage battery module M1 to Mn that requires bypass control. If the determination in step S1 is affirmative, the process proceeds to step S2, and if the determination in step S1 is negative, the process ends.

[0051] At the start of the process shown in the flowchart of Fig. 5, the pre-charge relay S4 is open, and the first system main relay S3A and the second system main relay S3B are closed. In the bypass units B1-Bn corresponding to the storage battery modules M1-Mn in the connected state, the bypass switch S2 is open, and the cut-off switch S1 is closed. On the other hand, in the bypass units B1-Bn corresponding to the storage battery modules M1-Mn in the bypassed state, the bypass switch S2 is closed, and the cut-off switch S1 is open. At the start of the process shown in the flowchart of Fig. 5, the smoothing capacitor C is in a charged state (a state after pre-charging).

[0052] In step S2, the string controller 102 records the current connection or bypass state of the storage battery modules M1 to Mn of the power storage string STR in an internal memory (not shown). Next, the string controller 102 repeatedly executes the loop process of steps S3 to S5 until the command value of the string current reaches a predetermined value (string current reduction process). Here, in steps S3 to S5, the string controller 102 gradually and continuously reduces the command value of the string current from the current value to the predetermined value by a predetermined amount ΔP1 at a time.

[0053] First, in step S3, the string controller 102 updates the command value of the string current to a value obtained by decreasing the command value by a predetermined amount ΔP1. This predetermined amount ΔP1 is set to a small amount suitable for the purpose of preventing a sudden change in the input / output power of the power storage system 1. When 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, when the difference between the current value of the string current and the predetermined value is relatively large, this predetermined amount ΔP1 may be smaller than the difference between the current value of the string current and the predetermined value. When this predetermined amount ΔP1 is smaller than the difference between the current value of the string current and the predetermined value, the string current is repeatedly updated multiple times.

[0054] Next, in step S4, the string controller 102 waits for a predetermined time T1 after transmitting the command value of the string current to the power converter PCS. This predetermined time T1 is set in consideration of the time required for the string controller 102 to control the power converter PCS and the rate of change of the string current.

[0055] Next, in step S5, the string controller 102 determines whether the string current has reached a predetermined value (whether the reduction of the string current has been completed). If a positive determination is made in step S5, the process proceeds to step S6, and if a negative determination is made in step S5, the process proceeds to step S3.

[0056] Next, in step S6, the string controller 102 transmits a control signal for switching the first system main relay S3A and the second system main relay S3B from Close to Open to the relay driver 103. This disconnects the power storage string STR from the power converter PCS.

[0057] Next, in step S7, the string controller 102 transmits a control signal to the relay driver 103 to open the cutoff switches S1 and the bypass switches S2 of all the bypass units B1 to Bn, thereby cutting off all the storage battery modules M1 to Mn.

[0058] Next, in step S8, the string controller 102 transmits a control signal to the power converter PCS to discharge the smoothing capacitor C. In this step, the charge in the smoothing capacitor C is discharged 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 S12). Note that the potential of the smoothing capacitor C does not need to be 0.

[0059] Next, in step S9, the string controller 102 transmits a control signal to the relay driver 103 to switch the second system main relay S3B from Open to Close.

[0060] Next, in step S10, the string controller 102 transmits a control signal to the relay driver 103 to switch the bypass switches S2 other than those of the bypass unit B' from Open to Close. As a result, the storage battery modules M1 to Mn other than the storage battery module M' are placed in the bypass state.

[0061] Next, in step S11, the string controller 102 transmits a control signal for switching the precharge relay S4 from Open to Close to the relay driver 103. As a result, the precharge circuit 10 is connected to the power line PL in a state in which the precharge circuit 10 bypasses the first system main relay S3A.

