Stationary battery system

Abstract

An object of the present application is to relatively easily obtain an I-V characteristic in a stationary battery system. The stationary battery system includes a plurality of battery packs connected in parallel with an external system. Each battery pack is connected in parallel with the external system via a corresponding PCU. A control device equally distributes a requested power Tw to each battery pack to discharge the requested power Tw requested from the external system from the battery system, and controls the PCUs to output an electric power of "Tw / n" from the battery packs. Furthermore, the control device controls the PCUs to periodically fluctuate a value obtained by dividing a sum of output currents of 2 battery packs by 2 to an output current corresponding to "Tw / n".

Description

Technical Field

[0001] This invention relates to a stationary battery system. Background Technology

[0002] Japanese Patent Application Publication No. 2015-195653 (Patent Document 1) discloses a battery system consisting of multiple secondary batteries connected in parallel. In this Patent Document 1, any one of the multiple secondary batteries is designated as a priority battery, and the battery capacity of the priority battery is estimated by discharging or charging only the priority battery.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2015-195653 Summary of the Invention

[0004] When a battery system is used as a stationary system for charging and discharging with an external system, the power requested from the external system is typically constant. Therefore, the discharge current of the battery system is also typically constant. Furthermore, during charging, constant current charging or constant current-constant voltage charging is usually performed.

[0005] To detect degradation of the secondary battery that makes up a battery system, the internal resistance of the secondary battery is sometimes measured and monitored. One method for measuring internal resistance is the IV characteristic of the secondary battery. To obtain the IV characteristic, it is necessary to measure and plot the voltage and current over a certain period of time and calculate its slope. However, in stationary battery systems, which typically operate at a constant current, it is difficult to measure the IV characteristic.

[0006] The purpose of this invention is to enable the relatively easy acquisition of IV characteristics in stationary battery systems.

[0007] The stationary battery system of the present invention is a stationary battery system that performs charging and discharging with an external system. The stationary battery system includes: multiple battery packs connected in parallel with the external system; multiple power conversion devices corresponding to the multiple battery packs and respectively disposed on power lines connecting each corresponding battery pack to the external system; and a control device that controls the multiple power conversion devices. The control device controls the power conversion devices so that, during the discharge of the stationary battery system, while maintaining the output of requested power from the external system, the output current of at least two battery packs periodically varies.

[0008] According to this structure, the stationary battery system consists of multiple battery packs connected in parallel. The battery packs are controlled such that, during the discharge of the stationary battery system, while maintaining the output of requested power from an external system, the output current of at least two battery packs varies periodically. Therefore, in battery packs with periodically varying output currents, IV characteristics can be obtained relatively easily.

[0009] Preferably, the control device calculates the internal resistance of the battery pack, whose output current varies periodically.

[0010] Based on this structure, for example, by obtaining the IV characteristics of a battery pack whose output current varies periodically, the internal resistance can be calculated with relatively high accuracy.

[0011] Preferably, the control device can perform the following processing: distributing the output current to each battery pack to discharge the requested power from the stationary battery system, and controlling the power conversion device to output the distributed output current from each battery pack; and when there is a request for internal resistance measurement, controlling the power conversion device to periodically change the output current of at least two battery packs while maintaining the output of the requested power.

[0012] According to this structure, in the absence of a request for internal resistance measurement, the allocated output current is output from each battery pack. This enables a stable power supply from the stationary battery system to external systems.

[0013] Preferably, the control device can perform the following processing: detect the current and voltage of the battery pack whose output current changes periodically, and determine the internal resistance of the battery pack based on the relationship between the current and the voltage.

[0014] Based on this structure, the internal resistance can be calculated according to the IV characteristics of the battery pack, which vary periodically with the output current.

[0015] Invention Effects

[0016] According to the present invention, IV characteristics can be obtained relatively easily in stationary battery systems. Attached Figure Description

[0017] Figure 1 This is a schematic structural diagram of the stationary battery system involved in this embodiment.

[0018] Figure 2 This is a flowchart illustrating an example of discharge mode switching control performed by a control device.

[0019] Figure 3 This is a diagram illustrating the output current of the battery pack in cyclic mode. Detailed Implementation

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, identical or corresponding parts in the drawings will be labeled with the same symbols, and their descriptions will not be repeated.

