Battery control device, power storage system, and battery control method

Abstract

To suppress variation in input / output power of a power storage system comprising a storage battery string provided with a plurality of storage batteries connected in series, and a plurality of bypass circuits for switching the storage batteries corresponding thereto by being provided for each of the storage batteries between a connection state and a bypass state; and to make it possible to remove an oxide film from a contact point part of mechanical type relays in the bypass circuits.SOLUTION: A storage battery control device 100 sets a string current to a first predetermined value by a power converter PC, and sets a state of connection of storage battery modules M1 to Mn or of bypass thereof by bypass switch units B1 to Bn to executes an oxide film removal treatment for opening / closing switches S1, S2 as mechanical relays in a state of satisfying a first condition, so as to satisfy the first condition under which a total voltage of a storage battery string STR becomes a withstand voltage or less of the bypass switch units B1 to Bn, and arc discharging is generated to the switches S1, S2 as the mechanical relays.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a storage battery control device, a power storage system, and a storage battery control method. [Background technology]

[0002] There is known an energy storage system in which a battery string includes a plurality of storage batteries connected in series and a bypass circuit provided for each storage battery for switching the corresponding storage battery between a connected state and a bypass state (see, for example, Patent Document 1). In the energy storage system described in Patent Document 1, bypass control is executed to bypass a storage battery that cannot discharge the required current, and discharging is performed from the other storage batteries. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-31247 A 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 of the energy storage system when bypass control is executed. Furthermore, in the energy storage system described in Patent Document 1, the total voltage of the storage battery string is applied to the switch of the bypass circuit when bypass control is executed, so it is necessary to use a switch with a high withstand voltage or to provide a protection circuit for the switch. When a protection circuit for the switch is provided, it is necessary to prevent a voltage exceeding the withstand voltage from being applied to the protection circuit. As a method for solving these problems, a method of executing bypass control after reducing the current of the storage battery string (hereinafter referred to as string current) by a power converter can be considered.

[0005] However, when a mechanical relay is used as a switch in a bypass circuit, if the string current is reduced before the switch is switched between open and closed, arc discharge may not occur at the contacts of the mechanical relay.Since an oxide film forms over time on the contacts of a mechanical relay, if no arc discharge occurs at the contacts, the oxide film formed on the contacts may not be removed, which may cause poor contact at the contacts.

[0006] In view of the above circumstances, the present invention has an object to provide a battery control device, a battery storage system, and a battery control method in a battery string including a plurality of storage batteries connected in series and a plurality of bypass circuits provided for each storage battery for switching a corresponding storage battery between a connected state and a bypass state, which are capable of suppressing fluctuations in the input / output power of the system and removing oxide films from the contact portions of the mechanical relays of the bypass circuits. [Means for solving the problem]

[0007] The battery control device of the present invention is a battery control device that controls a power storage system including a battery string and a power converter that converts input and output power of the battery string, wherein the battery string includes a plurality of batteries connected in series, a first switch provided between adjacent batteries, a bypass line that bypasses the first switch and the batteries, and a second switch provided in the bypass line, and includes a plurality of bypass circuits that switch the batteries between a connected state and a bypass state, wherein at least one of the first switch and the second switch is a mechanical relay, and the power converter sets a current of the battery string to a first predetermined value by the power converter so that a first condition is met that a total voltage of the battery string is equal to or lower than a withstand voltage of the bypass circuit and an arc discharge occurs in at least one of the first switch and the second switch which are mechanical relays, and sets a connected or bypassed state of the plurality of batteries to a predetermined state by the plurality of bypass circuits, and executes an oxide film removal process to open and close at least one of the first switch and the second switch which are mechanical relays when the first condition is met.

[0008] The power storage system of the present invention is a power storage system including a storage battery string, a power converter that converts input / output power of the storage battery string, and a storage battery control device that controls the storage battery string and the power converter, wherein the storage battery string includes a plurality of storage batteries connected in series, a first switch provided between adjacent storage batteries, a bypass line that bypasses the first switch and the storage batteries, and a second switch provided in the bypass line, and includes a plurality of bypass circuits that switch the storage batteries between a connected state and a bypass state, and at least one of the first switch and the second switch is is a mechanical relay, and the battery control device sets the current of the battery string to a first predetermined value using the power converter, sets the connection or bypass state of the multiple batteries to a predetermined state using the multiple bypass circuits, and executes an oxide film removal process to open and close at least one of the first switch and the second switch, which are mechanical relays, when the first condition is met, so that the total voltage of the battery string is equal to or lower than the withstand voltage of the bypass circuit and a first condition is met that an arc discharge occurs in at least one of the first switch and the second switch, which are mechanical relays.

[0009] The power storage system of the present invention is a power storage system including a storage battery string, a power converter that converts input and output power of the storage battery string, and a storage battery control device that controls the storage battery string and the power converter, wherein the storage battery string includes a plurality of storage batteries connected in series, a first switch that is a mechanical relay provided between the storage batteries adjacent to each other, a bypass line that bypasses the first switch and the storage batteries, and a second switch provided on the bypass line, and includes a plurality of bypass circuits that switch the storage batteries between a connected state and a bypass state, and a power converter that converts power between the first switch corresponding to the storage battery at the start end and the power converter, and between the storage battery at the end and the power converter. and a power storage and current suppression circuit having a power storage unit and a current suppression unit connected between the battery control device and a power converter, the battery control device sets all of the batteries to a bypass state using the multiple bypass circuits, and then executes a first oxide film removal process to switch any one of the batteries to a connected state using any one of the bypass circuits, and a maximum value of a transient current flowing through the connected batteries, the first switch, and the power storage and current suppression circuit is set so that a first condition is established in which a total voltage of the battery string becomes equal to or lower than a withstand voltage of the bypass circuit and an arc discharge occurs in the first switch when the battery control device executes the first oxide film removal process.

[0010] The battery control method of the present invention is a battery control method executed by a battery control device that controls a power storage system including a battery string and a power converter that converts input and output power of the battery string, wherein the battery string includes a plurality of batteries connected in series, a first switch provided between adjacent batteries, a bypass line that bypasses the first switch and the batteries, and a second switch provided in the bypass line, and includes a plurality of bypass circuits that switch the batteries between a connected state and a bypass state, and at least one of the first switch and the second switch is a mechanical relay, and the current of the battery string is set to a first predetermined value by the power converter so that a first condition is met that a total voltage of the battery string is equal to or lower than a withstand voltage of the bypass circuit and an arc discharge occurs in at least one of the first switch and the second switch which are mechanical relays, and an oxide film removal process is executed to open and close at least one of the first switch and the second switch which are mechanical relays when the first condition is met. Effect of the Invention

[0011] According to the present invention, in a power storage system including a battery string having a plurality of storage batteries connected in series and a plurality of bypass circuits provided for each storage battery for switching a corresponding storage battery between a connected state and a bypass state, it is possible to suppress fluctuations in the input / output power of the system and to remove oxide coatings from the contact portions of the mechanical relays of the bypass circuits. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a circuit diagram showing an outline of a power storage system including a battery control device according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a flowchart for explaining 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. [Diagram 3]FIG. 3 is a flow chart for explaining an oxide film removal process according to another embodiment of the present invention. [Figure 4] FIG. 4 is a circuit diagram showing an outline of a power storage system according to another embodiment of the present invention. [Diagram 5] FIG. 5 is a flowchart for explaining a process in which the battery control device shown in FIG. 4 switches the battery module that is the target of a bypass control request from a connected state to a bypass state. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention will be described below along with preferred embodiments. Note that the present invention is not limited to the embodiments shown below, and the embodiments can be appropriately modified within the scope of the present invention. In addition, in the embodiments shown below, some configurations are omitted from illustration and description, but for the details of the omitted technologies, publicly known or well-known technologies are appropriately applied within the scope of not causing any contradiction with the contents described below.