[0062] Next, in step S12, the string controller 102 transmits a control signal to the relay driver 103 to switch the cutoff switch S1' corresponding to the storage battery module M' from Open to Close. Next, in step S13, the string controller 102 waits for a predetermined time T2 after switching the cutoff switch S1' from Open to Close. This predetermined time T2 is the time required to charge the smoothing capacitor C and is set taking into account the time constant (τ=CR) between the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor R. As a result, a first oxide film removal process is executed, and the oxide film on the contact portion of the cutoff switch S1' is removed (see FIG. 2). Note that in step S13, the smoothing capacitor C is charged from the connected storage battery module M' via the precharge circuit 10; however, the smoothing capacitor C may also be charged from the string bus 4 side by operation of the power converter PCS.

[0063] Next, in step S14, the string controller 102 switches the cutoff switch S1' corresponding to the storage battery module M' from Close to Open, and then transmits a control signal to the relay driver 103 to switch the bypass switch S2' corresponding to the storage battery module M' from Open to Close. Next, in step S15, the string controller 102 waits for a predetermined time T3 after switching the bypass switch S2' from Open to Close. This predetermined time T3 is the time required for the smoothing capacitor C to discharge, and is set taking into account the time constant (τ=CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor R. As a result, a second oxide film removal process is executed, and the oxide film on the contact portion of the bypass switch S2' is removed (see FIG. 3).

[0064] Next, in step S16, the string controller 102 transmits a control signal for switching the precharge relay S4 from Close to Open to the relay driver 103. Next, in step S17, the string controller 102 transmits a control signal for switching the connected / bypass states of the storage battery modules M1 to Mn to a state that reflects bypass control to the relay driver 103. The state that reflects bypass control is a state in which the storage battery module M' that was determined to require bypass control in step S1 is placed in a bypass state from the connected / bypass states of the storage battery modules M1 to Mn stored in memory in step S2.

[0065] Next, in step S18, the string controller 102 transmits a control signal to the relay driver 103 to switch the precharge relay S4 from Open to Close. Next, in step S19, the string controller 102 waits for a predetermined time T4 after switching the precharge relay S4 from Open to Close. This predetermined time T4 is the time required to charge the smoothing capacitor C, and is set in consideration of the time constant (τ=CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor R. As a result, the precharge process is executed, and the smoothing capacitor C is charged (see FIG. 4).

[0066] Next, in step S20, the string controller 102 transmits a control signal to the relay driver 103 to switch the first system main relay S3A from Open to Close (maintaining the second system main relay S3B at Close), thereby connecting the power storage string STR to the power converter PCS.

[0067] Next, in step S21, the string controller 102 sends a control signal to the relay driver 103 to switch the precharge relay S4 from Close to Open. This completes the bypass control of the storage battery module M', the removal of the oxide film on the contact portions of the cutoff switch S1' and the bypass switch S2', and the precharge of the smoothing capacitor C. This completes the processing shown in the flowchart of FIG. 5.

[0068] As described above, in the energy storage system 1 according to this embodiment, the precharge circuit 10 including the precharge relay S4 is connected in parallel with the first system main relay S3A. As a result, when the smoothing capacitor C is not charged, such as at the start of the energy storage system 1, the first system main relay S3A is opened and the precharge relay S4 is closed, thereby suppressing the inrush current to the smoothing capacitor C. This makes it possible to prevent damage to the first system main relay S3A, the cutoff switch S1, and the bypass switch S2.

[0069] The battery control device 100 also executes a first oxide film removal process to remove an oxide film from the contact portion of the cutoff switch S1' corresponding to any one of the storage battery modules M'. In the first oxide film removal process, the cutoff switch S1' corresponding to any one of the storage battery modules M' is operated with the bypass switch S2' and the first system main relay S3A corresponding to the given storage battery module M' open and the pre-charge relay S4 closed. This generates an arc discharge of a certain current value or more at the contact portion of the cutoff switch S1', removing the oxide film from the contact portion.

[0070] The battery control device 100 also executes a second oxide film removal process to remove an oxide film from the contact portion of the bypass switch S2' corresponding to any of the storage battery modules M'. In the second oxide film removal process, the bypass switch S2' corresponding to any of the storage battery modules M' is operated with the cutoff switch S1' and the first system main relay S3A corresponding to the storage battery module M' in an open state and the precharge relay S4 in a closed state. This generates an arc discharge of a certain current value or more at the contact portion of the bypass switch S2', removing the oxide film from the contact portion.

