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

Abstract

A battery control device (100): sets a string current to a first predetermined value through a power converter (PC) so as to satisfy a first condition in which a total voltage of a battery string (STR) is equal to or less than a withstand voltage of bypass switching units (B1-Bn), and arcing is generated in switches (S1, S2) as mechanical relays; setting a connection or bypass state of the battery modules (M1-Mn) to a predetermined state by bypass switching units (B1-Bn); in a state in which the first condition is satisfied, oxide film removal processing for turning on / off switches (S1, S2), which are mechanical relays, is performed.

Description

Technical Field

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

[0002] A known power storage system includes a battery string comprising a plurality of storage batteries connected in series, and bypass circuits provided for each storage battery to switch the battery between a connected state and a bypass state (see, for example, Patent Document 1). In the power storage system described in Patent Document 1, bypass control is performed to bypass a storage battery that cannot discharge the required current, and discharge is performed from another storage battery.

[0003] Citation List

[0004] Patent Literature

[0005] Patent Document 1: JP2013-031247A Summary of the Invention

[0006] Technical issues

[0007] In the power storage system described in Patent Document 1, it is necessary to prevent large fluctuations in the input and output power of the power storage system during the execution of bypass control. In addition, in the power storage system described in Patent Document 1, since the total voltage of the battery string is applied to the switch of the bypass circuit when the bypass control is performed, it is necessary to use a switch with a high withstand voltage or provide a protection circuit for the switch. When providing a protection circuit for the switch, 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 performing bypass control after reducing the current of the battery string (hereinafter referred to as the string current) by a power converter is considered.

[0008] However, when a mechanical relay is used as a switch in a bypass circuit, if the switch is switched on and off after the string current decreases, arc discharge may not occur in the contacts of the mechanical relay. Since an oxide film forms on the contacts of the mechanical relay over time, when arc discharge does not occur in the contacts, the oxide film formed on the contacts is not removed, and contact failure may occur in the contacts.

[0009] In view of the foregoing, an object of the present invention is to provide a battery control device, a power storage system, and a battery control method that are capable of suppressing fluctuations in input and output power of the system and removing an oxide film from the contact portion of a mechanical relay of a bypass circuit in the power storage system. In the power storage system, a battery string includes a plurality of power storage cells connected in series and a plurality of bypass circuits provided for each of the power storage cells for switching the corresponding power storage cells between a connected state and a bypass state.

[0010] Solution to the problem

[0011] A battery control device according to an embodiment 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. The battery string includes a plurality of storage batteries connected in series, and a plurality of bypass circuits, each of the bypass circuits including a first switch provided between adjacent storage batteries, a bypass line that bypasses the first switch and the battery, and a second switch provided on the bypass line, and switches the battery between a connected state and a bypass state. At least one of the first and second switches is a mechanical relay, wherein the power converter sets the current of the battery string to a first predetermined value, and the plurality of bypass circuits sets the connected or bypass state of the plurality of storage batteries to a predetermined state, such that a total voltage of the battery string is equal to or less than a withstand voltage of the bypass circuit, and a first condition is satisfied. Under the first condition, arc discharge occurs in at least one of the first and second switches, which are mechanical relays. When the first condition is satisfied, an oxide film removal process is performed to open and close at least one of the first and second switches, which are mechanical relays.

[0012] According to an embodiment, a power storage system is a power storage system including: a battery string; a power converter configured to convert input and output power of the battery string; and a battery control device configured to control the battery string and the power converter, wherein the battery string includes: a plurality of batteries connected in series, and a plurality of bypass circuits, each of the bypass circuits including a first switch provided between the batteries adjacent to each other, a bypass line for bypassing the first switch and the battery, and a second switch provided on the bypass line, and switching the battery between a connected state and a bypass state, at least one of the first switch and the second switch One is a mechanical relay, and the battery control device sets the current of the battery string to a first predetermined value through the power converter, and sets the connection or bypass state of the plurality of batteries to a predetermined state through the plurality of bypass circuits, so that the total voltage of the battery string is equal to or less than the withstand voltage of the bypass circuit, and satisfies a first condition. Under the first condition, arc discharge occurs in at least one of the first switch and the second switch serving as the mechanical relay, and in the state where the first condition is satisfied, an oxide film removal process is performed to open and close the at least one of the first switch and the second switch serving as the mechanical relay.

[0013] The power storage system according to the embodiment is a power storage system including: a battery string; a power converter configured to convert input and output power of the battery string; and a battery control device configured to control the battery string and the power converter, wherein the battery string includes: a plurality of batteries connected in series, a plurality of bypass circuits, each of the bypass circuits including a first switch serving as a mechanical relay and provided between the batteries adjacent to each other, a bypass line for bypassing the first switch and the battery, and a second switch provided on the bypass line and switching the battery between a connected state and a bypass state, and a power storage and current suppression circuit connected between the first switch and the power converter corresponding to the battery at the starting end between the storage battery and the power converter at the terminal, and includes a storage unit and a current suppression unit, and the battery control device performs a first oxide film removal process after all the storage batteries are set to the bypass state by multiple bypass circuits, that is, any one of the storage batteries is switched to a connected state through any one of the bypass circuits, and when the battery control device performs the first oxide film removal process, the maximum value of the transient current flowing through the storage battery in the connected state, the first switch, and the storage and current suppression circuit is set so that the total voltage of the battery string is equal to or less than the withstand voltage of the bypass circuit, and satisfies a first condition, under which arc discharge occurs in the first switch.

[0014] The battery control method according to the embodiment is a battery control method executed by a battery control device that controls a power storage system, the power storage system including: a battery string, and a power converter that converts input and output power of the battery string, the battery string including: a plurality of batteries connected in series, and a plurality of bypass circuits, each of the bypass circuits including a first switch provided between the batteries adjacent to each other, a bypass line that bypasses the first switch and the battery, and a second switch provided on the bypass line, and switches the battery between a connected state and a bypass state, and at least one of the first switch and the second switch is a machine Mechanical relay, the battery control method includes: setting the current of the battery string to a first predetermined value through the power converter, and setting the connection or bypass state of the plurality of batteries to a predetermined state through the plurality of bypass circuits, so that the total voltage of the battery string is equal to or less than the withstand voltage of the bypass circuit, and satisfies a first condition, under which arc discharge occurs in at least one of the first switch and the second switch serving as the mechanical relay; and performing an oxide film removal process to open and close the at least one of the first switch and the second switch serving as the mechanical relay in a state where the first condition is satisfied.

[0015] Advantageous Effects of the Invention

[0016] According to the present invention, in a power storage system in which a battery string includes a plurality of storage batteries connected in series and a plurality of bypass circuits provided for each storage battery for switching the corresponding storage battery between a connected state and a bypass state, it is possible to suppress fluctuations in input and output power of the system and remove oxide films from the contact portions of mechanical relays of the bypass circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 FIG. 1 is a circuit diagram schematically showing a power storage system including a battery control device according to an embodiment of the present invention.

[0018] Figure 2 This is a flowchart showing a process of switching a battery module that is the target of a bypass control request from a connected state to a bypass state.

[0019] Figure 3 FIG. 1 is a flowchart illustrating an oxide film removal process according to another embodiment of the present invention.

