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

Abstract

This reduces costs while suppressing the inrush current between the battery and the smoothing capacitor. [Solution] The battery control device 100 determines in advance, before the start of charging or discharging of the battery string STR, the timing for switching between the connected state and the bypass state of the battery modules M1 to Mn by the bypass units B1 to Bn during the charging or discharging of the battery string STR. Based on the information of the above timing, it identifies the connected state of the battery modules M1 to Mn, calculates the string voltage which is the sum of the voltages of the identified connected battery modules M1 to Mn, and if the difference between the calculated string voltage and the voltage of the smoothing capacitor C exceeds a predetermined range, it charges or discharges the smoothing capacitor C with the power converter PCS to converge the difference between the string voltage and the voltage of the smoothing capacitor C to the above predetermined range.

Description

Technical Field

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

Background Art

[0002] As a power storage system in which a plurality of storage batteries are connected in series and a smoothing capacitor is connected in parallel with the plurality of storage batteries, there is known one that adjusts the potential difference between the smoothing capacitor and the plurality of storage batteries (for example, see Patent Documents 1 to 3). In the power storage system described in Patent Document 1, the total voltage of the smoothing capacitor and the plurality of storage batteries is detected, and the potential difference between the smoothing capacitor and the plurality of storage batteries is adjusted to suppress the inrush into the smoothing capacitor. Further, in the power storage system described in Patent Document 2, the inrush current into the capacitor located between the power distribution device and the plurality of storage batteries is suppressed by reducing the difference between the voltage of the power distribution device and the voltages of the plurality of storage batteries. Furthermore, in the power storage system described in Patent Document 3, a bypass section for switching the storage battery between a connected state and a bypass state is provided for each storage battery, and when discharging from the smoothing capacitor to the storage battery, the number of connected storage batteries is gradually reduced to suppress the inrush current from the smoothing capacitor to the storage battery.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an energy storage system where the above-mentioned bypass section is provided for each battery, when the connected / bypassed state of the batteries is switched by the bypass section, the total voltage fluctuation of the multiple batteries becomes steep, and there is a possibility that the potential difference adjustment between the smoothing capacitor and the total voltage of the multiple batteries may not be able to keep up. One way to suppress the inrush current between the smoothing capacitor and the batteries is to provide a precharge circuit. However, this incurs costs such as implementation costs for the precharge circuit and component replacement costs for the precharge relay.

[0005] In view of the above circumstances, the present invention aims to reduce costs and suppress inrush current between a battery and a smoothing capacitor in an energy storage system in which a plurality of batteries are connected in series and a bypass section is provided for each battery to switch between a connected state and a bypass state. [Means for solving the problem]

[0006] The present invention relates to a battery control device for controlling an energy storage system comprising: a plurality of batteries connected in series; an energy storage string having a plurality of bypass units provided for each battery to switch the battery between a connected state and a bypass state; a power converter connected to the positive and negative terminals of the energy storage string; a capacitor connected to the positive and negative terminals of the energy storage string; and a switch provided between the capacitor and the plurality of batteries. The battery control device for controlling an energy storage system comprising: a plurality of batteries connected in series; an energy storage string having a plurality of bypass units provided for each battery to switch the battery between a connected state and a bypass state; a power converter connected to the positive and negative terminals of the energy storage string; a capacitor connected to the positive and negative terminals of the energy storage string; and a switch provided between the capacitor and the plurality of batteries. During charging or discharging of the battery, before the bypass unit switches the connected state and bypass state of the battery according to the timing, the switch is switched from the closed state to the open state. After the bypass unit switches the connected state and bypass state of the battery according to the timing, the connected state of the battery is identified based on the timing information, and the string voltage, which is the sum of the voltages of the identified connected state of the battery, is calculated. If the difference between the calculated string voltage and the capacitor voltage exceeds a predetermined range, the power converter charges or discharges the capacitor to bring the difference between the string voltage and the capacitor voltage to the predetermined range.

[0007] The present invention relates to a battery control method for controlling a battery storage system using a control device, the system comprising: a battery storage string having a plurality of batteries connected in series; a plurality of bypass units provided for each battery to switch the battery between a connected state and a bypass state; a power converter connected to the positive and negative terminals of the battery storage string; a capacitor connected to the positive and negative terminals of the battery storage string; and a switch provided between the capacitor and the plurality of batteries, wherein the timing for switching the battery between the connected state and the bypass state by the bypass unit during charging or discharging of the battery storage string is predetermined before the start of charging or discharging of the battery storage string. During the charging or discharging of the power string, before the bypass unit switches the connected state and bypass state of the battery according to the timing, the switch is switched from the closed state to the open state. After the bypass unit switches the connected state and bypass state of the battery according to the timing, the connected state of the battery is identified based on the timing information, and the string voltage, which is the sum of the voltages of the identified connected state of the battery, is calculated. If the difference between the calculated string voltage and the capacitor voltage exceeds a predetermined range, the power converter charges or discharges the capacitor to bring the difference between the string voltage and the capacitor voltage to the predetermined range.

