Energy storage systems

Abstract

This provides an energy storage system that can prevent the terminal voltage from exceeding the rated voltage of the contactor provided in the battery pack when disconnected. [Solution] The energy storage system 10 comprises a plurality of battery units 12, a plurality of AC / DC converters 14, a power converter 16, and a control unit 18. Each of the plurality of battery units 12 comprises a plurality of battery packs 30 connected in parallel to each other and connected in series to each other. Each of the plurality of AC / DC converters 14 is connected in parallel to each battery unit 12 and converts the alternating current of the system 20 to direct current. The power converter 16 is connected to both ends of the series connection of the plurality of battery units 12 and converts the alternating current of the system 20 to direct current. Each battery pack 30 comprises a lithium-ion battery 32, a contactor 34, and a BMS 36. The control unit 18 controls the on / off switching of the contactor 34 and the operation of the power converter 16 and each AC / DC converter 14 based on battery data.

Description

Technical Field

[0001] The present invention relates to an energy storage system in which a plurality of battery packs are connected in parallel and in series with each other.

Background Art

[0002] Conventionally, battery packs mounted on electric vehicles and hybrid vehicles are assumed to be replaced with new battery packs when predetermined conditions are met. However, even used battery packs have sufficient performance for applications other than automobiles, and moreover, due to the spread of electric vehicles and hybrid vehicles, a large number of used battery packs are expected to be generated, so their reuse is desired. On the other hand, energy storage devices installed in buildings are expensive and many have limited capacity, so increasing their capacity and reducing their cost are desired. In response to these needs, an energy storage system using used battery packs has been proposed.

[0003] Patent Document 1 describes an integrated battery energy storage system including a plurality of second-life electric vehicle battery packs connected in a series / parallel arrangement. On the other hand, a configuration in which a converter is connected in parallel to each battery pack for voltage adjustment and recharge of a plurality of battery packs is disclosed. Patent Document 2 describes a power supply device that supplies power to an external device using a storage battery pack having a terminal portion electrically connectable to a plurality of different types of devices.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, the storage system described in Patent Document 1 has a problem in that, in order to increase the output voltage, multiple used battery packs are connected in series with each other. Therefore, if one of the used battery packs is disconnected, the output voltage of the multiple used battery packs connected in series is applied to the terminals of the contactor provided on the disconnected used battery pack, which exceeds the rated voltage of the contactor. Furthermore, this problem is independent of whether the battery pack is new or used, and is an unavoidable problem when multiple battery packs equipped with contactors are connected in series with each other. In addition, the power supply device described in Patent Document 2 has the problem that it does not take into account battery packs that have a contactor and BMS integrated into one unit, as well as lithium-ion batteries.

[0006] This invention has been made in view of the problems of the conventional invention, and the object of this invention is to provide an energy storage system that can prevent the terminal voltage at the time of disconnection from the rated voltage of the contactor provided in the battery pack from exceeding the rated voltage of the contactor provided in the battery pack, even when multiple battery packs are connected in series with each other in order to increase the output voltage. Furthermore, other objectives of the present invention, in addition to the above objectives, include simplifying the control during battery pack connection and equalization, and providing an energy storage system that can achieve a capacity equal to or greater than conventional systems while remaining inexpensive. [Means for solving the problem]

[0007] To achieve the above objective, the inventors conducted extensive research and first discovered that by connecting an AC / DC converter to each of several battery packs connected in series and outputting a predetermined voltage and current value, it is possible to prevent the terminal voltage from exceeding the rated voltage of the contactor provided in the battery pack when disconnected.

[0008] Furthermore, the inventors of this invention discovered that by providing a power supply for power outages, the output of the AC / DC converter can be continued even during a power outage, leading to the present invention.

