Stationary battery system

Abstract

To enable relatively easy acquisition of IV characteristics in stationary battery systems. [Solution] The stationary battery system includes a plurality of battery packs 100a to 100n connected in parallel to an external system. Each battery pack 100a to 100n is connected in parallel to the external system via a corresponding PCU. The control device distributes the requested power Tw from the external system equally to each battery pack 100 so that the requested power Tw is discharged from the battery system, and controls the PCU so that a power of "Tw / n" is output from the battery packs 100a to 100n. The control device 200 then controls the PCU so that the output current of the two battery packs 100a and 100b divided by 2 is equivalent to "Tw / n", and so that it fluctuates periodically.

Description

Technical Field

[0001] This disclosure relates to a stationary battery system.

Background Art

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

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When a battery system is used as a stationary type for performing charge and discharge with an external system, the power required from the external system is often constant power. Therefore, the discharge current of the battery system is also often a constant current. Also, when the battery system is charged, constant current charging or constant current constant voltage charging is often performed.

[0005] In order to detect deterioration etc. of the secondary batteries constituting the battery system, the internal resistance of the secondary batteries may be measured and monitored. As a method for measuring the internal resistance, the I-V characteristics of the secondary batteries may be used. In order to obtain the I-V characteristics, it is necessary to detect and plot the voltage and current over a certain period of time and find the slope. However, in a stationary battery system, it is often operated at a constant current, and it is difficult to measure the I-V characteristics.

[0006] The purpose of this disclosure is to enable relatively easy acquisition of IV characteristics in a stationary battery system. [Means for solving the problem]

[0007] The stationary battery system of this disclosure is a stationary battery system that charges and discharges in and out of an external system. The stationary battery system comprises a plurality of battery packs connected in parallel to each other to an external system, a plurality of power converters provided corresponding to the plurality of battery packs and each positioned on a power line connecting the corresponding battery pack to the external system, and a control device that controls the plurality of power converters. When the stationary battery system is discharged, the control device controls the power converters so that the output current of at least two battery packs fluctuates periodically while maintaining the output of the required power requested by the external system.

[0008] In this configuration, the stationary battery system consists of multiple battery packs connected in parallel. During discharge of the stationary battery system, the multiple battery packs are controlled so that the output current of at least two of the battery packs fluctuates periodically, while maintaining the output of the required power requested by the external system. This makes it relatively easy to obtain IV characteristics in battery packs with periodically fluctuating output currents.

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

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

[0011] Preferably, the control device allocates output current to each battery pack so that the requested power is discharged from the stationary battery system, controls the power converter so that the allocated output current is output from each battery pack, and when an internal resistance measurement request is made, controls the power converter so that the output current of at least two battery packs fluctuates periodically while maintaining the output of the requested power.

[0012] In this configuration, if there is no request for internal resistance measurement, the allocated output current is output from each battery pack. This allows for a stable power supply from the stationary battery system to the external system.

[0013] Preferably, the control device may detect the current and voltage of the battery pack whose output current fluctuates periodically, and measure the internal resistance of the battery pack from the relationship between the current and the voltage.

[0014] With this configuration, the internal resistance can be calculated from the IV characteristics of the battery pack, where the output current fluctuates periodically. [Effects of the Invention]

[0015] According to this disclosure, it becomes possible to obtain IV characteristics relatively easily in a stationary battery system. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic diagram of the stationary battery system according to this embodiment. [Figure 2] This flowchart shows an example of discharge mode switching control performed by the control unit. [Figure 3] This diagram illustrates the output current of the battery pack in cyclic mode. [Modes for carrying out the invention]

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

[0018] FIG. 1 is a schematic configuration diagram of a stationary battery system 1 according to the present embodiment. As shown in FIG. 1, the stationary battery system 1 is connected to an external system 2 by a power line L. Hereinafter, the stationary battery system 1 will also be simply referred to as the battery system 1. The battery system 1 can supply power from the external system 2 and can also discharge to the external system 2. The battery system 1 includes a plurality of battery packs 100. In the present embodiment, n battery packs 100a to 100n are provided. The number of battery packs 100 is arbitrary and may be 10 or may be 20.