[0008] The energy storage system according to the present invention comprises an energy storage string comprising a plurality of batteries connected in series, a plurality of bypass units provided for each battery that switch the battery between a connected state and a bypass state, a power converter connected to the positive and negative terminals of the energy storage string, a capacitor connected to the positive and negative terminals of the energy storage string, a switch provided between the capacitor and the plurality of batteries, and a battery control device that controls the bypass units, the power converter, and the switch, wherein the battery control device sets the timing for switching the connected state and the bypass state of the batteries by the bypass units during charging or discharging of the energy storage string before the start of charging or discharging of the energy storage string. The power converter is configured to first determine the timing, and during the charging or discharging of the energy storage string, before the bypass unit switches the connected state and bypass state of the storage battery according to the timing, the switch is switched from the closed state to the open state. After the bypass unit switches the connected state and bypass state of the storage battery according to the timing, the connected state of the storage battery is identified based on the timing information, the string voltage, which is the sum of the voltages of the identified connected state of the storage battery, is calculated, and if the difference between the calculated string voltage and the capacitor voltage exceeds a predetermined range, the power converter charges or discharges the capacitor to bring the difference between the string voltage and the capacitor voltage to within the predetermined range. [Effects of the Invention]

[0009] According to the present invention, in an energy storage system in which multiple 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, it is possible to reduce costs while suppressing the inrush current between the storage battery and the smoothing capacitor. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a schematic circuit diagram showing an energy storage system according to one embodiment of the present invention. [Figure 2]Figure 2 is a timing chart illustrating when each battery module is bypassed during a single charging cycle. [Figure 3] Figure 3 is a timing chart illustrating the timing of bypassing each battery module during a single discharge cycle. [Figure 4] Figure 4 is a flowchart illustrating the process of switching the connected / bypass state of a battery module that is subject to bypass control or connection control. [Modes for carrying out the invention]

[0011] 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.

[0012] 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 (not shown). The energy storage system 1 is a power source for stationary or vehicle-mounted use.

[0013] Each energy storage string STR comprises a power line PL and n (where n is an integer of 2 or more) battery modules M1 to Mn connected in series by the 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.

[0014] Battery modules M1 to Mn are charged by receiving power from the external grid via string bus 2 and power converter PCS. Conversely, battery modules M1 to Mn also supply power to the external grid via power converter PCS and string bus 2.

[0015] 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.

[0016] 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.

[0017] Each power converter PCS is either a DC / DC converter or an AC / DC converter and is connected to string bus 2. Furthermore, 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) are connected to the power converter PCS.

[0018] When the power converter PCS charges the energy storage string STR, it converts the voltage input from the string bus 2 according to the indicated value of the charging power (or current) and outputs it to a plurality of battery modules M1 to Mn. Here, the voltage on the energy storage string STR side changes according to the bypass state of the battery modules M1 to Mn (the number of battery modules M1 to Mn that are bypassed) and the charging state of the battery modules M1 to Mn. Therefore, when the power converter PCS charges the energy storage string STR, it converts the voltage input from the string bus 2 into the voltage on the energy storage string STR side and outputs it to a plurality of battery modules M1 to Mn.

[0019] When the power converter PCS discharges the energy storage string STR, it converts the voltage input from a plurality of battery modules M1 to Mn according to the indicated value of the discharging power (or current) and outputs it to the string bus 2. Here, the input voltage of the power converter PCS during discharging changes according to the bypass state of the battery modules M1 to Mn and the charging state of the battery modules M1 to Mn. As a result, variations occur in the input voltages of the plurality of power converters PCS during the discharge of the energy storage string STR. Therefore, when the energy storage string STR discharges, each power converter PCS converts the input voltage into an output voltage that is matched with the other power converters PCS.

[0020] The power converter PCS is a bidirectional converter. When the current flowing through the string bus 2 is alternating current, the power converter PCS includes synchronization means for following the change in the instantaneous value.

[0021] The energy storage string STR includes n bypass units B1 to Bn, n voltage sensors Vm, and various sensors (not shown). Each of the bypass units B1 to Bn and the voltage sensors Vm are provided for each of the battery modules M1 to Mn. Also, for each energy storage string STR, a system main relay S3, a smoothing capacitor C, and a voltage sensor Vc are provided.

