DC power control method and DC power supply system

Abstract

The droop characteristics are changed for each power conversion device so that the remaining energy of each DC power source approaches a target value. [Solution] In a DC power supply system (1), a power control unit (60) controls the power output by each of a plurality of power conversion devices (30) based on each of a plurality of droop characteristics corresponding to the plurality of power conversion devices (30). The power control unit (60) acquires a measurement value (SOCi(t)) indicating the SOC of each of the plurality of DC power sources (20), calculates an individual difference value (SOCDi(t)) for each of the plurality of DC power sources (20) based on the difference between the SOC indicated by the measurement value (SOCi(t)) and a target value (SOCRi), identifies a representative difference value representing the plurality of individual difference values ​​(SOCDi(t)) corresponding to the plurality of DC power sources (20), and changes each of the plurality of droop characteristics based on the difference between the individual difference value (SOCDi(t)) of the DC power source (20) corresponding to the droop characteristic and the representative difference value. The target value (SOCRi) is a target value of SOC individually determined for each of the plurality of DC power sources (20).

Description

[Technical Field]

[0001] The present invention relates to a DC power control method and a DC power supply system. [Background technology]

[0002] A known DC power supply system includes a plurality of DC power sources, such as storage batteries, and a plurality of power conversion devices corresponding to the plurality of DC power sources. For this type of DC power supply system, a known method controls the power output from the power conversion devices based on a droop characteristic that reduces the output voltage as the output current increases. Recently, a DC power supply system has been developed that performs control to change the droop characteristic. For example, Patent Document 1 discloses a control device that adjusts a control rule used for droop control of each power conversion device based on the difference between the remaining capacity of a first storage battery and the remaining capacity of a second storage battery so that the frequencies of use of the first storage battery and the second storage battery are similar. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-191698 Summary of the Invention [Problem to be solved by the invention]

[0004] However, control for aligning the remaining amounts (e.g., charging rates) of multiple storage batteries is not necessarily appropriate. For example, in a DC power supply system using multiple storage batteries of different types, the target charging rates for effective use of the multiple storage batteries may differ from one another. For this reason, it is required to change the droop characteristics for each power conversion device so that the charging rates of each of the multiple storage batteries approach the target values. Note that, even in DC power sources other than storage batteries, it is required to change the droop characteristics for each power conversion device so that the remaining energy (energy charging amount) of each of the multiple DC power sources approaches the target value. In consideration of the above circumstances, one aspect of the present invention aims to change the droop characteristics for each power conversion device so that the remaining energy of each of the multiple DC power sources approaches the target value. [Means for solving the problem]

[0005] A preferred aspect of the present invention provides a DC power control method for a DC power supply system having a plurality of DC power sources that perform at least one of outputting power to a DC bus and inputting power from the DC bus, and a plurality of power conversion devices that are provided corresponding to the plurality of DC power sources and perform power conversion between a corresponding one of the plurality of DC power sources and the DC bus, the method comprising: controlling the power output by each of the plurality of power conversion devices based on each of a plurality of droop characteristics that correspond to the plurality of power conversion devices and represent a relationship between a DC current or a DC power and a DC voltage; acquire remaining amount information indicating the remaining energy of each of the plurality of DC power sources; calculate an individual difference value for each of the plurality of DC power sources based on the difference between the remaining energy indicated by the remaining amount information and a remaining energy target value; identify a representative difference value representing the plurality of individual difference values ​​corresponding to the plurality of DC power sources; and change each of the plurality of droop characteristics based on the difference between the individual difference value and the representative difference value of the DC power source corresponding to the droop characteristic, wherein the remaining energy target value is a target value for the remaining energy individually set for each of the plurality of DC power sources.

[0006] A DC power supply system according to a preferred aspect of the present invention includes a plurality of DC power sources that perform at least one of outputting power to a DC bus and inputting power from the DC bus, a plurality of power conversion devices that are provided corresponding to the plurality of DC power sources and perform power conversion between a corresponding one of the plurality of DC power sources and the DC bus, and a control unit that corresponds to the plurality of power conversion devices and controls the power output by each of the plurality of power conversion devices based on each of a plurality of droop characteristics that represent the relationship between a DC current or a DC power and a DC voltage, a remaining energy target value, which is a target value for the remaining energy, is individually set for each of the plurality of DC power sources, and the control unit acquires remaining amount information indicating the remaining energy of each of the plurality of DC power sources, calculates an individual difference value for each of the plurality of DC power sources based on the difference between the remaining energy indicated by the remaining amount information and the remaining energy target value, identifies a representative difference value that represents the plurality of individual difference values ​​corresponding to the plurality of DC power sources, and changes each of the plurality of droop characteristics based on the difference between the individual difference value and the representative difference value of the DC power source corresponding to the droop characteristic. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is an explanatory diagram illustrating an example of a DC power supply system according to an embodiment; [Figure 2] FIG. 4 is a diagram for explaining droop characteristics. [Figure 3] FIG. 2 is an explanatory diagram illustrating an example of a time change in SOC when a DC power supply is charged. [Figure 4] FIG. 10 is an explanatory diagram for explaining an example of the operation of the power control unit when the DC power supply is charged. [Figure 5] FIG. 4 is an explanatory diagram for explaining an outline of adjustment of each droop characteristic. [Figure 6] FIG. 10 is an explanatory diagram for explaining an example of a change in SOC over time when a DC power supply is discharging. [Figure 7] 10 is an explanatory diagram for explaining an example of the operation of the power control unit when a DC power supply discharges. FIG. [Figure 8] 10 is a flowchart illustrating an example of the operation of a characteristic adjustment unit. [Figure 9] 10 is a flowchart illustrating an example of an operation of a command value calculation unit. [Figure 10] FIG. 13 is an explanatory diagram illustrating an example of a DC power supply system according to a seventh modification. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, the dimensions and scale of each part are appropriately different from those of the actual parts. Furthermore, the embodiments described below are preferred examples of the present invention, and therefore various technically preferable limitations are applied. However, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description to the effect that the present invention is limited.

[0009] A. Embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an example of an outline of a DC power supply system 1 according to an embodiment will be described with reference to FIG.

[0010] FIG. 1 is an explanatory diagram for explaining an example of a DC power supply system 1 according to an embodiment.

[0011] The DC power supply system 1 includes, for example, a DC bus 10, a plurality of DC power supplies 20, a plurality of BMSs (Battery Management Systems) 22, a plurality of power conversion devices 30, a plurality of controllers 32, a plurality of current measurement units 40, a plurality of voltage measurement units 50, and a power control unit 60. Note that while FIG. 1 illustrates an example in which there are two DC power supplies 20, two BMSs 22, two power conversion devices 30, two controllers 32, two current measurement units 40, and two voltage measurement units 50, the number of each of the DC power supplies 20, the BMSs 22, the power conversion devices 30, the controllers 32, the current measurement units 40, and the voltage measurement units 50 may be three or more. In addition, in FIG. 1, a lowercase alphabet (a or b) is added to the end of the reference numerals of the DC power supplies 20 to distinguish the multiple DC power supplies 20 from one another. Similarly, for multiple BMSs 22, multiple power conversion devices 30, multiple controllers 32, multiple current measurement units 40, and multiple voltage measurement units 50, etc., a lowercase alphabet (a or b) is added to the end of the symbol for each element.

