Power storage device

Abstract

In a power storage device 10, a battery module 40 can be charged and discharged. A discharge circuit 46 is connected between both ends of the battery module 40 and discharges the battery module 40. A control unit 50 controls the resistance value of the discharge circuit 46 to be smaller as the voltage of the battery module 40 is lower.

Description

Power storage device

[0001] The present disclosure relates to a power storage device.

[0002] In a data center, as a countermeasure against power outages, a backup power supply system using a secondary battery is generally used to hold power for several minutes until a generator starts up during a power outage. The backup power supply system includes a power storage device having a secondary battery and a control circuit that controls charging and discharging of the secondary battery. Generally, in a power storage device for a data center, the control circuit is operated by power supply from an upper system in order to suppress the current consumption from the secondary battery.

[0003] When the characteristics of the secondary battery deteriorate, it is necessary to discard the power storage device. When discarding the power storage device, it is necessary to discharge the secondary battery. Patent Document 1 discloses a processing device for a battery pack that discharges the battery pack while immersed in a fluid. Patent Document 2 discloses a battery discharge device for discharging a storage battery. Patent Document 3 discloses a discharge circuit for a capacitor that enables discharge control even when a discharge control switch element for controlling the discharge of the capacitor fails.

[0004] International Publication No. 2014 / 017085, Japanese Patent Application Laid-Open No. 2023-535136, Japanese Patent No. 6320657

[0005] In the technology of Patent Document 3, normally, when the voltage of the capacitor decreases, the discharge current becomes small and the discharge time becomes long.

[0006] The present disclosure has been made in view of such circumstances, and an object thereof is to provide a power storage device capable of shortening the discharge time while suppressing an overload from being applied to the discharge circuit.

[0007] To solve the above problems, a power storage device according to an aspect of the present disclosure includes a chargeable and dischargeable battery module, a discharge circuit connected between both ends of the battery module for discharging the battery module, and a control unit that controls the resistance value of the discharge circuit to be smaller as the voltage of the battery module decreases.

[0008] Furthermore, any combination of the above components, as well as any conversion of the expressions of this disclosure between devices, systems, methods, computer programs, etc., are also valid forms of this disclosure.

[0009] According to this disclosure, it is possible to provide an energy storage device that can shorten the discharge time while suppressing overloading of the discharge circuit.

[0010] This figure shows the configuration of the energy storage system according to the first embodiment. This figure is for explaining the energy storage system during maintenance. This figure shows the configuration of the energy storage device in Figure 1. This figure shows the configuration of the energy storage device according to the second embodiment. This figure shows an example of the characteristics of the discharge circuit in Figure 4.

[0011] (First Embodiment) Figure 1 shows the configuration of the energy storage system 1 according to the first embodiment. The energy storage system 1 is used, for example, as a backup power supply system in a data center. The energy storage system 1 comprises a first energy storage device 10a, a second energy storage device 10b, a third energy storage device 10c, a fourth energy storage device 10d, a fifth energy storage device 10e, a sixth energy storage device 10f, a DC bus 12, and a higher-level system 14. Hereinafter, the first energy storage device 10a, the second energy storage device 10b, the third energy storage device 10c, the fourth energy storage device 10d, the fifth energy storage device 10e, and the sixth energy storage device 10f will be collectively referred to as "energy storage device 10". Here, an example in which six energy storage devices 10 are provided will be described, but the number is not particularly limited.

[0012] Multiple energy storage devices 10 are housed in a rack 20. Each energy storage device 10 can be individually removed from the rack 20. The multiple energy storage devices 10 are electrically connected to a higher-level system 14 and a load 16 via a common DC bus 12. Each energy storage device 10 has a rechargeable battery module, as will be described later.

[0013] The higher-level system 14 has an AC / DC converter (not shown). Under normal conditions when the commercial power grid 18 is not experiencing a power outage, the AC / DC converter converts the AC power input from the commercial power grid 18 into DC power, outputs the DC power to the DC bus 12, and can supply DC power to the load 16 via the DC bus 12. The load 16 operates using the DC power as its power source. The AC / DC converter can also charge each of the battery modules of the multiple energy storage devices 10 via the DC bus 12. The DC power supplied from the AC / DC converter to the DC bus 12 is also used as a power source for the operation of the multiple energy storage devices 10. Therefore, the AC / DC converter can also be called an external power source for the energy storage devices 10. In the event of a power outage, each of the multiple energy storage devices 10 discharges to the backup load 16. The higher-level system 14 also supplies various control signals to the multiple energy storage devices 10 via wiring (not shown).