[0014] Fig. 1 is a circuit diagram showing an outline of a power storage system 1 including a battery control device 100 according to one embodiment of the present invention. As shown in this diagram, the power storage system 1 includes a plurality of battery strings STR, a plurality of power converters PC, a string bus 3, and the battery control device 100. The plurality of battery strings STR are connected in parallel to each other and to an external system (not shown) via the string bus 3. The power storage system 1 is a stationary or vehicle-mounted power source.

[0015] The storage battery string STR includes n (n is an integer of 2 or more) storage battery modules M1 to Mn connected in series. Although not particularly limited, the storage battery modules M1 to Mn in this embodiment are regenerated 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 cells of secondary batteries such as lithium ion batteries or lithium ion capacitors connected together.

[0016] The storage battery modules M1 to Mn are charged by receiving power from an external system via the string bus 3 and the power converter PC. In addition, the storage battery modules M1 to Mn supply power to the external system via the power converter PC and the string bus 3.

[0017] 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 a solar power generation system, 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 equipment, etc. are the loads. The drive motor is both a load and a generator.

[0018] The battery string STR may include n storage battery cells or storage battery packs connected in series, instead of the n storage battery modules M1 to Mn connected in series. The battery string STR may include a bypass circuit that bypasses each storage battery cell or each storage battery pack.

[0019] The power converter PC is a DC / DC converter or a DC / AC converter, and is connected to the string bus 3. In addition, the power converter PC is connected to the positive electrode of the starting storage battery module M1 and the negative electrode of the terminal storage battery module Mn.

[0020] When the storage battery string STR is being charged, the power converter PC converts the voltage input from the string bus 3 according to an instruction value of the charging power (or current) described below, and outputs the converted voltage to the multiple storage battery modules M1-Mn. Here, the voltage on the side of the storage battery string STR changes according to the bypass state of the storage battery modules M1-Mn (the number of bypassed storage battery modules M1-Mn) and the charging state of the storage battery modules M1-Mn. Therefore, when the storage battery string STR is being charged, the power converter PC converts the voltage input from the string bus 3 into the voltage on the side of the storage battery string STR, and outputs the converted voltage to the multiple storage battery modules M1-Mn.

[0021] When the storage battery string STR is discharged, the power converter PC converts the voltage input from the multiple storage battery modules M1 to Mn according to an instruction value of the discharge power (or current) described below, and outputs the converted voltage to the string bus 3. Here, the input voltage of the power converter PC 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 PC between the storage battery strings STR during discharge. Therefore, when the storage battery string STR is discharged, the power converter PC converts the input voltage to a voltage that is consistent with the other storage battery strings STR, and outputs the voltage to the string bus 3.

[0022] The power converter PC is a bidirectional converter. When the current flowing through the string bus 3 is an AC current, the power converter PC includes a synchronization means for tracking changes in instantaneous values.

[0023] The storage battery string STR includes n bypass switch units B1 to Bn, n voltage sensors 12, one current sensor 13, one voltage sensor 14, n temperature sensors (not shown), and a number of cell voltage sensors (not shown).

[0024] The voltage sensor 12 is connected between the positive and negative terminals of each of the storage battery modules M1 to Mn, detects the terminal voltage of each of the storage battery modules M1 to Mn, and transmits a detection signal to a string controller 102 described below. In addition, the current sensor 13 is provided on the power line PL of the storage battery string STR, detects the string current, and transmits a detection signal to the string controller 102. In addition, the voltage sensor 14 is provided on the power line PL of the storage battery string STR, detects the total voltage of the storage battery string STR, and transmits a detection signal to the string controller 102.

[0025] A temperature sensor is provided in each of the storage battery modules M1 to Mn to detect the temperature of each of the storage battery modules M1 to Mn and transmit a detection signal to the string controller 102. A cell voltage sensor is provided in each of the storage battery cells (not shown) in each of the storage battery modules M1 to Mn to detect the voltage of each storage battery cell and transmit a detection signal to the string controller 102.

[0026] The bypass switch units B1 to Bn are provided for each of the storage battery modules M1 to Mn. Each of the bypass switch units B1 to Bn includes a bypass line BL, switches S1 and S2, and a protection circuit 16. The bypass line BL is a power line that bypasses each of the storage battery modules M1 to Mn and the switch S2. The switch S1 is provided on the bypass line BL. The switch S1 is a mechanical relay. The switch S2 is provided between the positive electrode of each of the storage battery modules M1 to Mn and one end of the bypass line BL. The switch S2 is a mechanical relay.

[0027] The starting battery module M1 and the ending battery module Mn are connected to an external system via a power converter PC and a string bus 3. When the switch S1 is Open and the switch S2 is Closed in all the bypass switch units B1 to Bn, all the battery modules M1 to Mn are connected in series to the external system. On the other hand, when the switch S2 is Open and the switch S1 is Closed in any of the bypass switch units B1 to Bn, the battery module M1 to Mn corresponding to that bypass switch unit B1 to Bn is bypassed.

[0028] The protection circuit 16 includes a Zener diode D11 and a diode D12 connected in parallel to the switch S1, and a Zener diode D21 and a diode D22 connected in parallel to the switch S2, and provides overvoltage protection for the switches S1 and S2. The anode of the Zener diode D11 is connected to the anode of the diode D12. The anode of the Zener diode D21 is connected to the anode of the diode D22.

[0029] The cathode of the Zener diode D11 is connected to the bypass line BL between the switch S1 and the negative electrodes of the storage battery modules M1 to Mn, while the cathode of the diode D12 is connected to the bypass line BL between the switch S1 and the switch S2.

[0030] The cathode of the Zener diode D21 is connected to the power line PL between the switch S2 and the positive electrodes of the storage battery modules M1 to Mn, while the cathode of the diode D22 is connected to the bypass line BL between the switch S1 and the switch S2.

[0031] Here, in the case where the protection circuit 16 is not provided, the voltage applied across the contacts of the switch S2 when the switch S2 is cut off is the total voltage of the storage battery modules M1 to Mn in the connected state and the storage battery module M1 to Mn corresponding to the switch S2. In this case, the withstand voltage of the switch S2 needs to be equal to or higher than the total voltage of the n storage battery modules M1 to Mn (the voltage of the storage battery string STR when all the storage battery modules M1 to Mn are in the connected state). In contrast, in the case where the protection circuit 16 is provided, the voltage applied across the contacts of the switch S2 when the switch S2 is cut off is the Zener voltage of the Zener diode D21. In this case, the withstand voltage of the switch S2 only needs to be equal to or higher than the Zener voltage of the Zener diode D21. From the viewpoint of suppressing the loss occurring in the protection circuit 16 to the allowable loss or less, the input / output power is reduced by the power converter PC, and a large current is prevented from flowing into the protection circuit 16.