[0009] In other words, the present invention comprises a plurality of battery packs connected in parallel to each other, a plurality of battery units connected in series to each other, and each battery unit Individually Multiple AC / DC converters are connected in parallel to convert the alternating current of the grid into direct current, and multiple battery units are connected in series to both ends of this system, which also converts the alternating current of the grid into direct current. , different from any of the multiple AC / DC converters The system comprises a power converter and a control unit. Each battery pack includes a lithium-ion battery, a contactor for electrically connecting and disconnecting the lithium-ion battery, and a BMS (Battery Management System) that collects battery data output by the lithium-ion battery and transmits it to the control unit. The control unit is connected to the BMS, power converter, and AC / DC converter of each battery pack and provides an energy storage system that controls the on / off state of each contactor via each BMS and the operation of the power converter and each AC / DC converter based on the battery data.

[0010] In this invention, it is preferable that the control unit specifies the output voltage and output current of each AC / DC converter connected in parallel to each battery unit based on the voltage of the corresponding battery unit, and controls each AC / DC converter to apply a voltage higher than that of the corresponding battery unit to the corresponding battery unit. It is preferable that the control unit activates multiple AC / DC converters before activating the power converter, and while raising and lowering the output voltage of each AC / DC converter, controls the battery pack contactor to turn on when the difference between the output voltage of each AC / DC converter and the battery pack contactor falls within a preset voltage difference.

[0011] Furthermore, in the present invention, it is preferable that the control unit, when voltage variations occur among the multiple battery units and the voltage of the first battery unit becomes lower than the voltage of the second battery unit, controls the first AC / DC converter connected in parallel to the first battery unit to apply a voltage higher than the voltage of the second battery unit to the first battery unit and control the charging current to the first battery unit, thereby equalizing the voltage variations that have occurred among the multiple battery units. Each battery pack is preferably a used, undisassembled, second-hand item that has been previously used in an electric vehicle. [Effects of the Invention]

[0012] According to the present invention, it is possible to prevent the terminal voltage during disconnection from exceeding the rated voltage of the contactor provided in the battery pack. Furthermore, in addition to the above effects, the present invention simplifies the control during battery pack connection and equalization, and enables a capacity equal to or greater than conventional methods while remaining at a low cost. [Brief explanation of the drawing]

[0013] [Figure 1] Block diagram of the energy storage system of the present invention. [Figure 2] This is a block diagram illustrating the voltage when the battery pack is disconnected. [Figure 3] This block diagram shows a modified example of the energy storage system of the present invention. [Modes for carrying out the invention]

[0014] The energy storage system of the present invention will be described in detail below based on preferred embodiments shown in the accompanying drawings. Figure 1 is a block diagram of the energy storage system of the present invention.

[0015] The energy storage system 10 of the present invention comprises a plurality of battery units 12, a plurality of AC / DC converters 14, a power converter 16, and a control unit 18. Each of the plurality of battery units 12 comprises a plurality of battery packs 30 connected in parallel to each other and connected in series to each other. Each of the plurality of AC / DC converters 14 is connected in parallel to each battery unit 12 and converts the alternating current of the system 20 to direct current. The power converter 16 is connected to both ends of the series connection of the plurality of battery units 12 and converts the alternating current of the system 20 to direct current.

[0016] Each battery pack 30 includes a lithium-ion battery 32, a contactor 34, and a BMS 36. The contactor 34 electrically connects and disconnects the lithium-ion battery 32. The BMS 36 has a function of collecting battery data output from the lithium-ion battery 32 and transmitting it to the control unit 18. The control unit 18 is connected to the BMS 36, the power converter 16, and each AC / DC converter 14 of each battery pack 30, and based on the battery data, controls the on / off of each contactor 34 via each BMS 36 and controls the operations of the power converter 16 and each AC / DC converter 14.

[0017] That is, a plurality of battery packs 30 each including a lithium-ion battery 32, a contactor 34, and a BMS 36 are connected in parallel to each other to form the battery unit 12. A plurality of battery units 12 connected in series to each other are connected to the grid 20 via the AC / DC converter 14 and are also connected to the grid 20 via the power converter 16. On the opposite side of each AC / DC converter 14 connected to the grid 20, each battery unit 12 is connected. On the opposite side of the power converter 16 connected to the grid 20, both ends of the plurality of battery units 12 connected in series to each other are connected. The control unit 18 is connected to each AC / DC converter 14, the power converter 16, and each BMS 36 to form the energy storage system 10. The battery data is output from a voltage sensor, a current sensor, a temperature sensor, etc. provided in the lithium-ion battery 32. When the BMS 36 detects an abnormality of the battery pack 30 based on the battery data collected from the lithium-ion battery 32, the BMS 36 turns off the contactor 34 instead of the control unit 18. Also, the AC / DC converter 14 is preferably an insulated type although not particularly limited.