[0012] For example, the DC power supply system 1 supplies DC power output from each DC power source 20 to a DC bus 10, and charges each DC power source 20 by inputting DC power to each DC power source 20 via the DC bus 10.

[0013] The DC bus 10 is a bus to which DC power is supplied. DC power sources 20a and 20b are electrically connected in parallel to the DC bus 10. For example, the DC power source 20a is connected to the DC bus 10 via a power converter 30a, and the DC power source 20b is connected to the DC bus 10 via a power converter 30b. An external load 2 and an external power supply device 3 are also electrically connected to the DC bus 10. The power supply device 3 is a power source such as a solar cell or a fuel cell, and supplies DC power to the load 2 via the DC bus 10. Note that, for example, when the DC power output from the power supply device 3 is greater than the DC power supplied to the load 2, the surplus DC power corresponding to the difference between the DC power output from the power supply device 3 and the DC power supplied to the load 2 is input to the DC power sources 20a and 20b. For example, the DC power supply system 1 charges the DC power supplies 20a and 20b by inputting DC power output from the power supply device 3 to the DC power supplies 20a and 20b via the DC bus 10. The DC power supply system 1 also supplies the DC power output from the DC power supplies 20a and 20b to the load 2 via the DC bus 10.

[0014] Each of the multiple DC power sources 20 is, for example, an energy storage device that performs at least one of outputting power to the DC bus 10 and inputting power from the DC bus 10. Specifically, for example, the DC power sources 20 are storage batteries such as lithium-ion batteries that can charge and discharge power. For example, the DC power sources 20 have multiple battery cells. Note that the DC power sources 20 are not limited to storage batteries. For example, the DC power sources 20 may be fuel cells or power sources that store kinetic energy, such as a flywheel.

[0015] During discharging when DC power is output from each DC power supply 20, the DC power output from DC power supply 20a is output to the DC bus 10 via the power converter 30a, and the DC power output from DC power supply 20b is output to the DC bus 10 via the power converter 30b. Furthermore, during charging when DC power is input to each DC power supply 20, the DC power supplied to the DC bus 10 is input to DC power supply 20a via the power converter 30a, and the DC power supplied to the DC bus 10 is input to DC power supply 20b via the power converter 30b.

[0016] Here, the multiple DC power supplies 20 may be the same type of power supply or different types of power supplies. In this embodiment, it is assumed that the types of the DC power supplies 20a and 20b are different from each other. Therefore, in this embodiment, the characteristics of the DC power supplies 20a and 20b are different from each other.

[0017] Furthermore, the multiple BMSs 22 are provided corresponding to the multiple DC power supplies 20 and control the operation of the corresponding DC power supplies 20. For example, the BMS 22a controls the operation of the DC power supply 20a, and the BMS 22b controls the operation of the DC power supply 20b. Each BMS 22 transmits and receives signals (information) to and from the power control unit 60. For example, the BMS 22a acquires an energy charge amount indicating an energy charge state of the DC power supply 20a, and outputs remaining amount information indicating the acquired energy charge amount to the power control unit 60. Similarly, the BMS 22b acquires an energy charge amount of the DC power supply 20b, and outputs remaining amount information indicating the acquired energy charge amount to the power control unit 60. In this embodiment, the BMS 22 acquires a State of Charge (SOC) as the energy charge amount of the DC power supply 20. The SOC is, for example, an index indicating the charge rate or charge state of a battery, and is expressed as a percentage (%) where a fully charged state is 100. The energy charge amount and the SOC are examples of "remaining energy amount."

[0018] Each BMS 22 measures the SOC, which is the amount of charged energy of the corresponding DC power supply 20, by, for example, a voltage method or a current integration method (coulomb counting). For example, when the voltage method is used, the BMS 22a measures the SOC based on the voltage of the DC power supply 20a, and the BMS 22b measures the SOC based on the voltage of the DC power supply 20b. Furthermore, when the current integration method is used, the BMS 22a measures the SOC by performing a time integration of the current output from the DC power supply 20a, and the BMS 22b measures the SOC by performing a time integration of the current output from the DC power supply 20b. Note that the measured value SOCa in FIG. 1 indicates the measured SOC value notified from the BMS 22a to the power control unit 60 (the SOC value of the DC power supply 20a measured by the BMS 22a). Similarly, the measured value SOCb in FIG. 1 indicates the measured value of the SOC notified to the power control unit 60 from the BMS 22b (the value of the SOC of the DC power supply 20b measured by the BMS 22b).

[0019] Furthermore, each BMS 22 may acquire, for example, operating conditions such as the temperature, output voltage, and number of charge / discharge cycles of the corresponding DC power supply 20. Each BMS 22 includes, for example, a calculation device (not shown) such as a CPU (Central Processing Unit) and a storage device (not shown) such as a memory.

[0020] The multiple power conversion devices 30 are provided corresponding to the multiple DC power sources 20, and perform power conversion between a corresponding one of the multiple DC power sources 20 and the DC bus 10. For example, the power conversion device 30a performs power conversion between the DC power source 20a and the DC bus 10, and the power conversion device 30b performs power conversion between the DC power source 20b and the DC bus 10. Specifically, when the DC power source 20a is discharging, the power conversion device 30a converts DC power input from the DC power source 20a and outputs the converted power to the DC bus 10, and when the DC power source 20a is charging, the power conversion device 30a converts DC power input from the DC bus 10 and outputs the converted power to the DC power source 20a. Similarly, when the DC power supply 20b is discharging, the power conversion device 30b converts the DC power input from the DC power supply 20b and outputs it to the DC bus 10, and when the DC power supply 20b is charging, the power conversion device 30b converts the DC power input from the DC bus 10 and outputs it to the DC power supply 20b. That is, each power conversion device 30 functions as a bidirectional DC-DC converter. For example, each power conversion device 30 converts the voltage of the input DC power so as to increase or decrease it.

[0021] Each power conversion device 30 is, for example, a bidirectional DC-DC converter that includes a chopper circuit (not shown) having a switching element that performs switching operation based on a control signal. Examples of the switching element include a MOS-FET (Metal-Oxide-Semiconductor Field-Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor).

[0022] Furthermore, the multiple controllers 32 are provided corresponding to the multiple power conversion devices 30, and control the operation of the corresponding power conversion devices 30. For example, controller 32a controls the switching operation of power conversion device 30a based on a voltage command value VCa from the power control unit 60, and controller 32b controls the switching operation of power conversion device 30b based on a voltage command value VCb from the power control unit 60. Hereinafter, the voltage command values ​​VCa and VCb may be collectively referred to as a voltage command value VC.

[0023] Each controller 32 includes, for example, a gate driver circuit (e.g., a circuit corresponding to the gate signal generator 322i shown in FIG. 10) not shown that generates a control signal to be input to the gate terminal of the switching element based on the voltage command value VC. Each controller 32 also includes a calculation device (e.g., a CPU) not shown, and a storage device (e.g., a memory) not shown.