[0021] Figure 1 This is a schematic structural diagram of the stationary battery system 1 according to this embodiment. Figure 1As shown, the stationary battery system 1 is connected to the external system 2 via a power line L. Hereinafter, the stationary battery system 1 will also be simply referred to as battery system 1. Battery system 1 is capable of receiving power from the external system 2 and discharging into the external system 2. Battery system 1 includes multiple battery packs 100. In this embodiment, n battery packs 100a to 100n are included. The number of battery packs 100 is arbitrary, and can be 10 or 20.

[0022] The battery pack 100 is, for example, a battery group formed by connecting multiple individual cells (battery units 101) in series. The battery unit 101 can be, for example, a ternary lithium-ion battery (hereinafter also referred to as "NMC battery") or a lithium iron phosphate battery (hereinafter also referred to as "LFP battery"). Furthermore, the battery unit can be a nickel-metal hydride battery. The battery pack 100 can be adapted to use a battery pack (battery module) mounted in a vehicle.

[0023] refer to Figure 1 n battery packs 100a to 100n are connected in parallel to an external system 2. On the power line L connecting the battery packs 100a to 100n to the external system, a PCU (Power Control Unit) 110 (110a to 110n) is provided for each battery pack 100a to 100n. The PCU 110a to 110n includes an inverter and a DC / DC converter, and is controlled by a control device 200. The PCUs 110a to 110n control the charging and discharging of their respective battery packs 100a to 100n. The PCU 110 can be a PCU mounted in a vehicle. Furthermore, the PCU 110 is an example of the "power conversion device" of this invention.

[0024] A monitoring module 120 is provided on each battery pack 100a to 100n. The monitoring module 120 includes a voltage sensor, a current sensor, and a temperature sensor. The voltage sensor detects the voltage VB[V] of the corresponding battery pack 100. The voltage VB can be the voltage (cell voltage) of the battery cells 101 constituting the battery pack 100. Furthermore, the voltage sensor can be configured to detect the voltage of multiple battery cells 101 (e.g., three battery cells 101 connected in series), and the detected voltage of the multiple battery cells 101 is used as the voltage VB. The current sensor detects the current IB[A] input to and output to the corresponding battery pack 100. The current IB has a positive or negative sign indicating the direction of flow; the current charging the battery pack 100 (charging current) is detected as a positive (+) value, and the current discharging from the battery pack 100 (discharging current) is detected as a negative (-) value. The temperature sensor detects the temperature TB of the corresponding battery pack 100. The voltage VB, current IB, and temperature TB are output to the control device 200. Furthermore, the monitoring module 120 calculates the SOC (State of Charge) of the corresponding battery packs 100a to 100n and outputs it to the control device 200. Additionally, the SOC of the battery pack 100 can be calculated by the control device 200. SOC represents the charging state of the battery pack 100; a fully charged state is defined as SOC = 100% and a fully discharged state is defined as SOC = 0%.

[0025] External system 2 includes PCS (Power Conditioning System) 10, solar power generation device 20, load 30 and power system PG. Each battery pack 100a to 100n is connected in parallel to PCS10 via each PCU 110a to 110n.

[0026] PCS10 is a power conversion device capable of both AC / DC conversion (conversion from alternating current to direct current) and DC / AC conversion (conversion from direct current to alternating current). PCS10 receives direct current power, for example, from solar power generation device 20. PCS10 supplies alternating current power to load 30. Load 30 includes electrical products used in a household (e.g., air conditioners and lighting fixtures). PCS10 is connected to the power system PG for AC power transmission and reception. PCS10 tunes / synchronizes the power from battery system 1 and solar power generation device 20 with the power system PG.

[0027] The control device 200 includes a processor and memory, and receives instructions from a Home Energy Management System (HEMS) controller (not shown) or PCS 10 to control the battery system 1. For example, electricity generated by the solar power generation device 20 can be stored (charged) in the battery system 1. In the event of a power outage, the electricity stored in the battery system 1 can be supplied to the load 30, and in the event of a demand response (DR) request, the electricity stored in the battery system 1 can be supplied to the power system PG (countercurrent flow).

[0028] The internal resistance of the battery pack 100 (battery cell 101) can cause energy loss or voltage drop, which can adversely affect the performance and lifespan of the battery pack 100. Therefore, it is preferable to monitor the internal resistance of the battery pack 100 (battery cell 101).