[0071] Therefore, even when bypass control is performed after reducing the string current in order to suppress fluctuations in input / output power between the energy storage system 1 and an external system, it is possible to apply a voltage above a certain level to the contact points of the cutoff switch S1' and the bypass switch S2' to generate an arc discharge with a current value above a certain level, thereby removing the oxide film.

[0072] Furthermore, the smoothing capacitor C and the precharge circuit 10 are existing elements that are necessary for the configuration of the power storage string STR, regardless of whether the first oxide layer removal process and the second oxide layer removal process are performed. Therefore, the first oxide layer removal process and the second oxide layer removal process can be performed by utilizing the existing elements, the smoothing capacitor C and the precharge circuit 10, and therefore the oxide layer at the contact portion between the cutoff switch S1 and the bypass switch S2 can be removed without incurring an increase in cost, such as by implementing a new circuit such as a CR circuit.

[0073] Furthermore, in the energy storage system 1 according to this embodiment, the battery control device 100 executes the first oxide film removal process in a state in which the potential of the smoothing capacitor C is lower than the potential of the connected storage battery modules M1 to Mn. In the first oxide film removal process, the cutoff switch S1' is operated to form a circuit, and a current flows from the connected storage battery modules M1 to Mn to the smoothing capacitor C via the cutoff switch S1' and the precharge circuit 10. Therefore, an arc discharge of a certain current value or more occurs at the contact portion of the cutoff switch S1', and the oxide film on the contact portion is removed.

[0074] Furthermore, in the energy storage system 1 according to this embodiment, the battery control device 100 executes the second oxide film removal process while the smoothing capacitor C is charged. In the second oxide film removal process, the bypass switch S2' is operated to form a circuit, and the current discharged from the smoothing capacitor C flows through the bypass switch S2'. Therefore, an arc discharge of a certain current value or more occurs at the contact portion of the bypass switch S2', and the oxide film at the contact portion is removed.

[0075] Furthermore, in the energy storage system 1 according to this embodiment, the battery control device 100 executes a first oxide film removal process and a second oxide film removal process after executing a string current reduction process to reduce the string current to a predetermined value using the power converter PCS. This makes it possible to suppress fluctuations in input / output power between the energy storage system 1 and an external system, and also to apply a voltage above a certain level to the contact portions of the cutoff switch S1' and the bypass switch S2' to remove the oxide film from the contact portions.

[0076] Furthermore, in the energy storage system 1 according to this embodiment, the first system main relay S3A is provided between the storage battery module M1 on the total positive side of the energy storage string STR and the smoothing capacitor C. Furthermore, the second system main relay S3B is provided between the storage battery module Mn on the total negative side of the energy storage string STR and the smoothing capacitor C. This makes it possible to connect and disconnect both the total positive side and the total negative side of the energy storage string STR.

[0077] 6 is a circuit diagram showing an outline of an energy storage string STR' according to another embodiment of the present invention. As shown in this diagram, the energy storage string STR' according to this embodiment differs from the energy storage string STR of the above-described energy storage system 1 in that the above-described second system main relay S3B is not provided.

[0078] The bypass control of the power storage string STR' according to this embodiment differs from the bypass control of the power storage string STR of the power storage system 1 according to the above-described embodiment in that the second system main relay S3B is not switched between open and close.

[0079] In addition, the storage string STR' of this embodiment differs from the storage string STR of the storage system 1 of the above-described embodiment in that the smoothing capacitor C connecting the total + and total - of the storage string STR' is built into the power converter PCS.

[0080] Furthermore, the energy storage string STR' of this embodiment differs from the energy storage string STR of the energy storage system 1 of the above-described embodiment in that, in addition to the first oxide film removal process and the second oxide film removal process, a third oxide film removal process is performed to remove the oxide film from the contact portion of the system main relay S3.