[0019] The battery pack 100 is an assembled battery in which a plurality of single batteries (battery cells 101) are connected in series, for example. The battery cell 101 may be, for example, a ternary lithium-ion battery (hereinafter also referred to as an "NMC battery") or a lithium iron phosphate-based lithium-ion battery (hereinafter also referred to as an "LFP battery"). Further, the battery cell may be a nickel-hydrogen battery. The battery pack 100 may be one that uses a battery pack (battery module) mounted on a vehicle.

[0020] Referring to FIG. 1, the n battery packs 100a to 100n are connected to the external system 2 in parallel with each other. On the power line L connecting the battery packs 100a to 100n to the external system, PCUs (Power Control Units) 110 (110a to 110n) are provided for each of the battery packs 100a to 100n. The PCU 110 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 the corresponding battery packs 100a to 100n. The PCU 110 may be one that uses a PCU mounted on a vehicle. Note that the PCU 110 corresponds to an example of the "power conversion device" of the present disclosure.

[0021] Each battery pack 100a to 100n is provided with a monitoring module 120. 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 may be the voltage (cell voltage) of the battery cells 101 that make up the battery pack 100. The voltage sensor may also be provided to detect the voltage of multiple battery cells 101 (for example, three battery cells 101 connected in series), and the voltage of multiple battery cells 101 may be detected as the voltage VB. The current sensor detects the current IB [A] input 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 (discharge current) is detected as a negative (-) value. The temperature sensor detects the temperature TB of the corresponding battery pack 100. Voltage VB, current IB, and temperature TB are output to the control device 200. The monitoring module 120 also calculates the State of Charge (SOC) of the corresponding battery packs 100a to 100n and outputs it to the control device 200. The SOC of battery pack 100 may also be calculated by the control device 200. SOC represents the charge state of battery pack 100, with a fully charged state defined as SOC = 100[%] and a completely discharged state as SOC = 0[%].

[0022] External system 2 comprises a PCS (Power Conditioning System) 10, a solar power generation device 20, a load 30, and a power grid PG. Each battery pack 100a to 100n is connected in parallel to the PCS 10 via each PCU 110a to 110n.

[0023] The 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). The PCS10 receives DC power from, for example, the solar power generation device 20. The PCS10 supplies AC power to the load 30. The load 30 includes electrical products used in homes (such as air conditioners and lighting fixtures, etc.). The PCS10 performs grid connection with the power grid PG and exchanges AC power. The PCS10 synchronizes the power of the battery system 1 and the solar power generation device 20 with the power of the power grid PG.

[0024] The control device 200 includes a processor and a memory, and receives commands from a HEMS (Home Energy Management System) controller (not shown) or the PCS10 to control the battery system 1. For example, the power generated by the solar power generation device 20 may be stored (charged) in the battery system 1. During a power outage, the power stored in the battery system 1 may be supplied to the load 30, and when there is a request for downward DR (demand response), the power stored in the battery system 1 may be supplied (reverse power flow) to the power grid PG.

[0025] The internal resistance of the battery pack 100 (battery cell 101) causes energy loss and voltage drop, which has an adverse effect on 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).

[0026] Figure 2 is a flowchart showing an example of discharge mode switching control executed by the control device 200. This flowchart is repeatedly executed at predetermined intervals when there is a discharge request from the external system 2 (PCS10).

[0027] In step (hereinafter, step is abbreviated as "S") 10, the control device 200 determines whether the flag F is 1. The initial value of the flag F is 0, and the flag F is set to 1 in S13 described later. If the flag F is 0, a negative determination is made and the process proceeds to S11. If the flag F is 1, an affirmative determination is made and the process proceeds to S14.