[0022] Each bypass unit B1 to Bn is equipped with a trip switch S1, a bypass line BL, and a bypass switch S2. The trip switch S1 is a mechanical relay connected in series with each battery module M1 to Mn via a power line PL. The trip switch S1 is located on the positive side of the energy string STR relative to each battery module M1 to Mn and is connected to the positive terminal of each battery module M1 to Mn via the power line PL. Note that the trip switch S1 may also be a semiconductor switch.

[0023] The bypass line BL is a power line that bypasses each battery module M1 to Mn and the trip switch S1. One end of the bypass line BL is connected to the power line PL at node P1, and via the power line PL it is connected to the positive terminal of the trip switch S1. The other end of the bypass line BL is connected to the power line PL at node P2, and via the power line PL it is connected to the negative terminals 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 trip switch S1. Note that the bypass switch S2 may also be a semiconductor switch.

[0024] The starting battery module M1 and the ending battery module Mn are connected to the external system via power lines PL, power converters PCS, and string bus 2. When the bypass switch S2 opens and the circuit breaker switch S1 closes 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 opens and the bypass switch S2 closes 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.

[0025] Each voltage sensor Vm is provided for each battery module M1 to Mn, and detects the voltage of each battery module M1 to Mn and outputs it to the string controller 102. Alternatively, the voltage of each cell in each battery module M1 to Mn may be output to the string controller 102 from a cell voltage sensor (not shown), and the string controller 102 may determine the voltage of each battery module M1 to Mn based on the voltage of each cell.

[0026] 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. The system main relay S3 can be a mechanical relay, a semiconductor switch, or the like.

[0027] The smoothing capacitor C connects the total positive and total negative terminals of the energy storage string STR. Specifically, the smoothing capacitor C connects the system main relay S3 and the power converter PCS on the positive side of the power line PL, and the terminal battery module Mn and the power converter PCS on the negative side of the power line PL. The smoothing capacitor C is an element that stores electric charge, such as an electrolytic capacitor, film capacitor, or capacitor, and smooths the voltage input from the power converter PCS to the energy storage string STR.

[0028] The voltage sensor Vc detects the voltage across the plates of the smoothing capacitor C and outputs it to the string controller 102, which will be described later. Alternatively, instead of the voltage sensor Vc, a current sensor may be provided to detect the current flowing through the smoothing capacitor C, and the string controller 102 may determine the voltage across the smoothing capacitor C based on the current flowing through the smoothing capacitor C, the elapsed time, and the capacitance of the smoothing capacitor C.

[0029] The battery control device 100 comprises a system controller 101, a string controller 102, and a relay driver 103. The string controller 102 and relay driver 103 are provided for each battery storage string STR.

[0030] The string controller 102 transmits control signals to the relay driver 103 and power converter PCS of the corresponding energy storage string STR. The relay driver 103 controls the cutoff switches S1 and 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 and charges and discharges the smoothing capacitor C 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.

[0031] The string controller 102 performs functions such as detecting and estimating the state of the energy storage string STR, and notifying the system controller 101 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 a current sensor (not shown), detecting the voltage of battery modules M1 to Mn based on the detection signal of a voltage sensor Vm, detecting the temperature of battery modules M1 to Mn based on the detection signal of a temperature sensor (not shown), and detecting the voltage of battery cells based on the detection signal of a cell voltage sensor. Examples of estimating the state of the energy storage string STR include estimating the SOC (State of Charge) and SOH (State of Health) of battery modules M1 to Mn, and estimating the SOC and SOH of the energy storage string STR. Furthermore, examples of notifying the system controller 101 of equipment control requests include requests for switching control of the Open / Close switches S1 and S2 of bypass units B1 to Bn, and requests for control of the power converter PCS.

[0032] 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 IV characteristics (current-voltage characteristics) (slope of the straight line of the IV characteristics), and step response methods (all of which are methods that estimate using the time-dependent increase in internal resistance).

[0033] Various known methods for estimating the State of Charge (SOC) include the current integration method, the method of determining it from the Open Circuit Voltage (OCV) (voltage method), and a method that combines the current integration method and the voltage method. Furthermore, the 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.

[0034] The system controller 101 is a controller that comprehensively controls the entire energy storage system 1 and performs 1:m communication with multiple string controllers 102. The system controller 101 monitors the status of the energy storage strings STR, determines whether to grant or deny control requests for equipment from the string controllers 102, and notifies the string controllers 102 of the permission to grant control requests for equipment. The system controller 101 also sets the indicative value of the charge / discharge power (or current) for each energy storage string STR and transmits the indicative value of the charge / discharge power (or current) to the string controllers 102.

[0035] The system controller 101 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 102. The system controller 101 then calculates the instructed charge / discharge power (or current) to be allocated to each energy storage string STR, based on 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.