[0020] Figure 4 is a circuit diagram schematically showing a power storage system according to another embodiment of the present invention.

[0021] Figure 5 It shows Figure 4 The illustrated flowchart is a process for the battery control device to switch a battery module, which is the target of a bypass control request, from a connected state to a bypass state. DETAILED DESCRIPTION

[0022] The present invention will be described below with reference to preferred embodiments. The present invention is not limited to the embodiments described below, and the embodiments may be modified as appropriate without departing from the gist of the present invention. In the embodiments described below, some configurations may not be described or shown in the drawings, and regarding omitted technical details, publicly known or well-known technologies may be appropriately applied as long as they do not contradict the contents described below.

[0023] Figure 1 FIG. 1 is a circuit diagram schematically showing a power storage system 1 including a battery control device 100 according to an embodiment of the present invention. Figure 1 As shown, the power storage system 1 includes a plurality of battery strings STR, a plurality of power converters PC, a string bus 3, and a battery control device 100. The plurality of battery strings STR are connected in parallel to each other via the string bus 3 and are also connected to an external system (not shown). The power storage system 1 is a stationary or vehicle-mounted power source.

[0024] The battery string STR includes n battery modules M1 to Mn (n is an integer of 2 or greater) connected in series. While not particularly limited, the battery modules M1 to Mn of this embodiment are obtained by recycling used batteries, and the degree of deterioration of the battery modules M1 to Mn varies. The battery modules M1 to Mn are formed by connecting multiple secondary battery cells, such as lithium-ion batteries and lithium-ion capacitors.

[0025] The battery modules M1 to Mn are charged by being supplied with electric power from an external system via the string bus 3 and the power converter PC. The battery modules M1 to Mn are charged by being supplied with electric power to an external system via the power converter PC and the string bus 3.

[0026] External systems include loads, generators, and other components. When power storage system 1 is a stationary power source, household appliances and commercial power systems serve as loads, while solar photovoltaic power generation systems and other components serve as generators. On the other hand, when power storage system 1 is an onboard power source, loads include the drive motor, air conditioner, and various onboard electrical components. The drive motor acts as both a load and a generator.

[0027] The battery string STR may include n battery cells or battery groups connected in series, rather than n battery modules M1 to Mn connected in series. In addition, the battery string STR may include bypass circuits that bypass each battery cell or each battery group.

[0028] The power converter PC is a DC / DC converter or a DC / AC converter and is connected to the string bus 3. The power converter PC is connected to the positive electrode of the storage battery module M1 at the starting end and the negative electrode of the storage module Mn at the terminal end.

[0029] When charging the battery string STR, the power converter PC converts the voltage received from the string bus 3 according to the indicated value of the charging power (or current) described later, and outputs the converted voltage to the multiple battery modules M1 to Mn. The voltage on the battery string STR side varies depending on the bypass status of the battery modules M1 to Mn (the number of bypassed battery modules M1 to Mn) and the charge state of the battery modules M1 and Mn. Therefore, when charging the battery string STR, the power converter PC converts the voltage received from the string bus 3 to the voltage on the battery string STR side, and outputs the converted voltage to the multiple battery modules M1 to Mn.

[0030] When the battery string STR is discharging, the power converter PC converts the voltage received from the multiple battery modules M1 to Mn according to the indicated value of the discharge power (or current) described later, and outputs the converted voltage to the string bus 3. The voltage input to the power converter PC during discharge varies depending on the bypass state of the battery modules M1 to Mn and the state of charge of the battery modules M1 to Mn. Therefore, during discharge, the voltage input to the power converter PC varies between the battery strings STR. Therefore, when the battery strings STR are discharging, each power converter PC converts the input voltage to a voltage that matches that of the other battery strings STR and outputs the converted voltage to the string bus 3.

[0031] The power converter PC is a bidirectional converter. When the current flowing through the string bus 3 is alternating current, the power converter PC includes a synchronization unit for tracking instantaneous value changes.

[0032] Each 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 large number of battery voltage sensors (not shown).

[0033] The voltage sensor 12 is connected between the positive and negative terminals of each battery module M1 to Mn, detects the voltage between the terminals of each battery module M1-Mn, and transmits a detection signal to each string controller 102 described later. The current sensor 13 is provided on the power line PL of the battery string STR, detects the string current, and transmits a detection signal to the string controller 102. The voltage sensor 14 is provided on the power line PL of the battery string STR, detects the total voltage of the battery string STR, and transmits a detection signal to the string controller 102.

[0034] A temperature sensor is provided for each battery module M1 to Mn to detect the temperature of each battery module M1 to Mn and transmit the detection signal to the string controller 102. In addition, a cell voltage sensor is provided for each battery cell (not shown) of each battery module M1 to Mn to detect the voltage of the battery cell and transmit the detection signal to the string controller 102.

[0035] Bypass switch units B1 to Bn are provided for each of the battery modules M1 to Mn. Each bypass switch unit 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 battery modules M1 to Mn and the switch S2. Switch S1 is provided on the bypass line BL. Switch S1 is a mechanical relay. Switch S2 is provided between the positive electrode of each battery module M1 to Mn and one end of the bypass line BL. Switch S2 is a mechanical relay.

[0036] The battery module M1 at the start and the battery module Mn at the end are connected to the external system via the power converter PC and the string bus 3. When the switch S1 in all bypass switch units B1 to Bn is open and the switch S2 is closed, all battery modules M1 to Mn are connected in series to the external system. On the other hand, when the switch S2 in any one of the bypass switch units B1 to Bn is open and the switch S1 is closed, the battery module M1 to Mn corresponding to the bypass switch unit B1 to Bn is bypassed.

[0037] Protection circuit 16 includes a Zener diode D11 and a diode D12 connected in parallel with switch S1, and a Zener diode D21 and a diode D22 connected in parallel with switch S2, and provides overvoltage protection for switches S1 and S2. The anode of Zener diode D11 is connected to the anode of diode D12. The anode of Zener diode D21 is connected to the anode of diode D22.

[0038] The cathode of the Zener diode D11 is connected to the bypass line BL between the switch S1 and the negative electrode of one of the battery modules M1 to Mn. On the other hand, the cathode of the diode D12 is connected to the bypass line BL between the switch S1 and the switch S2.

[0039] The cathode of the Zener diode D21 is connected to the power line PL between the switch S2 and the positive electrode of one of the battery modules M1 to Mn. On the other hand, the cathode of the diode D22 is connected to the bypass line BL between the switch S1 and the switch S2.

[0040] Here, when the protection circuit 16 is not provided, the voltage applied across the contacts of switch S2 when switch S2 is disconnected is the total voltage of the connected battery modules M1 to Mn and the battery modules M1 to Mn corresponding to switch S2. In this case, the withstand voltage of switch S2 needs to be equal to or higher than the total voltage of the n battery modules M1 to Mn (the voltage of the battery string STR when all battery modules M1 to Mn are connected). On the other hand, when the protection circuit 16 is provided, the voltage applied across the contacts of switch S2 when switch S2 is disconnected becomes the Zener voltage of Zener diode D21. In this case, the withstand voltage of switch S2 can be equal to or higher than the Zener voltage of Zener diode D21. From the perspective of suppressing the losses generated in the protection circuit 16 to the allowable loss or less, the input and output power of the power converter PC is reduced, and large current is prevented from flowing into the protection circuit 16.