[0028] In S11, the control device 200 determines whether or not it is time for resistance measurement. Resistance measurement is the timing for measuring the internal resistance of the battery pack 100 (battery cell 101), and for example, it occurs at set intervals. The set interval is arbitrary and may be, for example, 24 hours, 1 week, or 1 month. If it is not time for resistance measurement, it is determined to be negative and the process proceeds to S12. If the timing of the current process is the timing for measuring the internal resistance of the battery pack 100, and it is time for resistance measurement, it is determined to be positive and the process proceeds to S13.

[0029] In S12, the control device 200 sets the discharge mode to normal mode and terminates the routine. In normal mode, the control device 200 evenly distributes the requested power Tw from the external system 2 (PCS10) to each battery pack 100 so that the requested power Tw 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 the PCUs 110a to 110n so that "Tw / n" power is output from the battery packs 100a to 100n. If the specifications of the battery packs 100a to 100n are the same and the voltage is the same, the output current of the battery packs 100a to 100n will be the same. Furthermore, the output power may be varied according to the SOC of each battery pack 100. For example, the required power Tw may be allocated to each battery pack 100 such that the output power increases for battery packs 100 with higher SOCs.

[0030] In S13, the control device 200 sets the discharge mode to cyclic mode, sets flag F to 1, and terminates the routine. In cyclic mode, the control device 200 controls PCUs 110a to 110n so that the requested power Tw from the external system 2 (PCS10) is discharged from the battery system 1, and so that the output currents of at least two battery packs 100 fluctuate periodically. Similar to normal mode, the control device 200 distributes the requested power Tw equally to each battery pack 100 and controls PCUs 110a to 110n so that a power of "Tw / n" is output from battery packs 100a to 100n. The control device 200 then controls PCUs 110a to 110n so that the output currents of at least two battery packs 100 fluctuate periodically.

[0031] Figure 3 illustrates the output current of the battery pack 100 in cyclic mode. In Figures 3(A) and (B), the solid line represents, for example, the output current of battery pack 100a, and the dashed line represents, for example, the output current of battery pack 100b. The dashed line represents the output current value corresponding to an output power of "Tw / n". Note that the other battery packs 100, excluding battery packs 100a and 100b, output an output current corresponding to "Tw / n". As shown in Figure 3, the control device 200 controls PCU 110a and PCU 110b so that the sum of the output currents of battery pack 100a and battery pack 100b divided by 2 becomes an output current corresponding to "Tw / n", and so that it fluctuates periodically.

[0032] In S13, if flag F is set to 1, S10 is affirmed 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 been completed. The control device 200 measures the internal resistance of the battery pack 100 when the discharge mode is cyclic mode. If the measurement of the internal resistance is completed, S14 is affirmed and the process proceeds to S15. If the measurement of the internal resistance is not completed, a negative determination is made and the routine ends.

[0033] In cyclic mode, when the battery system 1 is discharging, the control device 200 measures the internal resistance of the battery pack 100 whose output current fluctuates periodically. The internal resistance is determined by an IV plot. For example, it is calculated by plotting the current IB and voltage VB detected by the monitoring module 120 on a graph with current on the vertical axis and voltage on the horizontal axis for a certain period of time, and determining the slope of the straight line. In this embodiment, in cyclic mode, once the internal resistance of the battery pack 100 whose output current fluctuates periodically (for example, battery pack 100a and battery pack 100b) is calculated, the output current of the battery pack 100 whose internal resistance has been calculated (battery pack 100a and battery pack 100b) is controlled to a current equivalent to "Tw / n", and the output currents of the other two battery packs 100 are controlled to fluctuate periodically as shown in Figure 3. Then, the internal resistance of the battery pack 100 whose output current fluctuates periodically is measured. In this manner, when the internal resistances of all battery packs 100a to 100n have been calculated, it is determined in S14 that the measurement of internal resistances has been completed. The internal resistance calculated in this embodiment is the internal resistance of the battery cell 101 included in the voltage VB detected by the voltage sensor of the monitoring module 120.

