Power storage system

Abstract

In this power storage system (1), a positive side and a negative side of a power line (PL) connecting a plurality of storage battery modules (M1-Mn) in series are connected by a smoothing capacitor (C), a system main relay (S3) is provided between the smoothing capacitor (C) of the power line (PL) and the storage battery modules (M1-Mn), and the resistance value of a pre-charge circuit (10), in which a first resistor (Rp) and a first pre-charge relay (S4) connected in series are connected in parallel with the system main relay (S3), is variable due to a resistance value varying mechanism (11).

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 cutoff switch connected in series with the storage battery and a bypass switch connected in parallel with the storage battery and the cutoff switch are provided in the bypass unit. In this power storage system, when there is a storage battery that cannot discharge the required current, bypass control is executed in which the cutoff switch corresponding to the storage battery is in an open state and the bypass switch corresponding to the storage battery is in a closed state, and discharge is performed from other storage batteries in the connected state.

[0003] Japanese Patent Application Laid-Open No. 2013-31247

[0004] Assume a case where a switch for connecting / disconnecting the entire power storage string and a smoothing capacitor for connecting the positive side and the negative side of the power storage string are provided in the power storage system described in Patent Document 1. In this case, when the potential difference between the total voltage of the power storage string and the smoothing capacitor becomes large, the inrush current to the smoothing capacitor becomes large, so it is necessary to use a high-cost switch with a high withstand voltage for the switch through which the inrush current flows.

[0005] Therefore, it is conceivable to connect a precharge circuit in parallel to the switch for connecting / disconnecting the entire power storage string. In the precharge circuit, a relay and a resistor are connected in series, and the inrush current passes through the relay and the resistor. Here, in order to suppress the inrush current, it is necessary to increase the resistance value of the resistor in the precharge circuit.

[0006] In contrast, in the energy storage system described in Patent Document 1, it is necessary to prevent large fluctuations in input / output power between the energy storage string and the external system due to abrupt changes in the current of the energy storage string (hereinafter referred to as string current) during bypass control. Therefore, it is necessary to reduce the string current to a predetermined value before performing bypass control. On the other hand, if the interruption switch and bypass switch are mechanical relays, in order to remove the oxide film that forms on the contact portions of the interruption switch and bypass switch over time, it is necessary to operate the interruption switch and bypass switch with a voltage of a certain level or higher applied between the contacts of the interruption switch and bypass switch to generate an arc discharge with a current value of a certain level or higher at the contact portions.

[0007] 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 cutoff switch and bypass switch, preventing the generation of an arc discharge with a current above a certain level, which may result in insufficient removal of the oxide film. Therefore, a means is needed that allows both reducing the string current before operating the cutoff switch and bypass switch, and operating the cutoff switch and bypass switch with a voltage sufficient to remove the oxide film applied.

[0008] One possible method involves using a precharge circuit to switch the cutoff switch from open to closed while charging the smoothing capacitor with the power of any battery, or switching the bypass switch from open to closed while the smoothing capacitor is discharging. However, in this method, the resistance value of the precharge circuit resistor must be reduced in order to generate an arc discharge at the cutoff switch and the contact points of the bypass switch. If the resistance value of the precharge circuit resistor is reduced, the inrush current will increase, and the relay and resistor in the precharge circuit through which this inrush current flows will need to be high-voltage, high-cost components.

[0009] In view of the above circumstances, the present invention aims to alleviate the constraints caused by the resistance value of the precharge circuit in an energy storage system in which a capacitor, a switch for connecting / disconnecting the capacitor and the batteries, and a precharge circuit connected in parallel with the switch are provided on a power line connecting a plurality of batteries in series.

[0010] The energy storage system of the present invention comprises a power line connecting a plurality of batteries in series, a capacitor connecting the positive and negative sides of the power line, a first switch provided between the capacitor and the batteries of the power line for connecting or disconnecting the capacitor and the batteries of the power line, a resistor connected in parallel with the first switch to the power line, and a second switch for connecting or disconnecting the resistor and the power line, and a precharge circuit through which a precharge current flows to the capacitor, the precharge circuit comprising a resistance value variable unit for varying the resistance value of the resistor.

[0011] According to the present invention, in an energy storage system in which a capacitor, a switch for connecting / disconnecting the capacitor and the batteries, and a precharge circuit connected in parallel with the switch are provided on a power line connecting a plurality of batteries in series, the constraints caused by the resistance value of the precharge circuit can be alleviated.

[0012] Figure 1 is a schematic circuit diagram showing an outline of an energy storage system according to one embodiment of the present invention. Figure 2 is a circuit diagram for explaining the first oxide film removal process. Figure 3 is a circuit diagram for explaining the second oxide film removal process. Figure 4 is a circuit diagram for explaining the pre-charge process. Figure 5 is a flowchart for explaining 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 outline of an energy storage system according to another embodiment of the present invention.

