JP2016073021A - Power storage system and precharge method for power storage system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the time required for precharge.SOLUTION: A power storage system (1) related to the present invention includes a plurality of battery packs (2a-2l), voltage detection parts (6a-6l) for detecting voltages of the battery packs, and a control part (7) which controls charging/discharging. The control part performs control in such a manner that a battery pack of a charging object with a highest voltage is selected from among a plurality of battery packs of charging objects, the battery pack of the charging object with the highest voltage is brought into a non-chargeable state, the remaining battery packs of the charging objects are charged with a constant current, the battery pack of the charging object with the highest voltage is brought into a chargeable state on the basis of the fact that voltages of the remaining battery packs rise to voltages within a predetermined allowable range with respect to the voltage of the battery pack of the charging object with the highest voltage, and constant current charging is completed.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power storage system and a method for precharging a power storage system.

  In a power storage system in which a plurality of battery packs are connected in parallel, for example, by performing precharging (preliminary charging) in order to suppress cross current between the battery packs connected in parallel at the time of initial installation or replacement of the battery pack. The terminal voltage of each battery pack is equalized so that the battery pack can be discharged normally.

  As this type of power storage system, for example, Patent Document 1 is known. In this patent document 1, “all of the battery packs connected in parallel are connected to an external circuit, and in the power storage system provided with the control means for performing charge / discharge control in parallel, the control means are all All battery packs are charged so that the difference in voltage between all the battery packs is within a predetermined range by pre-charging with power supplied from an external circuit. The control to make the external circuit chargeable / dischargeable is performed "(refer to claim 1).

JP 2014-90595 A

  In the conventional precharge, all the battery packs are charged only, and constant current charging is performed, so that the voltages of the battery packs are made uniform. However, in this method, when another battery pack voltage approaches the battery pack with the highest voltage, the charging current flows through the battery pack with the highest voltage, and the voltage of the battery pack with the highest voltage also rises. It takes time for the voltages to be aligned. The aligned voltages are higher than the original battery pack voltage. This phenomenon will be described in detail with reference to FIG. As shown in FIG. 6B, when the constant current charging is performed, the voltage V2 of the battery pack 2b rises with time, and at time t1 close to the voltage V1 of the battery pack 2a, the value of the voltage V1 Rises. The charge voltage Vcg is higher than the voltage V2 due to the voltage drop due to the impedance of the charge switch and the discharge switch of the battery pack 2b. Therefore, when the voltage V1 and the voltage V2 approach each other, the charge voltage Vcg becomes higher than the voltage V1. is there.

  Therefore, the voltage difference between the battery pack 2a and the battery pack 2b is not easily reduced, and the constant current charging completion timing is delayed until time t3. As a result, the conventional precharge method has a problem that the time required for precharge is increased by the delay of completion of constant current charging. Patent Document 1 does not mention any technique for solving this problem.

  The present invention has been made to solve the above-described problems, and an object thereof is to shorten the time required for precharging in a power storage system in which a plurality of battery packs are connected in parallel.

  To achieve the above object, a power storage system according to the present invention includes a plurality of battery packs connected in parallel, a voltage detection unit that detects a voltage of each of the battery packs, and a control unit that controls charge and discharge. The control unit includes a plurality of battery packs or a plurality of battery packs satisfying a predetermined condition based on a detection result of the voltage detection unit. The charging target battery pack having the highest voltage is selected from the charging target battery packs, the charging target battery pack having the highest voltage is made unchargeable, and the plurality of charging target battery packs The remaining charge target battery packs except for the highest voltage charge target battery pack are subjected to constant current charging, and the remaining charge target battery packs are charged with the highest voltage charge target battery packs. Based on the increased to within the allowable range determined in advance and pressure, the addition to the ready charge a battery pack of the most voltage high charging target, and controlling so as to complete the constant-current charging.

