Electricity storage system
The power storage system addresses oxide film removal on switches by using a CR circuit and discharge circuit to manage string current and arc discharge, ensuring stable power flow and reduced downtime.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- YAZAKI CORP
- Filing Date
- 2025-11-12
- Publication Date
- 2026-05-21
AI Technical Summary
Existing power storage systems face challenges in efficiently removing oxide films from switch contacts while minimizing fluctuations in input/output power and reducing downtime, particularly when mechanical relays are used for bypass control.
A power storage system with a CR circuit and discharge circuit, including a first resistor, capacitor, and second resistor, is employed to manage oxide film removal on switches, using controlled string current reduction and arc discharge to minimize power fluctuations and shorten downtime.
The system effectively removes oxide films on switches while maintaining stable power flow, reducing downtime by optimizing the discharge time of capacitors and minimizing idle periods.
Smart Images
Figure JP2025039708_21052026_PF_FP_ABST
Abstract
Description
Power storage system
[0001] The present invention relates to a power storage system.
[0002] As a power storage system including a power storage string in which a plurality of storage batteries are connected in series, a bypass unit that switches the storage battery between a connected state and a bypass state is provided for each storage battery (see, for example, Patent Document 1). In the power storage system described in Patent Document 1, a first switch connected in series with the storage battery and a second switch connected in parallel with the storage battery and the first switch are provided in the bypass unit. In this power storage system, bypass control is executed in which the first switch corresponding to a storage battery that cannot discharge the required current is in an off state and the second switch corresponding to the storage battery is in a connected state, and discharge is performed from other storage batteries.
[0003] Japanese Patent Application Laid-Open No. 2013-31247
[0004] In the power storage system described in Patent Document 1, during bypass control, it is necessary to prevent a large fluctuation in the input / output power between the power storage string and an external system due to a sudden change in the current of the power storage string (hereinafter referred to as the string current). Therefore, it is necessary to execute bypass control after reducing the string current to a predetermined value. On the other hand, when the first switch and the second switch are mechanical relays, in order to remove the oxide film formed on the contact portions of the first switch and the second switch over time, a voltage of a certain level or more is applied between the contacts of the first switch and the second switch. In this state, it is necessary to operate the first switch and the second switch to generate arc discharge with a current value of a certain level or more at the contact portions.
[0005] If the string current is reduced before bypass control is performed to suppress fluctuations in input / output power between the energy storage string and the external system, a voltage above a certain level may not be applied to the contact points of the first and second switches, preventing the generation of an arc discharge with a current above a certain level, which could result in insufficient removal of the oxide film. Therefore, a means is needed that allows both reducing the string current before operating the first and second switches, and operating the first and second switches with a voltage sufficient to remove the oxide film applied.
[0006] One possible method involves connecting a CR circuit to a battery storage string and switching the first switch from Open to Close while charging the capacitor of the CR circuit with the power of any battery, or switching the second switch from Open to Close while the capacitor is discharging.
[0007] However, in this method, the resistance value of the CR circuit is determined by the magnitude of the current flowing through the first and second switches during the process of removing the oxide film from the contact portions of the first and second switches (hereinafter referred to as the oxide film removal process). In other words, from the viewpoint of applying a voltage above a certain level to the contact portions of the first and second switches to generate an arc discharge with a current value above a certain level, it is necessary to set the resistance value of the CR circuit to a certain level or higher.
[0008] On the other hand, if it is necessary to discharge the capacitors of the CR circuit before and after the oxide film removal treatment of the first and second switches, the discharge time of the CR circuit is determined according to the time constant (τ = CR) between the capacitance and resistance of the CR circuit. Here, the resistance of the CR circuit is constrained by the magnitude of the current flowing through the first and second switches during the oxide film removal treatment of the first and second switches. Therefore, it is not possible to set the resistance of the CR circuit lower by prioritizing the discharge time over the oxide film removal treatment.
[0009] The discharge time of the CR circuit corresponds to the pause period during which charging and discharging of the energy storage string is suspended. As the number of first and second switches subject to oxide film removal treatment increases, the discharge time of the CR circuit increases, and the pause period of the energy storage string increases. In an energy storage system composed of multiple energy storage strings, the amount of power that can be charged and discharged decreases when there are energy storage strings in a pause period.
[0010] In view of the above circumstances, the present invention aims to enable the removal of oxide film on the contact portion of the switch in the bypass section while suppressing fluctuations in input / output power between the energy storage system and an external system, and to shorten the downtime of the energy storage string, in an energy storage system in which a plurality of storage batteries are connected in series and a bypass section is provided for each storage battery to switch between a connected state and a bypass state.
[0011] The energy storage system of the present invention comprises a power line connecting a plurality of storage batteries in series, a first switch connected in series with the storage batteries, a second switch connected in parallel with the storage batteries and the first switch, a plurality of bypass sections provided for each storage battery, a CR circuit connecting the positive and negative sides of the power line, a second resistor connected in series, a third switch, and a discharge circuit connected in parallel with the capacitor.
[0012] According to the present invention, in an energy storage system in which multiple batteries are connected in series and a bypass section is provided for each battery to switch between a connected state and a bypass state, it is possible to remove the oxide film on the contact portion of the switch in the bypass section while suppressing fluctuations in input / output power between the energy storage system and an external system, and to shorten the downtime of the energy storage string.