[0018] Here, the voltage at the time of disconnection of the battery pack will be described. FIG. 2 is a block diagram for explaining the voltage at the time of disconnection of the battery pack. Disconnection means disconnecting the battery pack 30 from the grid 20. As an example, battery packs 30a and 30b corresponding to a plurality of battery packs 30 are connected in series with each other, and both ends thereof are connected to a load 38. Battery pack 30a includes a lithium-ion battery 32a, a contactor 34a, and a BMS 36a, and battery pack 30b includes a lithium-ion battery 32b, a contactor 34b, and a BMS 36b. When the voltages of both the lithium-ion battery 32a and the lithium-ion battery 32b are both 400 V, 800 V is applied across the terminals of the off contactor 34a.

[0019] Also, even if a plurality of contactors connected in series with each other are driven by one relay, the timings at which the contacts of the plurality of contactors move are not exactly the same, and it is known that all the loads are instantaneously applied to one contact. Therefore, even when the contactors 34a and 34b are controlled to be turned on and off simultaneously, 800 V is applied across one of the terminals, so there is a high possibility of exceeding the rated voltages of the contactors 34a and 34b. Here, the rated voltage is the reference voltage guaranteed by the manufacturer in order for the device or component to exhibit the performance as specified and ensure safety. When used at a voltage exceeding the rated voltage, the risks of dielectric breakdown, overheating, and fire increase.

[0020] Next, a modified example of the energy storage system of the present invention will be described. FIG. 3 is a block diagram showing a modified example of the energy storage system of the present invention. The energy storage system 40 is different from the energy storage system 10 in that the number of series connections of the battery unit 12 and the AC / DC converter 14 is three instead of two, and accordingly the output voltage is 1.5 times. However, since the others are the same, the same reference numerals are given to the same components, and the description thereof is omitted. The number of parallel connections of the battery packs 30 is three in FIGS. 1 and 3, but is not particularly limited and may be two or four or more. Also, the number of series connections of the battery unit 12 is two in FIG. 1 and three in FIG. 3, but is not particularly limited and may be four or more.

[0021] With this configuration, the energy storage system of the present invention can prevent the terminal voltage during disconnection from exceeding the rated voltage of the contactor provided in the battery pack, and can also simplify the control during battery pack connection and equalization.

[0022] Next, the battery pack 30 that constitutes the energy storage system 10 of the present invention will be described in detail. Each battery pack 30 is preferably a used battery pack that has been first used in an electric vehicle and is a second-hand item that has been collected and not disassembled.

[0023] In this case, each battery pack 30 is a used EV battery and contains a lithium-ion battery 32, a contactor 34, and a BMS 36. Furthermore, each battery pack 30 has been used without being repacked.

[0024] By adopting this configuration, the energy storage system of the present invention can achieve a capacity equal to or greater than that of conventional systems while remaining low-cost.

[0025] Next, the control methods for the AC / DC converter 14 and the power converter 16 during normal use will be described in detail. Here, "normal use" means that all contactors 34 of the battery packs 30 are turned on in a normal state and the lithium-ion batteries 32 can be charged with power from the grid 20.

[0026] The control unit 18 preferably specifies the output voltage and output current for each AC / DC converter 14 connected in parallel to each battery unit 12 based on the voltage of the corresponding battery unit 12. Furthermore, the control unit 18 preferably controls each AC / DC converter 14 to apply a voltage higher than that of the corresponding battery unit 12 to the corresponding battery unit 12.

[0027] In that case, the control unit 18 commands the power converter 16 to start and stop charging and discharging between the battery unit 12 and the power system 20. The control unit 18 cooperates with the power converter 16 in terms of power input and output with the power system 20 during charging and discharging, and stopping due to error monitoring. Since the voltage of the battery unit 12 changes due to charging and discharging, the control unit 18 changes the output voltage of the AC / DC converter 14 so that it does not deviate significantly from that voltage.