[0036] The string controller 102 performs charging and discharging of the energy storage string STR according to the assigned charge / discharge power instruction value. In this process, the string controller 102 does not connect all chargeable battery modules M1 to Mn and charge / discharge them all at once, but rather charges and discharges the chargeable battery modules M1 to Mn by connecting or bypassing them at predetermined timings before the start of charging and discharging.

[0037] Here, at the start of a charging cycle, the string controller 102 calculates the remaining charge capacity RC [Ah] of each battery module M1 to Mn using the following equation (1), and determines the timing for bypassing each battery module M1 to Mn during the execution of a charging cycle based on the calculated remaining charge capacity RC. RC = CC × (100 - SOC) / 100 …(1) However, CC is the current battery capacity [Ah] of each battery module M1 to Mn, and SOC is the state of charge [%] of each battery module M1 to Mn.

[0038] The current battery capacity CC of each battery module M1 to Mn is calculated using the following formula (2). CC = C0 × SOH / 100 …(2) However, C0 is the battery capacity [Ah] of each battery module M1 to Mn when new. SOH is the SOH of each battery module M1 to Mn.

[0039] The timing for bypassing each battery module M1 to Mn during a single charging cycle is determined during the first period, from the start to partway through the charging cycle, so that the difference in the remaining charge capacity RC of battery modules M1 to Mn decreases and converges to a predetermined range. During the second period, from the end of the first period to the end of the charging cycle, all battery modules M1 to Mn are connected. Details regarding the timing of bypassing each battery module M1 to Mn during a single charging cycle will be described later.

[0040] On the other hand, at the start of a discharge cycle, the string controller 102 calculates the remaining discharge capacity RD [Ah] of each battery module M1 to Mn using the following equation (3), and determines the timing for bypassing each battery module M1 to Mn during the execution of a discharge cycle based on the calculated remaining discharge capacity RD. RD = CC × SOC / 100 …(3)

[0041] The timing for bypassing each battery module M1 to Mn during a single discharge cycle is determined during the first period, from the start to partway through the discharge cycle, so that the difference in the remaining discharge capacity RD of battery modules M1 to Mn decreases and converges to a predetermined range. During the second period, from the end of the first period to the end of the discharge cycle, all battery modules M1 to Mn are connected. Details regarding the timing for bypassing each battery module M1 to Mn during a single discharge cycle will be described later.

[0042] The string controller 102 controls the voltage of the smoothing capacitor C so that the potential difference across the system main relay S3 converges to a predetermined range. As will be described in detail later, the string controller 102 performs the following processes (1) to (3). (1) The sum of the voltages of the connected battery modules M1 to Mn (hereinafter referred to as the string voltage) is calculated using the method described below. (2) Calculate the difference between the plate voltage of the smoothing capacitor C output from the voltage sensor Vc (hereinafter referred to as the capacitor voltage) and the string voltage. (3) If the difference between the capacitor voltage and the string voltage is outside the predetermined range, the power converter PCS is activated to charge and discharge the smoothing capacitor C, and the difference between the capacitor voltage and the string voltage is brought within the predetermined range.

[0043] Figure 2 is a timing chart illustrating the timing of bypassing each battery module M1-Mn during a single charging cycle. This figure shows an example of charging eight battery modules M1-M8. In this example, the remaining charge capacities RC of the eight battery modules M1-M8 at the start of the charging cycle are 100[Ah], 99[Ah], 98[Ah], 95[Ah], 90[Ah], 89[Ah], 87[Ah], and 86[Ah], respectively. Furthermore, in this example, the remaining charge capacities RC of battery modules M1-M8 are set to the minimum value at the start of the charging cycle (t0) (86[Ah] for battery module M8) at the end of the first period of the charging cycle (t6).

[0044] As shown in Figure 2, battery modules M2 to M8 with relatively small remaining charge capacity RC are preferentially bypassed, reducing the difference in remaining charge capacity RC among battery modules M1 to M8, and determining the timing of bypassing each battery module M1 to M8 during the first period so that their remaining charge capacity RC becomes equal. Specifically, battery module M1, which has the largest remaining charge capacity RC at the start of the first period, is continuously connected without being bypassed from the start to the end of the first period. On the other hand, battery module M8, which has the smallest remaining charge capacity RC at the start of the first period, is continuously bypassed without being connected from the start to the end of the first period. The other battery modules M2 to M7 are connected or bypassed during the first period from the start to the end.

[0045] Here, in the first period, the string voltage is the minimum allowable voltage V L The battery modules M2 to M7 that are bypassed are selected so as to satisfy the above conditions. In the example shown in Figure 2, three or more battery modules M1 to M7 are connected from the start to the end of the first period.