[0024] Furthermore, the multiple current measuring units 40 are provided corresponding to the multiple power conversion devices 30 and measure the current flowing in an electric circuit connecting the corresponding power conversion device 30 and the DC bus 10. For example, the current measuring unit 40a is connected to an electric circuit branching from the DC bus 10 toward the power conversion device 30a, and measures the current of the DC power output from the power conversion device 30a to the DC bus 10 and the current of the DC power input from the DC bus 10 to the power conversion device 30a. Similarly, the current measuring unit 40b is connected to an electric circuit branching from the DC bus 10 toward the power conversion device 30b, and measures the current of the DC power output from the power conversion device 30b to the DC bus 10 and the current of the DC power input from the DC bus 10 to the power conversion device 30b. Furthermore, the current measuring unit 40a transmits information indicating a current measurement value IMa, which is a measurement value of the current flowing in the electric circuit connecting the power conversion device 30a and the DC bus 10, to the power control unit 60. Furthermore, the current measuring unit 40b transmits to the power control unit 60 information indicating a current measurement value IMb, which is a measurement value of a current flowing through an electric path connecting the power conversion device 30b and the DC bus 10. Hereinafter, the current measurement values ​​IMa and IMb may be collectively referred to as the current measurement value IM.

[0025] Furthermore, the multiple voltage measurement units 50 are provided corresponding to the multiple power conversion devices 30, and measure the voltages of the electric paths connecting the corresponding power conversion devices 30 and the DC bus 10. For example, the voltage measurement unit 50a is connected to an electric path branching from the DC bus 10 toward the power conversion device 30a, and measures the voltage of the DC power output from the power conversion device 30a to the DC bus 10 and the voltage of the DC power input from the DC bus 10 to the power conversion device 30a. Similarly, the voltage measurement unit 50b is connected to an electric path branching from the DC bus 10 toward the power conversion device 30b, and measures the voltage of the DC power output from the power conversion device 30b to the DC bus 10 and the voltage of the DC power input from the DC bus 10 to the power conversion device 30b. Furthermore, the voltage measurement unit 50a transmits information indicating the measured value of the voltage of the electric path connecting the power conversion device 30a and the DC bus 10 to the power control unit 60. Furthermore, the voltage measurement unit 50b transmits information indicating the measured value of the voltage of the electric circuit connecting the power conversion device 30b and the DC bus 10 to the power control unit 60. Note that in Fig. 1, the signal paths between the voltage measurement units 50 and the power control unit 60 are not shown in order to make the drawing easier to see.

[0026] The power control unit 60 controls the power output by each of the multiple power conversion devices 30 based on each of the multiple droop characteristics corresponding to the multiple power conversion devices 30. The droop characteristic represents the relationship between DC current or DC power and DC voltage. Note that, since the multiple power conversion devices 30 correspond to the multiple DC power sources 20, the multiple droop characteristics can also be considered to correspond to the multiple DC power sources 20. In this embodiment, it is assumed that a droop characteristic representing the relationship between DC current and DC voltage is used. The droop characteristic will be described later with reference to FIG. 2.

[0027] Furthermore, for example, the power control unit 60 controls the voltage of the DC power output from each power conversion device 30, thereby controlling the DC power input to each DC power supply 20 or the DC power output from each DC power supply 20. The power control unit 60 includes, for example, a calculation unit (not shown) such as a CPU, and a storage unit (not shown) such as a memory. Note that the power control unit 60 may be configured by combining one or more CPUs with hardware such as an FPGA (Field Programmable Gate Array).

[0028] Furthermore, the power control unit 60 transmits and receives signals (information) to and from each of the BMS 22a, BMS 22b, controller 32a, and controller 32b. For example, the power control unit 60 acquires remaining amount information indicating a measured value SOCa of the SOC of the DC power supply 20a from the BMS 22a, and acquires remaining amount information indicating a measured value SOCb of the SOC of the DC power supply 20b from the BMS 22b.

[0029] Furthermore, the power control unit 60 acquires information indicating the measured current value IMa from the current measurement unit 40a, and acquires information indicating the measured current value IMb from the current measurement unit 40b. The power control unit 60 also acquires information indicating the measured voltage values ​​from each voltage measurement unit 50. The power control unit 60 also outputs a voltage command value VCa for controlling the voltage of the DC power output from the power conversion device 30a to the controller 32a, and outputs a voltage command value VCb for controlling the voltage of the DC power output from the power conversion device 30b to the controller 32b.

[0030] In this embodiment, as described above, the characteristics of the multiple DC power supplies 20 (20a and 20b) are different from each other. In this embodiment, it is assumed that the characteristics of each of the DC power supplies 20a and 20b are as follows. For example, the DC power supply 20a deteriorates more rapidly in a high SOC range than in a low SOC range, and the DC power supply 20b deteriorates more rapidly in a low SOC range than in a high SOC range. For this reason, as shown in FIG. 3 described later, target SOC values ​​SOCRa and SOCRb are individually set for each of the DC power supplies 20a and 20b. In this embodiment, it is assumed that the target SOC value SOCRa of the DC power supply 20a is 30% and the target SOC value SOCRb of the DC power supply 20b is 70%. Hereinafter, the target SOC values ​​SOCRa and SOCRb may be collectively referred to as target value SOCR. The target SOC value SOCR is an example of a "remaining energy target value."

[0031] The power control unit 60 changes each of the multiple droop characteristics based on the SOC, target value SOCR, and the like of the multiple DC power supplies 20. For example, in this embodiment, the droop characteristics are changed for each power conversion device 30 so that the timings at which the SOC reaches the target value SOCR in the multiple DC power supplies 20 become closer to each other. The change in the droop characteristics will be described later with reference to FIG. 4.

[0032] The configuration of the DC power supply system 1 is not limited to the example shown in Fig. 1. For example, the BMSs 22a and 22b may be included in the DC power supplies 20a and 20b, respectively, or may be included in the power control unit 60. Furthermore, for example, the controllers 32a and 32b may be included in the power conversion devices 30a and 30b, respectively, or may be included in the power control unit 60.

[0033] Next, an example of the droop characteristic will be described with reference to FIG.

[0034] FIG. 2 is a diagram for explaining the droop characteristic. FIG. 2 shows the droop characteristic representing the relationship between the measured current value IM and the voltage command value VC. The horizontal axis of FIG. 2 represents the measured current value IM, and the vertical axis represents the voltage command value VC. Note that, hereinafter, the droop characteristic will be described assuming that the direction of current when DC power supply 20 is discharging is positive. Therefore, in FIG. 2, when DC power supply 20 is charging, the measured current value IM is a negative value.

[0035] The droop characteristic is, for example, a characteristic that decreases the voltage of the electric circuit connecting the power converter 30 and the DC bus 10 in response to an increase in the current output from the power converter 30 to the DC bus 10. In other words, the droop characteristic is a characteristic that increases the voltage of the electric circuit connecting the power converter 30 and the DC bus 10 in response to a decrease in the current output to the DC bus 10. Here, when the DC power supply 20 is being charged, an increase in the current input to the DC power supply 20 can also be interpreted as a decrease in the current output to the DC bus 10. Therefore, in control based on the droop characteristic, when the DC power supply 20 is being charged, the voltage of the electric circuit connecting the power converter 30 and the DC bus 10 is controlled to increase in response to an increase in the current input to the DC power supply 20.