[0041] When the protection circuit 16 is not provided, the voltage applied across the contacts of switch S1 when switch S1 is open is the total voltage of the connected battery modules M1 to Mn. In this case, the withstand voltage of switch S1 needs to be equal to or higher than the total voltage of the (n-1) battery modules M1 to Mn (the voltage of the battery string STR when all but one of the battery modules M1 to Mn are connected). On the other hand, when the protection circuit 16 is provided, the voltage applied across the contacts of switch S1 when switch S1 is open becomes the Zener voltage of Zener diode D11. In this case, the withstand voltage of switch S1 can be equal to or higher than the Zener voltage of Zener diode D11. The protection circuit 16 includes two sets: Zener diode D11 and diode D12 connected in parallel with switch S1, and Zener diode D21 and diode D22 connected in parallel with switch S2, but may include either set. In this case, the voltage applied to switch S2 is the sum of the voltages of the adjacent battery modules M1 to Mn. Therefore, the withstand voltage of the contacts of the switch S2 needs to be higher than the sum of the Zener voltage and the voltages of the battery modules M1 to Mn.

[0042] The storage battery control device 100 includes a plurality of string controllers 102, a plurality of relay drivers 103, and a system controller 101. The string controller 102 and the relay driver 103 are provided for each storage battery string STR.

[0043] The string controller 102 sends control signals to the relay drivers 103 and power converters PC of the corresponding battery strings STR. The relay drivers 103 control the switches S1 and S2 of the corresponding bypass switch units B1 to Bn based on the control signals sent from the corresponding string controller 102. The power converters PC convert the charge and discharge power of the corresponding battery strings STR based on the control signals sent from the corresponding string controller 102. Furthermore, the power converters PC control the string current of the corresponding battery strings STR based on the control signals from the corresponding string controller 102.

[0044] The string controller 102 detects and estimates the status of the corresponding battery string STR, notifies the system controller 101 of device control requests, and performs other tasks. Examples of detecting the status of the battery string STR include detecting the string current of the battery string STR based on the detection signal of the corresponding current sensor 13, detecting the total voltage of the battery string STR based on the detection signal of the corresponding voltage sensor 14, detecting the voltage of the battery modules M1 to Mn based on the detection signal of the voltage sensor 12, detecting the temperature of the battery modules M1 to Mn based on the detection signal from the temperature sensor, and detecting the voltage of the battery cells based on the detection signal of the cell voltage sensor. Examples of estimating the status of the battery string STR include estimating the state of charge (SOC) and state of health (SOH) of the battery modules M1 to Mn, and estimating the SOC and SOH of the battery string STR. Furthermore, examples of device control requests notified to the system controller 101 include switch control requests for opening and closing switches S1 and S2 of bypass switch units B1 to Bn, and control requests for the power converter PC.

[0045] Examples of methods for estimating SOH include a method based on charge and discharge testing, a method based on current integration method, a method based on open circuit voltage measurement, a method based on terminal voltage measurement, a model-based method (the above is a method using time changes in SOC), a method based on AC impedance measurement, an acquisition method using a model-based adaptive digital filter, a method based on IV characteristics (current-voltage characteristics) through linear regression (straight line slope of IV characteristics), and a method based on step response (the above is a method for estimating using an increase in internal resistance over time).

[0046] Examples of methods for estimating SOC include various known methods such as a current integration method, an open circuit voltage (OCV)-based acquisition method (voltage method), and a method combining the current integration method and the voltage method. OCV can be estimated using various known estimation methods that utilize temporal changes in terminal voltage or temporal increases in internal resistance.

[0047] The system controller 101 is a controller that comprehensively controls the entire power storage system 1 and performs 1:m communication with multiple string controllers 102. The system controller 101 monitors the status of the storage battery strings STR, determines whether to approve device control requests from the string controllers 102, and notifies the string controllers 102 of the approval of the device control requests. The system controller 101 sets an indicated value for the charge and discharge power (or current) of each storage battery string STR and transmits this indicated value to the string controllers 102.

[0048] The system controller 101 monitors the battery strings STR based on the detection and estimation results of the battery string STR status transmitted from the string controller 102. The system controller 101 then calculates an indicated value of charge and discharge power (or current) to be distributed to each battery string STR based on the input and output power (or current) instructions for the entire power storage system 1 received from a higher-level system (not shown) and the battery string STR status.

[0049] Here, when the system controller 101 permits a switching control request (hereinafter referred to as a bypass control request) for opening and closing switches S1 and S2 of bypass switch units B1 to Bn (hereinafter referred to as B') for any of the battery modules M1 to Mn (hereinafter referred to as M'), each string controller 102 performs switching control to open and close switches S1 and S2 of the bypass switch unit B'. At this time, before performing switching control to open and close switches S1 and S2 of the bypass switch unit B', the string controller 102 performs a protection and oxide film removal process to protect the protection circuit 16 and remove the oxide film formed on the contact portions of switches S1 and S2.

[0050] The protection and 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 reduces the string current to a second predetermined value. The second predetermined value is lower than the first predetermined value (described later) and is set to a low value that suppresses fluctuations in the input and output power of the entire power storage system 1 within an allowable range during bypass control of the battery string STR. In this embodiment, the second predetermined value is 0, and when the string current is zero, the "second condition" is satisfied.

[0051] Here, during the string current reduction process, the string controller 102 gradually and continuously reduces the indicated value of the string current from its current value to a second predetermined value. Specifically, the string controller 102 repeatedly updates the indicated value of the string current by a predetermined amount ΔP1 obtained by equally dividing the difference between the current indicated value of the string current and the second predetermined value. At this time, the rate of change of the indicated value of the string current (the amount of change per change) is set to a level that suppresses fluctuations in the input and output power of the entire power storage system 1 within an allowable range. Therefore, the power converter PC gradually and continuously reduces the indicated value of the string current from its current value to the second predetermined value to suppress fluctuations in the input and output power of the entire power storage system 1 within an allowable range.

[0052] The bypass state switching process is a process for switching the states of the switches S1 and S2 of the bypass switch units B1 to Bn (hereinafter referred to as B") corresponding to the battery modules M1 to Mn (hereinafter referred to as M") that are not the objects 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 plurality of battery modules M" so as to satisfy the "first condition" of the battery string STR. The "first condition" refers to the condition that the total voltage of the 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 and S2 serving as mechanical relays. That is, the string controller 102 determines the connection or bypass state of the plurality of battery modules M" so that the total voltage of the 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. In addition, the string controller 102 sets the string current to the "first predetermined value" in the string current increase process described later so that arc discharge occurs in the switches S1 and S2 when the oxide film removal process is performed. Note that the battery module M″ to be connected is selected according to a priority order determined based on a predetermined standard. Here, in the discharge mode, at least one battery module M″ that is not the target of the bypass control request is set to the connected state.

[0053] The string current increasing process is a process of increasing the string current from a second predetermined value to a first predetermined value. The first predetermined value is set to a value at which arc discharge occurs in the contact portions of switches S1 and S2 during operation of the mechanical relays and an oxide film formed on the contact portions can be removed.