[0014] Figure 2 is a diagram illustrating the energy storage system 1 during maintenance. Figure 2 shows the situation in which the sixth energy storage device 10f, which has reached the end of its lifespan, is removed from the rack 20, and a new seventh energy storage device 10g is installed in the rack 20.

[0015] Figure 3 shows the configuration of the energy storage device 10 shown in Figure 1. The energy storage device 10 includes an energy storage unit 30, a capacitor C1, and a DC / DC converter 32.

[0016] The positive terminal T1 of the energy storage unit 30 is connected to the DC / DC converter 32. The negative terminal T2 of the energy storage unit 30 is also connected to the DC / DC converter 32. The energy storage unit 30 can supply DC power to the DC / DC converter 32 via the first terminal T1 and the second terminal T2. The energy storage unit 30 can also receive DC power from the DC / DC converter 32 via the first terminal T1 and the second terminal T2.

[0017] The DC / DC converter 32 is capable of converting voltage in both directions. When the energy storage unit 30 is discharging, the DC / DC converter 32 converts the voltage supplied from the energy storage unit 30 to a different voltage and supplies the converted voltage to the DC bus 12. Also, when the energy storage unit 30 is charging, the DC / DC converter 32 converts the voltage of the DC bus 12 to a different voltage and supplies the converted voltage to the energy storage unit 30.

[0018] Furthermore, the DC / DC converter 32 supplies power to the energy storage unit 30 to operate it, based on the power supplied from an external power supply 70 included in the higher-level system 14 via the DC bus 12. The external power supply 70 in the higher-level system 14 corresponds to the AC / DC converter described above.

[0019] The DC / DC converter 32 has a control unit 60. The control unit 60 can output a trigger signal to the energy storage unit 30 based on a control signal received from the higher-level system 14. The trigger signal will be described later.

[0020] One end of capacitor C1 is connected to the connection line between the first terminal T1 of the energy storage unit 30 and the DC / DC converter 32. The other end of capacitor C1 is grounded.

[0021] The energy storage unit 30 includes a battery module 40, a processing unit 42, a power supply circuit 44, a discharge circuit 46, a switch unit 48, a voltage detection unit 49, resistors R11, R12, ..., a switch SW10, and diodes D1, D2.

[0022] The battery module 40 includes n (where n is an integer of 2 or more) battery cells S1 to Sn connected in series. The battery cells S1 to Sn are rechargeable batteries, such as lithium-ion batteries.

[0023] The negative terminal of battery cell S1 is connected to the processing unit 42. The positive terminal of battery cell S1 is connected to the processing unit 42 via resistor R11. The positive terminal of battery cell S2 is connected to the processing unit 42 via resistor R12. Although not shown in the diagram, the positive terminals of the other battery cells are also connected to the processing unit 42 via resistors.

[0024] The negative terminal of the battery module 40 is connected to the second terminal T2. The positive terminal of the battery module 40 is connected to the first terminal T1 via the switch unit 48.

[0025] The switch unit 48 switches between making electrical contact between the positive terminal of the battery module 40 and the first terminal T1. The switch unit 48 includes a first transistor TR1 and a second transistor TR2. The first transistor TR1 and the second transistor TR2 are connected in series between one end of the battery module 40 and the first terminal T1. The first transistor TR1 is an FET for charge control. The second transistor TR2 is an FET for discharge control.

[0026] The power supply circuit 44 supplies power to the processing unit 42 based on the DC power of the external power supply 70 supplied from the upper system 14 via the DC / DC converter 32. The power supply circuit 44 includes, for example, a DC / DC converter.

[0027] Diode D1 has an anode to which power is supplied from the DC / DC converter 32 and a cathode connected to the input side of the power supply circuit 44.

[0028] One end of switch SW10 is connected to the positive terminal of battery module 40. The other end of switch SW10 is connected to the anode of diode D2. Switch SW10 is controlled by processing unit 42. The cathode of diode D2 is connected to the connection node between the cathode of diode D1 and power supply circuit 44.