[0013] 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.

[0014] 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 an energy storage string STR, a power converter PCS, a string bus 2, and a battery control device 100. Although not shown, the energy storage system 1 comprises a plurality of energy storage strings STR, which are connected in parallel to each other via the string bus 2 and are also connected to an external system (not shown). The energy storage system 1 is a power source for stationary or vehicle-mounted use.

[0015] 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, lithium-ion capacitors, and nickel-metal hydride batteries.

[0016] 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.

[0017] 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.

[0018] 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.

[0019] 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 (hereinafter referred to as the total + of the energy storage string STR) and the negative terminal of the ending battery module Mn (hereinafter referred to as the total - of the energy storage string STR).

[0020] 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.

[0021] 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.

[0022] 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 a synchronization means to track changes in instantaneous values.

[0023] The energy storage string STR comprises n bypass units B1 to Bn, a system main relay S3, a smoothing capacitor C, a pre-charge circuit 10, 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 StC.

[0024] 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.

[0025] 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.

[0026] 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 that bypass unit 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 that bypass unit B1 to Bn are bypassed. When it is not necessary to distinguish each bypass unit B1 to Bn from other bypass units B1 to Bn, they will be referred to as bypass unit Bx. Similarly, when it is not necessary to distinguish each battery module M1 to Mn from other battery modules M1 to Mn, they will be referred to as battery module Mx.

[0027] The smoothing capacitor C is connected between the total positive terminal of the energy storage string STR and the system main relay S3, and between the total negative terminal of the energy storage string STR and the terminal battery module Mn. The smoothing 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.

[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 + of the energy storage string STR and the trip switch S1 of the bypass unit B1 at the starting end. The system main relay S3 is also located between the smoothing capacitor C and the battery module M1 at the starting end. The system main relay S3 can be a mechanical relay, a semiconductor switch, or the like.

[0029] The pre-charge circuit 10 includes a first resistor Rp, a second resistor Rc, a first pre-charge relay S4, and a second pre-charge relay S5. The first pre-charge relay S4 is a mechanical relay, a semiconductor switch, etc. The first resistor Rp and the first pre-charge relay S4 are connected in series and are connected in parallel with the system main relay S3.

[0030] The second pre-charge relay S5 is a mechanical relay, a semiconductor switch, etc. The second resistor Rc and the second pre-charge relay S5 are connected in series, and the first resistor Rp and the first pre-charge relay S4 are connected in parallel. In addition, the second resistor Rc and the second pre-charge relay S5 are connected in parallel with the system main relay S3.

[0031] The precharge circuit 10 includes a resistance variable mechanism 11. The resistance variable mechanism 11 includes a first precharge relay S4 and a second precharge relay S5. When the first precharge relay S4 is closed and the second precharge relay S5 is open, the resistance value of the resistor in the precharge circuit 10 is the resistance value of the first resistor Rp. Conversely, when the first precharge relay S4 is open and the second precharge relay S5 is closed, the resistance value of the resistor in the precharge circuit 10 is the resistance value of the second resistor Rc.

[0032] The precharge circuit 10 is a circuit for charging (precharging) the smoothing capacitor C when the energy storage string STR is started up, etc. In this embodiment, in addition to the precharge process for charging the smoothing capacitor C, the precharge circuit 10 is used for a first oxide film removal process to remove the oxide film from the contact portion of the cutoff switch S1, and a second oxide film removal process to remove the oxide film from the contact portion of the bypass switch S2.

[0033] Here, the resistance value of the second resistor Rc is lower than the resistance value of the first resistor Rp. The resistance value of the first resistor Rp is set high from the viewpoint of suppressing the inrush current when the pre-charge process is executed. In contrast, the resistance value of the second resistor Rc is set low from the viewpoint of raising the current value when the first oxide film removal process and the second oxide film removal process are executed to a certain value or higher that generates an arc discharge in the cutoff switch S1 and the bypass switch S2.

[0034] The battery control device 100 comprises a string controller StC, a relay driver RD, and a system controller SyC. A system controller SyC is provided for each energy storage system 1. Although not shown in the diagram, the battery control device 100 comprises a plurality of string controllers StC and a plurality of relay drivers RD, with each string controller StC and each relay driver RD provided for each energy storage string STR.

[0035] The string controller StC transmits control signals to the relay driver RD and power converter PCS of the corresponding energy storage string STR. The relay driver RD controls the bypass switch S1 and bypass switch S2 of the bypass unit Bx, the system main relay S3, the first precharge relay S4, and the second precharge relay S5 according to the control signals transmitted from the string controller StC. 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 StC. The power converter PCS also controls the string current of the energy storage string STR according to the control signals from the string controller StC.

