Storage battery system

Abstract

According to the present invention, an electricity storage system comprises: a droop command generation unit that, when charging and discharging storage batteries of target units, which are at least two storage battery units among a plurality of storage battery units, generates a droop command for performing droop control on the basis of the slope of the droop characteristics of each of the target units; an acquisition unit that acquires an output power value actually output by a DC / DC converter on the basis of the droop command; and a droop command correction unit that corrects the droop command on the basis of the output power value. The droop command correction unit corrects the droop command on the basis of the ratio between an ideal power sharing ratio, which is the ratio of the powers to be output by the respective target units, and an actual power sharing ratio, which is the ratio of the output power values from the respective DC / DC converters of the target units.

Description

Battery storage system

[0001] This disclosure relates to a storage battery system. This application claims priority to Japanese Patent Application No. 2023-132301, filed on August 15, 2023, the contents of which are incorporated herein by reference.

[0002] Energy storage systems are used in various facilities, such as power generation facilities and factories that use renewable energy. The energy storage system includes a plurality of storage battery units each having a storage battery and a DC / DC converter, a power conditioning system (PCS), and a DC bus that connects the storage battery units and the PCS.

[0003] For example, when the power grid is short of power, the power storage system supplies power discharged from the storage batteries to the power grid via the PCS. In this case, the discharge power (load sharing) of each storage battery unit may be adjusted so that the SOC (State of Charge) of each storage battery is approximately uniform. Patent Documents 1 and 2 describe a technique for equalizing the load sharing, in which droop control is performed to adjust the output voltage by changing the drooping characteristics, thereby equalizing the load sharing between generators and storage batteries and between power supply devices.

[0004] Japanese Patent No. 3679949 Japanese Patent Application Laid-Open No. 2011-10442

[0005] However, the discharge power from the storage batteries of the storage battery unit is affected by the resistance (wiring resistance) of the wiring through which the power passes. Therefore, even if the configurations described in Patent Documents 1 and 2 are used, there may be a discrepancy between the target discharge power based on the command value adjusted by droop control and the actual discharge power output. As a result, there is a problem in that the load sharing among the multiple storage batteries cannot be sufficiently equalized.

[0006] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a storage battery system that can control discharge power with greater accuracy and equalize the load sharing among multiple storage batteries.

[0007] In order to solve the above problems, an energy storage system according to the present disclosure includes: a plurality of storage battery units each having a storage battery and a DC / DC converter that converts the voltage of charging / discharging power to / from the storage battery; a droop command generation unit that generates a droop command for performing droop control based on a gradient of the droop characteristics of each of target units, which are at least two storage battery units among the plurality of storage battery units, when charging / discharging the storage battery of the target unit; an acquisition unit that acquires an output power value actually output by the DC / DC converter based on the droop command; and a droop command correction unit that corrects the droop command based on the output power value, and the droop command correction unit corrects the droop command based on the ratio between an ideal power sharing rate that is the ratio of power that should be output by each of the target units between the at least two target units, and an actual power sharing rate that is the ratio of output power values ​​from the DC / DC converter of each of the target units between the at least two target units.

[0008] According to the storage battery system of the present disclosure, it is possible to control discharge power with higher accuracy and equalize the load sharing among multiple storage batteries.

[0009] 1 is a diagram illustrating an overall configuration of a power storage system according to an embodiment of the present disclosure. FIG. 2 is a block diagram illustrating a functional configuration of a control device of the power storage system. FIG. 3 is a block diagram illustrating a functional configuration of a droop command correction unit of the power storage system. FIG. 4 is a diagram illustrating a change in droop characteristics due to wiring resistance. FIG. 5 is a diagram illustrating an example of a simulation of the power storage system 1 configured as described above. FIG. 6 is a diagram illustrating the configuration of another correction method performed for comparison. FIG. 7 is a diagram illustrating an example of a simulation of the configuration shown in FIG.

