Storage battery system

Abstract

To equalize load sharing among a plurality of storage batteries by controlling discharge power with higher accuracy.SOLUTION: A power storage system comprises: a droop command generation part that generates a droop command for performing droop control based on a slope of droop characteristics of respective object units, when charging / discharging storage batteries of the object units that are at least two storage battery units among a plurality of storage battery units; an acquisition part for acquiring an output power value actually output by a DC / DC converter based on the droop command; and a droop command correction part for correcting the droop command based on the output power value. The droop command correction part corrects the droop command based on a rate of an idealistic power sharing ratio as a ratio of power that should be output at each of the object units to an actual power sharing ratio as a ratio of output power values from DC / DC converters of the respective object units.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a battery storage system. [Background technology]

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

[0003] For example, when the power of the power grid is insufficient, the power storage system supplies power discharged from the storage batteries to the power grid via the PCS. At this time, 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. As a technique for equalizing the load sharing, Patent Documents 1 and 2 describe a technique for equalizing the load sharing between generators and storage batteries and between power supply devices by performing droop control that adjusts the output voltage by changing the drooping characteristics. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3679949 [Patent Document 2] JP 2011-10442 A Summary of the Invention [Problem to be solved by the invention]

[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, a difference may occur between the target discharge power based on the command value adjusted by the droop control and the discharge power actually output. As a result, there is a problem 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 precision and equalize the load sharing among multiple storage batteries. [Means for solving the problem]

[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 for the storage battery; a droop command generating unit that generates a droop command for performing droop control based on a slope 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, the target unit being at least two storage battery units; 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 a ratio between an ideal power sharing rate that is a ratio of power to be output by each of the target units between the at least two target units and an actual power sharing rate that is a ratio of output power values ​​from the DC / DC converter of each of the target units between the at least two target units. Effect of the Invention

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

[0009] [Figure 1] 1 is a diagram illustrating an overall configuration of a power storage system according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is a block diagram showing a functional configuration of a control device of the power storage system. [Diagram 3] 4 is a block diagram showing a functional configuration of a droop command correction unit of the power storage system. FIG. [Figure 4] FIG. 13 is a diagram showing a change in droop characteristics due to wiring resistance. [Diagram 5] FIG. 11 is a diagram showing a simulation example of the power storage system 1 having the above-mentioned configuration. [Figure 6] FIG. 13 is a diagram showing the configuration of another correction method performed for comparison. [Figure 7] FIG. 7 is a diagram illustrating an example of a simulation of the configuration illustrated in FIG. 6. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the 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 the embodiment. (Overall configuration of the energy storage system) FIG. 1 is a diagram showing an overall configuration of a power storage system according to an 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 PCS2 is a power conditioner that is connected to the power grid. The PCS2 has a bidirectional inverter that converts AC power and DC power. The PCS2 converts DC power discharged from each storage battery unit 5 into AC power and outputs the AC power to the power grid. The PCS2 also converts AC power supplied from the power grid into DC power and outputs the DC power to each storage battery unit 5.

[0012] The control device 3 controls charging and discharging of each storage battery unit. A 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 the multiple storage battery units 5.

[0014] The multiple 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. ​​The DC / DC converter 51 converts the DC power supplied from the PCS 2 to a predetermined voltage in accordance with a command from the control device 3, and charges the storage battery 52. ​​The DC / DC converter 51 also converts the discharged power of the storage battery 52 to a predetermined voltage in accordance with a command from the control device 3, and supplies the voltage to the PCS 2.

[0015] (Functional configuration of the control device) FIG. 2 is a block diagram showing a functional configuration of a 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 .

[0016] The processor 31 operates according to a predetermined program to thereby fulfill the functions of 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 / discharging is performed in each DC / DC converter 51 of the multiple storage battery units 5 based on a command 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 setting value for the slope of the droop characteristics of the storage battery unit 5 (droop slope).

[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 keep 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 a process of changing the droop intercept of a target unit as part of the droop control when charging or discharging a desired power to a target unit that is at least one storage battery unit 5 among the multiple storage battery units 5.

[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 also 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 plurality of storage battery units 5, the target storage battery units 5 are 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 sharing rate of power (power sharing rate) that each target unit 5t should 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 rate P1 / Pt, P2 / Pt, ... is 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 in each target unit 5t.

[0022] Furthermore, the charge / discharge control unit 313 calculates the actual power sharing ratio 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 ratio 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 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 the droop command correction unit) FIG. 3 is a block diagram showing a functional configuration of a droop command correction unit of the power storage system. 3, a droop command D is input to the droop command correction unit 314 from a droop command generation unit 312. The droop command D includes a gradient K of the droop characteristic.