[0036] The string controller StC performs functions such as detecting and estimating the state of the energy storage string STR, and notifying the system controller SyC of equipment control requests. 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 module Mx based on the detection signal of the voltage sensor, detecting the temperature of the battery module Mx 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 module Mx, and estimating the State of Charge (SOC) and State of Health (SOH) of the energy storage string STR. Furthermore, examples of notifying the system controller SyC of equipment control requests include requests for switching control of the Open / Close switches S1 and S2 of the bypass unit Bx, and requests for control of the power converter PCS.

[0037] 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).

[0038] 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.

[0039] The system controller SyC is a controller that comprehensively controls the entire energy storage system 1 and performs 1:m communication with multiple string controllers StC. The system controller SyC monitors the status of the energy storage strings STR, determines whether to grant or deny control requests for equipment from the string controllers StC, and notifies the string controllers StC of the authorization of equipment control requests. The system controller SyC also sets the indicative value of the charge / discharge power (or current) for each energy storage string STR and transmits the indicative value of said charge / discharge power (or current) to the string controllers StC.

[0040] The system controller SyC monitors the state of the energy storage strings STR based on the detection and estimation results of the state of the energy storage strings STR transmitted from the string controller StC. Then, the system controller SyC calculates the instructed charge / discharge power (or current) to be allocated to each energy storage string STR, according to the input / output power (or current) instruction for the entire energy storage system 1 received from a higher-level system (not shown) and the state of the energy storage strings STR.

[0041] Here, each string controller StC executes the Open / Close switching control of the bypass switch S1 and bypass switch S2 of the bypass unit Bx corresponding to any of the battery modules Mx (hereinafter referred to as the bypass control request) when permitted by the system controller SyC. When the bypass control is executed, the string controller StC executes the first oxide film removal process and the second oxide film removal process.

[0042] During bypass control, the following processes are executed: string current reduction, first oxide film removal, second oxide film removal, bypass state switching, and pre-charge. The string current reduction process reduces 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 energy storage system 1 are kept within an acceptable range when bypass control of the energy storage string STR is executed.

[0043] Here, in the string current reduction process, the string controller StC gradually and continuously reduces the commanded value of the string current from the current value to a predetermined value. Specifically, the string controller StC repeatedly updates the commanded 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 commanded value of the string current. At this time, the change rate (amount of change per unit time) of the commanded value of the string current is set such that the 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 the fluctuations in the input / output power of the entire power storage system 1 within the allowable range.

[0044] 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 smoothing capacitor C is lower than the potential of the battery module M' targeted for bypass control. At this time, the system main relay S3 is Open, the first precharge relay S4 is Open, the second precharge relay S5 is Close, and the bypass switch S2 of the bypass unit B' is Open. Also, in other bypass units Bx, the cutoff switch S1 is Open and the bypass switch S2 is Close. Thereby, current flows through the cutoff switch S1, the second precharge relay S5, the second resistor Rc, the smoothing capacitor C, and the bypass switch S2 of the other bypass unit Bx from the battery module M', and the smoothing capacitor C is charged.

[0045] Here, the potential difference between the battery module M' and the smoothing capacitor C is set to a magnitude sufficient to generate an arc discharge that removes the oxide film on the contact portion of the cutoff switch S1 when the cutoff switch S1 of the bypass unit B' is switched. In the present embodiment, before the execution of the first oxide film removal process, the charge of the smoothing capacitor C is removed by the operation of the power converter PCS. Note that it is not necessary for the potential of the smoothing capacitor C to be 0 at the start point of the first oxide film removal process, and it may be at a low potential such that the oxide film on the contact portion of the cutoff switch S1 of the bypass unit B' can be removed when the cutoff switch S1 is switched.

[0046] Also, the charging time of the smoothing capacitor C is set in consideration of the time constant (τ = CR) of the capacitance (C) of the smoothing capacitor C and the resistance value (R) of the second resistor Rc so that a sufficient amount of charge flows from the battery module M' to the smoothing capacitor C to remove the oxide film on the contact portion of the cutoff switch S1.

[0047] Therefore, in the first oxide film removal process, the cutoff switch S1 is switched from Open to Close while a voltage sufficient to remove the oxide film on the contact portion is applied, thereby removing the oxide film on the contact portion of the cutoff switch S1.

[0048] FIG. 3 is a circuit diagram for explaining the second oxide film removal process. As shown in this figure, in the second oxide film removal process, with the smoothing capacitor C charged, the bypass switch S2 of the bypass unit B' is switched from Open to Close. At this time, the system main relay S3, the first precharge relay S4, and the cutoff switch S1 are Open, and the second precharge relay S5 is Close. Also, in other bypass units Bx, the cutoff switch S1 is Open and the bypass switch S2 is Close. As a result, the smoothing capacitor C discharges, and current flows through the second resistor Rc, the second precharge relay S5, the bypass switch S2, and the bypass switch S2 of the other bypass units Bx from the smoothing capacitor C.