[0054] Here, during the string current increase process, the string controller 102 gradually and continuously increases the string current indicated value from its current value (the second predetermined value) to the first predetermined value. Specifically, the string controller 102 repeatedly updates the string current indicated value by a predetermined amount ΔP2 obtained by equally dividing the difference between the current string current indicated value and the first predetermined value. At this time, the rate of change of the string current indicated value is set to a level that suppresses fluctuations in the input and output power of the entire power storage system 1 within an allowable range. Therefore, the power converter PC gradually and continuously increases the string current indicated value from its current value to the first predetermined value to suppress fluctuations in the input and output power of the entire power storage system 1 within an allowable range.

[0055] The oxide film removal process is a process in which, when a first condition is satisfied, arc discharge is generated in the contact portions of switches S1 and S2 of bypass switch unit B' to remove the oxide film formed on the contact portions. Specifically, when a string current of a first predetermined value flows through switch S2 of bypass switch unit B', string controller 102 switches switch S2 from closed to open, then from open to closed, and further from closed to open. Furthermore, when a string current of a first predetermined value flows through switch S1 of bypass switch unit B', string controller 102 switches switch S1 from closed to open, then from open to closed, and further from closed to open.

[0056] Before executing the protection and oxide film removal process, the string controller 102 records the connection or bypass status of the battery modules M1 to Mn of the battery string STR at the current point in time in a built-in memory (not shown). After executing the protection and oxide film removal process, the string controller 102 switches the on / off status of switches S1 and S2 of the bypass switch unit B", so that the connection or bypass status of the battery module M", which is not the subject of the bypass control request, returns to the status recorded in the memory. At this time, the string controller 102 switches the on / off status of switches S1 and S2 of the bypass switch unit B', so that the battery module M', which is the subject of the bypass control request, is in the bypass state.

[0057] Figure 2 This flowchart illustrates the process of switching a battery module M', the subject 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 battery modules M1 to Mn in the battery string STR and determines whether any of the battery modules M1 to Mn require bypass control. If the determination in step S1 is yes, the process proceeds to step S2. If the determination in step S1 is no, the process ends.

[0058] In step S2, the string controller 102 sends a bypass control request to the system controller 101 and determines whether a permission notification of the bypass control request is received from the system controller 101. If the determination in step S2 is yes, the process proceeds to step S3, and if the determination in step S2 is no, the process ends.

[0059] In step S3, the string controller 102 records the connection or bypass status of the battery modules M1 to Mn of the battery string STR at the current point in time in a built-in 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 by a predetermined amount ΔP1 to the second predetermined value.

[0060] First, in step S4, the string controller 102 updates the indicated value of the string current to a value reduced by a predetermined amount ΔP1. The predetermined amount ΔP1 is set to a small value to prevent sudden changes in the input and output power of the power storage system 1. When the difference between the current value of the string current and the second predetermined value is small, the predetermined amount ΔP1 may be equal to the difference between the current value of the string current and the second predetermined value. On the other hand, when the difference between the current value of the string current and the second predetermined value is relatively large, the predetermined amount ΔP1 may be smaller than the difference between the current value of the string current and the second predetermined value. When the 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.

[0061] Next, in step S5, after sending the indicated value of the string current to the power converter PC, the string controller 102 waits for a predetermined time T1. The predetermined time T1 is set in consideration of the time required for the string controller 102 to control the power converter PC and the speed of change of the string current.

[0062] Next, in step S6, the string controller 102 determines whether the string current has reached the second predetermined value (whether the string current reduction has been completed). If the determination in step S6 is yes, the process proceeds to step S7, and if the determination in step S6 is no, the process proceeds to step S4.

[0063] In steps S7 and S8, the string controller 102 performs bypass state switching processing. First, in step S7, the string controller 102 determines the connection or bypass state of the battery modules M'' that are not the subject of the bypass control request. In step S7, the battery modules M'' to be set to the connection state and the battery modules M'' to be set to the bypass state are determined so that when the string current of the first predetermined value flows, the total voltage of the battery string STR is equal to or lower than the withstand voltage of the protection circuit 16.

[0064] Next, in step S8, the string controller 102 switches the switches S1 and S2 of the bypass switch unit B" on / off, so that the connection or bypass state of the battery module M" that is not the object of the bypass control request is switched to the state determined in step S7. Next, in step S9, the string controller 102 switches the switches S1 and S2 of the bypass switch unit B' on / off, so that the battery module M' that is the object of the bypass control request is in the connected state.

[0065] Next, the string controller 102 repeatedly executes the loop process of steps S10 to S12 until the indicated value of the string current reaches the first predetermined value (string current increase process). Here, in steps S10 to S12, the string controller 102 gradually and continuously increases the indicated value of the string current from the current value by a predetermined amount ΔP2 to the first predetermined value.

[0066] First, in step S10, the string controller 102 updates the indicated value of the string current to a value increased by a predetermined amount ΔP2. The predetermined amount ΔP2 is set to a small value to prevent sudden changes in the input and output power of the power storage system 1. When the difference between the current value of the string current and the first predetermined value is small, the predetermined amount ΔP2 may be equal to the difference between the current value of the string current and the first predetermined value. On the other hand, when the difference between the current value of the string current and the first predetermined value is relatively large, the predetermined amount ΔP2 may be smaller than the difference between the current value of the string current and the first predetermined value. When the 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 repeatedly updated multiple times.

[0067] Next, in step S11, after sending the instruction value of the string current to the power converter PC, the string controller 102 waits for a predetermined time T2. The predetermined time T2 is set in consideration of the time required for the string controller 102 to control the power converter PC and the speed of change of the string current.

[0068] Next, in step S12, the string controller 102 determines whether the indicated value of the string current has reached the first predetermined value (whether the increase in the string current has been completed). If the determination in step S12 is yes, the process proceeds to step S13, and if the determination in step S12 is no, the process proceeds to step S10.

[0069] In steps S13 and S14, the string controller 102 performs an oxide film removal process. First, in step S13, the string controller 102 switches switch S2 of the bypass switch unit B' from closed to open (S13-1 in Table 1 below) while a string current of a first predetermined value flows through the switch S2. Then, the string controller 102 switches switch S2 from open to closed (S13-2 in Table 1 below), and then from closed to open (S13-3 in Table 1 below). As a result, arc discharge occurs in the contact portion of switch S2, and the oxide film formed at the contact portion is removed.

[0070] Next, in step S14, the string controller 102 switches the switch S1 of the bypass switch unit B' from open to closed so that the string current of the first predetermined value flows to 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 closed to open (S14-2 in Table 1 below), then switches from open to closed (S14-3 in Table 1 below), and further switches from closed to open (S14-4 in Table 1 below). Therefore, arc discharge occurs in the contact portion of the switch S1, and the oxide film formed at the contact portion is removed. It is not necessary to switch the switches S1 and S2 from closed to open, from open to closed, and from closed to open. For example, the switches S1 and S2 can be switched from closed to open or from open to closed only once.