[0046] In the example shown in Figure 2, first, at time t1, in addition to battery module M8, which has the smallest remaining charge capacity RC at time t0, battery modules M5, M6, and M7, which have relatively small remaining charge capacities RC at time t0 compared to the others, are bypassed. That is, at time t1, battery modules M1, M2, M3, and M4, which have relatively large remaining charge capacities RC at time t0 compared to the others, are connected. Between times t1 and t2, battery modules M1, M2, M3, and M4 are charged. The amount of charge of battery modules M1, M2, M3, and M4 between times t1 and t2 is 7 [Ah].

[0047] Next, at time t2, in addition to battery modules M5, M6, M7, and M8, battery module M3 is bypassed, and battery modules M1, M2, and M4 are connected. Between times t2 and t3, battery modules M1, M2, and M4 are charged. The amount of charge of battery modules M1, M2, and M4 between times t2 and t3 is 2 [Ah], and the remaining charge capacity RC of battery module M4 decreases to the target value of 86 [Ah].

[0048] Next, at time t3, battery module M4, whose remaining charge capacity RC has decreased to the target value, is bypassed along with battery modules M5 to M8, and battery module M3, which had been bypassed, is connected. Between time t3 and t4, the connected battery modules M1, M2, and M3 are charged. The amount of charge of battery modules M1, M2, and M3 between time t3 and t4 is 1 [Ah].

[0049] Next, at time t4, battery modules M2 and M6 are bypassed along with battery modules M4 and M8, whose remaining charge capacity RC is at the target value, and battery modules M5 and M7, which were previously bypassed, are connected. Between time t4 and t5, the connected battery modules M1, M3, M5, and M7 are charged. The amount of charge for battery modules M1, M3, M5, and M7 between time t4 and t5 is 1 [Ah]. As a result, the remaining charge capacity RC of battery module M7 decreases to the target value of 86 [Ah].

[0050] Next, at time t5, battery modules M4, M7, and M8, whose remaining charge capacity RC is at the target value, are bypassed, and the bypassed battery modules M2 and M6 are connected. Between time t5 and t6, the connected battery modules M1, M2, M3, M5, and M6 are charged. The amount of charge for battery modules M1, M2, M3, M5, and M6 between time t5 and t6 is 3 [Ah]. As a result, the remaining charge capacity RC of battery modules M1, M2, M3, M5, and M6 decreases to the target value of 86 [Ah], and the remaining charge capacity RC of all battery modules M1 to M8 becomes equal to the target value of 86 [Ah].

[0051] Next, during the second period from time t6 until the end of the charging cycle, all connected battery modules M1 to M8 are charged. The total charge of battery modules M1 to M8 from time t6 until the end of the charging cycle is 86 [Ah]. As a result, all battery modules M1 to M8 are fully charged.

[0052] Figure 3 is a timing chart illustrating the timing of bypassing each battery module M1-Mn during a single discharge cycle. This figure shows an example of discharging eight battery modules M1-M8. In this example, the remaining discharge capacities RD of the eight battery modules M1-M8 at the start of the discharge cycle (t0) are 100[Ah], 99[Ah], 98[Ah], 95[Ah], 90[Ah], 89[Ah], 87[Ah], and 86[Ah], respectively. Furthermore, in this example, the remaining discharge capacities RD of battery modules M1-M8 are set to the minimum value at the start of the discharge cycle (86[Ah] for battery module M8) at the end of the first period of the discharge cycle (t6).

[0053] As shown in Figure 3, battery modules M2 to M8, which have relatively smaller residual discharge capacities RD compared to others, are preferentially bypassed. The timing of bypassing each battery module M1 to Mn during the first period is determined so that the difference in residual discharge capacities RD among battery modules M1 to M8 decreases and their residual discharge capacities RD become equal. Specifically, battery module M1, which has the largest residual discharge capacities RD at the start of the first period, is continuously connected without being bypassed from the start to the end of the first period. On the other hand, battery module M8, which has the smallest residual discharge capacities RD at the start of the first period, is continuously bypassed without being connected from the start to the end of the first period. The other battery modules M2 to M7 are connected or bypassed during the period from the start to the end of the first period.

[0054] Here, in the first period, the string voltage is the minimum allowable voltage V L The battery modules M2 to M7 that are bypassed are selected so as to satisfy the above conditions. In the example shown in Figure 3, three or more battery modules M1 to M7 are connected from the start to the end of the first period.