[0036] For example, in the droop characteristic, the voltage command value VC for controlling the voltage of the electrical path connecting the power conversion device 30 and the DC bus 10 is expressed by equation (1) using the droop gain K, the initial voltage value Vint, and the current measurement value IM.

[0037] VC=Vint-K·IM …(1)

[0038] In this embodiment, the initial voltage value Vint is, for example, a rated voltage of the DC voltage supplied to the DC bus 10, and is set in advance. The droop gain K is a proportional constant that represents the ratio of the amount of change in voltage to the amount of change in current, and is a parameter also called a droop coefficient. The droop gain K is equal to the absolute value of the slope of the droop characteristic.

[0039] For example, the power control unit 60 subtracts the product of the current measurement value IM and the droop gain K from the initial voltage value Vint, and sets the resulting value as the voltage command value VC for controlling the voltage of the DC power output from the power conversion device 30. Specifically, for example, in control based on the droop characteristic shown in Fig. 2, when the current measurement value IM is a negative current value i1, that is, when the DC power supply 20 is charging, a voltage value V1 higher than the initial voltage value Vint (rated voltage) is calculated as the voltage command value VC. Also, for example, when the current measurement value IM is a positive current value i2, that is, when the DC power supply 20 is discharging, a voltage value V2 lower than the initial voltage value Vint (rated voltage) is calculated as the voltage command value VC.

[0040] Next, with reference to FIG. 3, an example of the change in SOC over time when the DC power supply 20 is being charged will be described.

[0041] Fig. 3 is an explanatory diagram illustrating an example of a change in SOC over time when DC power supply 20 is being charged. In Fig. 3, the horizontal axis represents time, and the vertical axis represents the SOC [%] of DC power supply 20. As described above, in this embodiment, it is assumed that the target SOC value SOCRa of DC power supply 20a is 30 [%], and the target SOC value SOCRb of DC power supply 20b is 70 [%]. In the following, the measured values ​​SOCa and SOCb measured at time t are also referred to as measured values ​​SOCa(t) and SOCb(t), respectively.

[0042] As shown in Fig. 3, when DC power supply 20 is being charged, the SOC increases over time. Time t1a in Fig. 3 indicates the timing when the SOC of DC power supply 20a during charging reaches target value SOCRa, and time t1b indicates the timing when the SOC of DC power supply 20b during charging reaches target value SOCRb. Hereinafter, the timing when the SOC of DC power supply 20 reaches target value SOCR may be referred to as the "arrival timing."

[0043] In the present embodiment, the power control unit 60 changes the droop gain K of the droop characteristics corresponding to each power conversion device 30 based on the measured value SOC and the target value SOCR of the SOC of the multiple DC power supplies 20, so that the timings at which the SOC reaches the target value SOCR are the same for DC power supplies 20a and 20b. As a result, in the present embodiment, while waiting for the SOC of one of DC power supplies 20a and 20b to reach the target value SOCR, it is possible to prevent the SOC of the other of DC power supplies 20a and 20b from exceeding and deviating from the target value SOCR.

[0044] Furthermore, for example, in a mode in which charging of the DC power source 20 whose SOC has reached the target value SOCR is stopped, the timing at which charging of the DC power source 20a is stopped and the timing at which charging of the DC power source 20b is stopped can be made closer to each other. That is, the period in which only one of the DC power sources 20a and 20b is charged can be shortened. During the period in which only one of the DC power sources 20a and 20b is charged, the voltage of the DC bus 10 tends to fluctuate more easily than during the period in which both the DC power sources 20a and 20b are charged. In this embodiment, even when charging of the DC power source 20 whose SOC has reached the target value SOCR is stopped, the period in which only one of the DC power sources 20a and 20b is charged can be shortened, thereby suppressing voltage fluctuations of the DC bus 10.

[0045] Here, the individual difference value SOCDa(t) is an index that indicates, as a numerical value greater than or equal to "0", the difference between the measured value SOCa(t) of the SOC of DC power supply 20a and the target value SOCRa, and is used when changing the droop gain K. For example, when the result of subtracting the measured value SOCa(t) from the target value SOCRa is greater than 0, the subtraction result is the individual difference value SOCDa(t), and when the subtraction result is equal to or less than 0, the individual difference value SOCDa(t) is "0". Similarly, the individual difference value SOCDb(t) is an index that indicates, as a numerical value greater than or equal to "0", the difference between the measured value SOCb(t) of the SOC of DC power supply 20b and the target value SOCRb, and is used when changing the droop gain K. For example, if the result of subtracting the measured value SOCb(t) from the target value SOCRb is greater than 0, the result is the individual difference value SOCDb(t), and if the result of the subtraction is less than or equal to 0, the individual difference value SOCDb(t) becomes "0".

[0046] Hereinafter, any one of the multiple DC power supplies 20 may be referred to as a DC power supply 20i. That is, hereinafter, when focusing on any one of the multiple DC power supplies 20, the subscript i is used instead of the subscripts a and b. Furthermore, hereinafter, when a component, signal, or the like of the DC power supply system 1 corresponds to the DC power supply 20i of the multiple DC power supplies 20, the subscript i may be added to a symbol representing the component, signal, or the like. For example, the individual difference value SOCDi(t) is an index that indicates, as a numerical value greater than or equal to "0," the difference between the measured value SOCi(t) of the SOC of any one of the multiple DC power supplies 20 and the target value SOCRi. When the DC power supply 20i is being charged, the individual difference value SOCDi(t) is expressed by Equation (2) using a function max() that returns the maximum value in parentheses.

[0047] SOCDi(t)=max(SOCRi-SOCi(t),0) …(2)

[0048] Next, an example of the operation of the power control unit 60 when the DC power supply 20 is charged will be described with reference to FIG.

[0049] FIG. 4 is an explanatory diagram illustrating an example of the operation of the power control unit 60 when the DC power supplies 20 are charged. Note that in FIG. 4, the operation of the power control unit 60 will be described with a focus on the DC power supply 20i among the multiple DC power supplies 20. Hereinafter, the measured current value IMi measured at time t will also be referred to as the measured current value IMi(t). However, the measurement time of the measured current value IMi(t) and the measurement time of the measured current value SOCi(t) are not necessarily the same time t. Hereinafter, the droop gain Ki, which changes with a change in the measured value SOCi(t), will also be referred to as the droop gain Ki(t), and the voltage command value VCi, which changes with a change in at least one of the droop gain Ki(t) and the measured current value IMi(t), will also be referred to as the voltage command value VCi(t). Also, in FIG. 4, as in FIG. 1, the signal path between the voltage measurement unit 50i and the power control unit 60 is omitted.

[0050] 4, power control unit 60 has, for example, a characteristic adjustment unit 620 that adjusts droop gain Ki(t) and a command value calculation unit 640 that calculates voltage command value VCi(t). Note that power control unit 60 may function as characteristic adjustment unit 620 and command value calculation unit 640 by executing a program (not shown), for example.