[0028] Next, the control method for the AC / DC converter 14 and the power converter 16 during a power outage will be described in detail. Here, a power outage means a state in which the power supply from the grid 20 is stopped. At least one of the AC / DC converter 14 and the power converter 16 detects the occurrence of a power outage and notifies the control unit 18.

[0029] During a power outage, the power converter 16 switches from normal operation with current control to independent operation with voltage control. Although the output power of the power converter 16 is momentarily interrupted, the control unit 18 continues to operate without interruption as power is supplied from the UPS (not shown) of the power outage control power system to the AC / DC converter 14, power converter 16, contactor 34, and BMS 36. Power is then supplied from the lithium-ion battery 32 to a specific load circuit (not shown) isolated from the grid 20 via the power converter 16, and at the same time, this power continues to apply voltage to each battery unit 12 as during normal use. To shut down the energy storage system 10, the main contactor (not shown) connected between the battery unit 12 and the power converter 16 is turned off, followed by turning off all contactors 34. When both the main contactor and all contactors 34 are turned off, no voltage exceeding the rated voltage of the contactor 34 is applied to the contactor 34.

[0030] With this configuration, the energy storage system of the present invention connects each battery section to an independent power source. As a result, only the output voltage of the battery section is applied to the contactor of each battery section, independently of the other battery sections. This prevents the terminal voltage from exceeding the rated voltage of the contactor when disconnected.

[0031] Next, the control method for the AC / DC converter 14 and contactor 34 when the battery pack 30 is connected will be described in detail. Here, "when the battery pack 30 is connected" means sequentially turning on the contactors 34, which are all turned off when the energy storage system 10 is shut down, and turning on the contactor 34 of the other battery pack 30 after replacing a battery pack 30 that is in an abnormal state due to failure or deterioration with another battery pack 30. The control unit 18 determines whether the lithium-ion battery 32 is in a normal or abnormal state based on battery data transmitted from the BMS 36 and a preset threshold. In addition, power from the grid 20 is used during normal use, and power from the UPS of the aforementioned power outage control power supply system is used during a power outage.

[0032] The control unit 18 preferably starts up the multiple AC / DC converters 14 before starting up the power converter 16. Then, while raising and lowering the output voltage of each AC / DC converter 14, the control unit 18 preferably controls the contactor 34 of the battery pack 30 to turn on when the difference between the output voltage of each AC / DC converter 14 and the battery pack 30 falls within a preset voltage difference.

[0033] In this case, first, the control unit 18 starts up the AC / DC converter 14 and changes the voltage of the AC / DC converter 14 from low voltage to high voltage or from high voltage to low voltage. Next, the control unit 18 calculates the voltage difference between the AC / DC converter 14 and the lithium-ion battery 32, and when the voltage difference becomes smaller than or equal to a preset value, it turns on the contactor 34 corresponding to that lithium-ion battery 32. At this time, the multiple contactors 34 can be turned on in any order.

[0034] Next, the control unit 18 specifies a low current value to the AC / DC converter 14 and controls it to charge the lithium-ion battery 32 with that current. When both ends of the series connection of the multiple battery units 12 become conductive, charging and discharging within the allowable current value of the lithium-ion battery 32 corresponding to the turned-on contactor 34 becomes possible, so the control unit 18 may activate the power converter 16. When connecting the battery pack 30 during a power outage, the power capacity of the UPS of the power outage control power supply system described above may be insufficient, so in that case, the power converter 16 is activated and the system switches to using power from the lithium-ion battery 32. Then, when the contactor 34 of the predetermined battery pack 30 to be operated is turned on, the system transitions to the normal operation or power outage operation described above. Note that the control unit 18 does not coordinate with the power converter 16 when connecting the battery pack 30.

[0035] With this configuration, the energy storage system of the present invention allows each battery section to change its voltage and turn on the contactor simultaneously and independently of other battery sections, thus simplifying the control when connecting the battery pack.