[0032] Furthermore, in the case where the protection circuit 16 is not provided, the voltage applied across the contacts of the switch S1 when the switch S1 is turned off is the total voltage of the connected storage battery modules M1 to Mn. In this case, the withstand voltage of the switch S1 needs to be equal to or higher than the total voltage of the (n-1) storage battery modules M1 to Mn (the voltage of the storage battery string STR when all storage battery modules M1 to Mn except one are in the connected state). In contrast, in the case where the protection circuit 16 is provided, the voltage applied across the contacts of the switch S1 when the switch S1 is turned off is the Zener voltage of the Zener diode D11. In this case, the withstand voltage of the switch S1 only needs to be equal to or higher than the Zener voltage of the Zener diode D11. The protection circuit 16 is configured with two pairs of the Zener diode D11 and diode D12 connected in parallel with the switch S1, and the Zener diode D21 and diode D22 connected in parallel with the switch S2, but may be configured with either one pair. In this case, the voltage applied to switch S2 is the sum of the voltages of the adjacent storage battery modules M1 to Mn, so the withstand voltage of the contacts of switch S2 needs to be greater than the Zener voltage plus the voltages of the storage battery modules M1 to Mn.

[0033] 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 battery string STR.

[0034] The string controller 102 transmits a control signal to the relay driver 103 and the power converter PC of the corresponding storage battery string STR. The relay driver 103 controls the switches S1, S2 of the corresponding bypass switch units B1-Bn according to the control signal transmitted from the corresponding string controller 102. Furthermore, the power converter PC converts the charging / discharging power of the corresponding storage battery string STR according to the control signal transmitted from the corresponding string controller 102. Furthermore, the power converter PC controls the string current of the corresponding storage battery string STR according to the control signal from the corresponding string controller 102.

[0035] The string controller 102 executes detection and estimation of the state of the corresponding storage battery string STR, notification of a request for device control to the system controller 101, etc. Examples of detection of the state of the storage battery string STR include detection of the string current of the storage battery string STR based on the detection signal of the corresponding current sensor 13, detection of the total voltage of the storage battery string STR based on the detection signal of the corresponding voltage sensor 14, detection of the voltage of the storage battery modules M1 to Mn based on the detection signal of the voltage sensor 12, detection of the temperature of the storage battery modules M1 to Mn based on the detection signal of the temperature sensor, and detection of the voltage of the storage battery cell based on the detection signal of the cell voltage sensor. Examples of estimation of the state of the storage battery string STR include estimation of the SOC (State of Charge) and SOH (State of Health) of the storage battery modules M1 to Mn, and estimation of the SOC and SOH of the storage battery string STR. Examples of notification of a request for device control to the system controller 101 include a request for switching control of the switches S1 and S2 of the bypass switch units B1 to Bn between Open / Close, and a request for control of the power converter PC.

[0036] 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 the change 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 of the IV characteristics), and step response methods (all of which are methods of estimation using the increase in internal resistance over time).

[0037] Methods for estimating the SOC include various known methods such as a current integration method, a method (voltage method) that is obtained from the OCV (Open Circuit Voltage), a method that combines the current integration method and the voltage method, etc. Also, the OCV can be estimated using various known methods that estimate the OCV using the change over time in the terminal voltage or the increase over time in the internal resistance.

[0038] 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 executes monitoring of the states of the storage battery strings STR, determining whether or not to accept a device control request from the string controllers 102, and notifying the string controllers 102 of permission of the device control request. In addition, the system controller 101 executes setting of instruction values ​​of the charge / discharge power (or current) of each storage battery string STR, and transmitting the instruction values ​​of the charge / discharge power (or current) to the string controllers 102.

[0039] The system controller 101 monitors the state of the storage battery strings STR based on the detection results and estimation results of the state of the storage battery 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 storage battery 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 storage battery strings STR.

[0040] Here, when a request (hereinafter referred to as a bypass control request) for Open / Close switching control of the switches S1, S2 of the bypass switch units B1-Bn (hereinafter referred to as B') for any of the storage battery modules M1-Mn (hereinafter referred to as M') is permitted by the system controller 101, each string controller 102 executes Open / Close switching control of the switches S1, S2 of the bypass switch unit B'. At this time, before executing the Open / Close switching control of the switches S1, S2 of the bypass switch unit B', the string controller 102 executes a protection / oxide film removal process for the purposes of protecting the protection circuit 16 and removing an oxide film formed on the contact portions of the switches S1, S2.

[0041] The protection / oxide film removal process includes a string current reduction process, a bypass state switching process, a string current increase process, and an oxide film removal process. The string current reduction process is a process for reducing the string current to a second predetermined value. The second predetermined value is a value lower than a first predetermined value described below, and is set to a low value that suppresses fluctuations in the input / output power of the entire power storage system 1 within an acceptable range during bypass control of the storage battery string STR. In this embodiment, the second predetermined value is 0, and the "second condition" is satisfied when the string current is 0.

[0042] 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 second predetermined value. Specifically, the string controller 102 repeatedly updates the command value of the string current by a predetermined amount ΔP1 obtained by equally dividing the difference between the current command value of the string current and the second 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 degree that suppresses the fluctuation of the input / output power of the entire power storage system 1 within an allowable range. As a result, the power converter PC gradually and continuously reduces the string current from the current value to the second predetermined value so as to suppress the fluctuation of the input / output power of the entire power storage system 1 within an allowable range.

[0043] The bypass state switching process is a process for switching the state of the switches S1, S2 of the corresponding bypass switch units B1-Bn (hereinafter, B") for the storage battery modules M1-Mn (hereinafter, M") that are not the target of the bypass control request. In the bypass state switching process, the string controller 102 determines the connection or bypass state ("predetermined state") of the multiple storage battery modules M" so that a "first condition" of the storage battery string STR is satisfied. The "first condition" is a condition in which the total voltage of the storage battery string STR is equal to or lower than the withstand voltage of the protection circuit 16, and arc discharge occurs in the switches S1, S2 that are mechanical relays. In other words, the string controller 102 determines the connection or bypass state of the multiple storage battery modules M" so that the total voltage of the storage battery string STR is equal to or lower than the withstand voltage of the protection circuit 16 when the oxide film removal process is performed. Furthermore, the string controller 102 sets the string current to a "first predetermined value" in a string current increasing process described later so that arc discharge occurs in the switches S1, S2 when the oxide film removal process is performed. The storage battery module M″ to be connected is selected according to a priority order determined by a predetermined criterion. Here, in the discharge mode, at least one of the storage battery modules M″ that is not the target of the bypass control request is set to a connected state.

[0044] The string current increasing process is a process for increasing the string current from a second predetermined value to a first predetermined value. The first predetermined value is set to a value that can remove the oxide film formed on the contact parts of the switches S1 and S2 by generating an arc discharge at the contact parts of the switches S1 and S2 when the switches S1 and S2 are mechanical relays and are operated.

[0045] Here, in the string current increasing process, the string controller 102 gradually and continuously increases the command value of the string current from a current value (a second predetermined value) to a first predetermined value. Specifically, the string controller 102 repeatedly updates the command value of the string current by a predetermined amount ΔP2 obtained by equally dividing the difference between the current command value of the string current and the first predetermined value. At this time, the rate of change of the command value of the string current is set to a degree that suppresses the fluctuation of the input / output power of the entire power storage system 1 within an allowable range. As a result, the power converter PC gradually and continuously increases the string current from the current value to the first predetermined value so as to suppress the fluctuation of the input / output power of the entire power storage system 1 within an allowable range.

[0046] The oxide film removal process is a process in which, when a first condition is satisfied, an arc discharge is generated at the contact portions of the switches S1 and S2 of the bypass switch unit B' to remove the oxide film formed at the contact portions. Specifically, the string controller 102 switches the switch S2 of the bypass switch unit B' from Close to Open, and then from Open to Close, and then from Close to Open, while a string current of a first predetermined value is flowing through the switch S2. The string controller 102 also switches the switch S1 of the bypass switch unit B' from Close to Open, and then from Open to Close, and then from Close to Open, while a string current of a first predetermined value is flowing through the switch S1.