[0049] Here, the potential of the smoothing capacitor C is set to a height sufficient to generate an arc discharge that removes the oxide film from the contact portion of the bypass switch S2 when the bypass switch S2 of the bypass unit B' is switched. In this embodiment, the charging time of the smoothing capacitor C during the execution of the second oxide film removal process is set considering the time constant (τ = CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the second resistor Rc.

[0050] Furthermore, the discharge time of the smoothing capacitor C is set considering the time constant (τ = CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the second resistor Rc, so that a sufficient amount of charge flows from the smoothing capacitor C to the bypass switch S2 to remove the oxide film on the contact portion of the bypass switch S2.

[0051] 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.

[0052] Figure 4 is a circuit diagram illustrating the pre-charge process. As shown in this figure, the pre-charge process is a process in which the smoothing capacitor C is charged from the connected battery module Mx via the pre-charge circuit 10. In this embodiment, after the smoothing capacitor C is discharged during the second oxide film removal process and its charge is removed, the process is performed with the battery module Mx, which is not subject to bypass control, either connected or bypassed.

[0053] During pre-charge processing, the bypass switch S1, system main relay S3, and second pre-charge relay S5 of bypass unit B' are open, while the bypass switch S2 and first pre-charge relay S4 of bypass unit B' are closed. Other battery modules Mx are either connected or bypassed depending on their charge status.

[0054] During the pre-charge process, the current flowing from the connected battery module Mx to the smoothing capacitor C passes through the pre-charge circuit 10 without going through the system main relay S3. Here, the potential difference between the decharged smoothing capacitor C and the entire connected battery module Mx becomes large, but during the pre-charge process, the inrush current to the smoothing capacitor C is suppressed by the first resistor Rp of the pre-charge circuit 10.

[0055] 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 StC monitors the battery module Mx 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.

[0056] At the start of the process shown in the flowchart of Figure 5, the first precharge relay S4 and the second precharge relay S5 are open, and the system main relay S3 is closed. In the bypass unit Bx corresponding to the connected battery module Mx, the bypass switch S2 is open and the cutoff switch S1 is closed. On the other hand, in the bypass unit Bx corresponding to the bypassed battery module Mx, 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 smoothing capacitor C is in a charged state (post-precharge state).

[0057] In step S02, the string controller StC records the current connection or bypass status of the battery module Mx of the energy storage string STR in its built-in memory (not shown). Next, the string controller StC 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 StC gradually and continuously reduces the indicated value of the string current by a predetermined amount ΔP1 from the current value to the predetermined value.

[0058] First, in step S03, the string controller StC 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.

[0059] Next, in step S04, the string controller StC waits for a predetermined time T1 after transmitting the string current instruction value to the power converter PCS. This predetermined time T1 is set considering the time required for the string controller StC to control the power converter PCS and the rate of change of the string current.

[0060] Next, in step S05, the string controller StC determines whether the string current has reached a predetermined value (i.e., whether the decrease in 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.

[0061] Next, in step S06, the string controller StC sends a control signal to the relay driver RD to switch the system main relay S3 from Close to Open. This disconnects the energy storage string STR from the power converter PCS.

[0062] Next, in step S07, the string controller StC sends a control signal to the relay driver RD to open the disconnect switch S1 and bypass switch S2 of all bypass units Bx. As a result, all battery modules Mx are shut off.

[0063] Next, in step S08, the string controller StC transmits a control signal to the power converter PCS to discharge the smoothing capacitor C. In this step, the charge of the smoothing capacitor C is removed so that the oxide film on the contact portion of the cutoff switch S1 can be removed in the first oxide film removal process (step S11). Note that the potential of the smoothing capacitor C does not need to be zero.

[0064] Next, in step S09, the string controller StC sends a control signal to the relay driver RD to switch the bypass switch S2 of the bypass units Bx other than bypass unit B' from Open to Close. As a result, the battery modules Mx other than battery module M' enter the bypass state.

[0065] Next, in step S10, the string controller StC sends a control signal to the relay driver RD to switch the second pre-charge relay S5 from Open to Close. As a result, the second resistor Rc is connected to the power line PL in a state that bypasses the system main relay S3.

[0066] Next, in step S11, the string controller StC sends a control signal to the relay driver RD to switch the cutoff switch S1 corresponding to the battery module M' from Open to Close. Next, in step S12, the string controller StC waits for a predetermined time T2 after switching the cutoff switch S1 corresponding to the battery module M' from Open to Close. This predetermined time T2 is the time required to charge the smoothing capacitor C and is set considering the time constant (τ = CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the second resistor Rc. As a result, the first oxide film removal process is executed and the oxide film on the contact portion of the cutoff switch S1 of the bypass unit B' is removed (see Figure 2). In step S12, the smoothing capacitor C is charged from the connected battery module Mx via the pre-charge circuit 10, but the smoothing capacitor C may also be charged from the string bus 2 side by the operation of the power converter PCS.