[0024] The droop command correcting unit 314 corrects the droop command D based on the output power value Pw actually output from the DC / DC converter 51. More specifically, the droop command correcting unit 314 corrects the droop command D by using the actual power sharing rate Rd and the ideal power sharing rate Rm calculated by the charge / discharge control unit 313 based on the output power value Pw. The droop command correcting unit 314 corrects the droop command D received from the droop command generating unit 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] 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. Slope adjustment unit 314b adjusts the slope K of the droop characteristic in droop command D input from droop command generation unit 312 based on the ratio Rd / Rm calculated by ratio calculation unit 314a. 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] The control device 3 outputs the corrected droop command D' generated by the droop command corrector 314 to the DC / DC converter 51. Such correction of the droop command D by the 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. The DC / DC converter 51 controls the power to be output to the PCS 2 side or the storage battery 52 side, based on the corrected droop command D' output from the control device 3.

[0029] The predetermined program executed by the processor 31 is stored in a computer-readable recording medium. The computer-readable recording medium refers to a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, etc. The computer program may be distributed to a computer via a communication line, and the computer that receives the program may execute the program. The program may be for realizing part of the above-mentioned functions. The program may be a so-called difference file (difference program) that can realize the above-mentioned functions in combination with a program already recorded 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 refers to 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] FIG. 4 is a diagram showing changes in droop characteristics due to wiring resistance. 4, in the droop characteristics G1 and G2 before correction, the output power of the DC / DC converter 51 is P1' and P2' at the operating point voltage Vt. These output voltages P1' and P2' each include a voltage drop due to the wiring resistance of the DC bus 4. On the other hand, in the droop characteristics G1a and G2a after the correction as described above, the output power becomes P1″ and P2″. ​​At this time, the slopes K1′ and K2′ of the droop characteristics G1a and G2a after the correction are smaller than the slopes K1 and K2 of the droop characteristic G1 before the correction.

[0034] (Simulation example) FIG. 5 is a diagram showing a simulation example of the power storage system 1 having the above-mentioned configuration. 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. In 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 correcting unit 314 and a state S2 in which correction was made using the droop command correcting unit 314. As a result, in the state S2 in which correction was made using the droop command correcting 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 another 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 deviation is multiplied by a gain in the gain section 101 and added to the gradient 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 rates was smaller in a state S12 in which correction was performed, compared to a state S11 in which correction was not performed. Furthermore, when the gain was gradually increased after state S12, the power sharing rates began to fluctuate in states S18 and S19, and eventually diverged.

[0036] (Action, effect) As described above, the energy storage system 1 according to this 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 to 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 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] Moreover, 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, but the above-mentioned embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and gist of the invention.

[0039] <Additional Notes> The power storage system 1 according to 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 a droop characteristic of each of the target units 5t, which is at least two of the plurality of storage battery units 5, when charging / discharging the storage battery 52 of the target unit 5t; and an acquisition unit 311 that acquires a value Pw of the output power, and a droop command correction unit 314 that corrects the droop command based on the output power value Pw, and the droop command correction unit 314 corrects the droop command D to the DC / DC converter 51 based on an ideal power sharing ratio Rm that is the ratio of power to be output by the target units 5t between at least two of the target units 5t, and an actual power sharing ratio Rd that is the ratio of output power values ​​Pw from the DC / DC converter 51 of each of the target units 5t between the at least two target units 5t.

[0041] This power storage system 1 corrects the droop command D to the DC / DC converter 51 based on an ideal power sharing rate Rm, which is the ratio of power to be output by each of the target units 5t, and an 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 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 the 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] Thereby, 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. [Explanation of symbols]

[0044] 1. Energy storage system 5…Battery unit 5t, 5t1~5t3...Target units 51...DC / DC converter 52…Battery 311…Acquisition Department 312...Droop command generating unit 314...Droop command correction unit 314a...Ratio calculation section 314b...Tilt adjustment section D…Droop command D': corrected droop command

Claims

1. A plurality of storage battery units each including a storage battery and a DC / DC converter that converts a 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 a droop characteristic of each of the target units when charging / discharging the storage battery of a target unit that is at least two of the plurality of storage battery units; an acquisition unit that acquires an output power value actually output by the DC / DC converter based on the droop command; a droop command correction unit that corrects the droop command based on the output power value, The droop command correction unit is an ideal power sharing ratio, which is a ratio of power to be output by each of the target units between at least two of the target units; and an actual power sharing rate, which is a ratio between the output power values ​​from the DC / DC converters of the target units, between at least two of the target units, correcting the droop command based on the ratio. Energy storage system.

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

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