[0013] Figure 1 is a schematic circuit diagram showing an energy storage system according to one embodiment of the present invention. Figure 2 is a circuit diagram illustrating the first oxide film removal process. Figure 3 is a circuit diagram illustrating the second oxide film removal process. Figure 4 is a circuit diagram illustrating the capacitor discharge process. Figure 5 is a flowchart illustrating the process of switching the battery module targeted by the bypass control request from the connected state to the bypass state. Figure 6 is a schematic circuit diagram showing an energy storage string according to another embodiment of the present invention.
[0014] The present invention will be described below in accordance with preferred embodiments. However, the present invention is not limited to the embodiments shown below, and embodiments can be modified as appropriate without departing from the spirit of the invention. Furthermore, in the embodiments shown below, some components are not illustrated or described; however, details of the omitted technologies can be appropriately referred to from publicly known or well-known technologies, to the extent that they do not contradict the content described below.
[0015] Figure 1 is a schematic circuit diagram of an energy storage system 1 according to one embodiment of the present invention. As shown in this figure, the energy storage system 1 comprises a plurality of energy storage strings STR, a plurality of power converters PCS, a string bus 2, and a battery control device 100. The plurality of energy storage strings STR are connected in parallel to each other via the string bus 2 and are also connected to an external system (an external system, not shown in the figure). The energy storage system 1 is a power source for stationary or vehicle-mounted use.
[0016] The energy storage string STR comprises n battery modules M1 to Mn (where n is an integer of 2 or more) connected in series by a power line PL. Although not particularly limited, the battery modules M1 to Mn in this embodiment are refurbished used batteries, and there are differences in the degree of degradation of each battery module M1 to Mn. The battery modules M1 to Mn are, for example, composed of multiple cells of secondary batteries such as lithium-ion batteries, nickel-metal hydride batteries, and lithium-ion capacitors.
[0017] Battery modules M1 to Mn are charged by power supplied from the external grid via the string bus 2 and the power converter PCS. Furthermore, battery modules M1 to Mn supply power to the external grid via the power converter PCS and the string bus 2.
[0018] The external system includes loads and generators. If the energy storage system 1 is stationary, the commercial power grid and facilities that consume electricity become the loads, and solar power generation systems become the generators. On the other hand, if the energy storage system 1 is vehicle-mounted, the drive motor, air conditioner, and various vehicle-mounted electrical components become the loads. Note that the drive motor can act as both a load and a generator.
[0019] The energy storage string STR may also consist of n battery cells or battery packs connected in series, instead of n battery modules M1 to Mn connected in series. In this case, the energy storage string STR may include a bypass section that bypasses each battery cell or battery pack.
[0020] The power converter PCS is either a DC / DC converter or a DC / AC converter and is connected to the string bus 2. The power converter PCS is also connected to the positive terminal of the starting battery module M1 (total + of the energy storage string STR) and the negative terminal of the ending battery module Mn (total - of the energy storage string STR).
[0021] The power converter PCS converts the voltage input from the string bus 2 to the battery storage string STR according to the specified value of the charging power (or current) and outputs it to multiple battery storage modules M1 to Mn during charging. Here, the voltage on the battery storage string STR side changes depending on the bypass state of the battery storage modules M1 to Mn (the number of battery storage modules M1 to Mn that are bypassed) and the charge state of the battery storage modules M1 to Mn. Therefore, the power converter PCS converts the voltage input from the string bus 2 to the voltage on the battery storage string STR side and outputs it to multiple battery storage modules M1 to Mn during charging.
[0022] The power converter PCS converts the voltages input from multiple battery modules M1 to Mn during the discharge of the energy storage string STR, according to the indicated discharge power (or current), and outputs them to the string bus 2. Here, the input voltage of the power converter PCS during discharge changes depending on the bypass state and charge state of the battery modules M1 to Mn. As a result, variations occur in the input voltages of the multiple power converter PCS during the discharge of the energy storage string STR. Therefore, during the discharge of the energy storage string STR, each power converter PCS converts its input voltage to an output voltage that matches that of the other power converter PCS.
[0023] The power converter PCS is a bidirectional converter. Furthermore, when the current flowing through the string bus 2 is alternating current, the power converter PCS is equipped with synchronization means to track changes in instantaneous values.
[0024] The energy storage string STR comprises n bypass units B1 to Bn, a system main relay S3, a CR circuit 10, a discharge circuit 11, a current sensor 3, and various sensors (not shown). The current sensor 3 is installed at any position on the power line PL that is always energized, and detects the string current and transmits a detection signal to the string controller 102.
[0025] Each bypass unit B1 to Bn is equipped with a circuit breaker switch S1, a bypass line BL, and a bypass switch S2. The circuit breaker switch S1 is a mechanical relay connected in series with each battery module M1 to Mn by a power line PL. The circuit breaker switch S1 is located on the positive side of the energy storage string STR, relative to each battery module M1 to Mn, and is connected to the positive terminal of each battery module M1 to Mn.
[0026] The bypass line BL is a power line that bypasses each battery module M1 to Mn and the circuit breaker switch S1. One end of the bypass line BL is connected to the circuit breaker switch S1, and the other end of the bypass line BL is connected to the negative terminal of each battery module M1 to Mn. The bypass line BL is equipped with a mechanical relay, the bypass switch S2. That is, the bypass switch S2 is connected in parallel with each battery module M1 to Mn and the circuit breaker switch S1.
[0027] The starting battery module M1 and the ending battery module Mn are connected to the external system via the power converter PCS and the string bus 2. When the bypass switch S2 is Open and the circuit breaker switch S1 is Closed in any of the bypass units B1 to Bn, the battery modules M1 to Mn corresponding to those bypass units B1 to Bn are connected in series to the external system. On the other hand, when the circuit breaker switch S1 is Open and the bypass switch S2 is Closed in any of the bypass units B1 to Bn, the battery modules M1 to Mn corresponding to those bypass units B1 to Bn are bypassed.