  ADVANTAGE OF THE INVENTION According to this invention, the required time of a precharge can be shortened in the electrical storage system which connected the some battery pack in parallel. Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

The block diagram which shows the internal structure of the uninterruptible power supply to which the electrical storage system which concerns on 1st Embodiment of this invention was applied. The block diagram which shows the detail of the electrical storage system which concerns on 1st Embodiment of this invention. The figure which shows the operation state of the charging / discharging switch of the battery pack in precharge. The time chart which shows the change of the state of the battery pack, etc. during a precharge. Operation | movement explanatory drawing of the uninterruptible power supply (UPS) shown in FIG. The figure which shows the comparison of the precharge time of this embodiment (a) and prior art (b).

  Hereinafter, an embodiment of a power storage system according to the present invention will be described with reference to the drawings.

“First Embodiment”
FIG. 1 is a block diagram showing an internal configuration of an uninterruptible power supply to which a power storage system according to the first embodiment of the present invention is applied, and FIG. 2 shows details of the power storage system according to the first embodiment of the present invention. FIG. As shown in FIG. 1, an uninterruptible power supply (hereinafter referred to as UPS) 20 is connected between a commercial power source (system) 11 and an AC load 12, and is charged by receiving power supply from the commercial power source 11. At the same time, in an emergency in which the commercial power supply 11 cannot be supplied, the power stored inside is supplied to the AC load 12. In FIG. 1, RY is a relay.

  The UPS 20 includes a bidirectional inverter 13, a bidirectional DC / DC converter 14, and the power storage system 1. The power storage system 1 includes a plurality of (for example, twelve) battery packs 2 a to 2 l and a control unit 7. The control unit 7 performs charge / discharge control of each of the battery packs 2a to 2l, and also performs state monitoring and control of the bidirectional inverter 13 and the bidirectional DC / DC converter 14.

  Next, the detailed configuration of the battery packs 2a to 2l will be described with reference to FIG. As shown in FIG. 2, the battery pack 2a is configured by connecting a charge switch 3a, which is a charge permission circuit, and a discharge switch 4a, which is a discharge permission circuit, in series with a storage battery 5a. Moreover, the battery pack 2a is provided with the voltage sensor (voltage detection part) 6a for detecting the terminal voltage of the storage battery 5a. In addition, what is necessary is just to determine the number of battery packs suitably according to a specification.

  The storage battery 5a is configured by, for example, an assembled battery formed by connecting a plurality of lithium ion secondary battery cells in series and / or in parallel.

  The charging switch 3a includes a semiconductor switch (for example, a power MOSFET) that controls whether or not energization is possible in the charging direction, and a diode connected in reverse parallel to the semiconductor switch. A body diode formed as a parasitic element in the semiconductor switch may be used instead of the diode.

  The discharge switch 4a includes a semiconductor switch (for example, a power MOSFET) that controls whether or not energization is performed in the discharge direction, and a diode that is connected in reverse parallel to the semiconductor switch. A body diode formed as a parasitic element in the semiconductor switch may be used instead of the diode.

  Since the battery packs 2b to 2l have the same configuration as the battery pack 2a, the description thereof is omitted here. In FIG. 2, R1 to R12 are wiring resistances, Icg is a charging current flowing through each battery pack via the bidirectional DC / DC converter 14, Vcg is a charging voltage, I1 to I12 are currents flowing through each battery pack, V1 -V12 shows the terminal voltage of each battery pack, respectively.

  Next, a precharge control method in the power storage system 1 will be described. FIG. 3 is a diagram showing the operating state of the charge / discharge switch of each battery pack during precharging, FIG. 4 is a time chart showing changes in the state of the battery pack during precharging, etc., FIG. 6 is a diagram showing a comparison of precharge time between the present embodiment and the prior art. In the first embodiment, all the battery packs 2a to 21 are charged. The precharge control will be described below by taking as an example a case where the battery pack 2a has the highest voltage V1.