[0047] Before executing the protective / oxide film removal process, the string controller 102 records the current connection or bypass state of the storage battery modules M1 to Mn of the storage battery string STR in an internal memory (not shown). Then, after executing the protective / oxide film removal process, the string controller 102 switches the Open / Close state of the switches S1, S2 of the bypass switch unit B″ so that the connection or bypass state of the storage battery module M″ that is not the target of the bypass control request is restored to the state recorded in the memory. At this time, the string controller 102 switches the Open / Close state of the switches S1, S2 of the bypass switch unit B′ so that the storage battery module M′ that is the target of the bypass control request is put into the bypass state.

[0048] 2 is a flowchart for explaining the process of switching the storage battery module M' that is the target of a bypass control request from a connected state to a bypass state (bypass control). First, in step S1, the string controller 102 monitors the storage battery modules M1-Mn of the storage battery string STR, and determines whether or not there is any storage battery module M1-Mn that requires bypass control. If a positive determination is made in step S1, the process proceeds to step S2, and if a negative determination is made in step S1, the process ends.

[0049] In step S2, the string controller 102 transmits a bypass control request to the system controller 101, and determines whether or not a notification of permission for the bypass control request has been received from the system controller 101. If a positive determination is made in step S2, the process proceeds to step S3, and if a negative determination is made in step S2, the process ends.

[0050] In step S3, the string controller 102 records the current connection or bypass state of the storage battery modules M1 to Mn of the storage battery string STR in an internal memory (not shown). Next, the string controller 102 repeatedly executes the loop process of steps S4 to S6 until the indicated value of the string current reaches a second predetermined value (string current reduction process). Here, in steps S4 to S6, the string controller 102 gradually and continuously reduces the indicated value of the string current from the current value to the second predetermined value by a predetermined amount ΔP1 at a time.

[0051] First, in step S4, the string controller 102 updates the indicated value of the string current to a value that is decreased by a predetermined amount ΔP1. This predetermined amount ΔP1 is set to a small amount so as to meet the purpose of preventing a sudden change in the input / output power of the power storage system 1. This predetermined amount ΔP1 may be equal to the difference between the current value of the string current and the second predetermined value when the difference between the current value of the string current and the second predetermined value is small. On the other hand, this predetermined amount ΔP1 may be smaller than the difference between the current value of the string current and the second predetermined value when the difference between the current value of the string current and the second predetermined value is relatively large. When this predetermined amount ΔP1 is smaller than the difference between the current value of the string current and the second predetermined value, the string current is repeatedly updated multiple times.

[0052] Next, in step S5, the string controller 102 waits for a predetermined time T1 after transmitting the command value of the string current to the power converter PC. This predetermined time T1 is set in consideration of the time required for the string controller 102 to control the power converter PC and the rate of change of the string current.

[0053] Next, in step S6, the string controller 102 determines whether the string current has reached a second predetermined value (whether the reduction of the string current has been completed). If a positive determination is made in step S6, the process proceeds to step S7, and if a negative determination is made in step S6, the process proceeds to step S4.

[0054] In steps S7 and S8, the string controller 102 executes a bypass state switching process. First, in step S7, the string controller 102 determines the connected or bypass state of the storage battery module M″ that is not the target of the bypass control request. In step S7, the storage battery module M″ to be placed in the connected state and the storage battery module M″ to be placed in the bypass state are determined so that the total voltage of the storage battery string STR is equal to or lower than the withstand voltage of the protection circuit 16 when a string current of a first predetermined value flows.

[0055] Next, in step S8, the string controller 102 switches between Open / Close the switches S1 and S2 of the bypass switch unit B″ so that the connected or bypassed state of the storage battery module M″ that is not the target of the bypass control request is switched to the state determined in step S7. Next, in step S9, the string controller 102 switches between Open / Close the switches S1 and S2 of the bypass switch unit B′ so that the storage battery module M′ that is the target of the bypass control request is brought into the connected state.

[0056] Next, the string controller 102 repeatedly executes the loop process of steps S10 to S12 until the command value of the string current reaches a first predetermined value (string current increasing process). Here, in steps S10 to S12, the string controller 102 gradually and continuously increases the command value of the string current from the current value to the first predetermined value by a predetermined amount ΔP2.

[0057] First, in step S10, the string controller 102 updates the command value of the string current to a value increased by a predetermined amount ΔP2. This predetermined amount ΔP2 is set to a small amount so as to meet the purpose of preventing a sudden change in the input / output power of the power storage system 1. This predetermined amount ΔP2 may be equal to the difference between the current value of the string current and the first predetermined value when the difference between the current value of the string current and the first predetermined value is small. On the other hand, this predetermined amount ΔP2 may be smaller than the difference between the current value of the string current and the first predetermined value when the difference between the current value of the string current and the first predetermined value is relatively large. When this predetermined amount ΔP2 is smaller than the difference between the current value of the string current and the first predetermined value, the string current is updated repeatedly multiple times.

[0058] Next, in step S11, the string controller 102 waits for a predetermined time T2 after transmitting the command value of the string current to the power converter PC. This predetermined time T2 is set in consideration of the time required for the string controller 102 to control the power converter PC and the rate of change of the string current.

[0059] Next, in step S12, the string controller 102 determines whether the command value of the string current has reached a first predetermined value (whether the increase in the string current has been completed). If a positive determination is made in step S12, the process proceeds to step S13, and if a negative determination is made in step S12, the process proceeds to step S10.

[0060] In steps S13 and S14, the string controller 102 executes an oxide film removal process. First, in step S13, the string controller 102 switches the switch S2 of the bypass switch unit B' from Close to Open while a string current of a first predetermined value flows through the switch S2 (S13-1 in Table 1 below). Then, the string controller 102 switches the switch S2 from Open to Close (S13-2 in Table 1 below), and further switches the switch S2 from Close to Open (S13-3 in Table 1 below). This generates an arc discharge at the contact portion of the switch S2, and the oxide film formed on the contact portion is removed.

[0061] Next, in step S14, the string controller 102 switches the switch S1 of the bypass switch unit B' from Open to Close to pass a string current of a first predetermined value through the switch S1 of the bypass switch unit B' (S14-1 in Table 1 below). Then, the string controller 102 switches the switch S1 of the bypass switch unit B' from Close to Open (S14-2 in Table 1 below), then from Open to Close (S14-3 in Table 1 below), and further from Close to Open (S14-4 in Table 1 below). This generates an arc discharge at the contact portion of the switch S1, and removes the oxide film formed on the contact portion. Note that it is not essential to switch the switches S1 and S2 from Close to Open, Open to Close, and Close to Open. For example, it is sufficient to switch the switches S1 and S2 from Close to Open or Open to Close only once. [Table 1]

[0062] Next, in step S15, the string controller 102 switches the Open / Close state of the switches S1 and S2 of the bypass switch unit B″ so that the connection or bypass state of the storage battery module M″ that is not the target of the bypass control request is restored to the state recorded in the memory in step S3. At this time, the string controller 102 switches the Open / Close state of the switches S1 and S2 of the bypass switch unit B′ so that the storage battery module M′ that is the target of the bypass control request is put into the bypass state. This ends the processing.