[0081] 7 is a circuit diagram for explaining the third oxide film removal process executed in the power storage string STR' of FIG. 6. As shown in this diagram, in the third oxide film removal process, the system main relay S3 is switched from Open to Close during the execution of the precharge process. At this time, the precharge relay S4 is Closed, the cutoff switch S1' in the bypass unit B' is Open, the bypass switch S2' is Closed, and the other bypass units B1 to Bn are either in the connected state or the bypass state. As a result, current flows from the connected storage battery modules M1 to Mn via the system main relay S3, and the smoothing capacitor C is charged.

[0082] Here, the time for the precharge process is determined taking into consideration the time constant (τ=CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor R, and the current value of the arc discharge required to remove the oxide film from the contact parts of the system main relay S3. Therefore, in the third oxide film removal process, the system main relay S3 is switched from open to close while a voltage sufficient to remove the oxide film from the contact parts is applied, thereby removing the oxide film from the contact parts of the system main relay S3.

[0083] Fig. 8 is a flowchart for explaining the process of switching the storage battery module M', which is the target of a bypass control request, from the connected state to the bypass state in the power storage string STR' in Fig. 6. First, step S1 shown in the flowchart in Fig. 5 is executed. At the start of the process shown in the flowchart in Fig. 8, the precharge relay S4 is open and the system main relay S3 is closed.

[0084] Next, steps S3 to S5 shown in the flowchart of FIG. 5 are executed. In steps S3 to S5, the target value (predetermined value) for reducing the string current is set to a value that is low enough not to cause large fluctuations in the input / output of the power storage system 1. However, it is also possible to set the predetermined value to the minimum value required to generate an arc discharge at the contacts of the system main relay S3. In this case, the system main relay S3 is switched from open to close while the string current is flowing through it, thereby generating an arc discharge at the contacts of the system main relay S3, thereby removing the oxide film on the contacts of the system main relay S3. In this case, the process for removing the oxide film on the contacts of the system main relay S3 (steps S36 to S40 described below) is not necessary.

[0085] In step S36, which follows step S5, the string controller 102 transmits a control signal for switching the system main relay S3 from Close to Open to the relay driver 103. This disconnects the power storage string STR' from the power converter PCS.

[0086] Next, in step S37, the string controller 102 transmits a control signal to the relay driver 103 to switch the storage battery module M', for which it was determined in step S1 that bypass control is necessary, to the bypass state. The control signal is a control signal to switch the bypass switch S2' corresponding to the storage battery module M' from open to close (keeping the cutoff switch S1' closed).

[0087] Next, in step S38, the string controller 102 transmits a control signal to the relay driver 103 to switch the pre-charge relay S4 from Open to Close. Next, in step S39, the string controller 102 transmits a control signal to the relay driver 103 to switch the system main relay S3 from Open to Close until a predetermined time T5 has elapsed since the pre-charge relay S4 was switched from Open to Close. This predetermined time T5 is set to the time required for the smoothing capacitor C to be charged with a charge necessary to remove an oxide film from the contact portion of the system main relay S3, taking into account the time constant (τ=CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor R. As a result, the oxide film from the contact portion of the system main relay S3 is removed during the pre-charge process (see FIG. 7).

[0088] Next, in step S40, the string controller 102 transmits a control signal for switching the precharge relay S4 from Close to Open to the relay driver 103. This completes the processing shown in the flowchart of FIG.

[0089] As described above, in the power storage string STR' according to this embodiment, the third oxide film removal process is performed to remove the oxide film from the contact portions of the system main relay S3 by operating the system main relay S3 while the charging current for the smoothing capacitor C is flowing through the system main relay S3. This makes it possible to suppress fluctuations in input / output power between the power storage string STR' and the external system and to remove the oxide film from the contact portions of the system main relay S3 while keeping costs down.

[0090] Furthermore, in the power storage string STR' according to this embodiment, by operating the system main relay S3 with the pre-charge relay S4 closed, the third oxide film removal process is realized in which the system main relay S3 is operated with the charging current of the smoothing capacitor C flowing through the system main relay S3. This makes it possible to remove the oxide film from the contact portion of the system main relay S3 by utilizing the smoothing capacitor C and the pre-charge circuit 10.