[0028] The system main relay S3 is located in a position on the power line PL that is always energized. Specifically, the system main relay S3 is located between the total positive terminal of the energy storage string STR and the trip switch S1 of the bypass unit B1 at the starting end, and is located on the total positive terminal side of the energy storage string STR than the connection point P1 between one end of the bypass line BL (the total positive terminal side of the energy storage string STR) and the power line PL. The system main relay S3 can be a mechanical relay, a semiconductor switch, or the like.
[0029] The CR circuit 10 comprises a capacitor C and a first resistor R1 connected in series, and connects the total positive side and total negative side of the energy storage string STR. One end of the first resistor R1 is connected to the power line PL on the total positive side of the energy storage string STR, between the system main relay S3 and the trip switch S1 of the bypass unit B1, and at the connection point P1 between one end of the bypass line BL of the bypass unit B1 and the power line PL. The other end of the first resistor R1 is connected to the capacitor C.
[0030] The positive side of capacitor C is connected to the other end of the first resistor R1. The negative side of capacitor C is connected to the power line PL between the battery module Mn and the total negative terminal of the energy storage string STR, and is on the total negative side of the energy storage string STR, further than the connection point P2 between the other end of the bypass line BL of the bypass unit Bn (the total negative side of the energy storage string STR) and the power line PL. Capacitor C is an element that stores electric charge, such as an electrolytic capacitor, film capacitor, or other capacitor, and smooths the voltage input from the power converter PCS to the energy storage string STR.
[0031] The discharge circuit 11 comprises a second resistor R2 and a discharge switch St connected in series, and is connected in parallel with the capacitor C. One end of the second resistor R2 is connected to the other end of the first resistor R1 and to the positive side of the capacitor C. The other end of the second resistor R2 is connected to the discharge switch St.
[0032] The discharge switch St is a transistor such as a bipolar transistor, FET (Field Effect Transistor), IGBT (Insulated Gate Bipolar Transistor), or mechanical relay, and in this embodiment, it is a bipolar transistor. The collector of the discharge switch St is connected to the other end of the second resistor R2. The emitter of the discharge switch St is connected to the power PL between the connection point P2 and the total negative terminal of the energy storage string STR. The base of the discharge switch St is connected to the string controller 102, which will be described later.
[0033] The discharge switch St is turned ON / OFF by a control signal output to the base from the string controller 102. When the discharge switch St is ON, the second resistor R2 is connected in series with the first resistor R1 and in parallel with the capacitor C. When the discharge switch St is OFF, the connection between the second resistor R2, the first resistor R1 and the capacitor C is broken.
[0034] Here, the resistance value of the first resistor R1 is determined according to the magnitude of the current flowing through the cutoff switch S1 or bypass switch S2 during the first and second oxide film removal processes. During the first and second oxide film removal processes, it is necessary to generate an arc discharge with a current value sufficient to remove the oxide film at the contact portion of the cutoff switch S1 or bypass switch S2. Therefore, the resistance value of the first resistor R1 needs to be sufficiently high to achieve the first and second oxide film removal processes.
[0035] On the other hand, before and after the first and second oxide film removal processes, capacitor C may be discharged to remove its charge and secure its charging capacity. In this case, the higher the resistance value of the first resistor R1, the longer the discharge time of capacitor C becomes, and the longer the time required for processing before or after the first and second oxide film removal processes. If the first and second oxide film removal processes are performed during bypass control, the processing time for bypass control becomes longer, and the idle period of the energy storage string STR becomes longer.
[0036] In contrast, in the energy storage system 1 according to this embodiment, when the discharge switch St is ON, the second resistor R2 is connected in parallel with the capacitor C, so that the discharge current of the capacitor C flows through the second resistor R2. As a result, the discharge time of the capacitor C is shortened compared to the case where the second resistor R2 is not connected in parallel with the capacitor C, and the idle period of the energy storage string STR is shortened.
[0037] Here, the resistance value of the second resistor R2 is set to a lower value than that of the first resistor R1. As a result, the discharge current of capacitor C flows more easily through the second resistor R2 than through the first resistor R1, further shortening the discharge time of capacitor C. The resistance value of the second resistor R2 is set to a value sufficient to suppress the inrush current to the discharge switch St.
[0038] The string controller 102 turns on the discharge switch St when capacitor C is discharged before and after the first and second oxide film removal processes. As a result, when capacitor C is discharged, the second resistor R2 is connected in parallel with capacitor C, and the discharge time of capacitor C is shortened.
[0039] The battery control device 100 comprises a plurality of string controllers 102, a plurality of relay drivers 103, and one system controller 101. The string controllers 102 and relay drivers 103 are provided for each battery storage string STR.
[0040] The string controller 102 transmits control signals to the relay driver 103, power converter PCS, and discharge switch St of the corresponding energy storage string STR. The relay driver 103 controls the cutoff switches S1 and bypass switches S2 of the bypass units B1 to Bn, and the system main relay S3, according to the control signals transmitted from the string controller 102. The power converter PCS converts the charge and discharge power of the energy storage string STR according to the control signals transmitted from the string controller 102. The power converter PCS also controls the string current of the energy storage string STR according to the control signals from the string controller 102. Furthermore, the discharge switch St turns ON / OFF according to the control signals from the string controller 102.