[0051] The characteristic adjustment unit 620 acquires, for example, the measured value SOCi(t) of the SOC of the DC power supply 20i from the BMS 22i. The characteristic adjustment unit 620 also acquires the measured values ​​SOCi(t) of the SOC of the other DC power supplies 20i from the BMSs 22i corresponding to the other DC power supplies 20i. That is, the characteristic adjustment unit 620 acquires the measured values ​​SOCi(t) of the SOC of the multiple DC power supplies 20 from the multiple BMSs 22. Then, the characteristic adjustment unit 620 changes the droop gain Ki(t) of the droop characteristic corresponding to the power conversion device 30i based on the measured values ​​SOCi(t) of the SOC of the DC power supplies 20i and the like so that the timings at which the SOC reaches the target value SOCR are consistent among the multiple DC power supplies 20.

[0052] For example, the characteristic adjusting unit 620 calculates an individual difference value SOCDi(t) of each of the multiple DC power supplies 20 using the measured values ​​SOCi(t) and target values ​​SOCRi of the multiple DC power supplies 20. The individual difference value SOCDi(t) of each DC power supply 20i is expressed by equation (2) described with reference to FIG. 3. However, the individual difference value SOCDi(t) differs between when the DC power supply 20i is charging and when the DC power supply 20i is discharging. The individual difference value SOCDi(t) when the DC power supply 20i is discharging will be described with reference to FIG. 6, which will be described later.

[0053] Furthermore, the characteristic adjusting unit 620 calculates an average difference value SOCDave, which is the average value of the individual difference values ​​SOCDi(t), as a representative difference value representing the individual difference values ​​SOCDi(t) corresponding to the DC power supplies 20. For example, when the number of the DC power supplies 20 is j (j is a natural number equal to or greater than 2), the average difference value SOCDave, which is the average value of the j individual difference values ​​SOCDi(t) corresponding to the j DC power supplies 20, is expressed by equation (3).

[0054] SOCDave=1 / j·ΣSOCDi(t) …(3)

[0055] It should be noted that "ΣSOCDi(t)" in equation (3) represents the sum of j individual difference values ​​SOCDi(t).

[0056] Furthermore, the characteristic adjusting unit 620 changes the droop gain Ki(t) based on the individual difference value SOCDi(t) and the average difference value SOCDave, etc., so that the timings at which the SOC reaches the target value SOCR are consistent across the multiple DC power supplies 20. For example, the droop gain Ki(t) is expressed using a control value based on the individual difference value SOCDi(t) and the average difference value SOCDave. For example, if the control value based on the individual difference value SOCDi(t) and the average difference value SOCDave is Ci(t), the control value Ci(t) is expressed by equation (4) using the average difference value SOCDave and the individual difference value SOCDi(t). Furthermore, the droop gain Ki(t) is expressed by equation (5) using the control value Ci(t), an initial value K0 of the droop gain Ki, and a symbol ^ indicating the exponent. Note that FIG. 4 illustrates an equation in which the control value Ci(t) expressed by equation (4) is substituted for the control value Ci(t) of equation (5).

[0057] Ci(t)=1+(SOCDave-SOCDi(t)) / 100 …(4) Ki(t)=K0·(Ci(t)^n) …(5)

[0058] The exponent n in equation (5) is a predetermined real number equal to or greater than 1. Note that, when the exponent n is large, the SOC of the DC power supply 20i reaches the target value SOCRi of the SOC of the DC power supply 20i more quickly than when the exponent n is small. Furthermore, the initial value K0 of the droop gain Ki is set in advance to a value that causes the voltage of the DC bus 10 to fall within upper and lower limits. Note that the upper and lower limits of the voltage are determined, for example, by the range of DC voltage within which the power conversion device 30, the load 2, and the power supply device 3 connected to the DC bus 10 can operate. In this embodiment, it is assumed that the initial value K0 of the droop gain Ki and the exponent n are common to multiple DC power supplies 20.

[0059] As can be seen from equations (4) and (5), when the individual difference value SOCDi(t) is smaller than the average difference value SOCDave, the droop gain Ki(t) is set to a value larger than the initial value K0. In this case, the power charging the DC power supply 20i is reduced compared to when the droop gain Ki(t) is set to the initial value K0. As a result, the SOC of the DC power supply 20i increases more slowly compared to when the droop gain Ki(t) is set to the initial value K0. Furthermore, when the individual difference value SOCDi(t) is larger than the average difference value SOCDave, the droop gain Ki(t) is set to a value smaller than the initial value K0. In this case, the power charging the DC power supply 20i is increased compared to when the droop gain Ki(t) is set to the initial value K0. As a result, the SOC of the DC power supply 20i increases more rapidly compared to when the droop gain Ki(t) is set to the initial value K0. When the individual difference value SOCDi(t) is equal to the average difference value SOCDave, the droop gain Ki(t) is set to the initial value K0.

[0060] When DC power supply 20 is charged, characteristic adjustment unit 620 calculates droop gain Ki(t) of the droop characteristic based on equations (2) to (5) and notifies command value calculation unit 640 of the calculated droop gain Ki(t). Note that characteristic adjustment unit 620 may store droop gain Ki(t) calculated based on equations (2) to (5) in a storage device (not shown) of power control unit 60. Furthermore, target value SOCRi of SOC of each DC power supply 20i, initial value K0 of droop gain Ki, and index n are stored in advance in a storage device (not shown) of power control unit 60.

[0061] The command value calculation unit 640 acquires, for example, a measured current value IMi(t) from the current measurement unit 40i corresponding to the power conversion device 30i. Then, the command value calculation unit 640 calculates a voltage command value VCi(t) based on the measured current value IMi(t) and the droop gain Ki(t) adjusted by the characteristic adjustment unit 620, and notifies the calculated voltage command value VCi(t) to the controller 32i. The voltage command value VCi(t) is expressed by equation (6), for example, using the droop gain Ki(t), the initial voltage value Vint, and the measured current value IMi(t).

[0062] VCi(t)=Vint-Ki(t)·IMi(t) …(6)

[0063] Note that equation (6) corresponds to equation (1) above, modified to focus on time t. However, as described above, the measurement time of the measured value SOCi(t) is not necessarily the same time t as the measurement time of the measured current IMi(t). For example, this embodiment assumes that the measurement interval of the SOC is longer than the measurement interval of the current. Therefore, the droop gain Ki(t) in equation (6) means the droop gain Ki changed closest to time t (the latest droop gain Ki at time t).

[0064] The command value calculation unit 640 calculates the voltage command value VCi(t) based on the equation (6) and notifies the calculated voltage command value VCi(t) to the controller 32i. The initial voltage value Vint is stored in advance in a storage device (not shown) of the power control unit 60.

[0065] In this embodiment, the droop gain Ki(t) adjusted by the characteristic adjusting unit 620 based on the difference between the average difference value SOCDave and the individual difference value SOCDi(t) is used to calculate the voltage command value VCi(t). Therefore, in this embodiment, it is possible to appropriately control the power output from the power conversion device 30i so that the timings at which the SOC reaches the target value SOCR are consistent among the multiple DC power supplies 20.

[0066] Next, an outline of the adjustment of each droop characteristic (more specifically, the adjustment of the droop gain Ki) will be described with reference to FIG.