[0067] Next, in step S13, the string controller StC switches the cutoff switch S1 corresponding to the battery module M' from Close to Open, and then sends a control signal to the relay driver RD to switch the bypass switch S2 corresponding to the battery module M' from Open to Close. Next, in step S14, the string controller StC switches the bypass switch S2 of the bypass unit B' from Open to Close and then waits for a predetermined time T3. This predetermined time T3 is the time required for the smoothing capacitor C to discharge, and is set considering the time constant (τ = CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the second resistor Rc. As a result, the second oxide film removal process is executed, and the oxide film on the contact portion of the bypass switch S2 of the bypass unit B' is removed (see Figure 3).

[0068] Next, in step S15, the string controller StC sends a control signal to the relay driver RD to switch the second precharge relay S5 from Close to Open. Next, in step S16, the string controller StC sends a control signal to the relay driver RD to switch the connected / bypass state of the battery module Mx 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 connected / bypass state of the battery module Mx stored in memory in step S02 is in the bypass state.

[0069] Next, in step S17, the string controller StC sends a control signal to the relay driver RD to switch the first precharge relay S4 from Open to Close. Next, in step S18, the string controller StC waits for a predetermined time T4 after switching the first precharge relay S4 from Open to Close. This predetermined time T4 is the time required to charge the smoothing capacitor C, and is set considering the time constant (τ = CR) between the capacitance (C) of the smoothing capacitor C and the resistance (R) of the first resistor Rp. As a result, the precharge process is executed and the smoothing capacitor C is charged (see Figure 4).

[0070] Next, in step S19, the string controller StC sends a control signal to the relay driver RD to switch the system main relay S3 from Open to Close. This connects the energy storage string STR to the power converter PCS.

[0071] Next, in step S20, the string controller StC sends a control signal to the relay driver RD to switch the first precharge relay S4 from Close to Open. This completes the bypass control of the battery module M', the removal of the oxide film from the contact portions of the cutoff switch S1 and bypass switch S2 of the bypass unit B', and the precharging of the smoothing capacitor C. This completes the process shown in the flowchart of Figure 5.

[0072] As described above, in the energy storage system 1 according to this embodiment, a precharge circuit 10, in which a first precharge relay S4 and a first resistor Rp are connected in series, is connected in parallel with the system main relay S3. Furthermore, the precharge circuit 10 is provided with a variable resistance mechanism 11 that makes the resistance value of the precharge circuit 10 variable. As a result, when the smoothing capacitor C is not charged, such as when the energy storage system 1 is started up, the system main relay S3 is opened and the first precharge relay S4 is closed, and the resistance value of the precharge circuit 10 is increased by the variable resistance mechanism 11, thereby suppressing the inrush current to the smoothing capacitor C. Consequently, the required withstand voltage of the first precharge relay S4 and the first resistor Rp through which the inrush current flows is reduced, so that low-cost components with a low withstand voltage can be used as the first precharge relay S4 and the first resistor Rp through which the inrush current flows.

[0073] On the other hand, in situations where it is desirable to lower the resistance value of the precharge circuit 10, such as when performing the first oxide film removal process or the second oxide film removal process, the resistance value of the precharge circuit 10 can be lowered by the resistance value variable mechanism 11. Therefore, the constraints on the energy storage string STR side processes, such as the first oxide film removal process and the second oxide film removal process, due to the influence of the resistance value of the first resistor Rp provided in the precharge circuit 10 can be alleviated.

[0074] In particular, the energy storage system 1 according to this embodiment is equipped with a bypass unit Bx for each battery module Mx, which includes a cutoff switch S1 and a bypass switch S2, and the string current is reduced before bypass control is performed in order to suppress fluctuations in input / output power between the energy storage system 1 and an external system. In such an energy storage system 1, when the first oxide film removal process is performed, the system main relay S3 is opened and the resistance value of the precharge circuit 10 is lowered by the resistance value variable mechanism 11, thereby allowing a high voltage to be applied to the contact portion of the cutoff switch S1. Similarly, when the second oxide film removal process is performed, the system main relay S3 is opened and the resistance value of the precharge circuit 10 is lowered by the resistance value variable mechanism 11, thereby allowing a high voltage to be applied to the contact portion of the bypass switch S2. Therefore, even under the constraint that bypass control must be performed after reducing the string current in order to suppress fluctuations in input / output power between the energy storage system 1 and the external system, it is possible to generate an arc discharge with a sufficient current value at the contact portions of the interruption switch S1 and the bypass switch S2, and to remove the oxide film formed at the contact portions of the interruption switch S1 and the bypass switch S2.