[0029] The discharge circuit 46 is connected to both ends of the battery module 40 via a switch unit 48, and can discharge the battery module 40 according to the control of the processing unit 42. The discharge circuit 46 has multiple sets of resistors and switches connected in series between the ends of the battery module 40. The multiple sets of resistors and switches are connected in parallel between the ends of the battery module 40. The discharge circuit 46 includes resistors R1 to R5 and switches SW1 to SW5. Switches SW1 to SW5 are controlled by the processing unit 42.

[0030] One end of resistor R1 is connected to the first terminal T1. The other end of resistor R1 is connected to one end of switch SW1. The other end of switch SW1 is connected to the second terminal T2.

[0031] One end of resistor R2 is connected to the first terminal T1. The other end of resistor R2 is connected to one end of switch SW2. The other end of switch SW2 is connected to the second terminal T2.

[0032] One end of resistor R3 is connected to the first terminal T1. The other end of resistor R3 is connected to one end of switch SW3. The other end of switch SW3 is connected to the second terminal T2.

[0033] One end of resistor R4 is connected to the first terminal T1. The other end of resistor R4 is connected to one end of resistor R5 and one end of switch SW5. The other end of resistor R5 is connected to one end of switch SW4. The other end of switch SW4 is connected to the second terminal T2. The other end of switch SW5 is connected to the second terminal T2. The resistance value of resistor R5 is greater than the resistance value of resistor R4. Switch SW5 can bypass resistor R5.

[0034] Note that resistors R4, R5 and switches SW4, SW5 are not required. Alternatively, resistors R1 to R3 and switches SW1 to SW3 are not required. In this case, the discharge circuit 46 can be formed by multiple resistors R4, R5 connected in series between the ends of the battery module 40, and there is no need to connect multiple resistors in parallel between the ends of the battery module 40.

[0035] Furthermore, there can be multiple sets of resistors and switches connected in series. The number of resistors R4 and R5 can also be multiple.

[0036] The processing unit 42 operates using power supplied from the power supply circuit 44. The processing unit 42 includes a control unit 50, a voltage detection unit 52, and a plurality of adjustment circuits B1, B2, ... The control unit 50 controls the charging and discharging of the battery module 40 by controlling the switch unit 48.

[0037] The voltage detection unit 52 detects the voltage of each battery cell S1 to Sn supplied via resistors R11, R12, ... and supplies the detection result to the control unit 50. During a predetermined period, such as during charging and discharging of the battery module 40, the control unit 50 monitors the voltage of each battery cell S1 to Sn based on the detection result from the voltage detection unit 52 and performs known equalization control, etc., based on the voltage of each battery cell S1 to Sn. Equalization control can also be called cell balance adjustment.

[0038] The adjustment circuits B1, B2, ... can also be called cell balance adjustment circuits, and allow for individual adjustment of the voltage of each battery cell S1 to Sn. The same number of adjustment circuits B1, B2, ... are provided as the number of battery cells S1 to Sn.

[0039] The adjustment circuit B1 can adjust the voltage of the corresponding battery cell S1. The adjustment circuit B1 has a resistor Rb1 and a switch SWb1 connected in series between the ends of the battery cell S1 via a resistor R11. When the switch SWb1 conducts, current flows from the battery cell S1 to the resistor Rb1, which can lower the voltage of the battery cell S1.

[0040] The adjustment circuit B2 can adjust the voltage of the corresponding battery cell S2. The adjustment circuit B2 has a resistor Rb2 and a switch SWb2 connected in series across the battery cell S2 via a resistor R12. When the switch SWb2 conducts, the voltage of the battery cell S2 can be reduced. Other adjustment circuits, not shown, are configured similarly.

[0041] When the energy storage device 10 is disconnected from the external power supply 70, the DC / DC converter 32 switches the energy storage device 10 to a low-power mode by stopping the power supply to the power supply circuit 44. The low-power mode can also be called a sleep mode, and it is a mode that suppresses the discharge of the battery module 40.