(First step)
When the precharge is started, the control unit 7 measures the voltages of the battery packs 2a to 2l based on the sensor data from the voltage sensors 6a to 6l. And the control part 7 selects the battery pack with the largest voltage (here, since the case where the battery pack 2a is the maximum voltage is described, the battery pack 2a is selected).

(Second step)
Next, the control unit 7 turns off the charging switch 3a of the battery pack 2a having the maximum voltage (unchargeable state), and turns on the charging switches 3b to 3l of the other battery packs 2b to 2l (see FIG. 3). That is, the battery packs 2b to 2l other than the battery pack 2a are brought into a chargeable state. As shown in FIG. 3, the discharge switches 4a to 4l of all the battery packs 2a to 2l are controlled to be off during the precharge.

  Next, the bidirectional inverter 13 and the bidirectional DC / DC converter 14 are operated by a command from the control unit 7 and start constant current charging for the battery pack. At this time, the battery pack 2a is not charged because the charging switch 3a is off. When the constant current charging is performed, the voltage and current of the battery packs 2b to 2l other than the maximum voltage are increased as shown in FIG.

(Third step)
Thereafter, on condition that the voltage of any one of the battery packs 2b to 2l is substantially equal to the voltage of the battery pack 2a, the control unit 7 turns on the charging switch 3a of the battery pack 2a to charge the battery pack 2a. To. Then, the control unit 7 sets the current output voltage to the voltage limit value for the bidirectional DC / DC converter 14. Thereby, it switches from constant current charge to constant voltage charge. That is, constant voltage charging is performed after time t2 (see FIG. 6A).

(4th step)
The controller 7 stops the constant voltage charging at the timing after the time t2 and when the charge end current value is detected. The control part 7 will be in the state (normal state) in which charging switch 3a-3l and discharge switch 4a-4l can be turned on, and charging / discharging is possible. Thus, in the present embodiment, the processing from the first step to the fourth step is performed, and the precharge is completed.

  The charge end current value is a current threshold value for determining that the battery is fully charged. Specifically, when configured to perform constant current-constant voltage charging, which is a general charging method for lithium ion batteries, the charging current decreases after shifting to constant voltage charging. When it becomes less than the value, it is determined that the battery is fully charged, and the charging operation is completely stopped. The current value at this time is the charge end current value.

  Supplementing the operation of the UPS 20, as shown in FIG. 5A, when the UPS 20 is stopped when the battery packs are not connected in parallel, when the system input is turned on, the UPS 20 After that, the battery packs 2a to 2l are precharged to return to the normal state. Further, as shown in FIG. 5B, when the battery pack is replaced when the UPS 20 is in the normal state, the UPS 20 performs precharging after the battery pack is replaced to return to the normal state.

  As described above, in the prior art, the timing of shifting to constant voltage charging was delayed until time t3. However, in this embodiment, the charging switch 3a of the battery pack 2a is turned off so that charging cannot be performed. Since all the battery packs 2a to 2l are shifted to constant voltage charging after the battery packs 2b to 21 are charged with constant current, the timing for shifting to constant voltage charging can be shortened to time t2. As a result, the time required for precharging can be shortened by the difference between time t3 and time t2. Further, since the voltage of each of the battery packs 2a to 2l does not become higher than V1 during the precharge, there is an advantage that damage of each of the battery packs 2a to 2l due to overvoltage can be prevented.

“Second Embodiment”
Next, a power storage system according to the second embodiment of the present invention will be described. The power storage system according to the second embodiment has the same configuration as that of the power storage system according to the first embodiment, and the only difference is the control of precharge by the control unit 7. Therefore, illustration and description of the hardware configuration are omitted, and only control will be described.