[0055] In the example shown in Figure 3, first, at time t1, in addition to battery module M8, which has the smallest remaining discharge capacity RD at time t0, battery modules M5, M6, and M7, which have relatively small remaining discharge capacities RD at time t0 compared to the others, are bypassed. That is, at time t1, battery modules M1, M2, M3, and M4, which have relatively large remaining discharge capacities RD at time t0 compared to the others, are connected. Between times t1 and t2, battery modules M1, M2, M3, and M4 discharge. The discharge amount of battery modules M1, M2, M3, and M4 between times t1 and t2 is 7 [Ah].

[0056] Next, at time t2, in addition to battery modules M5, M6, M7, and M8, battery module M3 is bypassed, and battery modules M1, M2, and M4 are connected. Between times t2 and t3, battery modules M1, M2, and M4 discharge. The discharge amount of battery modules M1, M2, and M4 between times t2 and t3 is 2 [Ah], and the remaining discharge capacity RD of battery module M4 decreases to the target value of 86 [Ah].

[0057] Next, at time t3, battery module M4, whose remaining discharge capacity RD has decreased to the target value, is bypassed along with battery modules M5 to M8, and battery module M3, which had been bypassed, is connected. Between time t3 and t4, the connected battery modules M1, M2, and M3 discharge. The discharge amount of battery modules M1, M2, and M3 between time t3 and t4 is 1 [Ah].

[0058] Next, at time t4, battery modules M2 and M6 are bypassed along with battery modules M4 and M8, whose remaining discharge capacity RD is at the target value, and battery modules M5 and M7, which were previously bypassed, are connected. Between times t4 and t5, the connected battery modules M1, M3, M5, and M7 discharge. The discharge amount of battery modules M1, M3, M5, and M7 between times t4 and t5 is 1 [Ah]. As a result, the remaining discharge capacity RD of battery module M7 decreases to the target value of 86 [Ah].

[0059] Next, at time t5, battery modules M4, M7, and M8, whose remaining discharge capacity RD is at the target value, are bypassed, and the bypassed battery modules M2 and M6 are connected. Between time t5 and t6, the connected battery modules M1, M2, M3, M5, and M6 discharge. The discharge amount of battery modules M1, M2, M3, M5, and M6 between time t5 and t6 is 3 [Ah]. As a result, the remaining discharge capacity RD of battery modules M1, M2, M3, M5, and M6 decreases to the target value of 86 [Ah], and the remaining discharge capacity RD of all battery modules M1 to M8 becomes equal to the target value of 86 [Ah].

[0060] Next, during the second period from time t6 until the end of the discharge cycle, all connected battery modules M1 to M8 discharge. The discharge amount of battery modules M1 to M8 from time t6 until the end of the discharge cycle is 86 [Ah]. As a result, all battery modules M1 to M8 are fully discharged.

[0061] Figure 4 is a flowchart illustrating the process of switching the connected / bypass state of battery modules M1 to Mn (hereinafter referred to as battery module M') that are subject to bypass control or connection control. At the start of the process shown in the flowchart of Figure 4, the system main relay S3 is in the Closed state, and the connected / bypass state of each battery module M1 to Mn is arbitrary. Also, the difference between the capacitor voltage and the string voltage is concentrated within a predetermined range.

[0062] First, the string controller 102 sends a control signal to the relay driver 103 to switch the system main relay S3 from Close to Open (step S01). As a result, the system main relay S3 opens, and the power converter PCS, smoothing capacitor C, and battery modules M1 to Mn are disconnected.

[0063] Next, the string controller 102 sends a control signal to the relay driver 103 to switch the disconnect switch S1 and bypass switch S2 corresponding to the battery module M' (step S02). If the battery module M' is subject to bypass control, first the disconnect switch S1 is switched from Close to Open, and then the bypass switch S2 is switched from Open to Close. On the other hand, if the battery module M' is subject to connection control, first the bypass switch S2 is switched from Close to Open, and then the disconnect switch S1 is switched from Open to Close.

[0064] Next, the string controller 102 calculates the string voltage (step S03). Here, at the start of the charging cycle, the string controller 102 determines the timing for bypassing each battery module M1 to Mn during the charging cycle, and monitors the connection / bypass status of each battery module M1 to Mn during the charging cycle. Also, at the start of the discharging cycle, the string controller 102 determines the timing for bypassing each battery module M1 to Mn during the discharging cycle, and monitors the connection / bypass status of each battery module M1 to Mn during the discharging cycle. Furthermore, the string controller 102 constantly monitors the voltage of each battery module M1 to Mn detected by the voltage sensor Vm.