[0041] The string controller 102 performs tasks such as detecting and estimating the state of the energy storage string STR, and notifying the system controller 101 of control requests for the equipment. Examples of detecting the state of the energy storage string STR include detecting the string current of the energy storage string STR based on the detection signal of the current sensor 3, detecting the total voltage of the energy storage string STR based on the detection signal of the voltage sensor (not shown), detecting the voltage of the battery modules M1 to Mn based on the detection signal of the voltage sensor, detecting the temperature of the battery modules M1 to Mn based on the detection signal of the temperature sensor (not shown), and detecting the voltage of the battery cells based on the detection signal of the cell voltage sensor (not shown). Examples of estimating the state of the energy storage string STR include estimating the State of Charge (SOC) and State of Health (SOH) of the battery modules M1 to Mn, and estimating the State of Charge (SOC) and State of Health (SOH) of the energy storage string STR. Furthermore, examples of notifications of equipment control requests to the system controller 101 include requests for switching control of the Open / Close states of the bypass switches S1 and S2 of the bypass units B1 to Bn, and requests for control of the power converter PCS and the discharge switch St.
[0042] Methods for estimating SOH include charge-discharge testing, current integration, open-circuit voltage measurement, terminal voltage measurement, model-based methods (all of which use the time-dependent change in SOC), AC impedance measurement, model-based methods using adaptive digital filters, linear regression from I-V characteristics (current-voltage characteristics) (slope of the straight line in the I-V characteristics), and step response methods (all of which are methods that estimate using the time-dependent increase in internal resistance).
[0043] Various known methods for estimating SOC include the current integration method, the method of determining SOC from OCV (Open Circuit Voltage) (voltage method), and methods combining the current integration method and the voltage method. Furthermore, OCV can be estimated using various known methods that utilize the change in terminal voltage over time or the increase in internal resistance over time.
[0044] The system controller 101 is a controller that comprehensively controls the entire power storage system 1, and performs 1:m communication with a plurality of string controllers 102. This system controller 101 monitors the state of the power storage string STR, determines whether to approve the control request of the device from the string controller 102, and notifies the approval of the control request of the device to the string controller 102. In addition, the system controller 101 sets the instruction value of the charge-discharge power (or current) of each power storage string STR, and transmits the instruction value of the charge-discharge power (or current) to the string controller 102.
[0045] The system controller 101 monitors the state of the power storage string STR based on the detection result or estimation result of the state of the power storage string STR transmitted from the string controller 102. Then, the system controller 101 calculates the instruction value of the charge-discharge power (or current) assigned to each power storage string STR according to the instruction of the input / output power (or current) of the entire power storage system 1 received from the upper system (not shown) and the state of the power storage string STR.
[0046] Here, when the system controller 101 permits the bypass control request (hereinafter referred to as the bypass control request) for any of the battery modules M1 to Mn in each string controller 102, when performing the bypass control of the battery modules M1 to Mn (hereinafter referred to as M'), the corresponding bypass units B1 to Bn (hereinafter referred to as B') perform the first oxide film removal process and the second oxide film removal process.
[0047] The first oxide film removal process is a process for removing the oxide film on the contact portion of the cutoff switch S1 (hereinafter referred to as S1') of the bypass unit B'. The second oxide film removal process is a process for removing the oxide film on the contact portion of the bypass switch S2 (hereinafter referred to as S2') of the bypass unit B'.
[0048] When bypass control is executed, a string current reduction process is executed before the execution of the first oxide film removal process and the second oxide film removal process, and a bypass state switching process is executed after the execution of the first oxide film removal process and the second oxide film removal process. The string current reduction process is a process of reducing the string current to a predetermined value. The predetermined value is set to a low value such that fluctuations in the input / output power of the entire power storage system 1 are suppressed within an allowable range when bypass control of the power storage string STR is executed.
[0049] Here, the string controller 102 gradually and continuously reduces the command value of the string current from the current value to the predetermined value in the string current reduction process. 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 value and the predetermined value of the command value of the string current. At this time, the change rate (amount of change per unit time) of the command value of the string current is set such that fluctuations in the input / output power of the entire power storage system 1 are suppressed within an allowable range. Thereby, the power converter PCS gradually and continuously reduces the string current from the current value to the predetermined value so as to suppress fluctuations in the input / output power of the entire power storage system 1 within an allowable range.
[0050] FIG. 2 is a circuit diagram for explaining the first oxide film removal process. As shown in this figure, in the first oxide film removal process, the cutoff switch S1' of the bypass unit B' is switched from Open to Close in a state where the potential of the capacitor C is lower than the potential of the power storage battery module M' targeted for bypass control. At this time, the system main relay S3 and the bypass switch S2' of the bypass unit B' are Open. Also, in the other bypass units B1 to Bn, the cutoff switch S1 is Open and the bypass switch S2 is Close, and the other power storage battery modules M1 to Mn are in a bypass state. Further, the discharge switch St is OFF, and the connection between the second resistor R2, the first resistor R1, and the capacitor C is interrupted. Thereby, current flows from the power storage battery module M' through the cutoff switch S1', the first resistor R1, the capacitor C, and the bypass switches S2 of the other bypass units B1 to Bn, and the capacitor C is charged.
[0051] Here, the potential difference between the battery module M' and the capacitor C is set to a size sufficient to generate an arc discharge that removes the oxide film from the contact portion of the cutoff switch S1' when the cutoff switch S1' is switched. In this embodiment, the capacitor C is discharged before the first oxide film removal process is executed, and the potential of the capacitor C decreases. Note that the potential of the capacitor C at the start of the first oxide film removal process does not need to be zero; it is sufficient that the potential is low enough to remove the oxide film from the contact portion of the cutoff switch S1' when the cutoff switch S1' is switched.