[0067] FIG. 5 is an explanatory diagram for explaining an outline of adjustment of each droop characteristic. Note that FIG. 5 assumes a case where the target value SOCRi of the SOC of DC power supply 20i is higher than the measured value SOCi(t). Therefore, the individual difference value SOCDi(t) represents a value obtained by subtracting the measured value SOCi(t) from the target value SOCRi of the SOC of DC power supply 20i. Furthermore, droop gain Ka(t) is the droop gain K of the droop characteristic corresponding to power conversion device 30a, and droop gain Kb(t) is the droop gain K of the droop characteristic corresponding to power conversion device 30b. Furthermore, charging power Pa is the power for charging DC power supply 20a, and charging power Pb is the power for charging DC power supply 20b. Hereinafter, charging powers Pa and Pb may be collectively referred to as charging power P.

[0068] 5 illustrates an overview of the adjustment of the droop characteristics by showing three examples, a first case, a second case, and a third case, of the magnitude relationship between the individual difference value SOCDa(t) of DC power supply 20a and the individual difference value SOCDb(t) of DC power supply 20b. In FIG. 5, to make the magnitude relationship between the individual difference values ​​SOCDa(t) and SOCDb(t) easier to understand, the relationship between the SOC level and the position on the drawing is different for DC power supply 20a and DC power supply 20b. For example, the target SOC value SOCRa for DC power supply 20a is 30% and the target SOC value SOCRb for DC power supply 20b is 70%. However, in the first case, the target value SOCRa is shown at a higher position than the target value SOCRb.

[0069] In the first case, the individual difference value SOCDa(t) of DC power supply 20a is larger than the individual difference value SOCDb(t) of DC power supply 20b. Therefore, in the droop gains Ka(t) and Kb(t) calculated based on equation (5) and the like described with reference to FIG. 4, the droop gain Ka(t) is smaller than the droop gain Kb(t). As a result, the charging power Pa of DC power supply 20a is larger than the charging power Pb of DC power supply 20b. As a result, the difference between the individual difference value SOCDa(t) of DC power supply 20a and the individual difference value SOCDb(t) of DC power supply 20b is smaller. During a period in which the individual difference value SOCDa(t) of DC power supply 20a is larger than the individual difference value SOCDb(t) of DC power supply 20b (i.e., the first case), a process of adjusting the droop gain Ka(t) to a value smaller than the droop gain Kb(t) is repeated. As a result, the individual difference value SOCDa(t) of the DC power supply 20a becomes equal to the individual difference value SOCDb(t) of the DC power supply 20b, or alternatively, the individual difference value SOCDa(t) of the DC power supply 20a becomes smaller than the individual difference value SOCDb(t) of the DC power supply 20b.

[0070] In the second case, the individual difference value SOCDa(t) of DC power supply 20a is equal to the individual difference value SOCDb(t) of DC power supply 20b. Therefore, the droop gains Ka(t) and Kb(t) calculated based on equation (5) and the like are equal to each other. As a result, the charging power Pa of DC power supply 20a and the charging power Pb of DC power supply 20b are equal to each other. That is, during the period in which the individual difference value SOCDa(t) of DC power supply 20a is equal to the individual difference value SOCDb(t) of DC power supply 20b (i.e., the second case), DC power supplies 20a and 20b are charged with the same charging power P. Therefore, for example, when the capacities of DC power supplies 20a and 20b are equal to each other, the timings at which the SOC reaches the target value SOCR are the same for DC power supplies 20a and 20b. If the capacity of DC power supply 20a is different from the capacity of DC power supply 20b, the individual difference value SOCDa(t) of DC power supply 20a will be different from the individual difference value SOCDb(t) of DC power supply 20b. In this case, the process of adjusting droop gain K described in the first case or the process of adjusting droop gain K described in the second case described later is executed.

[0071] In the third case, the individual difference value SOCDa(t) of DC power supply 20a is smaller than the individual difference value SOCDb(t) of DC power supply 20b. Therefore, in the droop gains Ka(t) and Kb(t) calculated based on equation (5) and the like, the droop gain Ka(t) is larger than the droop gain Kb(t). As a result, the charging power Pa for charging DC power supply 20a is smaller than the charging power Pb for charging DC power supply 20b. As a result, the difference between the individual difference value SOCDa(t) of DC power supply 20a and the individual difference value SOCDb(t) of DC power supply 20b is smaller. During a period in which the individual difference value SOCDa(t) of DC power supply 20a is smaller than the individual difference value SOCDb(t) of DC power supply 20b (i.e., the third case), a process of adjusting the droop gain Ka(t) to a value larger than the droop gain Kb(t) is repeated. As a result, the individual difference value SOCDa(t) of the DC power supply 20a becomes equal to the individual difference value SOCDb(t) of the DC power supply 20b, or alternatively, the individual difference value SOCDa(t) of the DC power supply 20a becomes greater than the individual difference value SOCDb(t) of the DC power supply 20b.

[0072] As described above, in this embodiment, the droop gains Ka and Kb are adjusted so that the individual difference value SOCDa(t) of DC power supply 20a and the individual difference value SOCDb(t) of DC power supply 20b are equal to each other. As a result, the timings at which the SOC reaches the target value SOCR for DC power supplies 20a and 20b become closer to each other. That is, in this embodiment, the droop gains Ka and Kb are adjusted so that the timings at which the SOC reaches the target value SOCR for DC power supplies 20a and 20b become the same.

[0073] Next, an outline of the operation of the power control unit 60 when the DC power supply 20 discharges will be described with reference to FIGS.

[0074] 6 is an explanatory diagram illustrating an example of a change in SOC over time when the DC power supply 20 discharges. The horizontal axis of Fig. 6 represents time, and the vertical axis represents the SOC [%] of the DC power supply 20.

[0075] As shown in Fig. 6, when DC power supply 20 is discharging, the SOC decreases over time. Time t2a in Fig. 6 indicates the timing at which the SOC of DC power supply 20a during discharging reaches target value SOCRa, and time t2b indicates the timing at which the SOC of DC power supply 20b during discharging reaches target value SOCRb.

[0076] In the present embodiment, also when discharging the DC power supply 20, as in the case of charging, the power control unit 60 adjusts the droop gain K of the droop characteristics corresponding to each power conversion device 30 so that the timings at which the SOC reaches the target value SOCR are the same for the DC power supplies 20a and 20b. As a result, in the present embodiment, also when discharging the DC power supply 20, the same effects as those achieved when charging the DC power supply 20 described with reference to Fig. 3 can be obtained. For example, in the present embodiment, even when discharging the DC power supply 20, while waiting for the SOC of one of the DC power supplies 20a and 20b to reach the target value SOCR, it is possible to prevent the SOC of the other of the DC power supplies 20a and 20b from exceeding and deviating from the target value SOCR.

[0077] When the DC power supply 20 is discharging, the subtrahend and the minuend are reversed in the subtraction in the equation (2) described above with reference to Fig. 3. Therefore, when the DC power supply 20i is discharging, the individual difference value SOCDi(t) is expressed by equation (7) using the function max() that returns the maximum value in the parentheses.

[0078] SOCDi(t)=max(SOCi(t)-SOCRi,0) …(7)

[0079] For example, when the DC power supply 20a is discharging, if the result of subtracting the target value SOCRa from the measured value SOCa(t) is greater than 0, the result of the subtraction is the individual difference value SOCDa(t), and if the result of the subtraction is equal to or less than 0, the individual difference value SOCDa(t) becomes "0." Similarly, when the DC power supply 20b is discharging, if the result of subtracting the target value SOCRb from the measured value SOCb(t) is greater than 0, the result of the subtraction is the individual difference value SOCDb(t), and if the result of the subtraction is equal to or less than 0, the individual difference value SOCDb(t) becomes "0."