[0091] FIG. 9 is a circuit diagram showing an outline of an energy storage string STR″ according to another embodiment of the present invention. As shown in this diagram, the energy storage string STR″ according to this embodiment is not provided with the above-described second system main relay S3B, similar to the above-described energy storage string STR′, and switching of the second system main relay S3B is not executed during bypass control.

[0092] Furthermore, in the power storage string STR" according to this embodiment, a smoothing capacitor C is built into the power converter PCS, similar to the power storage string STR' described above. Furthermore, in the power storage string STR" according to this embodiment, a third oxide layer removal process is performed in addition to the first oxide layer removal process and the second oxide layer removal process, similar to the power storage string STR' described above.

[0093] On the other hand, the power storage string STR″ according to this embodiment is different from the above-described power storage string STR′ in that it is provided with a CR circuit for removing the oxide film on the system main relay S3, and the oxide film on the system main relay S3 is removed using the charge / discharge current of the capacitor Cc of the CR circuit.

[0094] As shown in FIG. 9 , the power storage string STR″ includes a capacitor Cc and a resistor Rc. The capacitor Cc and the resistor Rc are connected in series, and the resistor Rc is connected to the power line PL between the system main relay S3 and the cutoff switch S1 of the bypass unit B1, and the capacitor Cc is connected to the power line PL between the storage battery module Mn and the terminal - of the power storage string STR″. Alternatively, the capacitor Cc may be connected to the power line PL between the system main relay S3 and the cutoff switch S1 of the bypass unit B1, and the resistor Rc may be connected to the power line PL between the storage battery module Mn and the terminal - of the power storage string STR″.

[0095] FIG. 10 is a circuit diagram for explaining the third oxide film removal process executed in the power storage string STR" of FIG. 9. As shown in this diagram, in the third oxide film removal process in the power storage string STR", the charge in the smoothing capacitor C is removed by the power converter PCS, and then the system main relay S3 is switched from open to closed. At this time, the pre-charge relay S4 is open, and in all of the bypass units B1 to Bn, the cutoff switch S1 and the bypass switch S2 are open. As a result, a current flows from the capacitor Cc to the smoothing capacitor C via the system main relay S3, and the smoothing capacitor C is charged.

[0096] Here, the charging time of the smoothing capacitor C is determined taking into consideration the time constant (τ=CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor Rc, and the current value of the arc discharge required to remove the oxide film from the contact portions of the system main relay S3. Therefore, in the third oxide film removal process executed in the power storage string STR", the system main relay S3 is switched from open to close while a voltage sufficient to remove the oxide film from the contact portions is applied, thereby removing the oxide film from the contact portions of the system main relay S3.

[0097] FIG. 11 is a flowchart for explaining the process of switching the storage battery module M′ that is the target of a bypass control request in the power storage string STR″ of FIG. 9 from the connected state to the bypass state. First, steps S1 to S5 are executed in the same manner as the process shown in the flowchart of FIG. 5. At the start of the process shown in the flowchart of FIG. 11, the precharge relay S4 is open and the system main relay S3 is closed.

[0098] Next, step S36 is executed in the same manner as the process shown in the flowchart of Fig. 8, and the system main relay S3 is opened. Next, in step S47, the string controller 102 transmits a control signal to the relay driver 103 to open the bypass switches S2 and the cutoff switches S1 of all the bypass units B1 to Bn. As a result, all the storage battery modules M1 to Mn are put into the cutoff state.

[0099] Next, in step S48, the string controller 102 transmits a control signal to the power converter PCS to cause it to operate so as to discharge the smoothing capacitor C. Next, in step S49, the string controller 102 transmits a control signal to the relay driver 103 to switch the system main relay S3 from Open to Close, during the lapse of a predetermined time T5 from when the charge in the smoothing capacitor C is discharged. This predetermined time T5 is set to the time required for the smoothing capacitor C to be charged with a charge necessary to remove the oxide film on the system main relay S3, taking into consideration the time constant (τ=CR) of the capacitance (C) of the capacitor Cc and the resistance value (R) of the resistor Rc. As a result, the oxide film on the contact portions of the system main relay S3 is removed while the smoothing capacitor C is being charged (see FIG. 10).