[0010] Hereinafter, an embodiment of a power storage system according to the present disclosure will be described with reference to the accompanying drawings. However, the present disclosure is not limited to this embodiment. (Overall Configuration of Power Storage System) Fig. 1 is a diagram showing the overall configuration of a power storage system according to one embodiment. As shown in Fig. 1, the power storage system 1 includes a PCS (Power Conditioning System) 2, a control device 3, a DC bus 4, and a plurality of storage battery units 5.

[0011] The PCS 2 is a power conditioner connected to the power grid. The PCS 2 has a bidirectional inverter that converts AC power to DC power. The PCS 2 converts DC power discharged from each storage battery unit 5 into AC power and outputs it to the power grid. The PCS 2 also converts AC power supplied from the power grid into DC power and outputs it to each storage battery unit 5.

[0012] The control device 3 controls the charging and discharging of each storage battery unit. The specific functional configuration of the control device 3 will be described later.

[0013] The DC bus 4 is a bus for connecting the PCS 2 and a plurality of storage battery units 5 .

[0014] The plurality of storage battery units 5 are connected in parallel to the PCS 2 via the DC bus 4. Each storage battery unit 5 includes a DC / DC converter 51 and a storage battery 52. ​​In accordance with a command from the control device 3, the DC / DC converter 51 converts the DC power supplied from the PCS 2 to a predetermined voltage and charges the storage battery 52. ​​In addition, in accordance with a command from the control device 3, the DC / DC converter 51 converts the discharge power of the storage battery 52 to a predetermined voltage and supplies it to the PCS 2.

[0015] (Functional Configuration of Control Device) Fig. 2 is a block diagram showing the functional configuration of the control device of the power storage system. As shown in Fig. 2, the control device 3 includes a processor 31, a memory 32, a storage 33, and a communication interface 34.

[0016] The processor 31 operates in accordance with a predetermined program to function as an acquisition unit 311, a droop command generation unit 312, a charge / discharge control unit 313, and a droop command correction unit 314.

[0017] The acquisition unit 311 acquires the output power value Pw actually output from each DC / DC converter 51 when charging or discharging is performed in each DC / DC converter 51 of the multiple storage battery units 5 based on instructions from the control device 3.

[0018] The droop command generation unit 312 generates a droop command D for performing droop control of each storage battery unit 5. The droop command generation unit 312 outputs the generated droop command D to the droop command correction unit 314. The droop command D includes a set value for the slope of the droop characteristic (droop slope) of the storage battery unit 5.

[0019] Normal droop control changes the droop slope while fixing the droop intercept of each storage battery unit 5 to an initial value (zero) so as to maintain the voltage of the DC bus 4 within a predetermined voltage range and suppress variations in the state (SOC, etc.) of each storage battery unit 5. In addition, the droop command generator 312 according to this embodiment may perform, as part of the droop control, a process of changing the droop intercept of a target unit, which is at least one storage battery unit 5 among the multiple storage battery units 5, when charging or discharging desired power to or from the target unit.

[0020] The charge / discharge control unit 313 controls the charge / discharge operation of the storage batteries 52 of the multiple storage battery units 5. The charge / discharge control unit 313 can charge / discharge the storage batteries 52 in all of the multiple storage battery units 5. The charge / discharge control unit 313 can also charge / discharge the storage batteries 52 in at least two or more storage battery units 5 out of the multiple storage battery units 5. The charge / discharge control unit 313 can also charge / discharge the storage battery 52 in only one storage battery unit 5 out of the multiple storage battery units 5.