[0052] Furthermore, the charging time of capacitor C is set according to the time constant (τ = CR) between the capacitance (C) of capacitor C and the resistance (R) of the first resistor R1, so that a sufficient amount of charge flows from the battery module M' to capacitor C to remove the oxide film on the contact portion of the cutoff switch S1'.
[0053] Therefore, in the first oxide film removal process, the cutoff switch S1' is switched from Open to Close when a voltage sufficient to remove the oxide film from the contact portion is applied, thereby removing the oxide film from the contact portion of the cutoff switch S1'.
[0054] Figure 3 is a circuit diagram illustrating the second oxide film removal process. As shown in this figure, during the second oxide film removal process, with capacitor C charged, the bypass switch S2' is switched from Open to Close. At this time, the system main relay S3 and the cutoff switch S1' are Open. In addition, in the other bypass units B1 to Bn, the cutoff switch S1 is Open and the bypass switch S2 is Close, and the other battery modules M1 to Mn are in a bypass state. Furthermore, the discharge switch St is OFF, and the connection between the second resistor R2, the first resistor R1 and capacitor C is disconnected. As a result, current flows from capacitor C through the first resistor R1, the bypass switch S2', and the bypass switches S2 of the other bypass units B1 to Bn.
[0055] Here, the potential of capacitor C is set to a height sufficient to generate an arc discharge that removes the oxide film at the contact portion of bypass switch S2' when the bypass switch S2' is switched. In this embodiment, the charging time of capacitor C during the execution of the second oxide film removal process is set according to the time constant (τ = CR) between the capacitance (C) of capacitor C and the resistance (R) of the first resistor R1.
[0056] Furthermore, the discharge time of capacitor C is set according to the time constant (τ = CR) between the capacitance (C) of capacitor C and the resistance (R) of the first resistor R1, so that a sufficient amount of charge flows from capacitor C to the bypass switch S2' to remove the oxide film on the contact portion of the bypass switch S2'.
[0057] Therefore, in the second oxide film removal process, the bypass switch S2' is switched from Open to Close when a voltage sufficient to remove the oxide film from the contact portion is applied, thereby removing the oxide film from the contact portion of the bypass switch S2'.
[0058] Figure 4 is a circuit diagram illustrating the discharge process of capacitor C. The discharge process of capacitor C shown in this figure is performed to lower the potential of capacitor C before the first oxide film removal process is executed.
[0059] As shown in Figure 4, during the discharge process of capacitor C, the discharge switch St is ON, and the second resistor R2 is connected to the first resistor R1 and capacitor C. At this time, the system main relay S3 is OFF. Also, in all bypass units B1 to Bn, the cutoff switch S1 and bypass switch S2 are OFF, and all battery modules M1 to Mn are in the cutoff state.
[0060] Here, because the resistance value of the second resistor R2 is lower than that of the first resistor R1, the discharge current of capacitor C flows more easily through the second resistor R2 than through the first resistor R1. As a result, the discharge current of capacitor C flows through the second resistor R2 and the discharge switch St.
[0061] Figure 5 is a flowchart illustrating the process of switching the battery module M' that is the target of a bypass control request from a connected state to a bypass state. First, in step S01, the string controller 102 monitors the battery modules M1 to Mn of the energy storage string STR and determines whether or not there is a battery module M' that requires bypass control. If the determination in step S01 is positive, the process proceeds to step S02; if the determination in step S01 is negative, the process ends.
[0062] At the start of the process shown in the flowchart of Figure 5, the system main relay S3 is closed and the discharge switch St is off. In the bypass units B1 to Bn corresponding to the connected battery modules M1 to Mn, the bypass switch S2 is open and the cutoff switch S1 is closed. On the other hand, in the bypass units B1 to Bn corresponding to the bypassed battery modules M1 to Mn, the bypass switch S2 is closed and the cutoff switch S1 is open. Also, at the start of the process shown in the flowchart of Figure 5, the capacitor C is in a charged state.
[0063] In step S02, the string controller 102 records the current connection or bypass status of the battery modules M1 to Mn of the energy storage string STR in its built-in memory (not shown). Next, the string controller 102 repeatedly executes the loop processing of steps S03 to S05 until the indicated value of the string current reaches a predetermined value (string current reduction processing). Here, in steps S03 to S05, the string controller 102 gradually and continuously reduces the indicated value of the string current by a predetermined amount ΔP1 from the current value to the predetermined value.
[0064] First, in step S03, the string controller 102 updates the indicated value of the string current to a value reduced by a predetermined amount ΔP1. This predetermined amount ΔP1 is set to a small amount to suit the purpose of preventing abrupt changes in the input and output power of the energy storage system 1. If the difference between the current value of the string current and the predetermined value is small, this predetermined amount ΔP1 may be equal to the difference between the current value of the string current and the predetermined value. On the other hand, if the difference between the current value of the string current and the predetermined value is relatively large, this predetermined amount ΔP1 may be less than the difference between the current value of the string current and the predetermined value. If this predetermined amount ΔP1 is less than the difference between the current value of the string current and the predetermined value, the string current update is repeated multiple times.
[0065] Next, in step S04, the string controller 102 waits for a predetermined time T1 after transmitting the string current instruction value to the power converter PCS. This predetermined time T1 is set according to the time required for the string controller 102 to control the power converter PCS and the rate of change of the string current.
[0066] Next, in step S05, the string controller 102 determines whether the string current has reached a predetermined value (i.e., whether the decrease in the string current has been completed). If the determination in step S05 is positive, the process proceeds to step S06; if the determination in step S05 is negative, the process proceeds to step S03.