[0100] Next, in step S50, the string controller 102 transmits a control signal for switching the system main relay S3 from Close to Open to the relay driver 103. Next, in step S51, the string controller 102 transmits a control signal for switching the connected / bypass states of the storage battery modules M1 to Mn to a state that reflects bypass control to the relay driver 103. The state that reflects bypass control is a state in which the storage battery module M' that was determined to require bypass control in step S1 is placed in a bypass state based on the connected / bypass states of the storage battery modules M1 to Mn recorded in memory in step S2.

[0101] Next, in step S52, the string controller 102 transmits a control signal to the relay driver 103 to switch the precharge relay S4 from Open to Close. Next, in step S53, the string controller 102 waits for a predetermined time T4 after switching the precharge relay S4 from Open to Close. This predetermined time T4 is the time required to charge the smoothing capacitor C, and is set in consideration of the time constant (τ=CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the resistor R. As a result, the precharge process is executed, and the smoothing capacitor C is charged.

[0102] Next, in step S54, the string controller 102 transmits a control signal to the relay driver 103 to switch the system main relay S3 from Open to Close. As a result, the power storage string STR" is connected to the power converter PCS.

[0103] Next, in step S55, the string controller 102 transmits a control signal for switching the precharge relay S4 from Close to Open to the relay driver 103. This completes the processing shown in the flowchart of FIG.

[0104] As described above, the power storage string STR″ according to this embodiment is provided with the oxide film removal capacitor Cc and the oxide film removal resistor Rc, which are connected in series. The oxide film removal capacitor Cc and the oxide film removal resistor Rc are connected between the system main relay S3 and the shutoff switch S1 on the total + side of the power storage string STR″, and to the total − side of the power storage string STR″. In the power storage string STR″ configured in this manner, the third oxide film removal process is executed by operating the system main relay S3 with the pre-charge relay S4 open. In this third oxide film removal process, the charging current or discharging current of the smoothing capacitor C flows between the smoothing capacitor C and the oxide film removal capacitor Cc via the system main relay S3. This makes it possible to realize the third oxide film removal process, in which the system main relay S3 is operated while the charging current or discharging current of the smoothing capacitor C is flowing through the system main relay S3.

[0105] FIG. 12 shows a storage string STR according to another embodiment of the present invention. α As shown in this figure, the power storage string STR α Similarly to the above-described power storage strings STR′ and STR″, the above-described second system main relay S3B is not provided, and switching of the second system main relay S3B is not executed during bypass control.

[0106] In addition, the storage string STR according to this embodiment α In the power storage string STR according to this embodiment, a smoothing capacitor C is built into the power converter PCS, similar to the power storage strings STR' and STR'' described above. α In the case of the power storage strings STR′ and STR″, the third oxide layer removal process is performed in addition to the first oxide layer removal process and the second oxide layer removal process, as in the case of the power storage strings STR′ and STR″. α As with the above-mentioned storage string STR”, a CR circuit for removing the oxide film from the system main relay S3 is provided.

[0107] On the other hand, the storage string STR according to this embodiment α is a resistor R connected in parallel with the capacitor Cc for removing the oxide film. α and a switch St are provided.

[0108] As shown in Figure 12, the storage string STR α So, the resistance R α and switch St are connected in series, and resistor R α is connected to the resistor Rc, and the switch St is connected to the storage string STR α The switch St is connected to the resistor Rc, and the resistor R α The storage string STR α may be connected to the total of

[0109] The switch St is a transistor such as a bipolar transistor, a FET (Field Effect Transistor), an IGBT (Insulated Gate Bipolar Transistor), a mechanical relay, or the like, and in this embodiment is a bipolar transistor. α The emitter of the switch St is connected to the power line PL, and the base of the switch St is connected to the string controller 102 (see FIG. 1).