[0042] For example, when the power storage device 10 is manufactured in a factory, power is supplied from an external power source of an inspection machine to the DC / DC converter 32, the power storage device 10 operates, and the power storage device 10 is inspected by the inspection machine. After the inspection, when the inspection machine is removed and the power supply is stopped, the DC / DC converter 32 stops supplying power to the power supply circuit 44. Thereby, it can be set to a low power consumption mode at the time of shipping the product.

[0043] Also, when the power storage device 10 is removed from the rack 20 during maintenance and the power supply from the external power source 70 in the upper system 14 is stopped, the DC / DC converter 32 stops supplying power to the power supply circuit 44. Thereby, it can be set to a low power consumption mode during maintenance.

[0044] When the voltage detection unit 49 detects that the voltage at the anode of the diode D1, that is, the voltage supplied from the DC / DC converter 32 to the power supply circuit 44, is less than a predetermined lower limit voltage, the voltage detection unit 49 outputs a signal indicating a voltage drop to the processing unit 42. The output of this signal indicates that the power storage device 10 has been disconnected from the external power source 70 and the power supply from the external power source 70 has stopped.

[0045] When the control unit 50 receives a signal from the voltage detection unit 49, the control unit 50 conducts the switch SW10. Thereby, the output voltage of the battery module 40 is supplied to the input side of the power supply circuit 44 via the diode D2, and the power supply circuit 44 supplies power to the processing unit 42 based on the power of the battery module 40. Also, when the control unit 50 receives a signal from the voltage detection unit 49, the control unit 50 controls the second transistor TR2 to be in a non-conducting state, thereby controlling the switch unit 48 to be in a non-conducting state, controlling the resistance value of the discharge circuit 46 to a predetermined value regardless of the voltage of the battery module 40, discharging the charge of the connection line between the switch unit 48 and the DC / DC converter 32 to the discharge circuit 46, and then operating in the low power consumption mode. The charge of this connection line includes the charge of the capacitor C1. The control unit 50, for example, controls the switch SW1 to be in a conducting state, controls the switches SW2 to SW5 to be in a non-conducting state, and discharges the charge of the capacitor C1 etc. via the resistor R1.

[0046] The voltage detection unit 52 detects the voltage V1 of the first terminal T1, that is, the voltage V1 at one end of the resistor R1, and supplies the detection result to the control unit 50. The control unit 50 monitors the voltage V1 at one end of the resistor R1 based on the detection result by the voltage detection unit 52, and when this voltage V1 becomes below a predetermined threshold voltage, it operates in the low power consumption mode.

[0047] On the other hand, when the control unit 50 receives a trigger signal from the DC / DC converter 32, it causes the power supply circuit 44 to be supplied with power based on the power of the battery module 40 instead of the power of the external power supply 70. The trigger signal is a signal for switching to the discard mode. Specifically, when the control unit 50 receives the trigger signal, it conducts the switch SW10. Thereby, the output voltage of the battery module 40 is supplied to the input side of the power supply circuit 44 via the diode D2. Note that the control unit 50 controls the switch SW10 to be in a non-conductive state when it has not received a signal from the voltage detection unit 49 or the trigger signal. Also, when the control unit 50 has not received a signal from the voltage detection unit 49 or the trigger signal, it does not discharge to the discharge circuit 46, and based on the voltages of the plurality of battery cells S1 to Sn, it adjusts the cell balance of the plurality of battery cells S1 to Sn in the plurality of adjustment circuits B1, B2,....

[0048] Also, when the control unit 50 receives the trigger signal, it controls the switch unit 48 to be in a conductive state by conducting the second transistor TR2, and discharges the battery module 40 to the discharge circuit 46 in that state.

[0049] When discarding the power storage device 10, in a state where the power storage device 10 to be discarded is stored in the rack 20 and connected to the DC bus 12, for example, the user operates an operation input unit (not shown) provided in the upper system 14, and a trigger signal is supplied to the power storage unit 30 of the power storage device 10 to be discarded, and that power storage device 10 is switched to the discard mode. After that, even if the power storage device 10 to be discarded is removed from the rack 20, the power storage device 10 to be discarded can continue to operate in the discard mode using the power of the battery module 40.

[0050] The trigger signal may also be supplied from an operation input unit (not shown) such as a switch provided on the energy storage device 10 when the user operates the said operation input unit. The trigger signal may also be supplied from an inspection machine or the like connected to the energy storage device 10.