[0034] In S15, the discharge mode is set to normal mode, flag F is set to 0, and the routine ends.

[0035] According to this embodiment, the stationary battery system 1 is composed of a plurality of battery packs 100 connected in parallel. When the stationary battery system 1 is discharged, the plurality of battery packs 100 are controlled so that the output current of at least two of the battery packs fluctuates periodically while maintaining the output of the required power Tw requested by the external system 2. This makes it relatively easy to obtain the IV characteristics and measure the internal resistance of the battery packs 100 whose output current fluctuates periodically.

[0036] In this embodiment, the control device 200 allocates output current to each battery pack 100 so that the requested power Tw is discharged from the stationary battery system 1, and controls the PCU 110 to output the allocated output current from each battery pack 100 (normal mode). When an internal resistance measurement request is received, the control device 200 controls the power converter so that the output current of at least two battery packs 100 fluctuates periodically while maintaining the output of the requested power Tw (cyclic mode). In normal mode, the allocated output current is output from each battery pack 100. This enables a stable supply of power from the stationary battery system 1 to the external system 2.

[0037] In the above embodiment, in cyclic mode, the output currents of the two battery packs 100 fluctuated periodically. However, the output currents of three or more battery packs 100 may also be made to fluctuate periodically. For example, if three battery packs 100 are used, the control device 200 may control the corresponding PCU 110 so that the value obtained by dividing the sum of the output currents of the three battery packs 100 by 3 becomes an output current equivalent to "Tw / n", and so that it fluctuates periodically.

[0038] In cyclic mode, all battery packs 100a to 100n included in the stationary battery system 1 may be divided into two groups, and the output current of each battery pack 100 may be periodically varied. For example, the output current of the battery packs 100 in the first group may be periodically varied as shown by the solid line in Figure 3, and the output current of the battery packs 100 in the second group may be periodically varied as shown by the dashed line in Figure 3. The currents of all battery packs 100 may then be varied so that the sum of their output currents divided by n equals "Tw / n". In this case, since the output current of all battery packs 100 is periodically varied, the measurement of internal resistance can be completed in a relatively short time.

[0039] In the above embodiment, a normal mode and a cyclic mode were set as the discharge modes. However, when discharging from the stationary battery system 1, the discharge may always be performed in cyclic mode. In this case, the internal resistance of the battery pack 100 may be measured at an appropriate timing.

[0040] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of Symbols]

[0041] 1 stationary battery system, 2 external systems, 10 PCS, 20 photovoltaic power generation devices, 30 loads, 100 battery packs, 101 single cells, 110 PCUs, 120 monitoring modules, 200 control devices, PG power grid.

Claims

1. A stationary battery system that performs charging and discharging in and out of an external system, The external system comprises a plurality of battery packs connected to each other in parallel, Multiple power converters are provided corresponding to the aforementioned multiple battery packs, and each is positioned on a power line connecting the corresponding battery pack to the external system. The system comprises a control device for controlling a plurality of the aforementioned power conversion devices, The control device is During the discharge of the aforementioned stationary battery system, A stationary battery system that controls the power converter so that the output current of at least two of the battery packs fluctuates periodically, while maintaining the output of the requested power requested by the external system.

2. The control device is The stationary battery system according to claim 1, which calculates the internal resistance of the battery pack in which the output current fluctuates periodically.

3. The control device is The power converter is controlled such that the requested power is discharged from the stationary battery system, and that output power is allocated to each of the battery packs, and that the allocated output power is output from each of the battery packs. A stationary battery system according to claim 1 or 2, wherein, when a request for internal resistance measurement is received, the power converter is controlled so that the output currents of at least two of the battery packs fluctuate periodically while maintaining the output of the requested power.

4. The control device is The stationary battery system according to claim 3, which detects the current and voltage of the battery pack whose output current fluctuates periodically, and measures the internal resistance of the battery pack from the relationship between the current and the voltage.

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