[0065] The string controller 102 identifies the connected state of each battery module M1 to Mn based on predetermined information about the timing of bypassing each battery module M1 to Mn, and calculates the string voltage by summing the voltages of the identified connected battery modules M1 to Mn. For example, in a battery string STR in which 14 battery modules M1 to M14 are connected in series, the voltages of each battery module M1 to M14 are as follows. [Table 1]

[0066] In this case, if all battery modules M1 to M14 are connected, the string voltage will be 426V (=33 + 32 + 31 + (30 × 11)). Also, if only battery module M1 is bypassed and battery modules M2 to M14 are connected, the string voltage will be 393V, and if only battery module M4 is bypassed and battery modules M1 to M3 and M5 to M14 are connected, the string voltage will be 396V.

[0067] Alternatively, the string voltage may be calculated assuming that the voltage of all battery modules M1 to M14 is constant (for example, 33.6V). In this case, the string voltage is calculated as follows, depending on the number of bypassed battery modules M1 to M14 (hereinafter referred to as the bypass count). [Table 2]

[0068] Next, the string controller 102 calculates the difference between the capacitor voltage transmitted from the voltage sensor Vc and the string voltage calculated in step S03 (step S04). Next, the string controller 102 determines whether the difference between the capacitor voltage and the string voltage calculated in step S04 is within a predetermined range (step S05). Here, the "predetermined range" is set according to the allowable value of the inrush current caused by the difference between the capacitor voltage and the string voltage.

[0069] If the difference between the capacitor voltage and the string voltage is outside a predetermined range (NO in step S05), the string controller 102 sends a control signal to the power converter PCS to charge or discharge the smoothing capacitor C (step S06). Here, if the capacitor voltage is higher than the string voltage, the smoothing capacitor C is discharged by the operation of the power converter PCS. Conversely, if the capacitor voltage is lower than the string voltage, the smoothing capacitor C is charged by the operation of the power converter PCS.

[0070] The string controller 102 sends a control signal to the power converter PCS to charge or discharge the smoothing capacitor C, then recalculates the difference between the capacitor voltage and the string voltage (step S04), and determines whether the difference between the capacitor voltage and the string voltage is within a predetermined range (step S05).

[0071] If the difference between the capacitor voltage and the string voltage is within a predetermined range (YES in step S05), the string controller 102 sends a control signal to the relay driver 103 to switch the system main relay S3 from Open to Close (step S07). As a result, the system main relay S3 closes, and the power converter PCS and smoothing capacitor C are connected to each battery module M1 to Mn.

[0072] As described above, the battery control device 100 according to this embodiment performs the following processes (1) to (4). (1) The timing for switching between the connection state and the bypass state of the battery modules M1 to Mn by the bypass units B1 to Bn while the energy storage string STR is being charged or discharged is determined in advance before the start of charging or discharging of the energy storage string STR. (2) While the energy storage string STR is being charged or discharged, before the bypass units B1 to Bn switch the connection state and bypass state of the battery modules M1 to Mn according to the timing described above, the system main relay S3 is switched from the closed state to the open state. (3) After the connection state and bypass state of battery modules M1 to Mn are switched by bypass units B1 to Bn according to the above timing, the battery modules M1 to Mn in the connection state are identified based on the above timing information, and the string voltage, which is the sum of the voltages of the identified battery modules M1 to Mn in the connection state, is calculated. (4) If the difference between the calculated string voltage and the capacitor voltage exceeds a predetermined range, the power converter PCS charges or discharges the smoothing capacitor C to bring the difference between the string voltage and the capacitor voltage to the predetermined range.

[0073] As a result, when the bypass units B1 to Bn switch between the connected state and the bypass state of the battery modules M1 to Mn during charging and discharging of the energy storage string STR, the difference between the capacitor voltage and the string voltage can be quickly concentrated within a predetermined range, regardless of sharp fluctuations in the string voltage. Therefore, the inrush current between the energy storage string STR and the smoothing capacitor C can be suppressed while reducing the implementation cost of the precharge circuit and the cost of replacing precharge relay components.

[0074] Furthermore, the battery control device 100 according to this embodiment determines the timing such that the remaining charge of multiple battery modules M1 to Mn is equalized within a predetermined period from the start of charging or discharging of the battery string STR, and after the remaining charge of multiple battery modules M1 to Mn is equalized, all battery modules M1 to Mn are connected. This makes it possible to maintain the connected state of battery modules M1 to Mn until just before the end of one charging or discharging cycle, and to use the capacity of battery modules M1 to Mn efficiently.

[0075] 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.

[0076] For example, in the above embodiment, a pre-charge circuit is not provided, but a pre-charge circuit may be provided. Even in this case, the control of this embodiment allows switching between the connected state and the bypass state of battery modules M1 to Mn without using the pre-charge circuit, thereby reducing the number of operations of the pre-charge circuit and lowering the cost of replacing pre-charge relay components.