[0036] Next, the control method for the AC / DC converter 14 during the equalization of the battery pack 30 will be explained in detail. Here, the equalization of the battery pack 30 refers to the case where voltage variations that have occurred among the multiple battery units 12 are eliminated. The control unit 18 determines whether or not voltage variations have occurred based on the battery data transmitted from the BMS 36 and a preset threshold.

[0037] The control unit 18 preferably controls the first AC / DC converter connected in parallel to the first battery unit when voltage variations occur among the multiple battery units 12 and the voltage of the first battery unit becomes lower than the voltage of the second battery unit. The control unit 18 then preferably equalizes the voltage variations that have occurred among the multiple battery units 12 by applying a voltage higher than the voltage of the second battery unit to the first battery unit and controlling the charging current to the first battery unit.

[0038] In this case, among the multiple battery units 12 connected in series, the battery unit 12 with the lowest voltage is supplementally charged by the AC / DC converter 14 connected in parallel to that battery unit 12, thereby equalizing the voltage variation that has occurred among the multiple battery units 12.

[0039] With this configuration, the energy storage system of the present invention can recharge a battery section with a low voltage independently of other battery sections, thus simplifying the control of equalizing the battery pack. The energy storage system of the present invention is basically configured as described above.

[0040] Although the energy storage system of the present invention has been described in detail above, the present invention is not limited to the above description, and various improvements and modifications may be made without departing from the spirit of the present invention. [Industrial applicability]

[0041] The energy storage system of the present invention has the effect of preventing the terminal voltage from exceeding the rated voltage of the contactor provided in the battery pack when disconnected, as well as simplifying the control during connection and equalization of the battery pack, and enabling it to have a large capacity equivalent to or greater than conventional systems at a low cost, making it industrially useful. [Explanation of Symbols]

[0042] 10, 40 Energy storage systems 12 Battery section 14 AC / DC Converters 16 Power Converters 18 Control Unit 20 lines 30, 30a, 30b battery packs 32, 32a, 32b Lithium-ion batteries 34, 34a, 34b Contactors 36, 36a, 36b BMS 38 load

Claims

1. Each unit is equipped with multiple battery packs connected in parallel to each other, and multiple battery units are connected in series to each other, Each is individually connected in parallel to each battery section, and consists of multiple AC / DC converters that convert the alternating current of the system into direct current, A power converter, different from any of the aforementioned AC / DC converters, is connected to both ends of the series connection of the aforementioned multiple battery units and converts the alternating current of the grid into a direct current. It has a control unit and Each battery pack comprises a lithium-ion battery, a contactor for electrically connecting and disconnecting the lithium-ion battery, and a BMS having the function of collecting battery data output by the lithium-ion battery and transmitting it to the control unit. The control unit is connected to the BMS of each battery pack, the power converter, and each AC / DC converter, and controls the on / off state of each contactor via each BMS and the operation of the power converter and each AC / DC converter based on the battery data, as an energy storage system.

2. The energy storage system according to claim 1, wherein the control unit specifies an output voltage and output current to each AC / DC converter connected in parallel to each battery unit based on the voltage of the corresponding battery unit, and controls each AC / DC converter to apply a voltage higher than that of the corresponding battery unit to each corresponding battery unit.

3. The energy storage system according to claim 1, wherein the control unit starts the plurality of AC / DC converters before starting the power converter, and controls the battery pack contactor to turn on when the difference between the output voltage of each AC / DC converter and the output voltage of each AC / DC converter becomes within a preset voltage difference while the output voltage of each AC / DC converter is raised or lowered.

4. The energy storage system according to claim 1, wherein the control unit controls a first AC / DC converter connected in parallel to the first battery unit when a voltage variation occurs among the plurality of battery units and the voltage of the first battery unit becomes lower than the voltage of the second battery unit, thereby applying a voltage higher than the voltage of the second battery unit to the first battery unit and controlling the charging current to the first battery unit to equalize the voltage variation that occurred among the plurality of battery units.

5. The energy storage system according to any one of claims 1 to 4, wherein each battery pack is a used battery that has been first used in an electric vehicle and is a second-hand product that has been recovered and not disassembled.

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