[0071] [Table 1]

[0072]

[0073] Next, in step S15, the string controller 102 switches the on / off states of switches S1 and S2 of the bypass switch unit B" to restore the connection or bypass state of the battery module M", which is not the subject of the bypass control request, to the state recorded in the memory in step S3. At this time, the string controller 102 switches the on / off states of switches S1 and S2 of the bypass switch unit B' to place the battery module M', which is the subject of the bypass control request, in the bypass state. The process then ends.

[0074] As described above, the battery control device 100 of this embodiment sets the string current to a first predetermined value via the power converter PC and sets the connection or bypass status of the multiple battery modules M1 to Mn to a predetermined state via the multiple bypass switch units B1 to Bn. As a result, the total voltage of the battery string STR is equal to or lower than the withstand voltage of the bypass switch units B1 to Bn, and the first condition for arc discharge to occur at the contacts of the switches S1 and S2, which function as mechanical relays, is satisfied. Then, while the first condition is satisfied, the battery control device 100 performs an oxide film removal process, opening and closing the switches S1 and S2, which function as mechanical relays. Thereafter, the battery control device 100 performs bypass control of the battery module M', which is the subject of the bypass control request. Furthermore, the battery control device 100 restores the connection or bypass status of the battery module M'', which is not the subject of the bypass control request, to its original state.

[0075] Specifically, the battery control device 100 of this embodiment reduces the string current to a first predetermined value via the power converter PC, and then executes bypass control of the battery module M' that is the subject of the bypass control request. This prevents large fluctuations in the input and output power of the power storage system 1 that exceed the permissible range from occurring during bypass control.

[0076] Furthermore, the battery control device 100 of this embodiment sets the string current to a predetermined first value, through the power converter PC, at which arc discharge occurs at the contacts of switches S1 and S2, and then switches switches S1 and S2 on and off. This removes the oxide film formed on the contacts of switches S1 and S2, which function as mechanical relays.

[0077] Furthermore, the battery control device 100 of this embodiment sets the battery modules M1 to Mn in a connected or bypassed state during the oxide film removal process 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 to Bn. Therefore, even when the withstand voltage of the protection circuit 16 and switches S1 and S2 is set lower than the total voltage of the battery string STR, overvoltage can be prevented from being applied to the protection circuit 16 and switches S1 and S2 of the bypass switch units B1 to Bn, which are the targets of the oxide film removal process, during the oxide film removal process. Consequently, low-cost Zener diodes or mechanical relays with low withstand voltages can be used for the protection circuit 16 and switches S1 and S2 of the bypass switch units B1 to Bn, reducing the cost of the bypass switch units B1 to Bn.

[0078] The battery control device 100 of this embodiment reduces the string current to a second predetermined value via the power converter PC to satisfy the second condition. Thereafter, while the second condition is satisfied, the battery control device 100 sets the connection or bypass state of the battery modules M1 to Mn via the plurality of bypass switch units B1 to Bn to a "predetermined state" that takes into account the withstand voltages of the bypass switch units B1 to Bn and the total voltage of the battery string STR.

[0079] Here, the second predetermined value is lower than the first predetermined value and is set low enough to suppress fluctuations in the input and output power of the power storage system 1 within an allowable range when bypass control of the battery modules M1 to Mn is executed by the bypass switch units B1 to Bn. Therefore, when the connection or bypass state of the battery modules M1 to Mn is switched to the "predetermined state" by the bypass switch units B1 to Bn while the second condition is satisfied, fluctuations in the input and output power of the power storage system 1 can be suppressed within an allowable range.

[0080] In the power 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. Furthermore, the battery control device 100 sets the total voltage of the battery string STR during oxide film removal processing so as not to exceed the allowable loss of the protection circuit 16. Consequently, the withstand voltage of the switches S1 and S2 can be set higher than the Zener voltage of the protection circuit 16, while the withstand voltage of the switches S1 and S2 can be set lower than the total voltage of the battery string STR. Consequently, the cost of the switches S1 and S2 can be reduced.

[0081] The battery control device 100 of this embodiment gradually and continuously changes the string current indicated value while changing the string current to a first predetermined value. Specifically, the battery control device 100 repeatedly changes the string current indicated value toward the first predetermined value by an amount less than the difference between the first predetermined value and the current value (predetermined amount ΔP2) until the indicated value reaches the first predetermined value. Consequently, when the string current reaches the first predetermined value, fluctuations in the input and output power of the power storage system 1 can be suppressed within an allowable range.

[0082] The battery control device 100 of this embodiment gradually and continuously changes the string current indication value when changing the string current to the second predetermined value. Specifically, the battery control device 100 repeatedly changes the string current indication value toward the second predetermined value by an amount less than the difference between the second predetermined value and the current value (predetermined amount ΔP1) until the indication value reaches the second predetermined value. Therefore, when the string current reaches the second predetermined value, fluctuations in the input and output power of the power storage system 1 can be suppressed within an allowable range.

[0083] The battery control device 100 of this embodiment records the current connection or bypass status of the battery modules M1 to Mn in its internal memory before switching the current connection or bypass status of the battery modules M1 to Mn to the "predetermined status" via the bypass switch units B1 to Bn. After performing the oxide film removal process, the battery control device 10 restores the connection / bypass status of the battery modules M1 to Mn to the status recorded in the memory via the bypass switch units B1 to Bn, excluding the battery module M' that is the target of bypass control. This allows the oxide film on the switches S1 and S2 to be removed, and after the oxide film removal process, the connection or bypass status of the battery modules M1 to Mn can be restored to the desired state.

[0084] Figure 3: is a flowchart showing an oxide film removal process according to another embodiment of the present invention. The process shown in the flowchart is a process for removing the oxide film of the switches S1 and S2 of the bypass switch unit B" corresponding to the battery module M" that is not the object of the bypass control request. First, in step S101, the string controller 102 monitors the battery modules M1 to Mn of the battery string STR and determines whether there is a battery module M' that requires bypass control. If it is determined to be no in step S101, the process proceeds to step S102, and if it is determined to be yes in step S101, the process ends. When there is a battery module M' that requires bypass control (yes in step S101), execute Figure 2 The processing of steps S2 to S15 in .

[0085] In step S102, the connection or bypass status of the battery modules M1 to Mn of the battery string STR at the current point in time is recorded in a built-in 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 by a predetermined amount ΔP3 to the third predetermined value.

[0086] First, in step S103, the string controller 102 updates the indicated value of the string current to a value reduced by a predetermined amount ΔP3. The predetermined amount ΔP3 is set to a small value to prevent sudden changes in the input and output power of the power storage system 1. When the difference between the current value of the string current and the third predetermined value is small, the predetermined amount ΔP3 may be equal to the difference between the current value of the string current and the third predetermined value. On the other hand, when the difference between the current value of the string current and the third predetermined value is relatively large, the predetermined amount ΔP3 may be smaller than the difference between the current value of the string current and the third predetermined value. When the 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.

[0087] The third predetermined value is set to a value that satisfies the conditions of the first and second predetermined values ​​described above. Specifically, the third predetermined value is set to a value that suppresses fluctuations in the input and output power of the entire power storage system 1 within an allowable range during bypass control of the battery modules M1 to Mn, and at which arc discharge occurs at the contact portion of switches S1 and S2 when they are switched between open and closed.