[0080] Next, an example of the operation of the power control unit 60 when the DC power supply 20 discharges will be described with reference to FIG.

[0081] 7 is an explanatory diagram for explaining an example of the operation of the power control unit 60 when discharging the DC power supply 20. The operation of the power control unit 60 when discharging the DC power supply 20 is the same as the operation of the power control unit 60 when charging the DC power supply 20 described in FIG. 4, except for the formula for calculating the individual difference value SOCDi(t).

[0082] The individual difference value SOCDi(t) when DC power supply 20 is discharging is expressed by equation (7) described in Fig. 6. The average difference value SOCDave, control value Ci(t), and droop gain Ki(t) are expressed by equations (3), (4), and (5) described in Fig. 4, respectively, in the same way as when DC power supply 20 is charging. Note that Fig. 7, like Fig. 4, illustrates an equation in which control value Ci(t) expressed by equation (4) is substituted for control value Ci(t) in equation (5).

[0083] As described above, in the present embodiment, even when the DC power supplies 20 are discharging, the droop gain Ki(t) adjusted by the characteristic adjusting unit 620 based on the difference between the average difference value SOCDave and the individual difference value SOCDi(t) is used to calculate the voltage command value VCi(t). Therefore, in the present embodiment, even when the DC power supplies 20 are discharging, it is possible to appropriately control the power output from the power conversion device 30i so that the timings at which the SOCs reach the target value SOCR are consistent among the plurality of DC power supplies 20.

[0084] Here, the significance of setting the target value SOCR of the SOC for each DC power supply 20 will be briefly explained using a storage battery as an example.

[0085] Storage batteries are classified into several types, such as lead batteries, lithium-ion batteries, redox flow batteries, and sodium-sulfur (NAS) batteries, depending on the materials used for the electrodes and electrolytes. The costs and response speeds of storage batteries vary among these types. Furthermore, multiple types of storage batteries may be connected to the DC bus 10. For example, a combination of low-cost lead batteries and lithium-ion batteries capable of quickly discharging large amounts of power is conceivable. When such a combination is used, in situations where load output fluctuations are anticipated, it is conceivable that the lithium-ion batteries, which have a faster response, will be preferentially charged. For example, the target SOC value SOCR of a first storage battery with a faster response speed among the multiple storage batteries is set higher than the target SOC value SOCR of a second storage battery with a slower response speed among the multiple DC power sources 20.

[0086] Furthermore, the rate at which a battery deteriorates varies depending on its SOC and the material it is made of. For example, the following is stated in the document "Japan Science and Technology Agency, Low Carbon Society Strategy Center, 'Survey on the Deterioration Behavior of Lithium-ion Batteries,' Report LCS-FY2019-SR-01, 2020."

[0087] A lithium-ion battery (hereinafter referred to as a "first-configuration battery") whose positive electrode is made of NMC (a ternary positive electrode material, mainly composed of nickel, manganese, and cobalt) and whose negative electrode is made of graphite deteriorates more readily at higher SOCs and less readily at lower SOCs. Similarly, a lithium-ion battery (hereinafter referred to as a "second-configuration battery") whose positive electrode is made of LFP (LiFePO4, lithium iron phosphate) and whose negative electrode is made of graphite deteriorates more readily at higher SOCs and less readily at lower SOCs, similar to the first-configuration battery, but deteriorates less readily than a first-configuration battery at higher SOCs.

[0088] Considering the above-mentioned tendency, when the above-mentioned two types of storage batteries are connected to the DC bus 10, it may be possible to minimize the deterioration of the storage batteries by charging the batteries of the second configuration preferentially to maintain a high SOC and reducing the power charged to the batteries of the first configuration to maintain a low SOC.

[0089] As described above, when multiple storage batteries are connected to the DC bus 10, it is preferable to set a target SOC value SOCR for each storage battery and adjust the power charged and discharged by the storage battery so as to achieve the target value SOCR.

[0090] In the present embodiment, as described above, the droop gain K of the droop characteristics is adjusted for each power conversion device 30 based on the difference between the target value SOCR and the measured SOC until the SOC reaches the target value SOCR in each of the multiple DC power supplies 20. As a result, in the present embodiment, it is possible to adjust the power charged and discharged by the DC power supplies 20 so that each of the multiple DC power supplies 20 achieves the target value SOCR.

[0091] Next, an example of the operation of the characteristic adjusting section 620 will be described with reference to FIG.

[0092] Fig. 8 is a flowchart showing an example of the operation of characteristic adjusting section 620. Note that the operation shown in Fig. 8 is repeatedly executed at a predetermined first interval, for example.

[0093] First, in step S100, the characteristic adjusting unit 620 acquires the measured value SOCi(t) of the SOC of each DC power supply 20i. For example, the characteristic adjusting unit 620 acquires the measured value SOCa(t) of the SOC of DC power supply 20a from the BMS 22a and the measured value SOCb(t) of the SOC of DC power supply 20b from the BMS 22b.

[0094] Next, in step S120, the characteristic adjustment unit 620 calculates an individual difference value SOCDi(t) of each DC power supply 20i based on the target value SOCRi of each DC power supply 20i and the measurement value SOCi(t) of each DC power supply 20i acquired in step S100. For example, when the DC power supply 20 is being charged, the characteristic adjustment unit 620 calculates the individual difference value SOCDi(t) based on equation (2) described with reference to FIG. 3. Furthermore, for example, when the DC power supply 20 is being discharged, the characteristic adjustment unit 620 calculates the individual difference value SOCDi(t) based on equation (7) described with reference to FIG. Note that the characteristic adjustment unit 620 may determine whether the DC power supply 20i is being charged or discharged based on the measured current value IMi(t) measured by the current measurement unit 40i.

[0095] Next, in step S140, characteristic adjusting unit 620 calculates an average difference value SOCDave, which is the average value of the individual difference values ​​SOCDi(t) of the plurality of DC power supplies 20i calculated in step S120.

[0096] Next, in step S160, characteristic adjustment unit 620 calculates control value Ci(t) for each droop characteristic. For example, characteristic adjustment unit 620 calculates control value Ci(t) for each droop characteristic by substituting average difference value SOCDave calculated in step S140 and individual difference value SOCDi(t) calculated in step S120 into equation (4) described with reference to FIG.

[0097] Next, in step S180, characteristic adjustment unit 620 changes each droop characteristic using control value Ci(t) calculated in step S160. For example, characteristic adjustment unit 620 calculates droop gain Ki(t) of each droop characteristic by substituting control value Ci(t) calculated in step S160 for control value Ci(t) in equation (5) described with reference to FIG.

[0098] As described above, in this embodiment, it is possible to appropriately calculate the droop gain Ki(t) of the droop characteristic when the DC power supply 20 is charged and when the DC power supply 20 is discharged. Then, based on each droop characteristic with the adjusted droop gain Ki(t), the command value calculation unit 640 calculates the voltage command value VCi(t) for each power conversion device 30i.