  When precharging is started, the control unit 7 checks the voltage of each of the battery packs 2a to 2l and selects only the battery pack that satisfies a predetermined condition. Here, as the predetermined condition described above, for example, N of the battery packs 2a to 2l having a higher voltage (N is a natural number of 2 or more), and N of the battery packs 2a to 2l having a lower voltage. If any one of the three conditions of the battery packs 2a to 2l with a small voltage difference is set, it is more likely that the precharge will be completed in a shorter time than the condition of the battery pack installation position number. .

  Then, the control unit 7 selects the battery pack having the highest voltage from the specific battery pack selected as the charging target, turns off the charging switch of the battery pack, turns on the charging switch of the remaining battery packs, Turn off the charging switch of the external battery pack and perform constant current charging. When the voltage value is approximately the same as the maximum value of the battery pack to be charged, make the battery pack with the highest voltage ready for charging and constant current charging. To complete. When the precharge for the selected battery pack is completed, the control unit 7 sets only the selected battery pack in a dischargeable state.

  According to this configuration, since only the necessary battery pack is precharged, the time required for precharge can be further shortened. Of course, when all the battery packs are precharged, it is necessary to precharge all the remaining battery packs other than the battery pack having the maximum voltage as described in the first embodiment.

  In addition, in order to make the transition to constant voltage charging even faster, a predetermined allowable voltage value is reached even if the remaining battery pack is almost the same as the battery pack of the maximum voltage among the battery packs to be charged. In this case, the control unit 7 may control the bidirectional DC / DC converter 14 to control the charging of the battery pack so that the constant current charging is shifted to the constant voltage charging.

  In addition, this invention is not limited to embodiment mentioned above, Various modifications are included. For example, the above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. Further, a part of the configuration of an embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of an embodiment. Moreover, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Power storage system 2a-2l Battery pack 3a-3l Charge switch 4a-4l Discharge switch 5a-5l Storage battery 6a-6l Voltage sensor (voltage detection part)
7 Control unit

Claims (4)

A plurality of battery packs connected in parallel; a voltage detection unit that detects the voltage of each battery pack; and a control unit that controls charge and discharge.
The controller is
Based on the detection result of the voltage detection unit, from among a plurality of battery packs to be charged configured by all battery packs of the plurality of battery packs or some battery packs satisfying a predetermined condition, The battery pack with the highest voltage to be charged is selected, the battery pack with the highest voltage to be charged is made unchargeable, and the battery with the highest voltage among the plurality of battery packs to be charged is selected. Charge the remaining battery pack except the battery pack at a constant current,
Based on the fact that the remaining battery pack to be charged has risen to a predetermined allowable range with the voltage of the battery pack to be charged having the highest voltage, a state in which the battery pack to be charged with the highest voltage can be charged And a control system for controlling to complete the constant current charging. In claim 1,
The power storage system according to claim 1, wherein the predetermined allowable range is set such that the remaining battery pack to be charged and the voltage of the battery pack to be charged having the highest voltage are substantially the same. In claim 1 or 2,
N of the plurality of battery packs having the highest voltage (where N is a natural number of 2 or more), N of the plurality of battery packs having the lowest voltage, and the voltage difference of the plurality of battery packs A power storage system characterized in that any one of N having a small number is set to the predetermined condition. A precharge method for a power storage system, comprising: a plurality of battery packs connected in parallel; a voltage detection unit that detects a voltage of each battery pack; and a control unit that performs charge / discharge control,
Based on the detection result of the voltage detection unit, from among a plurality of battery packs to be charged configured by all battery packs of the plurality of battery packs or some battery packs satisfying a predetermined condition, A first step of selecting a battery pack to be charged with the highest voltage;
The charging target battery pack having the highest voltage is made unchargeable, and the remaining charging target battery packs excluding the charging target battery pack having the highest voltage among the plurality of charging target battery packs. A second step of constant current charging;
Based on the fact that the remaining battery pack to be charged has risen to a predetermined allowable range with the voltage of the battery pack to be charged having the highest voltage, a state in which the battery pack to be charged with the highest voltage can be charged And a third step of completing the constant current charging.