[0029] Figure 2 This is a flowchart illustrating an example of discharge mode switching control performed by control device 200. This flowchart is repeatedly executed at predetermined intervals when a discharge request is received from external system 2 (PCS10).

[0030] In step (hereinafter referred to as "S") 10, the control device 200 determines whether the flag F is 1. The initial value of the flag F is 0, and in S13 described later, the flag F is set to 1. If the flag F is 0, the determination is negative, and proceeds to S11; if the flag F is 1, the determination is positive, and proceeds to S14.

[0031] In S11, the control device 200 determines whether it is a resistance measurement period. The resistance measurement period is the time when the internal resistance of the battery pack 100 (battery cell 101) is measured; for example, it may be a set period. The set period is arbitrary; for example, it can be 24 hours, 1 week, or 1 month. If it is not a resistance measurement period, the determination is negative, and the process proceeds to S12. If the current processing time is the time when the internal resistance of the battery pack 100 is measured and it is a resistance measurement period, the determination is positive, and the process proceeds to S13.

[0032] In S12, the control device 200 sets the discharge mode to normal mode and ends the current routine. In normal mode, the control device 200 equally distributes the requested power Tw to each battery pack 100 so that the requested power Tw requested from the external system 2 (PCS10) is discharged from the battery system 1. In this embodiment, the battery system 1 has n battery packs 100 (100a to 100n), so the output power (discharge power) of each battery pack 100 is "Tw / n". The control device 200 controls PCUs 110a to 110n to output power of "Tw / n" from battery packs 100a to 100n. When battery packs 100a to 100n have the same specifications and equal voltage, the output current of battery packs 100a to 100n is equal. Additionally, the output power can be adjusted based on the SOC of each battery pack 100. For example, the requested power Tw can be allocated to each battery pack 100 so that the battery pack 100 with a higher SOC outputs more power.

[0033] In S13, the control device 200 sets the discharge mode to cyclic mode and sets flag F to 1, ending the current routine. In cyclic mode, the control device 200 controls PCUs 110a to 110n to discharge the requested power Tw from external system 2 (PCS10) from battery system 1, and the output current of at least two battery packs 100 varies periodically. Similar to the normal mode, the control device 200 equally distributes the requested power Tw to each battery pack 100 and controls PCUs 110a to 110n to output power of “Tw / n” from battery packs 100a to 100n. Moreover, the control device 200 controls PCUs 110a to 110n to vary the output current of at least two battery packs 100 periodically.

[0034] Figure 3 This is a diagram illustrating the output current of battery pack 100 in cycle mode. Figure 3 of Figure 3 (A) and Figure 3 In (B), solid lines represent, for example, the output current of battery pack 100a, and dashed lines represent, for example, the output current of battery pack 100b. Double-dotted lines indicate the output current value equivalent to "Tw / n". Additionally, other battery packs 100 besides battery packs 100a and 100b output current equivalent to "Tw / n". For example... Figure 3 As shown, the control device 200 controls PCU110a and PCU110b so that the sum of the output current of battery pack 100a and the output current of battery pack 100b divided by 2 becomes the output current equivalent to "Tw / n" and changes periodically.

[0035] In S13, if flag F is set to 1, the condition is affirmative in S10, and the process proceeds to S14. In S14, it is determined whether the measurement of the internal resistance of the battery pack 100 (battery cell 101) has ended. When the discharge mode is cycle mode, the control device 200 performs the measurement of the internal resistance of the battery pack 100. If the measurement of the internal resistance has ended, the condition is affirmative in S14, and the process proceeds to S15. If the measurement of the internal resistance has not ended, the condition is negative, and the current routine procedure ends.

[0036] When discharging from battery system 1 in cyclic mode, control device 200 measures the internal resistance of battery pack 100, whose output current varies periodically. The internal resistance is determined using an IV graph. For example, it is calculated by plotting the slope of a straight line obtained by monitoring module 120 over a certain period of time on a graph with current on the vertical axis and voltage on the horizontal axis. In this embodiment, in cyclic mode, if the internal resistance of battery pack 100 (e.g., battery pack 100a and battery pack 100b) whose output current varies periodically is calculated, the output current of battery pack 100 (battery pack 100a and battery pack 100b) with the calculated internal resistance is controlled to a current equivalent to "Tw / n", such as... Figure 3 As shown, the output current of the other two battery packs 100 is controlled to vary periodically. Furthermore, the internal resistance of the battery packs 100 whose output current varies periodically is measured. Thus, when the internal resistance of all battery packs 100a to 100n is calculated, the internal resistance measurement is considered complete in S14. In this embodiment, the internal resistance calculated is the internal resistance of the battery cell 101 contained in the voltage VB detected by the voltage sensor of the monitoring module 120.