[0063] As described above, the battery control device 100 of this embodiment sets the string current to a first predetermined value by the power converter PC, and sets the connection or bypass state of the multiple storage battery modules M1 to Mn to a predetermined state by the multiple bypass switch units B1 to Bn. This establishes a first condition in which the total voltage of the storage battery string STR becomes equal to or lower than the withstand voltage of the bypass switch units B1 to Bn and an arc discharge occurs at the contact portion of the switches S1 and S2 which are mechanical relays. Then, in a state in which the first condition is established, the battery control device 100 executes an oxide film removal process for opening and closing the switches S1 and S2 which are mechanical relays. Thereafter, the battery control device 100 executes bypass control of the storage battery module M' which is the target of the bypass control request. In addition, the battery control device 100 restores the connection state or bypass state of the storage battery module M" which is not the target of the bypass control request to the original state.

[0064] That is, the battery control device 100 of this embodiment reduces the string current to a first predetermined value by the power converter PC, and then executes bypass control of the battery module M' that is the target of the bypass control request. This makes it possible to prevent large fluctuations that exceed the allowable range in the input / output power of the energy storage system 1 when the bypass control is executed.

[0065] In addition, the battery control device 100 of this embodiment sets the string current to a first predetermined value by the power converter PC at which arc discharge occurs at the contacts of the switches S1 and S2, and then switches the predetermined switches S1 and S2 between open and close. This makes it possible to remove oxide films formed on the contacts of the switches S1 and S2, which are mechanical relays.

[0066] Furthermore, the battery control device 100 of this embodiment sets the connection or bypass state of the battery modules M1-Mn when the oxide film removal process is performed so that the total voltage of the battery string STR is equal to or lower than the withstand voltage of the bypass switch units B1-Bn. This makes it possible to prevent overvoltage from being applied to the protection circuit 16 and the switches S1 and S2 of the bypass switch units B1-Bn that are the targets of the oxide film removal process when the oxide film removal process is performed, even if the withstand voltage of the protection circuit 16 and the switches S1 and S2 are set lower than the total voltage of the battery string STR. This makes it possible to use low-cost Zener diodes and mechanical relays with low withstand voltages for the protection circuit 16 and the switches S1 and S2 of the bypass switch units B1-Bn, thereby reducing the cost of the bypass switch units B1-Bn.

[0067] Furthermore, the battery control device 100 of this embodiment uses the power converter PC to reduce the string current to a second predetermined value to satisfy the second condition. After that, when the second condition is satisfied, the battery control device 100 sets the connection or bypass state of the battery modules M1-Mn using the multiple bypass switch units B1-Bn to a "predetermined state" that takes into consideration the withstand voltages of the bypass switch units B1-Bn and the total voltage of the battery string STR.

[0068] Here, the second predetermined value is set lower than the first predetermined value and low enough to suppress fluctuations in input / output power of the energy storage system 1 within an acceptable range when the bypass switch units B1-Bn execute bypass control of the storage battery modules M1-Mn. This makes it possible to suppress fluctuations in input / output power of the energy storage system 1 within an acceptable range when the connection or bypass state of the storage battery modules M1-Mn is switched to the "predetermined state" by the bypass switch units B1-Bn in a state where the second condition is established.

[0069] Furthermore, in the energy storage system 1 of this embodiment, the bypass switch units B1 to Bn include a protection circuit 16 that protects the switches S1 and S2 from overvoltage, and the battery control device 100 sets the total voltage of the battery string STR during the oxide film removal process so as not to exceed the allowable loss of the protection circuit 16. This allows the withstand voltage of the switches S1 and S2 to be set higher than the Zener voltage of the protection circuit 16, and therefore the withstand voltage of the switches S1 and S2 can be set lower than the total voltage of the battery string STR. This allows the cost of the switches S1 and S2 to be reduced.

[0070] Furthermore, the battery control device 100 of this embodiment gradually and continuously changes the command value of the string current when changing the string current to the first predetermined value. Specifically, the battery control device 100 repeatedly executes a process of changing the command value of the string current toward the first predetermined value by an amount of change (a predetermined amount ΔP2) smaller than the difference between the first predetermined value and the current value, until the command value of the string current reaches the first predetermined value. This makes it possible to suppress fluctuations in the input / output power of the energy storage system 1 within an allowable range when changing the string current to the first predetermined value.

[0071] Furthermore, the battery control device 100 of this embodiment gradually and continuously changes the command value of the string current when changing the string current to the second predetermined value. Specifically, the battery control device 100 repeatedly executes a process of changing the command value of the string current toward the second predetermined value by an amount of change (predetermined amount ΔP1) smaller than the difference between the second predetermined value and the current value, until the command value of the string current reaches the second predetermined value. This makes it possible to suppress fluctuations in the input / output power of the energy storage system 1 within an allowable range when changing the string current to the second predetermined value.

[0072] Furthermore, the battery control device 100 of this embodiment records the current connection or bypass state of the battery modules M1-Mn in a built-in memory before switching the connection or bypass state of the battery modules M1-Mn to a "predetermined state" using the bypass switch units B1-Bn. After executing the oxide film removal process, the battery control device 100 causes the bypass switch units B1-Bn to return the connection or bypass state of the battery modules M1-Mn to the state recorded in the memory, except for the battery module M' that is the target of bypass control. This makes it possible to remove the oxide film on the switches S1 and S2, and to set the connection or bypass state of the battery modules M1-Mn to a desired state after executing the oxide film removal process.

[0073] FIG. 3 is a flowchart for explaining an oxide film removal process according to another embodiment of the present invention. The process shown in this flowchart is for removing oxide films on the switches S1, S2 of the bypass switch unit B″ corresponding to a storage battery module M″ that is not the target of a bypass control request. First, in step S101, the string controller 102 monitors the storage battery modules M1 to Mn of the storage battery string STR and determines whether or not there is a storage battery module M′ that requires bypass control. If a negative determination is made in step S101, the process proceeds to step S102, and if a positive determination is made in step S101, the process ends. Note that if there is a storage battery module M′ that requires bypass control (YES in step S101), the processes of steps S2 to S15 in FIG. 2 are executed.

[0074] In step S102, the current connection or bypass state of the storage battery modules M1 to Mn of the storage battery string STR is recorded in an internal memory (not shown). Next, the string controller 102 repeatedly executes the loop process of steps S103 to S105 until the indicated value of the string current reaches a third predetermined value (string current reduction process). Here, in steps S103 to S105, the string controller 102 gradually and continuously reduces the indicated value of the string current from the current value to the third predetermined value by a predetermined amount ΔP3 at a time.

[0075] First, in step S103, the string controller 102 updates the indicated value of the string current to a value that is decreased by a predetermined amount ΔP3. This predetermined amount ΔP3 is set to a small amount so as to meet the purpose of preventing a sudden change in the input / output power of the power storage system 1. This predetermined amount ΔP3 may be equal to the difference between the current value of the string current and the third predetermined value when the difference between the current value of the string current and the third predetermined value is small. On the other hand, this predetermined amount ΔP3 may be smaller than the difference between the current value of the string current and the third predetermined value when the difference between the current value of the string current and the third predetermined value is relatively large. When this predetermined amount ΔP3 is smaller than the difference between the current value of the string current and the third predetermined value, the string current is repeatedly updated multiple times.

[0076] The third predetermined value is set to a value that satisfies both the conditions of the first predetermined value and the second predetermined value described above. That is, the third predetermined value is set to a value that suppresses fluctuations in input / output power of the entire power storage system 1 within an allowable range during bypass control of the storage battery modules M1 to Mn, and that generates an arc discharge at the contact portions of the switches S1 and S2 when the switches S1 and S2 are switched between Open and Close.

[0077] Next, in step S104, the string controller 102 waits for a predetermined time T3 after transmitting the command value of the string current to the power converter PC. This predetermined time T3 is set in consideration of the time required for the string controller 102 to control the power converter PC and the rate of change of the string current.