[0067] Next, in step S06, the string controller 102 sends a control signal to the relay driver 103 to switch the system main relay S3 from Close to Open. This disconnects the energy storage string STR from the power converter PCS.
[0068] Next, in step S07, the string controller 102 sends a control signal to the relay driver 103 to open the disconnection switches S1 and bypass switches S2 of all bypass units B1 to Bn. As a result, all battery modules M1 to Mn are turned off.
[0069] Next, in step S08, the string controller 102 turns on the discharge switch St, and in step S09, it waits for a predetermined time T2 after turning on the discharge switch St. The predetermined time T2 is the discharge time of capacitor C until the charge of capacitor C becomes 0, and is determined according to the time constant (τ = CR) between the capacitance (C) of capacitor C and the resistance value (R) of the second resistor R2.
[0070] Next, in step S10, the string controller 102 turns off the discharge switch St. Note that in steps S08 to S10, it is sufficient that the charge on capacitor C is removed so that the oxide film on the contact portion of the interruption switch S1' can be removed in the first oxide film removal process (step S12), but it is not necessary for the potential of capacitor C to be 0.
[0071] Next, in step S11, the string controller 102 sends a control signal to the relay driver 103 to switch the bypass switches S2, other than the bypass unit B', from Open to Close. As a result, the battery modules M1 to Mn, other than the battery module M', enter a bypass state.
[0072] Next, in step S12, the string controller 102 sends a control signal to the relay driver 103 to switch the cutoff switch S1' corresponding to the battery module M' from Open to Close. This executes the first oxide film removal process, and the oxide film on the contact portion of the cutoff switch S1' is removed (see Figure 2).
[0073] Next, in step S13, the string controller 102 waits for a predetermined time T3 after switching the cutoff switch S1' from Open to Close. This predetermined time T3 is the time required for the battery module M' and the capacitor C to reach the same potential, and is set according to the time constant (τ = CR) between the capacitance (C) of the capacitor C and the resistance (R) of the first resistor R1.
[0074] Next, in step S14, the string controller 102 sends a control signal to the relay driver 103 to switch the cutoff switch S1' corresponding to the battery module M' from Close to Open, and then switch the bypass switch S2' corresponding to the battery module M' from Open to Close. This executes the second oxide film removal process, and the oxide film on the contact portion of the bypass switch S2' is removed (see Figure 3).
[0075] Next, in step S15, the string controller 102 sends a control signal to the relay driver 103 to switch the connection / bypass state of the battery modules M1 to Mn to a state that reflects the bypass control. The state that reflects the bypass control is the state in which the battery module M' which was determined to require bypass control in step S01 based on the connection / bypass state of the battery modules M1 to Mn recorded in memory in step S02 is in the bypass state.
[0076] Next, in step S16, the string controller 102 sends a control signal to the relay driver 103 to switch the system main relay S3 from Open to Close. This completes the process shown in the flowchart of Figure 5.
[0077] As described above, the energy storage system 1 according to this embodiment includes a CR circuit 10. The CR circuit 10 comprises a first resistor R1 and a capacitor C connected in series, and connects the positive and negative sides of the power line PL. As a result, the CR circuit 10 and the energy storage string STR can form a charge / discharge circuit for the capacitor C. Therefore, by operating the cutoff switch S1 while the charge / discharge current of the capacitor C is flowing through it, the oxide film on the contact portion of the cutoff switch S1 can be removed. Also, by operating the bypass switch S2 while the charge / discharge current of the capacitor C is flowing through it, the oxide film on the contact portion of the bypass switch S2 can be removed.
[0078] Here, the energy storage system 1 includes a discharge circuit 11. The discharge circuit 11 includes a second resistor R2 connected in series and a discharge switch St, and is connected in parallel with the capacitor C. As a result, by turning the discharge switch St OFF, the second resistor R2 can be disconnected from the CR circuit 10, and the first and second oxide film removal processes using the CR circuit 10 can be performed. On the other hand, by turning the discharge switch St ON, the second resistor R2 can be connected to the CR circuit 10, forming a discharge circuit 11 in which the discharge current of the capacitor C flows through the second resistor R2. By allowing the discharge current of the capacitor C to flow not only through the first resistor R1 but also through the second resistor R2, the discharge time of the capacitor C can be shortened, and the idle period of the energy storage string STR can be shortened.
[0079] In particular, in the energy storage system 1 according to this embodiment, the resistance value of the second resistor R2 is set lower than the resistance value of the first resistor R1. As a result, the discharge current of the capacitor C flows more easily through the second resistor R2 than through the first resistor R1, thus further shortening the discharge time of the capacitor C.
[0080] Furthermore, in the energy storage system 1 according to this embodiment, the first resistor R1 is connected to the positive side of the power line PL, the capacitor C is connected to the negative side of the power line PL, the second resistor R2 is connected to the first resistor R1, and the discharge switch St is connected to the negative side of the power line PL. Here, because the discharge switch St is connected to the negative side of the power line PL, if the discharge switch St is a transistor switch, the emitter, collector, or base of the discharge switch St can be grounded (reference potential).