[0110] The string controller 102 outputs a drive signal to the base of the switch St to turn the switch St on and off. When the switch St is turned on, the resistor R α is connected in series to a resistor Rc and in parallel to a capacitor Cc for removing oxide film.

[0111] The resistance value of resistor Rc is determined by the magnitude of the current flowing through cutoff switch S1, bypass switch S2, or system main relay S3 in the first to third oxide film removal processes. In the first to third oxide film removal processes, an arc discharge with a current value sufficient to remove the oxide film from the contacts of cutoff switch S1, bypass switch S2, or system main relay S3 must be generated. Therefore, the resistance value of resistor Rc must be set to a value large enough to achieve the first to third oxide film removal processes.

[0112] On the other hand, there are cases where the capacitor Cc is discharged before and after the first to third oxide layer removal processes. In this case, the larger the resistance value of the resistor Rc, the longer the discharge time of the capacitor Cc, and the longer the time required for the pre-process or post-process of the first to third oxide layer removal processes. If the first to third oxide layer removal processes are performed while bypass control is being executed, the processing time of the bypass control will be longer.

[0113] In contrast, the storage string STR according to this embodiment α So, when the switch St is ON, the resistor R α is connected in parallel with the capacitor Cc, the discharge current of the capacitor Cc flows through the resistor R α This causes the resistor R α The discharge time of the capacitor Cc is shorter than when the capacitor Cc is not connected in parallel.

[0114] where the resistance R α The resistance value of the resistor Rc is set to a value smaller than the resistance value of the resistor Rc. This allows the discharge current of the capacitor Cc to flow through the resistor Rc rather than through the resistor Rc. αThis allows current to flow more easily, further shortening the discharge time of the capacitor Cc.

[0115] The string controller 102 turns on the switch St when the capacitor Cc is being discharged. α is connected in parallel to the capacitor Cc, shortening the discharge time of the capacitor Cc.

[0116] FIG. 13 shows a storage string STR according to another embodiment of the present invention. β As shown in this figure, the power storage string STR β differs from the storage string STR of the above-described storage system 1 in that the above-described first system main relay S3A is not provided and the precharge circuit 10 is connected in parallel with the second system main relay S3B.

[0117] In addition, the storage string STR according to this embodiment β In each of the bypass units B1 to Bn, the cutoff switch S1 is connected to the storage string STR rather than the storage battery modules M1 to Mn. β The power storage string STR differs from the power storage string STR of the above-described power storage system 1 in that it is provided on the negative side of the power storage string STR.

[0118] The power storage string STR according to this embodiment β The bypass control differs from the bypass control of the storage string STR of the storage system 1 described above in that the first system main relay S3A is not switched between open and close, and the second system main relay S3B is switched between open and close instead of the first system main relay S3A.

[0119] 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.

[0120] For example, in the above-described embodiment, the cutoff switch S1, the bypass switch S2, and the system main relay S3 are mechanical relays, but at least one of the cutoff switch S1, the bypass switch S2, and the system main relay S3 may be a semiconductor switch. In this case, the first oxide film removal process, the second oxide film removal process, or the third oxide film removal process may be performed only on at least one of the cutoff switch S1, the bypass switch S2, and the system main relay S3, which are mechanical relays.

[0121] Furthermore, the timings for performing the first oxide layer removal process, the second oxide layer removal process, and the third oxide layer removal process, and the storage battery modules M1 to Mn to be subjected to the first oxide layer removal process and the second oxide layer removal process may be set appropriately.

[0122] Furthermore, in the first oxide film removal process, it is not essential to remove the oxide film on 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 on the contact portion of the cutoff switch S1 using the discharge current of the smoothing capacitor C.

[0123] Furthermore, in the second oxide film removal process, it is not essential to remove the oxide film on 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 on the contact portion of the bypass switch S2 may be removed using the charging current of the smoothing capacitor C by forming a circuit by operating the bypass switch S2 to charge the smoothing capacitor C.