[0037] In S15, the discharge mode is set to normal mode and the flag F is set to 0, ending the current routine.

[0038] According to this embodiment, the stationary battery system 1 is composed of multiple battery packs 100 connected in parallel. The multiple battery packs 100 are controlled such that, during the discharge of the stationary battery system 1, while maintaining the output of the requested power Tw requested from the external system 2, the output current of at least two battery packs periodically varies. Therefore, in the battery packs 100 with periodically varying output currents, IV characteristics can be obtained relatively easily, and internal resistance can be measured.

[0039] According to this embodiment, the control device 200 distributes the output current to each battery pack 100 to discharge the requested power Tw from the stationary battery system 1, and controls the PCU 110 to output the distributed output current from each battery pack 100 (normal mode). When there is a request for internal resistance measurement, the control device 200 controls the power conversion device to periodically vary the output current of at least two battery packs 100 while maintaining the output of the requested power Tw (cyclic mode). In normal mode, the distributed output current is output from each battery pack 100. Thus, power can be stably supplied from the stationary battery system 1 to the external system 2.

[0040] In the above embodiment, in the cyclic mode, the output current of the two battery packs 100 varies periodically. However, it is also possible to vary the output current of three or more battery packs 100 periodically. For example, when dealing with three battery packs 100, the control device 200 can control the corresponding PCU 110 so that the sum of the output currents of the three battery packs 100 divided by 3 becomes the output current equivalent to "Tw / n" and varies periodically.

[0041] In cyclic mode, all battery packs 100a to 100n included in the stationary battery system 1 can be divided into two groups, causing the output current of the battery pack 100 to vary periodically. For example, the output current of the battery packs 100 included in the first group can be varied as follows: Figure 3 The solid line shown changes periodically, causing the output current of the battery pack 100 included in the second group to vary as follows: Figure 3 The output current of all battery packs 100 varies periodically, as shown by the dashed line. Furthermore, the sum of the output currents of all battery packs 100 divided by n becomes "Tw / n". In this case, the output currents of all battery packs 100 vary periodically, thus allowing the measurement of internal resistance to be completed in a relatively short time.

[0042] In the above embodiment, a normal mode and a cycle mode are set as discharge modes. However, when discharging from the stationary battery system 1, discharge can always be performed in cycle mode. In this case, the internal resistance of the battery pack 100 can be measured at appropriate times.

[0043] The embodiments disclosed herein are considered illustrative in all respects and not restrictive. The scope of the invention is defined not by the description of the above embodiments but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0044] Symbol Explanation

[0045] 1-Stationary battery system, 2-External system, 10-PCS, 20-Solar power generation device, 30-Load, 100-Battery pack, 101-Single cell (battery unit), 110-PCU, 120-Monitoring module, 200-Control device, PG-Power system.

Claims

1. A stationary battery system for charging and discharging with an external system, characterized in that it comprises: Multiple battery packs are connected in parallel with the external system; Multiple power conversion devices, corresponding to the multiple battery packs, are respectively configured on the power lines connecting each corresponding battery pack to the external system; and A control device that controls multiple power conversion devices. The control device controls the power conversion device so that, while maintaining the output of requested power from the external system during the discharge of the stationary battery system, the output current of at least two of the battery packs periodically varies.

2. The stationary battery system according to claim 1, characterized in that, The control device calculates the internal resistance of the battery pack as the output current varies periodically.

3. The stationary battery system according to claim 1 or 2, characterized in that, The control device performs the following processing: The output power is distributed to each of the battery packs to discharge the requested power from the stationary battery system, and the power conversion device is controlled to output the distributed output power from each of the battery packs; and When an internal resistance measurement request is received, the power conversion device is controlled to maintain the output of the requested power while the output current of at least two of the battery packs varies periodically.

4. The stationary battery system according to claim 3, characterized in that, The control device performs the following processing: The current and voltage of the battery pack, whose output current varies periodically, are detected, and the internal resistance of the battery pack is determined based on the relationship between the current and the voltage.

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