[0021] In the following description, when charging / discharging the storage batteries 52 of at least two storage battery units 5 out of the multiple storage battery units 5, the target storage battery units 5 will be appropriately referred to as target units 5t. When charging / discharging the storage batteries 52 of at least two target units 5t, the charge / discharge control unit 313 sets a power sharing rate (power sharing rate) for each target unit 5t to share in charging / discharging and output. The multiple target units 5t output power P1, P2, ... according to the power sharing rate set for each target unit 5t. The power Pt output from the PCS2 is the sum of these powers P1, P2, .... The power sharing rate is the ratio P1 / Pt, P2 / Pt, ... of the power P1, P2, ... output by each target unit 5t to the power Pt output from the PCS2. The power sharing rates P1 / Pt, P2 / Pt, ... are determined based on the slope of the droop characteristic set for each storage battery 52 of each storage battery unit 5. The charge / discharge control unit 313 calculates the ideal power sharing rate Rm according to the power sharing rate set for each target unit 5t.

[0022] Furthermore, the charge / discharge control unit 313 calculates the actual power sharing rate Rd, based on the output power value Pw actually output from the DC / DC converter 51, acquired by the acquisition unit 311. The actual power sharing rate Rd correlates with the ratio of the output power values ​​Pw from the DC / DC converter 51 of each of the target units 5t, between at least two target units 5t. The above-mentioned ideal power sharing rate Rm and actual power sharing rate Rd are calculated for each of the multiple target units 5t. The charge / discharge control unit 313 outputs the calculated ideal power sharing rate Rm and actual power sharing rate Rd to the droop command correction unit 314.

[0023] (Functional Configuration of Droop Command Correction Unit) Fig. 3 is a block diagram showing the functional configuration of the droop command correction unit of the power storage system. As shown in Fig. 3, the droop command correction unit 314 receives a droop command D from the droop command generation unit 312. The droop command D includes a gradient K of the droop characteristic.

[0024] The droop command corrector 314 corrects the droop command D, based on the output power value Pw that is actually output from the DC / DC converter 51. More specifically, the droop command corrector 314 corrects the droop command D, using the actual power sharing rate Rd and the ideal power sharing rate Rm that are calculated by the charge / discharge control unit 313 based on the output power value Pw. The droop command corrector 314 corrects the droop command D received from the droop command generator 312, based on the ideal power sharing rate Rm and the actual power sharing rate Rd received from the charge / discharge control unit 313.

[0025] The droop command corrector 314 includes a ratio calculator 314a and a slope adjuster 314b.

[0026] The ratio calculation unit 314a is a divider in terms of hardware. The ratio calculation unit 314a calculates the ratio Rd / Rm of the actual power sharing rate Rd to the ideal power sharing rate Rm input from the charge / discharge control unit 313.

[0027] Slope adjustment unit 314b is a multiplier in terms of hardware. Based on the ratio Rd / Rm calculated by ratio calculation unit 314a, slope adjustment unit 314b adjusts the slope K of the droop characteristic in droop command D input from droop command generation unit 312. Slope adjustment unit 314b multiplies the slope K of the droop characteristic in droop command D by the ratio Rd / Rm to calculate the adjusted slope K' (K' = K × Rd / Rm). Droop command correction unit 314 generates a droop command D' having the calculated adjusted slope K'.

[0028] Control device 3 outputs corrected droop command D' generated by droop command corrector 314 to DC / DC converter 51. Such correction of droop command D by droop command corrector 314 is performed for each DC / DC converter 51 of the multiple storage battery units 5. As a result, the corrected droop command D' is output to each DC / DC converter 51 of the multiple storage battery units 5. DC / DC converter 51 controls the power output to PCS 2 or storage battery 52 based on the corrected droop command D' output from control device 3.

[0029] The predetermined program executed by the processor 31 is stored on a computer-readable recording medium. Computer-readable recording media include magnetic disks, magneto-optical disks, CD-ROMs, DVD-ROMs, and semiconductor memories. The computer program may be distributed to a computer via a communication line, and the computer that receives the distribution may execute the program. The program may also be a program for implementing some of the above-described functions. Furthermore, the program may be a so-called differential file (differential program) that can realize the above-described functions in combination with a program already stored in the computer system.