[0051] When the control unit 50 receives a trigger signal, it monitors the voltage V1 at one end of the resistor R1, i.e., the voltage of the battery module 40, during discharge by the discharge circuit 46, based on the detection result by the voltage detection unit 52. During discharge by the discharge circuit 46, the control unit 50 controls the resistance value of the discharge circuit 46 to decrease as the voltage V1 at one end of the resistor R1 decreases. The control unit 50 controls the resistance value of the discharge circuit 46 by controlling switches SW1 to SW5.

[0052] The control unit 50 controls switch SW1 to a conductive state and switches SW2 to SW5 to a non-conductive state when the voltage of the battery module 40 is equal to or greater than a predetermined first determination voltage. The first determination voltage is lower than the maximum voltage of the battery module 40. As a result, a discharge current flows through resistor R1. The resistance value of resistor R1 is set to a value that does not overload resistor R1. Therefore, excessive heat generation of resistor R1 can be suppressed.

[0053] The control unit 50 controls switches SW1 and SW2 to a conductive state and switches SW3 to SW5 to a non-conductive state when the voltage of the battery module 40 is less than the first determination voltage and greater than or equal to a predetermined second determination voltage. The second determination voltage is lower than the first determination voltage. As a result, discharge current flows through resistors R1 and R2 which are connected in parallel. Therefore, the resistance value of the discharge circuit 46 can be reduced compared to the case where discharge current flows only through resistor R1, and the discharge current can be increased.

[0054] The control unit 50 controls switches SW1, SW2, and SW3 to a conductive state and switches SW4 and SW5 to a non-conductive state when the voltage of the battery module 40 is less than the second determination voltage and greater than or equal to a predetermined third determination voltage. The third determination voltage is lower than the second determination voltage. As a result, discharge current flows through the parallel-connected resistors R1 to R3. Therefore, the resistance value of the discharge circuit 46 can be reduced and the discharge current can be increased compared to the case where discharge current flows only through resistors R1 and R2.

[0055] The control unit 50 controls switches SW1, SW2, SW3, and SW4 to a conductive state and switch SW5 to a non-conductive state when the voltage of the battery module 40 is less than the third determination voltage and greater than or equal to a predetermined fourth determination voltage. The fourth determination voltage is lower than the third determination voltage. As a result, discharge current flows through resistors R1 to R5. Therefore, the resistance value of the discharge circuit 46 can be reduced and the discharge current can be increased compared to the case where discharge current flows only through resistors R1 to R3.

[0056] The control unit 50 controls switches SW1 to SW5 to a conductive state when the voltage of the battery module 40 is below the fourth determination voltage. As a result, discharge current flows through resistors R1 to R4. The resistance value of resistor R5 is set to be sufficiently larger than the resistance value of resistor R4 and sufficiently smaller than the resistance value when switch SW5 is conductive, so almost no discharge current flows through resistor R5. Therefore, the resistance value of the discharge circuit 46 can be reduced compared to the case when discharge current flows through resistors R1 to R5, and the discharge current can be increased.

[0057] Thus, as the voltage of the battery module 40 decreases, the resistance value of the discharge circuit 46 is controlled to be smaller. Compared to the case where discharge current flows only through resistor R1 regardless of the voltage of the battery module 40, the discharge current can be increased. Therefore, the discharge time can be shortened compared to the case where discharge current flows only through resistor R1. In addition, overload on the discharge circuit 46 can be suppressed.

[0058] The control unit 50 monitors the voltage of each of the multiple battery cells S1 to Sn during discharge by the discharge circuit 46 based on the detection result by the voltage detection unit 52. If the voltage of any of the multiple battery cells S1 to Sn falls below a predetermined fifth determination voltage during discharge by the discharge circuit 46, the control unit 50 stops the discharge of the discharge circuit 46 and controls the switches SWb1, SWb2, ... to conduct, thereby causing each of the multiple battery cells S1 to Sn to discharge individually into the adjustment circuits B1, B2, .... The fifth determination voltage is lower than the fourth determination voltage and may be, for example, around 1V. The fifth determination voltage is set in advance so that there is no possibility of polarity reversal of the battery cell if the voltage of the battery cell is higher than the fifth determination voltage. For example, with respect to battery cell S1 and adjustment circuit B1, when switch SWb1 conducts, a discharge current flows in the direction of arrow A1 in Figure 3. In discharge using adjustment circuits B1, B2, ..., each battery cell is discharged individually, so the voltage of each battery cell asymptotically approaches 0V, preventing polarity reversal of battery cells S1 to Sn. It is also possible to fully discharge each battery cell S1 to Sn. In other words, it is possible to discharge to a lower voltage while suppressing polarity reversal.