[0088] Next, in step S104, the string controller 102 waits for a predetermined time T3 after sending the instruction value of the string current to the power converter PC. The predetermined time T3 is set in consideration of the time required for the string controller 102 to control the power converter PC and the speed of change of the string current.

[0089] Next, in step S105, the string controller 102 determines whether the indicated value of the string current has reached a third predetermined value (whether the reduction of the string current has been completed). If the determination in step S105 is yes, the process proceeds to step S106, and if the determination in step S105 is no, the process proceeds to step S103.

[0090] Next, in step S106 , the string controller 102 switches on / off the switches S1 and S2 of the bypass switch units B1 to Bn corresponding to the battery modules M1 to Mn so that the battery modules M1 to Mn targeted for the oxide film removal process are in a connected state.

[0091] Next, in steps S107 and S108, the string controller 102 performs an oxide film removal process. First, in step S107, the string controller 102 switches switch S2 from closed to open (S107-1 in Table 2 below) while a string current of a third predetermined value flows through each switch S2 of the bypass switch units B1 to Bn, which are the targets of the oxide film removal process. The string controller 102 then switches switch S2 from open to closed (S107-2 in Table 2 below), and then from closed to open (S107-3 in the table below). As a result, arc discharge occurs at the contact portion of switch S2, and the oxide film formed at the contact portion is removed.

[0092] Next, in step S108, the string controller 102 switches each switch S1 of the bypass switch units B1 to Bn, which are the targets of the oxide film removal process, from open to closed, and allows a string current of a third predetermined value to flow through the switch S1 (S108-1 in Table 2 below). The string controller 102 then switches the switch S1 from closed to open (S108-2 in Table 2 below), then from open to closed (S108-3 in Table 2 below), and further from closed to open (S108-4 in Table 2 below). As a result, arc discharge occurs at the contact portion of the switch S1, and the oxide film formed at the contact portion is removed.

[0093] [Table 2]

[0094]

[0095] Next, in step S109 , the string controller 102 switches the switches S1 and S2 of the bypass switch units B1 to Bn on / off so that the connection or bypass state of the battery modules M1 to Mn returns to the state recorded in the memory in step S102 .

[0096] As described above, in the process of this embodiment, after the string current is reduced to the third predetermined value by the power converter PC, bypass control is performed on the battery modules M1 to Mn that are not the targets of the oxide film removal process. Therefore, it is possible to prevent the input and output power of the power storage system 1 from fluctuating significantly beyond the allowable range during the execution of bypass control.

[0097] In the process of this embodiment, power converter PC sets the string current to a third predetermined value at which arc discharge occurs at the contact portion of switches S1 and S2, and switches switches S1 and S2 on and off. This removes the oxide film formed at the contact portion of switches S1 and S2, which function as mechanical relays.

[0098] Furthermore, in the process of this embodiment, even when the withstand voltage of the protection circuit 16 and the switches S1 and S2 is set to be lower than the total voltage of the battery string STR, it is possible to prevent overvoltage from being applied to the protection circuit 16 and the switches S1 and S2 of the bypass switch cells B1 to Bn, which are the targets of the oxide film removal process, during the oxide film removal process. Therefore, it is possible to use low-cost Zener diodes or mechanical relays with low withstand voltage for the protection circuit 16 and the switches S1 and S2 of the bypass switch cells B1 to Bn, and the cost of the bypass switch cells B1 to Bn can be reduced.

[0099] Figure 4 2 is a circuit diagram schematically showing a power storage system 2 according to another embodiment of the present invention. The same components as those in the above embodiment are denoted by the same reference numerals, and the description of the above embodiment is incorporated into the same.

[0100] like Figure 4 As shown, in the power storage system 2 of this embodiment, each battery string STR includes a string disconnect switch 11 and a CR circuit 15. The string disconnect switch 11 is provided between each power converter PC and the battery module M1 at the starting end. The string disconnect switch 11 connects or disconnects the power converter PC and the battery module M1 at the starting end. The purpose of providing the string disconnect switch 11 is to prevent the charge of the capacitor C described later from flowing to the power converter PC. For example, in cases where the above purpose can be achieved without the string disconnect 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 brought into a relatively high state relative to the impedance of the battery string STR, the string disconnect switch 11 may not be provided.

[0101] CR circuit 15 includes a capacitor C and a resistor R connected in series. One end of resistor R is connected to capacitor C, and the other end of resistor R is connected to power line PL between string disconnect switch 11 and bypass switch unit B1 at the starting end. On the other hand, capacitor C is connected to power line PL between bypass switch unit Bn and power converter PC at the ending end.

[0102] Figure 4 The figure shows the state before bypass control of battery module M1 is executed, when battery module M1 is the target battery module M' for a bypass control request. In this state, battery module M1 is connected, with switch S1 open and switch S2 closed in bypass switch unit B1. Meanwhile, battery modules M2 through Mn are in bypass mode, with switch S1 closed and switch S2 open in bypass switch units B2 through Bn. The string disconnect switch 11 is open.

[0103] In this state, a transient current flows from the positive electrode of the 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 battery module M1 via the switches S1 of the bypass switch units B2 to Bn. Figure 4 In the illustrated state, the maximum value of the transient current flowing through the battery module M1, the switch S2 of the bypass switch unit B1, the CR circuit 15, and the like, charging the capacitor C, is set to a first predetermined value. This "first predetermined value" is set to a value at which, during the operation of the switch S2, which functions as a mechanical relay, the transient current flowing through the battery module M1, the switch S2 of the bypass switch unit B1, the CR circuit 15, and the like, causes arc discharge at the contacts of the switch S2, charging the capacitor C and removing the oxide film formed on the contacts. This "first predetermined value" is set so that, when the transient current flows through the battery module M1, the switch S2, the CR circuit 15, and the like, the total voltage of the battery string STR does not exceed the allowable loss of the protection circuit 16.

[0104] The battery control device 200 switches the battery module M1 from Figure 4 The connection state shown is switched to the bypass state. 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, when the battery module M1 is switched to the bypass state, the maximum value of the transient current flowing through the capacitor C, the switch S1 of the bypass switch unit B1, and the like is set to a fourth predetermined value. The "fourth predetermined value" is set to a value at which, during operation of the switch S1, which functions as a mechanical relay, arc discharge occurs in the contacts of the switch S1 due to the transient current flowing through the capacitor C, the switch S1, and the like, and the oxide film formed on the contacts can be removed. The "fourth predetermined value" is set so that when the transient current flows through the capacitor C, the switch S1, and the like, the total voltage of the battery string STR does not exceed the allowable loss of the protection circuit 16.

[0105] Figure 5 It shows Figure 4The flowchart shown is a process by which the battery control device 200 switches the battery module M', which is the subject of a bypass control request, from a connected state to a bypass state. This process will be described using the case where the battery module M', which is the subject of the bypass control request, is the battery module M1. However, the same process can be performed on other battery modules M2 through Mn. Furthermore, it is not essential to perform the oxide film removal process on the battery module M', which is the subject of the bypass control request; it is sufficient to appropriately determine the battery modules M1 through Mn for which the oxide film removal process is performed and the timing for performing the oxide film removal process.

[0106] First, in step S201, the string controller 102 monitors the battery modules M1 to Mn of the battery string STR and determines whether there is a battery module M' that requires bypass control. If the determination in step S201 is yes, the process proceeds to step S202. If the determination in step S202 is no, the process ends.