[0124] In the above-described embodiment, the command value of the string current is gradually and continuously changed over time by a predetermined amount ΔP1 to the target value. However, for example, when the influence of the change in the string current on the input / output power of the power storage system 1 is minor, the command values ​​of the string current may be changed all at once.

[0125] Furthermore, in the above-described embodiment, a circuit including a resistor R and a precharge relay S4 is given as an example of the precharge circuit 10. However, the precharge circuit 10 only needs to have a function of suppressing inrush current to the smoothing capacitor C, and for example, a constant current diode or the like may be provided instead of the resistor R. [Explanation of symbols]

[0126] 1: Energy storage system 10: Precharge circuit 100: Battery control device (control unit) B1 to Bn, B': Bypass unit (bypass section) C: Smoothing capacitor Cc: Capacitor (oxide film removal capacitor) M1 to Mn, M': Battery modules (batteries) PCS: Power converter Rc: Resistance (resistance for removing oxide film) S1, S1': Shut-off switch (first switch) S2, S2': Bypass switch (second switch) S3: System main relay (third switch) S3A: 1st system main relay (3rd switch) S3B: Second system main relay (third switch, fifth switch) S4: Precharge relay (fourth switch) STR: Energy storage string STR': Storage string STR”: Energy storage string STR α : Energy storage string STR β : Energy storage string

Claims

1. A power storage system including a power storage string in which a plurality of storage batteries are connected in series, and a power converter that converts input and output power of the power storage string, The storage string is a plurality of bypass units each including a first switch provided for each of the storage batteries and a second switch connected in parallel to the first switch and the storage batteries, and configured to switch the storage batteries between a connected state and a bypass state; a smoothing capacitor connecting the positive and negative sides of the power storage string; a third switch provided between the storage battery on the most positive side or the storage battery on the most negative side and the smoothing capacitor; a precharge circuit connected in parallel with the third switch to suppress an inrush current to the smoothing capacitor; a fourth switch provided in the precharge circuit; a control unit that controls the first switch, the second switch, the third switch, and the fourth switch; Equipped with The control unit a first oxide film removal process for removing an oxide film on a contact portion of the first switch by operating the first switch corresponding to any one of the storage batteries in a state in which the second switch and the third switch corresponding to the any one of the storage batteries are open and the fourth switch is closed; a second oxide film removal process for removing an oxide film on a contact portion of the second switch by operating the second switch corresponding to any one of the storage batteries in a state in which the first switch and the third switch corresponding to any one of the storage batteries are open and the fourth switch is closed; a third oxide film removal process for removing an oxide film on a contact portion of the third switch by operating the third switch while a charging current or a discharging current of the smoothing capacitor is flowing through the third switch; The power storage system performs at least one of the above processes.

2. The power storage system according to claim 1 , wherein the control unit executes the first oxide film removal process in a state where the potential of the smoothing capacitor is lower than the potential of the storage battery in a connected state.

3. The power storage system according to claim 1 or 2, wherein the control unit executes the second oxide film removal process in a state where the smoothing capacitor is charged.

4. 3. The power storage system according to claim 1, wherein the control unit performs at least one of the first oxide film removal process, the second oxide film removal process, and the third oxide film removal process after performing a string current reduction process to reduce a current of the power storage string to a predetermined value using the power converter.

5. the third switch is provided between the storage battery closest to the positive side and the smoothing capacitor, The power storage system according to claim 1 or 2, further comprising a fifth switch provided between the storage battery on the most negative side and the smoothing capacitor.

6. The power storage system according to claim 1 or 2, wherein the control unit performs the third oxide film removal process by operating the third switch while keeping the fourth switch closed.

7. an oxide film removal capacitor connecting a portion between the third switch and the first switch closest to the positive side of the power storage string, and the negative side of the power storage string; an oxide layer removal resistor connected in series with the oxide layer removal capacitor; Equipped with The power storage system according to claim 1 or 2, wherein the control unit performs the third oxide film removal process by operating the third switch with the fourth switch open.

Images