[0059] Thus, in disposal mode, as long as the overall voltage of the battery module 40 is higher than the fifth determination voltage, the discharge circuit 46 can discharge the battery module 40 at high speed, shortening the discharge time. When the voltage of the battery module 40 falls below the fifth determination voltage, the adjustment circuits B1, B2, ... discharge each battery cell, thereby preventing polarity reversal of battery cells S1 to Sn.

[0060] In addition, a discharge termination voltage lower than the fifth determination voltage may be set. In this case, during discharge by the adjustment circuit, the control unit 50 may, for each battery cell, control the switch of the adjustment circuit corresponding to the battery cell to a non-conducting state when the voltage of that battery cell reaches the discharge termination voltage, thereby stopping the discharge of that battery cell. This makes it possible to stop the discharge of each battery cell S1 to Sn at the desired discharge termination voltage.

[0061] The control unit 50 and the control unit 60 are realized through the collaboration of hardware resources and software resources, respectively. Hardware resources can include a CPU, GPU, DSP, FPGA, and other LSIs. Software resources can include operating systems, applications, and other programs.

[0062] According to this embodiment, when a trigger signal is received, power is supplied to the power supply circuit 44 based on the power of the battery module 40 instead of the external power supply 70, so that the battery module 40 can continue to discharge even if the external power supply 70 is removed. As a result, multiple energy storage devices 10 can be discharged in parallel without using multiple external power supplies, and the time required to complete the discharge of multiple energy storage devices 10 can be shortened. Once switched to disposal mode, no user operation is required, and the discharge can be completed.

[0063] Even when the energy storage device 10 is switched to disposal mode and discharged while connected to the rack 20, the internal discharge circuit 46 can be used to continue discharging for disposal after the energy storage device 10 has been removed from the rack. Therefore, when discharging for disposal, a replacement energy storage device 10 can be attached to the rack 20 without waiting for the discharge to be completed. Furthermore, there is no need to connect an external discharge device to the energy storage device 10.

[0064] Therefore, in the energy storage device 10, where the processing unit 42 controls the discharge of the battery module 40 based on the power of the external power supply 70, the discharge can be performed more efficiently.

[0065] Furthermore, in waste mode, discharge is performed using the discharge circuit 46, which is used when switching to low power consumption mode, and the adjustment circuits B1, B2, ..., which are used for cell balance adjustment. Therefore, there is no need to newly provide a discharge circuit and adjustment circuit dedicated to waste mode in the energy storage device 10. Thus, it is possible to suppress the enlargement of the energy storage device 10, the complexity of its configuration, the increase in the number of parts, and the increase in cost.

[0066] (Second Embodiment) In the second embodiment, the configuration and control of the discharge circuit 46 differ from those of the first embodiment. The differences from the first embodiment will be explained below.

[0067] Figure 4 shows the configuration of the energy storage device 10 according to the second embodiment. The discharge circuit 46 includes a resistor R1 and a switch SW1. One end of the resistor R1 is connected to the first terminal T1. The other end of the resistor R1 is connected to one end of the switch SW1. The other end of the switch SW1 is connected to the second terminal T2. The resistor R1 and the switch SW1 are connected in series between both ends of the battery module 40 via a switch unit 48.

[0068] The control unit 50 supplies a pulse signal of a predetermined period to the switch SW1 to cause it to conduct, and controls the duty cycle of the pulse signal. The duty cycle represents the on-duty cycle.

[0069] When the control unit 50 receives a signal from the voltage detection unit 49, that is, when the power supply from the external power supply 70 stops, it controls the switch unit 48 to a non-conducting state by controlling the second transistor TR2 to a non-conducting state, controlling the duty cycle of the pulse signal to a predetermined value regardless of the voltage of the battery module 40, and discharging the charge on the connection line between the switch unit 48 and the DC / DC converter 32 into the discharge circuit 46, before operating in low power consumption mode. The predetermined value is, for example, 100%. In this case, as in the first embodiment, the switch SW1 is maintained in a conductive state. Therefore, the charge can be discharged at high speed.