[0030] The memory 32 has a memory area necessary for the operation of the processor 31 .

[0031] The storage 33 is a so-called auxiliary storage device, such as a hard disk drive (HDD), a solid state drive (SSD), etc. The storage 33 stores data that each part of the processor 31 acquires, generates, and references during processing.

[0032] The communication interface 34 is an interface for transmitting and receiving various data and control signals (output power value Pw, droop command D) between each storage battery unit.

[0033] 4 is a diagram showing changes in droop characteristics due to wiring resistance. As shown in FIG. 4, for droop characteristics G1 and G2 before correction, the output power of DC / DC converter 51 is P1' and P2' at operating point voltage Vt. These output voltages P1' and P2' each include a voltage drop due to the wiring resistance of DC bus 4. On the other hand, for droop characteristics G1a and G2a after correction as described above, the output power is P1" and P2". In this case, the slopes K1' and K2' of the droop characteristics G1a and G2a after correction are smaller than the slopes K1 and K2 of the droop characteristic G1 before correction.

[0034] (Simulation Example) Fig. 5 is a diagram showing a simulation example of the energy storage system 1 configured as described above. As shown in Fig. 5, the three target units 5t1 to 5t3 were intentionally given wiring impedances so that their power sharing rates were significantly different. For these three target units 5t1 to 5t3, a comparison was made between a state S1 in which no correction was made using the droop command correction unit 314 and a state S2 in which correction was made using the droop command correction unit 314. As a result, in the state S2 in which correction was made using the droop command correction unit 314, the power sharing rates of the three target units 5t1 to 5t3 overlapped.

[0035] FIG. 6 is a diagram showing another correction method performed for comparison. In the other correction method shown in FIG. 6 , after calculating the deviation of the actual power sharing rate Rd from the ideal power sharing rate Rm, the result is multiplied by a gain in gain section 101 and added to the slope K of the droop characteristics. FIG. 7 is a diagram showing an example of a simulation of the configuration shown in FIG. 6 . As shown in FIG. 7 , in the configuration shown in FIG. 6 , in the three target units 5t1, 5t2, and 5t3, the variation in the power sharing rate was smaller in state S12 where correction was performed, compared to state S11 where correction was not performed. Furthermore, when the gain was increased stepwise from state S12 onwards, the power sharing rate began to fluctuate in states S18 and S19, and eventually diverged.

[0036] (Actions and Effects) As described above, the power storage system 1 according to the present embodiment corrects the droop command D to the DC / DC converter 51 based on the ideal power sharing rate Rm, which is the ratio of the power that should be output by each of the target units 5t, and the actual power sharing rate Rd, which is the ratio of the output power value Pw from each of the DC / DC converters 51 of the target units 5t. In this way, by correcting the droop command D according to the magnitude of the output power that is actually output by the DC / DC converter 51, the difference between the droop command D and the actual output power value Pw gradually becomes smaller. Therefore, it is possible to control the discharge power with higher accuracy and equalize the load sharing among the multiple storage batteries 52.

[0037] Furthermore, the ratio calculation unit 314a calculates the ratio Rd / Rm of the actual power sharing rate Rd to the ideal power sharing rate Rm, and the slope adjustment unit 314b adjusts the slope K of the droop characteristics based on the calculated ratio Rd / Rm, thereby making it possible to gradually reduce the difference between the droop command D and the actual output power value Pw.

[0038] As described above, the embodiments according to the present disclosure have been described. However, the above-described embodiments are presented as examples and are not intended to limit the scope of the disclosure. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the disclosure. These embodiments and their modifications are included in the scope and spirit of the disclosure, as well as in the disclosure described in the claims and their equivalents.

[0039] <Additional Notes> The power storage system 1 described in the embodiment can be understood, for example, as follows.