[0075] Furthermore, in the energy storage system 1 according to this embodiment, the battery control device 100 controls the variable resistance mechanism 11 so that the resistance value of the precharge circuit 10 becomes lower than that during the precharge process when the first oxide film removal process is executed. This makes it possible to avoid the first oxide film removal process being constrained by the resistance value of the precharge circuit 10.

[0076] Furthermore, in the energy storage system 1 according to this embodiment, the battery control device 100 controls the variable resistance mechanism 11 so that the resistance value of the precharge circuit 10 becomes lower than that during the precharge process when the second oxide film removal process is executed. This makes it possible to avoid the second oxide film removal process being constrained by the resistance value of the precharge circuit 10.

[0077] Furthermore, the variable resistance mechanism 11 includes a first precharge relay S4 and a second precharge relay S5. The precharge circuit 10 also includes a first resistor Rp and a second resistor Rc. The first resistor Rp is connected in parallel with the system main relay S3 to the power line PL, and the second resistor Rc is connected in parallel with the first resistor Rp and the first precharge relay S4, and has a lower resistance value than the first resistor Rp. The first precharge relay S4 is connected in series with the first resistor Rp, and the second precharge relay S5 is connected in series with the second resistor Rc. As a result, by closing the first precharge relay S4 and opening the second precharge relay S5, the resistance value of the precharge circuit 10 can be set to the resistance value of the first resistor Rp. In contrast, by opening the first precharge relay S4 and closing the second precharge relay S5, the resistance value of the precharge circuit 10 can be set to the resistance value of the second resistor Rc (< the resistance value of the first resistor Rp). Therefore, the resistance value of the precharge circuit 10 can be set to a resistance value that suppresses inrush current when the precharge process is executed, or to a resistance value that generates an arc discharge with a sufficient current value at the contact portions of the cutoff switch S1 and the bypass switch S2 when the first oxide film removal process and the second oxide film removal process are executed.

[0078] Figure 6 is a schematic circuit diagram showing another embodiment of the energy storage system 1' of the present invention. As shown in this figure, the energy storage system 1' of this embodiment includes a precharge circuit 10' instead of the precharge circuit 10 described above. Components similar to those in the above embodiments are denoted by the same reference numerals, and the descriptions of the above embodiments will be used accordingly.

[0079] The precharge circuit 10' includes a first resistor Rp1, a second resistor Rp2, a first precharge relay S4, and a second precharge relay S5. The precharge circuit 10' also includes a resistance variable mechanism 11'. The resistance variable mechanism 11' includes a second precharge relay S5.

[0080] The first resistor Rp1, the second resistor Rp2, and the first precharge relay S4 are connected in series. The first resistor Rp1, the second resistor Rp2, and the first precharge relay S4 are connected in parallel with the system main relay S3. The second precharge relay S5 is connected in parallel with the second resistor Rp2.

[0081] When the first precharge relay S4 is open, the first resistor Rp1 and the second resistor Rp2 are disconnected from the power line PL. When the first precharge relay S4 is closed, the first resistor Rp1 and either the second resistor Rp2 or the second precharge relay S5 are connected to the power line PL.

[0082] Here, when the first precharge relay S4 and the second precharge relay S5 are in the Closed state, the second resistor Rp2 is in a bypass state and disconnected from the first resistor Rp1, so the resistance value of the precharge circuit 10' becomes the resistance value of the first resistor Rp1. In contrast, when the first precharge relay S4 is in the Closed state and the second precharge relay S5 is in the Open state, the first resistor Rp1 and the second resistor Rp2 are connected in series, so the resistance value of the precharge circuit 10 becomes the sum of the resistance values ​​of the first resistor Rp1 and the second resistor Rp2.

[0083] The sum of the resistance values ​​of the first resistor Rp1 and the second resistor Rp2 is set high from the perspective of suppressing the inrush current when the pre-charge process is executed. In contrast, the resistance value of the first resistor Rp1 is set low from the perspective of raising the current value during the execution of the first oxide film removal process and the second oxide film removal process to a certain value or higher that generates an arc discharge in the cutoff switch S1 and the bypass switch S2.

[0084] Note that connecting the second pre-charge relay S5 in parallel with the second resistor Rc is not mandatory; the second pre-charge relay S5 may also be connected in parallel with the first resistor Rp.

[0085] 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.