[0078] Next, in step S105, the string controller 102 determines whether the command value of the string current has reached a third predetermined value (whether the reduction of the string current has been completed). If a positive determination is made in step S105, the process proceeds to step S106, and if a negative determination is made in step S105, the process proceeds to step S103.

[0079] Next, in step S106, the string controller 102 switches between Open and Close the switches S1, S2 of the bypass switch units B1 to Bn corresponding to the storage battery modules M1 to Mn targeted for the oxide film removal process so that the storage battery modules M1 to Mn are in a connected state.

[0080] Next, in steps S107 and S108, the string controller 102 executes an oxide film removal process. First, in step S107, the string controller 102 switches the switch S2 of the bypass switch unit B1 to Bn that is the target of the oxide film removal process from Close to Open while a string current of a third predetermined value flows through the switch S2 (S107-1 in Table 2 below). Then, the string controller 102 switches the switch S2 from Open to Close (S107-2 in Table 2 below), and then switches it from Close to Open (S107-3 in Table 2 below). As a result, an arc discharge occurs at the contact portion of the switch S2, and the oxide film formed on the contact portion is removed.

[0081] Next, in step S108, the string controller 102 switches the switch S1 of the bypass switch unit B1 to Bn targeted for the oxide film removal process from Open to Close to pass a string current of a third predetermined value through the switch S1 (S108-1 in Table 2 below). Then, the string controller 102 switches the switch S1 from Close to Open (S108-2 in Table 2 below), then from Open to Close (S108-3 in Table 2 below), and again from Close to Open (S108-4 in Table 2 below). This generates an arc discharge at the contact portion of the switch S1, and the oxide film formed on the contact portion is removed. [Table 2]

[0082] Next, in step S109, the string controller 102 switches the switches S1, S2 of the bypass switch units B1-Bn between Open and Close so that the connection or bypass state of the storage battery modules M1-Mn returns to the state recorded in the memory in step S102. This ends the process.

[0083] As described above, in the process of this embodiment, the power converter PC reduces the string current to the third predetermined value, and then executes bypass control of the storage battery modules M1 to Mn that are not the target of the oxide film removal process. This makes it possible to prevent large fluctuations that exceed the allowable range from occurring in the input / output power of the energy storage system 1 when the bypass control is executed.

[0084] In the process of this embodiment, the power converter PC sets the string current to a third predetermined value at which arc discharge occurs at the contact points of the switches S1 and S2, and then executes the Open / Close switching of the predetermined switches S1 and S2. This makes it possible to remove the oxide film formed on the contact points of the switches S1 and S2, which are mechanical relays.

[0085] Furthermore, in the process of this embodiment, even if the withstand voltages of the protection circuit 16 and the switches S1, S2 are set lower than the total voltage of the storage battery string STR, it is possible to prevent an overvoltage from being applied to the protection circuit 16 and the switches S1, S2 of the bypass switch units B1-Bn that are the targets of the oxide film removal process when the oxide film removal process is performed. Therefore, low-cost Zener diodes and mechanical relays with low withstand voltages can be used for the protection circuit 16 and the switches S1, S2 of the bypass switch units B1-Bn, and the cost of the bypass switch units B1-Bn can be reduced.

[0086] 4 is a circuit diagram showing an outline of a power storage system 2 according to another embodiment of the present invention. Note that the same reference numerals are used for configurations similar to those in the above-described embodiment, and the description of the above-described embodiment is incorporated herein.

[0087] As shown in FIG. 4, in the energy storage system 2 of this embodiment, each storage battery string STR includes a string cutoff switch 11 and a CR circuit 15. The string cutoff switch 11 is provided between each power converter PC and the starting storage battery module M1. This string cutoff switch 11 connects or disconnects the power converter PC and the starting storage battery module M1. The string cutoff switch 11 is provided for the purpose of preventing the charge of a capacitor C, which will be described later, from flowing to the power converter PC. Note that, if the above purpose can be achieved without the string cutoff switch 11, such as when the operation of the power converter PC can be stopped and the impedance of the power converter PC can be made relatively high compared to the impedance of the storage battery string STR, the string cutoff switch 11 does not need to be provided.

[0088] The CR circuit 15 includes a capacitor C and a resistor R connected in series. One end of the resistor R is connected to the capacitor C, and the other end of the resistor R is connected to the power line PL between the string cutoff switch 11 and the starting bypass switch unit B1. On the other hand, the capacitor C is connected to the power line PL between the ending bypass switch unit Bn and the power converter PC.

[0089] 4 shows a state before bypass control of the storage battery module M1 is executed when the storage battery module M1 is the storage battery module M' that is the target of a bypass control request. In this state, the storage battery module M1 is in a connected state, and in the bypass switch unit B1, the switch S1 is open and the switch S2 is closed. On the other hand, the storage battery modules M2 to Mn are in a bypass state, and in the bypass switch units B2 to Bn, the switch S1 is closed and the switch S2 is open. Also, the string interruption switch 11 is open.

[0090] In this state, a transient current flows from the positive electrode of the storage battery module M1 to the CR circuit 15 via the switch S2 of the bypass switch unit B1, charges the capacitor C, and flows to the negative electrode of the storage battery module M1 via the switch S1 of the bypass switch units B2 to Bn. Here, the maximum value of the transient current flowing through the storage battery module M1, the switch S2 of the bypass switch unit B1, the CR circuit 15, etc. and charging the capacitor C in the state shown in FIG. 4 is set to a first predetermined value. The "first predetermined value" is set to a value that can cause an arc discharge to occur at the contact portion of the switch S2 due to the transient current flowing through the storage battery module M1, the switch S2 of the bypass switch unit B1, the CR circuit 15, etc. and charging the capacitor C when the switch S2, which is a mechanical relay, is activated, and can remove the oxide film formed on the contact portion. The "first predetermined value" is also set so that the total voltage of the storage battery string STR does not exceed the allowable loss of the protection circuit 16 when the transient current flows through the storage battery module M1, the switch S2, the CR circuit 15, etc.

[0091] The battery control device 200 switches the battery module M1 from the connection state shown in FIG. 4 to the bypass state when the capacitor C of the CR circuit 15 is charged. When the battery module M1 is switched to the bypass state, a transient current flows through the capacitor C, the switch S1 of the bypass switch unit B1, and the bypass switch units B2 to Bn. Here, the maximum value of the transient current flowing through the capacitor C, the switch S1 of the bypass switch unit B1, and the like when the battery module M1 is switched to the bypass state is set to a fourth predetermined value. The "fourth predetermined value" is set to a value that can cause an arc discharge at the contact portion of the switch S1 due to the transient current flowing through the capacitor C, the switch S1, and the like when the switch S1, which is a mechanical relay, is operated, and can remove the oxide film formed on the contact portion. The "fourth predetermined value" is also set so that the total voltage of the battery string STR does not exceed the allowable loss of the protection circuit 16 when the transient current flows through the capacitor C and the switch S1, and the like.

[0092] Fig. 5 is a flowchart for explaining the process by which the battery control device 200 shown in Fig. 4 switches the storage battery module M' that is the target of the bypass control request from a connected state to a bypass state. Note that this process will be explained taking as an example a case where the storage battery module M' that is the target of the bypass control request is the storage battery module M1, but similar processes may be performed when the other storage battery modules M2 to Mn are the storage battery module M' that is the target of the bypass control request. Also, it is not essential to perform the oxide film removal process on the storage battery module M' that is the target of the bypass control request, and the storage battery modules M1 to Mn that perform the oxide film removal process and the timing for performing the oxide film removal process may be set appropriately.