[0107] In step S202, the string controller 102 sends a bypass control request to the system controller 101 and determines whether a permission notification of the bypass control request is received from the system controller 101. If the determination in step S202 is yes, the process proceeds to step S203, and if the determination in step S202 is no, the process ends.

[0108] In step S203, the string controller 102 records the connection or bypass status of the battery modules M1 to Mn of the battery string STR at the current point in time in a built-in memory (not shown). Next, the string controller 102 repeats the loop processing of steps S204 to S206 until the indicated value of the string current reaches a second predetermined value (string current reduction process). The "second predetermined value" is a value lower than the "first predetermined value" and "fourth predetermined value" described above and is set to a low value to suppress fluctuations in the input and output power of the entire power storage system 1 within an allowable range during bypass control of the 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 indicated value of the string current from the current value by a predetermined amount ΔP1 to the second predetermined value.

[0109] First, in step S204, the string controller 102 updates the indicated value of the string current to a value reduced by a predetermined amount ΔP1. The predetermined amount ΔP1 is set to a small value to prevent sudden changes in the input and output power of the power storage system 1. When the difference between the current value of the string current and the second predetermined value is small, the predetermined amount ΔP1 may be equal to the difference between the current value of the string current and the second predetermined value. On the other hand, when the difference between the current value of the string current and the second predetermined value is relatively large, the predetermined amount ΔP1 may be smaller than the difference between the current value of the string current and the second predetermined value. When the 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.

[0110] Next, in step S205, the string controller 102 waits for a predetermined time T1 after sending the instruction value of the string current to the power converter PC. The predetermined time T1 is set in consideration of the time required for the string controller 102 to control the power converter PC and the speed of change of the string current.

[0111] Next, in step S206, the string controller 102 determines whether the string current has reached the second predetermined value (whether the string current reduction has been completed). If the determination in step S206 is yes, the process proceeds to step S207, and if the determination in step S206 is no, the process proceeds to step S204.

[0112] In step S207 , the string controller 102 opens (opens) the string disconnect switch 11 . When the string current is sufficiently reduced by the power converter PC, it is not necessary to disconnect the battery string STR by the string disconnect switch 11 .

[0113] Next, in step S208, the string controller 102 sets the battery modules M2 to Mn that are not the targets of the bypass control request to the bypass state (see Figure 4 Next, in step S209, the string controller 102 connects the battery module M1, which is the target of the bypass control request. Specifically, switch S1 of the bypass switch unit B1 is opened, and then switch S2 of the bypass switch unit B1 is closed. At this point, a transient current flows through the battery module M1, switch S2 of the bypass switch unit B1, CR circuit 15, and so on, causing arc discharge at the contact of switch S2 of the bypass switch unit B1, and removing the oxide film formed on the contact.

[0114] Next, in step S210, the string controller 102 waits for a predetermined time T4 starting from step S209. The 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 until the CR circuit 15 escapes transients and reaches a steady state, and is obtained based on the time constant τ (=C×R).

[0115] Next, in step S211, the string controller 102 switches the 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, the switch S1 of the bypass switch unit B1, and so on, causing arc discharge at the contact of the switch S1 of the bypass switch unit B1, and removing the oxide film formed on the contact.

[0116] Next, in step S212 , the string controller 102 waits for a predetermined time T5 from step S211 . The 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 obtained based on the time constant τ (=C×R).

[0117] Next, in step S213, the string controller 102 switches the on / off states of switches S1 and S2 of the bypass switch units B2 to Bn to restore the connection or bypass state of the battery modules M2 to Mn that are not the subject of the bypass control request to the state recorded in the memory in step S203. The process then ends.

[0118] As described above, in the power storage system 2 of this embodiment, the battery string STR includes a CR circuit 15 connected between the switch S2 corresponding to the battery module M1 at the starting end and the power converter PC, and between the battery module Mn and the power converter PC at the ending end. In the power storage system 2, the battery control device 200 performs the following first oxide film removal process.

[0119] (First Oxide Film Removal Process)

[0120] All the battery modules M1 to Mn are set to the bypass state by the plurality of bypass switch units B1 to Bn, and then any one of the battery modules M1 is switched to the connection state by any one of the bypass switch units B1.

[0121] Here, when battery control device 200 performs the first oxide film removal process, the maximum value of the transient current flowing through the connected battery module M1, the switch S2 of the bypass switch unit B1, the CR circuit 15, and the like is set so that the total voltage of the battery string STR is equal to or less than the withstand voltage of the bypass switch units B1 to Bn and the first condition for arc discharge to occur in the switch S2 of the bypass switch unit B1 is satisfied. Therefore, during the execution of the first oxide film removal process, the transient current flowing through any one of the battery module M1, the switch S2 of the bypass switch unit B1, the CR circuit 15, and the like causes an arc discharge in the switch S2 of the bypass switch unit B1, and the oxide film formed on the switch S2 can be removed.

[0122] The battery control device 200 performs the following second oxide film removal process.

[0123] (Second Oxide Film Removal Process)

[0124] After the first oxide film removal process is performed, any one of the bypass switch units B1 switches the battery module M1 in the connected state to the bypass state.

[0125] Here, when battery control device 200 performs the second oxide film removal process, the maximum value of the transient current flowing through CR circuit 15, switch S1 of bypass switch unit B1, and the like is set so that the total voltage of battery string STR is equal to or less than the withstand voltage of bypass switch units B1 to Bn and the second condition for arc discharge to occur in switch S1 of bypass switch unit B1 is satisfied. Therefore, during the execution of the second oxide film removal process, the transient current flowing through CR circuit 15, switch S1 of bypass switch unit B1, and the like causes arc discharge to occur in switch S1 of bypass switch unit B1, and the oxide film formed on switch S1 can be removed.

[0126] Although the present invention has been described above based on the above embodiments, the present invention is not limited to the above embodiments, and modifications can be made without departing from the gist of the present invention, or known or well-known technologies can be appropriately combined.

[0127] For example, in the above embodiment, switches S1 and S2 are mechanical relays, but at least one of switches S1 and S2 may be a semiconductor switch. In this case, the oxide film removal process may be performed on only one of switches S1 and S2 that is a mechanical relay.

[0128] The timing for performing the oxide film removal process and the battery modules M1 to Mn to be subjected to the oxide film removal process can be appropriately set. Furthermore, it is not necessary to provide the protection circuit 16 in the bypass switch units B1 to Bn. When the protection circuit 16 is not provided, the total voltage of the battery string STR during the oxide film removal process can be set to be equal to or lower than the withstand voltage of the switches S1 and S2 serving as mechanical relays.

[0129] In the above embodiment, the string current indication value is gradually and continuously changed to the target value by predetermined amounts ΔP1, ΔP2, and ΔP3 over time. However, for example, when the change in string current has little effect on the input and output power of power storage system 1, the string current indication value may be changed all at once.

[0130] In addition, in the above embodiment, the CR circuit 15 is illustrated as a power storage and current suppression circuit, but the power storage and current control circuit only needs to have the function of storing charge and the function of suppressing current. For example, a constant current diode or a current control circuit can be set instead of the resistor R.