[0086] For example, in the above embodiment, the resistance value of the precharge circuit 10 is changed to suppress the inrush current during the execution of the precharge process and to address the increase in the applied voltage to the cutoff switch S1 and the bypass switch S2 during the execution of the first oxide film removal process and the second oxide film removal process. Furthermore, bypass control is performed in the above embodiment. However, it is not essential to perform the first oxide film removal process, the second oxide film removal process, and bypass control. For example, the resistance value of the precharge circuit 10 may be changed to address the change in the string voltage of the energy storage string STR.

[0087] Furthermore, in the above-described embodiment, the cutoff switch S1 and the bypass switch S2 are mechanical relays, but at least 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.

[0088] Furthermore, the timing for executing 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.

[0089] 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 smoothing capacitor C. In the first oxide film removal process, the cutoff switch S1 may be operated to form a circuit and discharge the smoothing capacitor C, thereby removing the oxide film from the contact portion of the cutoff switch S1 using the discharge current of the smoothing capacitor C.

[0090] Furthermore, in the second oxide film removal process, it is not essential to remove the oxide film from the contact portion of the bypass switch S2 using the discharge current of the smoothing capacitor C. In the second oxide film removal process, the oxide film from the contact portion of the bypass switch S2 may be removed by operating the bypass switch S2 to form a circuit and charge the smoothing capacitor C, thereby using the charging current of the smoothing capacitor C.

[0091] 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 systems 1,1' is negligible, the indicated values ​​of the string current may be changed simultaneously.

[0092] 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 [6].

[0093] [1] Energy storage system (1) comprising: a power line (PL) connecting a plurality of storage batteries (M1 to Mn) in series; a capacitor (C) connecting the positive and negative sides of the power line (PL); a first switch (S3) provided between the capacitor (C) of the power line (PL) and the storage batteries (M1 to Mn) to connect or disconnect the capacitor (C) of the power line (PL) and the storage batteries (M1 to Mn); a precharge circuit (10) through which a precharge current flows to the capacitor (C), wherein the precharge circuit (10) comprises: a power line (PL) connecting a plurality of storage batteries (M1 to Mn) in series; a capacitor (C) connecting the positive and negative sides of the power line (PL); a first switch (S3) provided between the capacitor (C) and the storage batteries (M1 to Mn) to connect or disconnect the capacitor (C); a precharge circuit (10) through which a precharge current flows to the capacitor (C); the precharge circuit (10) comprises a resistance value variable unit (11) to vary the resistance value of the resistors (Rp, Rc). [2] The energy storage system (1) according to [1], comprising a third switch (S1) connected in series with the batteries (M1 to Mn) by the power line (PL), and a fourth switch (S2) connected in parallel with the batteries (M1 to Mn) and the third switch (S1), and further comprising a plurality of bypass sections (B1 to Bn) provided for each of the batteries (M1 to Mn). [3] The device comprises a control unit (100) that controls the first switch (S3), the second switches (S4, S5), the third switch (S1), the fourth switch (S2), and the resistance variable unit (11), wherein the control unit (100) opens the fourth switch (S2) corresponding to any of the storage batteries (M1 to Mn), disconnects the connection between the capacitor (C) of the power line (PL) and the storage batteries (M1 to Mn) using the first switch (S3), connects the resistors (Rp, Rc) and the power line (PL) using the second switches (S4, S5), and operates the third switch (S1) corresponding to any of the storage batteries to perform a first oxide film removal process that removes the oxide film on the contact portion of the third switch (S1), The energy storage system (1) according to [2], wherein the resistance variable unit (11) is controlled so that when the first oxide film removal process is performed, the resistance value of the resistors (Rp, Rc) is lower than when the pre-charge process is performed in which the capacitor (C) is charged with the pre-charge current.[4] The device comprises a control unit (100) that controls the first switch (S3), the second switches (S4, S5), the third switch (S1), the fourth switch (S2), and the resistance variable unit (11), wherein the control unit (100) performs a second oxide film removal process by opening the third switch (S1) corresponding to any of the storage batteries (M1 to Mn), disconnecting the connection between the capacitor (C) of the power line (PL) and the storage batteries (M1 to Mn) using the first switch (S3), connecting the resistors (Rp, Rc) and the power line (PL) using the second switches (S4, S5), and operating the fourth switch (S2) corresponding to any of the storage batteries (M1 to Mn) to remove the oxide film on the contact portion of the fourth switch (S2), [2] The energy storage system (1) according to [2], wherein when the second oxide film removal process is performed, the resistance variable unit (11) is controlled so that the resistance value of the resistors (Rp, Rc) is lower than when the pre-charge process is performed in which the capacitor (C) is charged with the pre-charge current. [5] The resistor comprises a first resistor (Rp) connected in parallel with the first switch (S3) to the power line (PL), and a second resistor (Rc) connected in parallel with the first switch (S3) and the first resistor (Rp) to the power line (PL), and having a lower resistance value than the first resistor (Rp), and the resistance variable unit (11) comprises a pair of second switches (S4, S5), one of the second switches (S4) connected in series with the first resistor (Rp), and the other of the second switches (S5) connected in series with the second resistor (Rc). [6] The resistor comprises a first resistor (Rp1) connected in parallel with the first switch (S3) to the power line (PL), and a second resistor (Rp2) connected in series with the first resistor (Rp1) and in parallel with the first switch (S3) to the power line (PL), and having a lower resistance value than the first resistor (Rp1), and the resistance value variable unit (11') comprises a fifth switch (S5) connected in parallel with the first resistor (Rp1) or the second resistor (Rp2) to the energy storage system (1') according to [1] or [2].