[0081] Furthermore, in the energy storage system 1 according to this embodiment, the battery control device 100 performs a first oxide film removal process, a second oxide film removal process, and a capacitor C discharge process. In the first oxide film removal process, with the bypass switch S2' corresponding to any battery module M' open and the connection between the second resistor R2 and the capacitor C interrupted by the discharge switch St, the cutoff switch S1' corresponding to any battery module M' is operated, thereby removing the oxide film from the contact portion of the cutoff switch S1'. In the second oxide film removal process, with the cutoff switch S1' corresponding to any battery module M' open and the connection between the second resistor R2 and the capacitor C interrupted by the discharge switch St, the bypass switch S2' corresponding to any battery module M' is operated, thereby removing the oxide film from the contact portion of the bypass switch S2'. Furthermore, before performing at least one of the first oxide film removal treatment and the second oxide film removal treatment, the capacitor C is discharged while the second resistor R2 and the capacitor C are connected by the discharge switch St.
[0082] Here, in order to prevent large fluctuations in input / output power between the energy storage string STR and the external system due to abrupt changes in string current during bypass control, it is necessary to reduce the string current to a predetermined value before performing bypass control. Even in such cases, by operating the interruption switch S1' and bypass switch S2' with a voltage above a certain level applied between the contacts of the interruption switch S1' and bypass switch S2', an arc discharge with a current value above a certain level can be generated at the contact portion. Therefore, the oxide film on the contact portion of the interruption switch S1' and bypass switch S2' can be removed.
[0083] Furthermore, it may be necessary to discharge capacitor C before or after at least one of the first oxide film removal treatment and the second oxide film removal treatment. In such cases, the discharge current of capacitor C can be passed through the second resistor R2, or through the first resistor R1 and the second resistor R2, thereby shortening the discharge time of capacitor C compared to the case where the second resistor R2 is not connected to capacitor C. Consequently, the time during which the energy storage string STR is idle during the discharge period of capacitor C can be shortened.
[0084] Figure 6 is a schematic circuit diagram showing a power storage string STR' according to another embodiment of the present invention. The power storage string STR' shown in this figure comprises a CR circuit 10' and a discharge circuit 11'. Components similar to those in the above-described embodiment are denoted by the same reference numerals, and the description of the above-described embodiment will be used by reference.
[0085] In the CR circuit 10', the positive side of capacitor C is connected to the power line PL on the total positive side of the energy storage string STR', between the system main relay S3 and the cutoff switch S1 of the bypass unit B1, and at the connection point P1 between one end of the bypass line BL of the bypass unit B1 and the power line PL. The negative side of capacitor C is connected to one end of the first resistor R1.
[0086] Furthermore, in the CR circuit 10', the other end of the first resistor R1 is connected to the power line PL between the battery module Mn and the total negative terminal of the energy storage string STR', and is on the total negative side of the energy storage string STR' than the connection point P2 between the other end of the bypass line BL of the bypass unit Bn and the power line PL.
[0087] In the discharge circuit 11', the discharge switch St and the second resistor R2, which are connected in series, are connected in parallel with the capacitor C. One end of the second resistor R2 is connected to one end of the first resistor R1 and to the negative side of the capacitor C. The other end of the second resistor R2 is connected to the discharge switch St.
[0088] The emitter of the discharge switch St is connected to the other end of the second resistor R2. The collector of the discharge switch St is connected to the power line PL between the system main relay S3 and the trip switch S1 of the bypass unit B1, and on the total positive side of the energy storage string STR', beyond the connection point P1 between one end of the bypass line BL of the bypass unit B1 and the power line PL. The base of the discharge switch St is connected to the string controller 102 (see Figure 1).
[0089] The discharge switch St turns ON when a control signal is output to the base from the string controller 102. When the discharge switch St is ON, the second resistor R2 is connected in series with the first resistor R1 and in parallel with the capacitor C. When the second resistor R2 is connected, the discharge current of the capacitor C flows through the discharge switch St and the second resistor R2.
[0090] Although the present invention has been described above based on the embodiments described above, the present invention is not limited to the embodiments described above, and modifications may be made, or publicly known or well-known technologies may be combined as appropriate, without departing from the spirit of the present invention.
[0091] For example, in the above embodiment, the resistance value of the second resistor R2 is set lower than that of the first resistor R1, so that the discharge current of capacitor C flows more easily through the second resistor R2 than through the first resistor R1. However, this is not essential, and the resistance value of the second resistor R2 may be set to be higher than or equal to that of the first resistor R1. Even in this case, the discharge current of capacitor C flows not only through the first resistor R1 but also through the second resistor R2, thereby shortening the discharge time of capacitor C.
[0092] Furthermore, in the above-described embodiment, the discharge treatment of capacitor C was performed before the first oxide film removal treatment, but it may also be performed after the first oxide film removal treatment, before the second oxide film removal treatment, or after the second oxide film removal treatment.
[0093] Furthermore, in the above-described embodiment, the cutoff switch S1 and the bypass switch S2 are mechanical relays, but one of the cutoff switch S1 and the bypass switch S2 may be a semiconductor switch. In this case, the first oxide film removal treatment or the second oxide film removal treatment only needs to be performed on one of the mechanical relays, the cutoff switch S1 and the bypass switch S2.
[0094] Furthermore, the timing for performing the first oxide film removal process and the second oxide film removal process, as well as the battery modules M1 to Mn targeted by the first and second oxide film removal processes, can be set as appropriate.
[0095] Furthermore, in the first oxide film removal process, it is not essential to remove the oxide film from the contact portion of the cutoff switch S1 using the charging current of the capacitor C. In the first oxide film removal process, the cutoff switch S1 may be operated to form a circuit and discharge the capacitor C, thereby removing the oxide film from the contact portion of the cutoff switch S1 using the discharge current of the capacitor C.