[0131] Although various embodiments have been described above, it goes without saying that the present invention is not limited to these examples. Obviously, those skilled in the art may propose various modifications or corrections within the scope of the claims, and it should be understood that such modifications or corrections naturally fall within the technical scope of the present invention. In addition, the components described in the above embodiments may be freely combined without departing from the gist of the present invention.

[0132] This application is based on Japanese patent application (No. 2023-38380) filed on March 13, 2023, the contents of which are incorporated herein by reference.

[0133] Reference Symbol List

[0134] 1: Power storage system

[0135] 2: Power storage system

[0136] 15: CR circuit (electricity storage and current suppression circuit)

[0137] 16: Protection circuit

[0138] 100: Battery control device

[0139] 200: Battery control device

[0140] B1 to Bn, B', B": Bypass switch unit (bypass circuit)

[0141] BL: Bypass line

[0142] M1 to Mn, M', M": Battery modules (batteries)

[0143] PC: Power Converter

[0144] S1: switch (second switch, mechanical relay)

[0145] S2: switch (first switch, mechanical relay)

[0146] STR: battery string

[0147] ΔP1: Predetermined amount (small change)

[0148] ΔP2: Predetermined amount (small change)

[0149] ΔP3: Predetermined amount (small change)

Claims

1. A battery control device that controls a power storage system. The power storage system includes: Battery strings, and a power converter that converts input and output power of the battery string, The battery string comprises: multiple batteries connected in series, and A plurality of bypass circuits, each of the bypass circuits including a first switch provided between adjacent storage batteries, a bypass line for bypassing the first switch and the storage battery, and a second switch provided on the bypass line, and switching the storage battery between a connected state and a bypass state, wherein At least one of the first switch and the second switch is a mechanical relay, The current of the battery string is set to a first predetermined value through the power converter, and the connection or bypass state of the plurality of batteries is set to a predetermined state through the plurality of bypass circuits, so that the total voltage of the battery string is equal to or less than the withstand voltage of the bypass circuit, and a first condition is satisfied, under which arc discharge occurs in at least one of the first switch and the second switch, which are mechanical relays, and In a state where the first condition is satisfied, an oxide film removal process is performed to open and close at least one of the first switch and the second switch as a mechanical relay.

2. The battery control device according to claim 1, wherein: reducing the current of the battery string by the power converter to satisfy a second condition, wherein the current of the battery string is a second predetermined value lower than the first predetermined value under the second condition; In a state where the second condition is satisfied, the connection or bypass state of the plurality of batteries is set to the predetermined state through the plurality of bypass circuits, and In a state where the connection or bypass state of the plurality of storage batteries is set to the predetermined state, the current of the storage battery string is increased to the first predetermined value by the power converter, and the first condition is satisfied.

3. The battery control device according to claim 1 or 2, wherein: The bypass circuit includes a protection circuit for protecting at least one of the first switch and the second switch from overvoltage, and The withstand voltage of the bypass circuit is equal to or higher than the Zener voltage of the protection circuit.

4. The battery control device according to claim 1 or 2, wherein: When the current of the battery string is changed to the first predetermined value, the following process is repeatedly performed until the indicated value reaches the first predetermined value: the indicated value of the current of the battery string is changed toward the first predetermined value by an amount smaller than a difference between the first predetermined value and a current value.

5. The battery control device according to claim 2, wherein: When the current of the battery string is changed to the second predetermined value, the following process is repeatedly performed until the indicated value reaches the second predetermined value: the indicated value of the current of the battery string is changed toward the second predetermined value by an amount smaller than a difference between the second predetermined value and a current value.

6. The battery control device according to claim 1 or 2, wherein: Before setting the connection or bypass state of the plurality of storage batteries to the predetermined state through the plurality of bypass circuits, recording the connection or bypass state of the plurality of storage batteries at a current point in time in a storage unit, and After the oxide film removal process is performed, the connection or bypass state of the plurality of batteries, except for the battery that needs to be switched between the connection state and the bypass state, is restored to the state recorded in the storage unit through the plurality of bypass circuits.

7. A power storage system comprising: Battery string; a power converter configured to convert input and output power of the battery string; as well as A battery control device configured to control the battery string and the power converter, wherein: The battery string comprises: multiple batteries connected in series, and a plurality of bypass circuits, each of the bypass circuits including a first switch provided between adjacent storage batteries, a bypass line for bypassing the first switch and the storage battery, and a second switch provided on the bypass line, and switching the storage battery between a connected state and a bypass state; At least one of the first switch and the second switch is a mechanical relay, and The battery control device The current of the battery string is set to a first predetermined value through the power converter, and the connection or bypass state of the plurality of batteries is set to a predetermined state through the plurality of bypass circuits, so that the total voltage of the battery string is equal to or less than the withstand voltage of the bypass circuit, and a first condition is satisfied, under which arc discharge occurs in at least one of the first switch and the second switch, which are mechanical relays, and In a state where the first condition is satisfied, an oxide film removal process is performed to open and close the at least one of the first switch and the second switch as a mechanical relay.

8. A power storage system comprising: Battery string; a power converter configured to convert input and output power of the battery string; as well as A battery control device configured to control the battery string and the power converter, wherein: The battery string comprises: Multiple batteries connected in series, a plurality of bypass circuits, each of the bypass circuits including a first switch serving as a mechanical relay and provided between adjacent storage batteries, a bypass line for bypassing the first switch and the storage battery, and a second switch provided on the bypass line, and switching the storage battery between a connected state and a bypass state; and a power storage and current suppression circuit connected between the first switch corresponding to the storage battery at the start end and the power converter, and between the storage battery and the power converter at the end end, and including a power storage unit and a current suppression unit, and The battery control device The first oxide film removal process is performed after all the storage batteries are set to the bypass state by the plurality of the bypass circuits, that is, any one of the storage batteries is switched to the connected state by any one of the bypass circuits, and When the battery control device performs the first oxide film removal process, the maximum value of the transient current flowing through the battery in the connected state, the first switch, and the storage and current suppression circuit is set so that the total voltage of the battery string is equal to or less than the withstand voltage of the bypass circuit and a first condition is satisfied. Under the first condition, arc discharge occurs in the first switch.

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

10. A battery control method, executed by a battery control device for controlling a power storage system, The power storage system includes: Battery strings, and a power converter that converts input and output power of the battery string, The battery string comprises: multiple batteries connected in series, and a plurality of bypass circuits, each of the bypass circuits including a first switch provided between adjacent storage batteries, a bypass line for bypassing the first switch and the storage battery, and a second switch provided on the bypass line, and switching the storage battery between a connected state and a bypass state; and At least one of the first switch and the second switch is a mechanical relay, The battery control method includes: setting the current of the battery string to a first predetermined value through the power converter, and setting the connection or bypass state of the plurality of batteries to a predetermined state through the plurality of bypass circuits, so that the total voltage of the battery string is equal to or less than the withstand voltage of the bypass circuit and a first condition is satisfied, under which arc discharge occurs in at least one of the first switch and the second switch, which are mechanical relays; and In a state where the first condition is satisfied, an oxide film removal process is performed to open and close the at least one of the first switch and the second switch as a mechanical relay.

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