[0094] 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.

[0095] This application is based on Japanese Patent Application No. 2024-184735 filed on October 21, 2024, the contents of which are incorporated herein by reference.

[0096] According to the present invention, in an energy storage system in which a capacitor, a switch for connecting / disconnecting the capacitor and the batteries, and a precharge circuit connected in parallel with the switch are provided on a power line connecting a plurality of batteries in series, it is possible to provide an energy storage system that can alleviate the constraints caused by the resistance value of the precharge circuit. The present invention, which achieves this effect, is useful with respect to energy storage systems.

[0097] 1: Energy storage system 1': Energy storage system 10: Precharge circuit 10': Precharge circuit 11: Variable resistance mechanism (variable resistance section) 11': Variable resistance mechanism (variable resistance section) 100: Battery control device (control unit) B1 to Bn, Bx, B': Bypass unit (bypass section) C: Smoothing capacitor (capacitor) M1 to Mn, Mx, M': Battery module (battery) PL: Power line Rp: First resistor (resistor) Rp1: First resistor (resistor) Rc: Second resistor (resistor) Rp2: Second resistor (resistor) S1: Cut-off switch (third switch) S2: Bypass switch (fourth switch) S3: System main relay (first switch) S4: First precharge relay (second switch) S5 : Second pre-charge relay (second switch, fifth switch)

Claims

1. An energy storage system comprising: a power line connecting a plurality of storage batteries in series; a capacitor connecting the positive and negative sides of the power line; a first switch provided between the capacitor and the storage batteries of the power line for connecting or disconnecting the capacitor and the storage batteries of the power line; a resistor connected in parallel with the first switch to the power line; and a second switch for connecting or disconnecting the resistor and the power line, wherein a precharge circuit through which a precharge current flows to the capacitor, the precharge circuit comprising a variable resistance unit for varying the resistance value of the resistor.

2. The energy storage system according to claim 1, comprising a third switch connected in series with the battery by the power line, and a fourth switch connected in parallel with the battery and the third switch, and further comprising a plurality of bypass sections provided for each battery.

3. The energy storage system according to claim 2, comprising a first switch, a second switch, a third switch, a fourth switch, and a control unit for controlling the variable resistance unit, wherein the control unit performs a first oxide film removal process to remove an oxide film from the contact portion of the third switch by opening the fourth switch corresponding to any of the storage batteries, disconnecting the power line between the capacitor and the storage battery using the first switch, connecting the resistor and the power line using the second switch, and operating the third switch corresponding to any of the storage batteries, and controlling the variable resistance unit to remove an oxide film from the contact portion of the third switch when the first oxide film removal process is performed, such that the resistance value of the resistor is lower than when a pre-charge process is performed to charge the capacitor with the pre-charge current.

4. The energy storage system according to claim 2, comprising a first switch, a second switch, a third switch, a fourth switch, and a control unit for controlling the variable resistance unit, wherein the control unit performs a second oxide film removal process to remove an oxide film from the contact portion of the fourth switch by opening the third switch corresponding to any of the storage batteries, disconnecting the power line between the capacitor and the storage battery using the first switch, connecting the resistor and the power line using the second switch, and operating the fourth switch corresponding to any of the storage batteries, and controlling the variable resistance unit to remove an oxide film from the contact portion of the fourth switch when the second oxide film removal process is performed, such that the resistance value of the resistor is lower than when a pre-charge process is performed to charge the capacitor with the pre-charge current.

5. The energy storage system according to claim 1 or 2, wherein the resistor comprises a first resistor connected in parallel with the first switch to the power line, and a second resistor connected in parallel with the first switch and the first resistor to the power line and having a lower resistance value than the first resistor, and the resistance value variable unit comprises a pair of second switches, one of which is connected in series with the first resistor, and the other of which is connected in series with the second resistor.

6. The energy storage system according to claim 1 or 2, wherein the resistor comprises a first resistor connected in parallel with the first switch to the power line, and a second resistor connected in series with the first resistor and in parallel with the first switch to the power line, and having a lower resistance value than the first resistor, and the resistance value variable unit comprises a fifth switch connected in parallel with the first resistor or the second resistor.

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