[0040] (1) A power storage system 1 according to a first aspect includes a plurality of storage battery units 5 each having a storage battery 52 and a DC / DC converter 51 that converts the voltage of charging / discharging power for the storage battery 52; a droop command generation unit 312 that generates a droop command for performing droop control based on a slope K of the droop characteristic of each of target units 5t when charging / discharging the storage battery 52 of at least two of the plurality of storage battery units 5; and an output power actually output by the DC / DC converter 51 based on the droop command. and a droop command correction unit 314 that corrects the droop command, based on an ideal power sharing rate Rm that is the ratio of power that should be output by the target units 5 t, between at least two of the target units 5 t, and an actual power sharing rate Rd that is the ratio of output power values ​​Pw from the DC / DC converters 51 of the target units 5 t, between at least two of the target units 5 t.

[0041] This power storage system 1 corrects the droop command D to the DC / DC converter 51 based on the ideal power sharing rate Rm, which is the ratio of the power that should be output by each of the target units 5t, and the actual power sharing rate Rd, which is the ratio of the output power value Pw from each of the DC / DC converters 51 of the target units 5t. By correcting the droop command D in this way according to the magnitude of the output power that is actually output by the DC / DC converter 51, the difference between the droop command D and the actual output power value Pw gradually becomes smaller. Therefore, it is possible to control the discharge power with higher accuracy and equalize the load sharing among the multiple storage batteries 52.

[0042] (2) The power storage system 1 according to a second aspect is the power storage system 1 of (1), wherein the droop command correction unit 314 includes a ratio calculation unit 314a that calculates a ratio Rd / Rm of the actual power sharing rate Rd to the ideal power sharing rate Rm, and a slope adjustment unit 314b that adjusts a slope K of the droop characteristics, based on the ratio Rd / Rm calculated by the ratio calculation unit 511, and corrects a droop command D to the DC / DC converter 51, based on the slope K of the droop characteristics adjusted by the slope adjustment unit 314b.

[0043] As a result, the ratio calculation unit 511 calculates the ratio Rd / Rm of the actual power sharing rate Rd to the ideal power sharing rate Rm, and the slope adjustment unit 314b adjusts the slope K of the droop characteristics based on the calculated ratio Rd / Rm, thereby making it possible to gradually reduce the difference between the droop command D and the actual output power value Pw.

[0044] According to the above-described aspect, discharge power is controlled with higher accuracy, and load sharing among a plurality of storage batteries is equalized.

[0045] REFERENCE SIGNS LIST 1 Energy storage system 5 Storage battery unit 5t, 5t1 to 5t3 Target unit 51 DC / DC converter 52 Storage battery 311 Acquisition unit 312 Droop command generation unit 314 Droop command correction unit 314a Ratio calculation unit 314b Slope adjustment unit D Droop command D' Corrected droop command

Claims

1. A power storage system comprising: a plurality of storage battery units each having a storage battery and a DC / DC converter that converts the voltage of charging / discharging power for the storage battery; a droop command generating unit that generates a droop command for performing droop control based on a gradient of the droop characteristics of each of the target units, which are at least two storage battery units among the plurality of storage battery units, when charging / discharging the storage battery of the target unit; an acquisition unit that acquires an output power value actually output by the DC / DC converter based on the droop command; and a droop command correction unit that corrects the droop command based on the output power value, wherein the droop command correction unit corrects the droop command based on a ratio between an ideal power sharing ratio, which is the ratio of power to be output by each of the target units between the at least two target units, and an actual power sharing ratio, which is the ratio of output power values ​​from the DC / DC converter of each of the target units between the at least two target units.

2. The power storage system according to claim 1, wherein the droop command correction unit comprises: a ratio calculation unit that calculates a ratio of the actual power sharing rate to the ideal power sharing rate; and a slope adjustment unit that adjusts a slope of the droop characteristic based on the ratio calculated by the ratio calculation unit, and corrects the droop command based on the slope of the droop characteristic adjusted by the slope adjustment unit.

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