[0093] First, in step S201, the string controller 102 monitors the storage battery modules M1 to Mn of the storage battery string STR and determines whether or not there is a storage battery module M' that requires bypass control. If a positive determination is made in step S201, the process proceeds to step S202, and if a negative determination is made in step S201, the process ends.

[0094] In step S202, the string controller 102 transmits a bypass control request to the system controller 101, and determines whether or not a notification of permission for the bypass control request has been received from the system controller 101. If a positive determination is made in step S202, the process proceeds to step S203, and if a negative determination is made in step S202, the process ends.

[0095] In step S203, the string controller 102 records the current connection or bypass state of the storage battery modules M1 to Mn of the storage battery string STR in an internal memory (not shown). Next, the string controller 102 repeatedly executes the loop process of steps S204 to S206 until the command value of the string current reaches a second predetermined value (string current reduction process). The "second predetermined value" is a value lower than the above-mentioned "first predetermined value" and "fourth predetermined value", and is set to a low value that suppresses the fluctuation of the input / output power of the entire power storage system 1 within an allowable range during bypass control of the storage battery string STR. In this embodiment, the second predetermined value is 0. Here, in steps S204 to S206, the string controller 102 gradually and continuously reduces the command value of the string current from the current value to the second predetermined value by a predetermined amount ΔP1 at a time.

[0096] First, in step S204, the string controller 102 updates the command value of the string current to a value that is decreased by a predetermined amount ΔP1. This predetermined amount ΔP1 is set to a small amount so as to meet the purpose of preventing a sudden change in the input / output power of the power storage system 1. This predetermined amount ΔP1 may be equal to the difference between the current value of the string current and the second predetermined value when the difference between the current value of the string current and the second predetermined value is small. On the other hand, this predetermined amount ΔP1 may be smaller than the difference between the current value of the string current and the second predetermined value when the difference between the current value of the string current and the second predetermined value is relatively large. When this predetermined amount ΔP1 is smaller than the difference between the current value of the string current and the second predetermined value, the string current is repeatedly updated multiple times.

[0097] Next, in step S205, the string controller 102 waits for a predetermined time T1 after transmitting the command value of the string current to the power converter PC. This predetermined time T1 is set in consideration of the time required for the string controller 102 to control the power converter PC and the rate of change of the string current.

[0098] Next, in step S206, the string controller 102 determines whether the string current has reached a second predetermined value (whether the reduction of the string current has been completed). If a positive determination is made in step S206, the process proceeds to step S207, and if a negative determination is made in step S206, the process proceeds to step S204.

[0099] In step S207, the string controller 102 opens (disconnects) the string cutoff switch 11. Note that, when the string current is sufficiently reduced by the power converter PC, it is not essential that the string cutoff switch 11 cuts off the storage battery string STR.

[0100] Next, in step S208, the string controller 102 puts the storage battery modules M2 to Mn that are not the target of the bypass control request into a bypass state (see FIG. 4). Next, in step S209, the string controller 102 puts the storage battery module M1 that is the target of the bypass control request into a connected state. Specifically, the switch S1 of the bypass switch unit B1 is opened, and then the switch S2 of the bypass switch unit B1 is closed. At this time, a transient current flows through the storage battery module M1, the switch S2 of the bypass switch unit B1, the CR circuit 15, etc., and an arc discharge occurs at the contact portion of the switch S2 of the bypass switch unit B1, thereby removing the oxide film formed on the contact portion.

[0101] Next, in step S210, the string controller 102 waits for a predetermined time T4 from step S209. This predetermined time T4 is set in consideration of the time required to charge the capacitor C. Here, the time required to charge the capacitor C corresponds to the time required for the CR circuit 15 to leave the transient state and reach the steady state, and is calculated based on a time constant τ (=C×R).

[0102] Next, in step S211, the string controller 102 switches the storage battery module M1, which is the target of the bypass control request, from the connected state to the bypass state. Specifically, the switch S2 of the bypass switch unit B1 is opened, and then the switch S1 of the bypass switch unit B1 is closed. At this time, a transient current flows through the capacitor C and the switch S1 of the bypass switch unit B1, etc., and an arc discharge is generated at the contact portion of the switch S1 of the bypass switch unit B1, thereby removing the oxide film formed on the contact portion.

[0103] Next, in step S212, the string controller 102 waits for a predetermined time T5 from step S211. This predetermined time T5 is set in consideration of the time required to discharge the capacitor C. Here, the time required to discharge the capacitor C is calculated based on a time constant τ (=C×R).

[0104] Next, in step S213, the string controller 102 switches the Open / Close states of the switches S1, S2 of the bypass switch units B2 to Bn so that the connection or bypass state of the storage battery modules M2 to Mn that are not the target of the bypass control request returns to the state recorded in the memory in step S203. This ends the process.

[0105] As described above, in the power storage system 2 of the present embodiment, the storage battery string STR includes the CR circuit 15 connected between the switch S2 corresponding to the starting storage battery module M1 and the power converter PC, and between the terminal storage battery module Mn and the power converter PC. In this power storage system 2, the storage battery control device 200 executes the following first oxide film removal process. (First oxide film removal process) All of the storage battery modules M1 to Mn are set to a bypass state by the plurality of bypass switch units B1 to Bn, and thereafter, any one of the storage battery modules M1 is switched to a connected state by any one of the bypass switch units B1.

[0106] Here, the maximum value of the transient current flowing through the connected battery module B1, the switch S2 of the bypass switch unit B1, the CR circuit 15, etc. is set so that the total voltage of the battery string STR becomes equal to or lower than the withstand voltage of the bypass switch units B1 to Bn and a first condition for an arc discharge to occur in the switch S2 of the bypass switch unit B1 is satisfied when the battery control device 200 performs the first oxide film removal process. As a result, when the first oxide film removal process is performed, an arc discharge can be generated in the switch S2 of the bypass switch unit B1 by the transient current flowing through any one of the storage battery modules M1, the switch S2 of the bypass switch unit B1, the CR circuit 15, etc., to remove the oxide film formed in the switch S2.

[0107] In addition, the battery control device 200 executes the following second oxide film removal process. (Second oxide film removal process) After the first oxide film removal process is performed, the connected storage battery module M1 is switched to a bypass state by one of the bypass switch units B1.

[0108] Here, the maximum value of the transient current flowing through the CR circuit 15 and the switch S1 of the bypass switch unit B1 is set so that the total voltage of the battery string STR becomes equal to or lower than the withstand voltage of the bypass switch units B1 to Bn and a second condition for arc discharge to occur in the switch S1 of the bypass switch unit B1 is satisfied when the battery control device 200 performs the second oxide film removal process. As a result, when the second oxide film removal process is performed, the transient current flowing through the CR circuit 15 and the switch S1 of the bypass switch unit B1 can cause arc discharge to occur in the switch S1 of the bypass switch unit B1, thereby removing the oxide film formed in the switch S1.

[0109] 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 without departing from the spirit of the present invention, and publicly known or well-known technologies may be combined as appropriate.

[0110] For example, in the above embodiment, the switches S1 and S2 are mechanical relays, but at least one of the switches S1 and S2 may be a semiconductor switch. In this case, the oxide film removal process needs to be performed on only one of the switches S1 and S2, which is a mechanical relay.

[0111] Furthermore, the timing of performing the oxide film removal process and the storage battery modules M1-Mn to be subjected to the oxide film removal process may be set appropriately. Furthermore, it is not essential to provide the bypass switch units B1-Bn with the protection circuit 16. If the protection circuit 16 is not provided, the total voltage of the storage battery string STR during the execution of the oxide film removal process may be set to be equal to or lower than the withstand voltage of the switches S1 and S2, which are mechanical relays.