[0070] On the other hand, when the control unit 50 receives a trigger signal from the DC / DC converter 32, it controls the switch unit 48 to a conductive state by making the second transistor TR2 conduct, and controls the duty cycle of the pulse signal to increase as the voltage of the battery module 40 decreases, causing the battery module 40 to discharge into the discharge circuit 46. In other words, the control unit 50 performs PWM control and increases the time that the switch SW1 conducts during a predetermined cycle as the voltage of the battery module 40 decreases.

[0071] The control unit 50 sets the duty cycle to a first value if the voltage of the battery module 40 is equal to or greater than a predetermined first determination voltage. The first value is set to a value that does not overload the resistor R1. That is, the first value is set to a value that keeps the average power consumed by the resistor R1 within the rated range. Therefore, excessive heat generation of the resistor R1 can be suppressed.

[0072] The control unit 50 sets the duty cycle to a second value greater than the first value if the voltage of the battery module 40 is less than the first determination voltage and greater than or equal to a predetermined second determination voltage. The second value is also set to a value that keeps the average power consumed by resistor R1 within the rated range. Therefore, while suppressing excessive heat generation of resistor R1, the discharge current can be increased compared to the case where the duty cycle is the first value.

[0073] The control unit 50 sets the duty cycle to a third value greater than the second value if the voltage of the battery module 40 is less than the second determination voltage and greater than or equal to a predetermined third determination voltage. The third value is also set to a value that keeps the average power consumed by resistor R1 within the rated range. Therefore, while suppressing excessive heat generation of resistor R1, the discharge current can be increased compared to the case where the duty cycle is the second value.

[0074] Here, we have shown an example of controlling the duty cycle in three stages, but it is possible to control it in multiple stages. Alternatively, the duty cycle may be continuously controlled according to the voltage of the battery module 40.

[0075] Figure 5 shows an example of the characteristics of the discharge circuit 46 in Figure 4. Figure 5 shows an example of the relationship between the power (W), average power (W), on-duty cycle (%), and average current (mA) of the discharge circuit 46 and the voltage (V) of the battery module 40. The power of the discharge circuit 46 represents the power when switch SW1 is ON. In the example in Figure 5, due to PWM control, the average power and average current are almost constant regardless of the voltage of the battery module 40. Therefore, overloading of the discharge circuit 46 can be suppressed.

[0076] Furthermore, similar to the first embodiment, if the voltage of any of the battery cells S1 to Sn falls below a predetermined fifth determination voltage during discharge by the discharge circuit 46, the control unit 50 stops the discharge by the discharge circuit 46 and controls the switches SWb1, SWb2, ... to a conductive state, thereby causing each of the battery cells S1 to Sn to discharge individually into the adjustment circuits B1, B2, .... The fifth determination voltage is lower than the third determination voltage. This prevents polarity reversal of the battery cells S1 to Sn.

[0077] According to this embodiment, the duty cycle of the pulse signal is controlled to be larger as the voltage of the battery module 40 decreases, so the decrease in discharge current due to the decrease in the voltage of the battery module 40 can be suppressed. In addition, the discharge time of the battery module 40 can be shortened while suppressing the application of an overload to the discharge circuit 46. Furthermore, since the discharge circuit 46 can be realized with one resistor R1 and one switch SW1, the discharge circuit 46 can be made smaller and the number of components in the discharge circuit 46 can be reduced compared to the first embodiment.

[0078] Similar to the first embodiment, in waste mode, discharge is performed by the discharge circuit 46 used when switching to low power consumption mode, so there is no need to newly provide a discharge circuit dedicated to waste mode in the energy storage device 10.

[0079] The present disclosure has been described above based on embodiments. These embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible for each component or combination of processing processes, and that such modifications are also within the scope of the present disclosure.

[0080] The embodiments may be specified by the following items.