[0096] Furthermore, in the second oxide film removal process, it is not essential to remove the oxide film on the contact portion of the bypass switch S2 using the discharge current of capacitor C. In the second oxide film removal process, the oxide film on the contact portion of the bypass switch S2 may be removed by operating the bypass switch S2 to form a circuit and charge capacitor C, thereby using the charging current of capacitor C.
[0097] Furthermore, in the above-described embodiment, the indicated value of the string current is changed gradually and continuously over time by a predetermined amount ΔP1 until it reaches the target value. However, for example, if the effect of the change in string current on the input and output power of the energy storage system 1 is minor, the indicated values of the string current may be changed simultaneously.
[0098] Here, the features of the embodiments of the energy storage system according to the present invention described above are briefly summarized and listed below in [1] to [4].
[0099] [1] Energy storage system (1) comprising: a power line (PL) connecting a plurality of storage batteries (M1 to Mn, M') in series; first switches (S1, S1') connected in series with the storage batteries (M1 to Mn, M'); second switches (S2, S2') connected in parallel with the storage batteries (M1 to Mn, M') and the first switches (S1, S1'); a plurality of bypass sections (B1 to Bn, B') provided for each of the storage batteries (M1 to Mn, M'); a CR circuit (10) connecting the positive and negative sides of the power line (PL) and comprising a capacitor (C) and a first resistor (R1) connected in series; and a discharge circuit (11, 11') connected in parallel with the capacitor (C) and comprising a second resistor (R2) and a third switch (St) connected in series. [2] The energy storage system (1) according to [1], wherein the resistance value of the second resistor (R2) is lower than the resistance value of the first resistor (R1). [3] The energy storage system (1) according to [1] or [2], wherein the first resistor (R1) is connected to the positive side of the power line (PL), the capacitor (C) is connected to the negative side of the power line (PL), the second resistor (R2) is connected to the first resistor (R1), and the third switch (St) is connected to the negative side of the power line (PL).[4] A control unit (100) that controls the first switches (S1, S1'), the second switches (S2, S2'), and the third switch (St), the control unit (100) performs a first oxide film removal process which removes the oxide film on the contact portion of the first switch (S1) by operating the first switch (S1, S1') corresponding to any of the storage batteries (M1 to Mn, M') with the second switches (S2, S2') corresponding to any of the storage batteries (M1 to Mn, M') open and the connection between the second resistor (R2) and the capacitor (C) interrupted by the third switch (St), The energy storage system (1) according to [1] or [2], wherein at least one of the following is performed: a first switch (S1, S1') corresponding to any of the aforementioned storage batteries (M1 to Mn, M') is opened, the connection between the second resistor (R2) and the capacitor (C) is interrupted by the third switch (St), and the second switch (S2, S2') corresponding to any of the aforementioned storage batteries (M1 to Mn, M') is operated to remove the oxide film on the contact portion of the second switch (S2, S2'); and before or after performing at least one of the first oxide film removal process and the second oxide film removal process, the second resistor (R2) and the capacitor (C) are connected by the third switch (St), and the capacitor (C) is discharged.
[0100] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
[0101] This application is based on Japanese Patent Application No. 2024-197315 filed on November 12, 2024, the contents of which are incorporated herein by reference.
[0102] According to the present invention, in an energy storage system in which multiple batteries are connected in series and a bypass section is provided for each battery to switch between a connected state and a bypass state, it is possible to remove the oxide film on the contact portion of the switch in the bypass section while suppressing fluctuations in input / output power between the energy storage system and an external system, and to shorten the idle period of the energy storage string. The present invention, which achieves this effect, is useful with respect to energy storage systems.
[0103] 1: Energy storage system 10: CR circuit 10': CR circuit 11: Discharge circuit 11': Discharge circuit 100: Battery control device (control unit) B1 to Bn, B': Bypass unit (bypass section) C: Capacitor M1 to Mn, M': Battery module (battery) PL: Power line R1: First resistor R2: Second resistor S1, S1': Cut-off switch (first switch) S2, S2': Bypass switch (second switch) St: Discharge switch (third switch) STR: Energy storage string STR': Energy storage string
Claims
1. An energy storage system comprising: a power line connecting multiple storage batteries in series; a first switch connected in series with the storage batteries; a second switch connected in parallel with the storage batteries and the first switch, with multiple bypass sections provided for each storage battery; a CR circuit connecting the positive and negative sides of the power line, with a capacitor and a first resistor connected in series; and a discharge circuit connected in parallel with the capacitor, with a second resistor and a third switch connected in series.
2. The energy storage system according to claim 1, wherein the resistance value of the second resistor is lower than the resistance value of the first resistor.
3. The energy storage system according to claim 1 or 2, wherein the first resistor is connected to the positive side of the power line, the capacitor is connected to the negative side of the power line, the second resistor is connected to the first resistor, and the third switch is connected to the negative side of the power line.
4. The energy storage system according to claim 1 or 2, comprising a control unit that controls the first switch, the second switch, and the third switch, wherein the control unit performs at least one of the following: a first oxide film removal process, which removes an oxide film from the contact portion of the first switch by operating the first switch corresponding to the arbitrary battery with the second switch corresponding to the arbitrary battery open and the connection between the second resistor and the capacitor disconnected by the third switch; and a second oxide film removal process, which removes an oxide film from the contact portion of the second switch by operating the second switch corresponding to the arbitrary battery with the first switch corresponding to the arbitrary battery open and the connection between the second resistor and the capacitor disconnected by the third switch; and before or after performing at least one of the first oxide film removal process and the second oxide film removal process, a discharge process, which discharges the capacitor with the second resistor and the capacitor connected by the third switch.