[0112] In the above embodiment, the command values ​​of the string currents are gradually and continuously changed over time by the predetermined amounts ΔP1, ΔP2, and ΔP3 to the target value. However, for example, when the effect of the change in the string current on the input / output power of the energy storage system 1 is minor, the command values ​​of the string currents may be changed all at once.

[0113] Furthermore, in the above-described embodiment, the CR circuit 15 is given as an example of the power storage and current suppression circuit, but the power storage and current suppression circuit only needs to have the function of storing charge and the function of suppressing current, and for example, a constant current diode or a current control circuit may be provided instead of the resistor R. [Explanation of symbols]

[0114] 1: Energy storage system 2: Energy storage system 15: CR circuit (storage and current suppression circuit) 16:Protection circuit 100: Battery control device 200: Battery control device B1~Bn, B', B": Bypass switch unit (bypass circuit) BL: Bypass line M1~Mn, M', M": Battery module (battery) PC: Power converter S1: Switch (second switch, mechanical relay) S2: Switch (first switch, mechanical relay) STR: Battery string ΔP1: Predetermined amount (small change) ΔP2: Predetermined amount (small change) ΔP3: Predetermined amount (small change)

Claims

1. A battery control device that controls a power storage system including a battery string and a power converter that converts input and output power of the battery string, The battery string comprises: A plurality of storage batteries connected in series; a plurality of bypass circuits each including a first switch provided between adjacent storage batteries, a bypass line bypassing the first switch and the storage batteries, and a second switch provided in the bypass line, and switching the storage batteries between a connected state and a bypass state; Equipped with At least one of the first switch and the second switch is a mechanical relay, a current of the battery string is set to a first predetermined value by the power converter, and a connection or bypass state of the plurality of batteries is set to a predetermined state by the plurality of bypass circuits, so that a first condition is established in which a total voltage of the battery string is equal to or lower than a withstand voltage of the bypass circuit and an arc discharge occurs in at least one of the first switch and the second switch, which are mechanical relays; The battery control device executes an oxide film removal process to open and close at least one of the first switch and the second switch, which are mechanical relays, when the first condition is satisfied.

2. reducing a current in the battery string by the power converter such that a second condition is satisfied in which the current in the battery string is a second predetermined value that is lower than the first predetermined value; setting a connection or bypass state of the plurality of storage batteries to the predetermined state by the plurality of bypass circuits when the second condition is satisfied; 2. The battery control device according to claim 1, wherein, when a connection or bypass state of the plurality of storage batteries is set to the predetermined state, the power converter increases a current of the storage battery string to the first predetermined value, thereby satisfying the first condition.

3. the bypass circuit includes a protection circuit that performs overvoltage protection for at least one of the first switch and the second switch; 3. The battery control device according to claim 1, wherein the withstand voltage of the bypass circuit is equal to or higher than a Zener voltage of the protection circuit.

4. 3. The battery control device according to claim 1, wherein when changing the current of the battery string to the first predetermined value, a process of changing an instruction value of the current of the battery string toward the first predetermined value by an amount smaller than the difference between the first predetermined value and a current value is repeatedly executed until the instruction value reaches the first predetermined value.

5. 3. The battery control device according to claim 2, wherein, when changing the current of the battery string to the second predetermined value, a process of changing an instruction value of the current of the battery string toward the second predetermined value by an amount smaller than the difference between the second predetermined value and a current value is repeatedly executed until the instruction value reaches the second predetermined value.

6. Before setting the connection or bypass states of the plurality of storage batteries to the predetermined states by the plurality of bypass circuits, a current connection or bypass state of the plurality of storage batteries is recorded in a storage unit; 3. The battery control device according to claim 1, wherein after the oxide film removal process is performed, the connection or bypass state of the plurality of storage batteries is restored to the state recorded in the memory unit by the plurality of bypass circuits, except for the storage battery that needs to be switched between the connection state and the bypass state.

7. A battery string; a power converter that converts input / output power of the storage battery string; a battery control device that controls the battery string and the power converter; A power storage system comprising: The battery string comprises: A plurality of storage batteries connected in series; a plurality of bypass circuits each including a first switch provided between adjacent storage batteries, a bypass line bypassing the first switch and the storage batteries, and a second switch provided in the bypass line, and switching the storage batteries between a connected state and a bypass state; Equipped with At least one of the first switch and the second switch is a mechanical relay, The battery control device includes: a current of the battery string is set to a first predetermined value by the power converter, and a connection or bypass state of the plurality of batteries is set to a predetermined state by the plurality of bypass circuits, so that a first condition is established in which a total voltage of the battery string is equal to or lower than a withstand voltage of the bypass circuit and an arc discharge occurs in at least one of the first switch and the second switch, which are mechanical relays; The power storage system executes an oxide film removal process to open and close at least one of the first switch and the second switch, which are mechanical relays, when the first condition is satisfied.

8. A battery string; a power converter that converts input / output power of the storage battery string; a battery control device that controls the battery string and the power converter; A power storage system comprising: The battery string comprises: A plurality of storage batteries connected in series; a plurality of bypass circuits each including a first switch that is a mechanical relay provided between adjacent storage batteries, a bypass line that bypasses the first switch and the storage batteries, and a second switch provided in the bypass line, and switching the storage batteries between a connected state and a bypass state; a power storage and current suppression circuit connected between the first switch corresponding to the storage battery at a starting point and the power converter, and between the storage battery at a terminal point and the power converter, the power storage and current suppression circuit including a power storage unit and a current suppression unit; Equipped with The battery control device includes: a first oxide film removal process is performed in which, after all of the storage batteries are set to a bypass state by the plurality of bypass circuits, one of the storage batteries is switched to a connected state by one of the bypass circuits; a first condition for generating an arc discharge in the first switch is satisfied when the first oxide film removal process is performed by the battery control device, and a maximum value of a transient current flowing through the connected battery, the first switch, and the storage and current suppression circuit is set.

9. the second switch is a mechanical relay; The battery control device includes: After the first oxide film removal process is performed, a second oxide film removal process is performed to switch the connected storage battery to a bypass state by any one of the bypass circuits; 9. The energy storage system according to claim 8, wherein a maximum value of a transient current flowing through the energy storage and current suppression circuit and the second switch is set so that a total voltage of the energy storage string becomes equal to or lower than a withstand voltage of the bypass circuit and a second condition for an arc discharge to occur in the second switch is satisfied when the second oxide film removal process is performed by the energy storage control device.

10. A battery control method executed by a battery control device that controls a power storage system including a battery string and a power converter that converts input / output power of the battery string, comprising: The battery string comprises: A plurality of storage batteries connected in series; a plurality of bypass circuits each including a first switch provided between adjacent storage batteries, a bypass line bypassing the first switch and the storage batteries, and a second switch provided in the bypass line, and switching the storage batteries between a connected state and a bypass state; Equipped with At least one of the first switch and the second switch is a mechanical relay, a current of the battery string is set to a first predetermined value by the power converter, and a connection or bypass state of the plurality of batteries is set to a predetermined state by the plurality of bypass circuits, so that a first condition is established in which a total voltage of the battery string is equal to or lower than a withstand voltage of the bypass circuit and an arc discharge occurs in at least one of the first switch and the second switch, which are mechanical relays; A battery control method comprising: executing an oxide film removal process for opening and closing at least one of the first switch and the second switch, which are mechanical relays, when the first condition is satisfied.

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