[0081] [Item 1] A power storage device (10) comprising: a rechargeable battery module (40); a discharge circuit (46) connected between both ends of the battery module (40) for discharging the battery module (40); and a control unit (50) that controls the resistance value of the discharge circuit (46) to decrease as the voltage of the battery module (40) decreases. This makes it possible to shorten the discharge time of the battery module while suppressing overloading of the discharge circuit.

[0082] [Item 2] The energy storage device (10) according to Item 1, further comprising: a DC / DC converter (32); a switch unit (48) for switching between making a connection between one end of the battery module (40) and the DC / DC converter (32); wherein, when the power supply from the external power source (70) is stopped, the control unit (50) controls the switch unit (48) to a non-conductive state, controls the resistance value of the discharge circuit (46) to a predetermined value regardless of the voltage of the battery module (40), discharges the charge of the connection line between the switch unit (48) and the DC / DC converter (32) into the discharge circuit (46), and then operates in a low power consumption mode; and when the control unit (50) receives a trigger signal, controls the switch unit (48) to a conductive state, controls the resistance value of the discharge circuit (46) to decrease as the voltage of the battery module (40) decreases, and discharges the battery module (40) into the discharge circuit (46). In this case, there is no need to install a new discharge circuit to discharge the battery module.

[0083] [Item 3] The energy storage device (10) according to item 1 or 2, characterized in that the discharge circuit (46) comprises a first resistor (R1) and a first switch (SW1) connected in series between the ends of the battery module (40), and a second resistor (R2) and a second switch (SW2) connected in series between the ends of the battery module (40), and the control unit (50) controls the resistance value of the discharge circuit (46) by controlling the first switch (SW1) and the second switch (SW2). In this case, the resistance value of the discharge circuit can be controlled with a simple configuration.

[0084] [Item 4] The energy storage device (10) according to item 1 or 2, characterized in that the discharge circuit (46) comprises a first resistor (R4) and a second resistor (R5) connected in series between the ends of the battery module (40), and a switch (SW5) that can bypass the second resistor, and the control unit (50) controls the resistance value of the discharge circuit (46) by controlling the switch (SW5). In this case, the resistance value of the discharge circuit can be controlled with a simple configuration.

[0085] This disclosure can be used in energy storage devices.

[0086] 1...Energy storage system, 10...Energy storage device, 12...DC bus, 14...Higher-level system, 30...Energy storage unit, 32...DC / DC converter, 40...Battery module, 42...Processing unit, 44...Power supply circuit, 46...Discharge circuit, 48...Switch unit, 49...Voltage detection unit, 50...Control unit, 52...Voltage detection unit, 60...Control unit, 70...External power supply, B1, B2...Adjustment circuit, R1, R2, R3, R4, R5, R11, R12, Rb1, Rb2...Resistors, S1, S2...Battery cell, SW1, SW2, SW3, SW4, SW5, SW10, SWb1, SWb2...Switches.

Claims

1. An energy storage device comprising: a rechargeable battery module; a discharge circuit connected between both ends of the battery module for discharging the battery module; and a control unit that controls the resistance value of the discharge circuit to decrease as the voltage of the battery module decreases.

2. The energy storage device according to claim 1, further comprising: a DC / DC converter; a switch unit for switching between conducting or not conducting between one end of the battery module and the DC / DC converter, wherein the control unit, when power supply from an external power source is stopped, controls the switch unit to a non-conductive state, controls the resistance value of the discharge circuit to a predetermined value regardless of the voltage of the battery module, discharges the charge of the connection line between the switch unit and the DC / DC converter into the discharge circuit, and then operates in a low power consumption mode; and when the control unit receives a trigger signal, controls the switch unit to a conductive state, controls the resistance value of the discharge circuit to decrease as the voltage of the battery module decreases, and discharges the battery module into the discharge circuit.

3. The energy storage device according to claim 1 or 2, wherein the discharge circuit comprises a first resistor and a first switch connected in series between the ends of the battery module, and a second resistor and a second switch connected in series between the ends of the battery module, and the control unit controls the resistance value of the discharge circuit by controlling the first switch and the second switch.

4. The energy storage device according to claim 1 or 2, wherein the discharge circuit comprises a first resistor and a second resistor connected in series between the ends of the battery module, and a switch that can bypass the second resistor, and the control unit controls the resistance value of the discharge circuit by controlling the switch.

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