[0077] Furthermore, the timing for bypassing each battery module M1 to Mn by each bypass unit B1 to Bn during charging or discharging of the energy storage string STR is not limited to the above embodiment, but can be appropriately determined in advance depending on the application and operating conditions of the energy storage system.

[0078] Furthermore, the capacitor is not necessarily required to be placed between the system main relay S3 and the power converter PCS, and may be built into the power converter PCS. In addition, the system main relay S3 is not necessarily required to be placed on the positive terminal side of the energy storage string STR, and may be placed on the negative terminal side of the energy storage string STR. [Explanation of Symbols]

[0079] 1: Energy storage system 100: Battery control device (control device) B1~Bn: Bypass unit (bypass section) C: Smoothing capacitor (capacitor) M1~Mn, M': Battery module (battery) PCS: Power Converter S3: System main relay (switch) STR: Energy Storage String RC: Remaining charge capacity (remaining amount) RD: Discharge capacity (remaining charge)

Claims

1. A battery control device for controlling an energy storage system comprising: a plurality of batteries connected in series; an energy storage string having a plurality of bypass units provided for each battery to switch the battery between a connected state and a bypass state; a power converter connected to the positive and negative terminals of the energy storage string; a capacitor connected to the positive and negative terminals of the energy storage string; and a switch provided between the capacitor and the plurality of batteries, wherein the battery control device controls the energy storage system, The timing for switching between the connected state and the bypass state of the battery by the bypass unit during the charging or discharging of the energy storage string is predetermined before the start of charging or discharging of the energy storage string. During the charging or discharging of the energy storage string, before the bypass unit switches between the connected state and the bypass state of the battery according to the timing, the switch is switched from the closed state to the open state. After the bypass unit switches between the connected state and the bypass state of the battery according to the timing, the connected state of the battery is identified based on the timing information, and the string voltage, which is the sum of the voltages of the identified connected state of the battery, If the difference between the calculated string voltage and the capacitor voltage exceeds a predetermined range, the power converter charges or discharges the capacitor to bring the difference between the string voltage and the capacitor voltage to within the predetermined range. Battery control device.

2. The timing is determined such that, within a predetermined period from the start of charging or discharging of the energy storage string, the remaining charge of the multiple storage batteries is equalized, and after the remaining charge of the multiple storage batteries is equalized, all of the storage batteries are connected. The battery control device according to claim 1.

3. A battery control method for controlling a battery storage system using a control device, the system comprising: a battery storage string having a plurality of batteries connected in series; a plurality of bypass units provided for each battery to switch the battery between a connected state and a bypass state; a power converter connected to the positive and negative terminals of the battery storage string; a capacitor connected to the positive and negative terminals of the battery storage string; and a switch provided between the capacitor and the plurality of batteries, wherein the battery control method controls the battery storage system using a control device. The timing for switching between the connected state and the bypass state of the battery by the bypass unit during the charging or discharging of the energy storage string is predetermined before the start of charging or discharging of the energy storage string. During the charging or discharging of the energy storage string, before the bypass unit switches between the connected state and the bypass state of the battery according to the timing, the switch is switched from the closed state to the open state. After the bypass unit switches between the connected state and the bypass state of the battery according to the timing, the connected state of the battery is identified based on the timing information, and the string voltage, which is the sum of the voltages of the identified connected state of the battery, If the difference between the calculated string voltage and the capacitor voltage exceeds a predetermined range, the power converter charges or discharges the capacitor to bring the difference between the string voltage and the capacitor voltage to within the predetermined range. Battery control method.

4. A battery storage string comprising a plurality of batteries connected in series, and a plurality of bypass units provided for each battery that switch between a connected state and a bypass state, A power converter to which the positive and negative terminals of the aforementioned energy storage string are connected, A capacitor connected to the positive and negative sides of the aforementioned energy storage string, A switch is provided between the capacitor and the plurality of storage batteries, The bypass section, the power converter, and the battery control device that controls the switch. Equipped with, The aforementioned battery control device is The timing for switching between the connected state and the bypass state of the battery by the bypass unit during the charging or discharging of the energy storage string is predetermined before the start of charging or discharging of the energy storage string. During the charging or discharging of the energy storage string, before the bypass unit switches between the connected state and the bypass state of the battery according to the timing, the switch is switched from the closed state to the open state. After the bypass unit switches between the connected state and the bypass state of the battery according to the timing, the connected state of the battery is identified based on the timing information, and the string voltage, which is the sum of the voltages of the identified connected state of the battery, If the difference between the calculated string voltage and the capacitor voltage exceeds a predetermined range, the power converter charges or discharges the capacitor to bring the difference between the string voltage and the capacitor voltage within the predetermined range. Energy storage system.

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