[0099] Fig. 9 is a flowchart showing an example of the operation of command value calculation unit 640. Note that the operation shown in Fig. 9 is repeatedly executed at a predetermined second interval that is shorter than the repetition interval (first interval) of the operation shown in Fig. 8, for example.

[0100] First, in step S200, the command value calculation unit 640 acquires the current measurement value IMi(t) of the current flowing in the electric path connecting each power electronics device 30i and the DC bus 10. For example, the command value calculation unit 640 acquires the current measurement value IMa(t) of the current flowing in the electric path connecting the power electronics device 30a and the DC bus 10 from the current measurement unit 40a, and acquires the current measurement value IMb(t) of the current flowing in the electric path connecting the power electronics device 30b and the DC bus 10 from the current measurement unit 40b.

[0101] Next, in step S220, command value calculation unit 640 calculates a voltage command value VCi(t) for each power electronics device 30i. For example, command value calculation unit 640 calculates voltage command value VCi(t) based on equation (6) described in Fig. 4. Note that, for example, as droop gain Ki(t) in equation (6), the droop gain Ki (latest droop gain Ki) changed by the operation shown in Fig. 8 at the timing closest to the start of the operation shown in Fig. 9 is used.

[0102] Next, in step S240, the command value calculation unit 640 notifies the controller 32 of each power electronics device 30 of the voltage command value VC(t) calculated in step S220. The power output by each power electronics device 30 is controlled by the voltage command value VC(t) for each power electronics device 30.

[0103] As described above, in the present embodiment, the command value calculation unit 640 calculates the voltage command value VCi(t) for each power conversion device 30i based on each droop characteristic adjusted so that the SOC of each DC power supply 20i approaches the target value SOCRi.

[0104] As described above, in this embodiment, the DC power control method for the DC power supply system 1 is realized by the power control unit 60. The DC power supply system 1 includes a plurality of DC power sources 20 that perform at least one of outputting power to a DC bus 10 and inputting power from the DC bus 10, a plurality of power conversion devices 30 that are provided corresponding to the plurality of DC power sources 20 and that perform power conversion between a corresponding one of the plurality of DC power sources 20 and the DC bus 10, and a power control unit 60 that corresponds to the plurality of power conversion devices 30 and controls the power output by each of the plurality of power conversion devices 30 based on each of a plurality of droop characteristics that represent the relationship between a DC current or a DC power and a DC voltage. A target value SOCRi that is a target value of SOC is individually set for each of the plurality of DC power sources 20. The power control unit 60 acquires a measurement value SOCi(t) indicating the SOC of each of the multiple DC power supplies 20, calculates an individual difference value SOCDi(t) for each of the multiple DC power supplies 20 based on the difference between the SOC indicated by the measurement value SOCi(t) and a target value SOCRi, identifies a representative difference value (e.g., an average difference value SOCDave) representative of the multiple individual difference values ​​SOCDi(t) corresponding to the multiple DC power supplies 20, and changes each of the multiple droop characteristics based on the difference between the individual difference value SOCDi(t) of the DC power supply 20 corresponding to the droop characteristic and the representative difference value.

[0105] As described above, in this embodiment, the droop characteristics are changed for each power conversion device 30 based on the difference between the representative difference value representing the plurality of individual difference values ​​SOCDi(t) corresponding to the plurality of DC power supplies 20 and the individual difference value SOCDi(t) of the DC power supply 20i. As a result, in this embodiment, the droop characteristics can be changed for each power conversion device 30 so that the timings at which the SOC reaches the target value SOCR are matched among the plurality of DC power supplies 20.

[0106] Furthermore, in this embodiment, the power control unit 60 calculates an average value (average difference value SOCDave) of the multiple individual difference values ​​SOCDi(t) as a representative difference value, calculates a control value Ci(t) for each of the multiple droop characteristics based on the difference between the individual difference value SOCDi(t) and the average difference value SOCDave, and changes each of the multiple droop characteristics based on the nth power of the control value Ci(t) (n is a real number greater than or equal to 1). For example, the power control unit 60 changes a droop gain Ki(t), which indicates the ratio of the amount of change in voltage to the amount of change in DC current or DC power, for each of the multiple droop characteristics based on the nth power of the control value Ci(t). As a result, in this embodiment, the droop characteristics can be changed for each power conversion device 30 so that the SOC efficiently approaches the target value SOCRi and the timing at which the SOC reaches the target value SOCR coincides among the multiple DC power sources 20. In particular, using a large exponent n allows the SOC of the DC power source 20 to reach the target value SOCRi more quickly. When the exponent n is "1", it is not necessary to perform a power calculation, and therefore it is possible to prevent the calculation process from becoming complicated when adjusting the droop gain Ki(t).

[0107] B: Modified example The above-described exemplary embodiments may be modified in various ways. Specific examples of modifications that may be applied to the above-described embodiments are given below. Two or more of the following examples may be combined together as long as they are not mutually inconsistent.

[0108] B1: First modified example In the above-described embodiment, an example was given in which the average difference value SOCDave is calculated as a representative difference value representing the multiple individual difference values ​​SOCDi(t) corresponding to the multiple DC power supplies 20. However, the present invention is not limited to this example. For example, the representative difference value representing the multiple individual difference values ​​SOCDi(t) corresponding to the multiple DC power supplies 20 may be the median value of the multiple individual difference values ​​SOCDi(t). Specifically, for example, if the five individual difference values ​​SOCDi(t) are 15%, 20%, 30%, 40%, and 50%, the characteristic adjustment unit 620 may specify 30%, which is the median value of the five individual difference values ​​SOCDi(t), as the representative difference value. Alternatively, the representative difference value may be the average value of the maximum and minimum values ​​of the multiple individual difference values ​​SOCDi(t). For example, in the above-described numerical example, 32.5%, which is the average value of the maximum value 50% and the minimum value 15%, may be specified as the representative difference value. As described above, in this modified example, the same effects as those of the above-described embodiment can be obtained.

[0109] B2: Second variant In the above-described embodiment and modified example, a lower limit may be set for the droop gain K. As described above, the same effects as those of the above-described embodiment can be obtained in this modified example. Furthermore, in this modified example, a lower limit is set for the droop gain K, so that, for example, it is possible to prevent the droop gain K from becoming 0 or close to 0. For example, when the droop gain K approaches 0 (when the slope of the droop characteristic becomes gentle), the control of the DC power supply system 1 may become unstable. For example, the current and voltage of the DC bus 10 may oscillate. In this modified example, by appropriately setting the lower limit for the droop gain K, it is possible to prevent the control of the DC power supply system 1 from becoming unstable.

[0110] B3: Third variant In the above-described embodiment and modified example, the droop characteristic representing the relationship between DC current and DC voltage is used to calculate the voltage command value VCi(t). However, the present invention is not limited to such an embodiment. For example, a plurality of droop characteristics representing the relationship between DC power and DC voltage may be used to calculate the voltage command value VCi(t). That is, the power control unit 60 may calculate the voltage command value VCi(t) using the droop characteristic representing the relationship between DC power and DC voltage. Furthermore, the power conversion device 30 may be controlled using a current command value or a power command value instead of the voltage command value VCi(t). For example, the power control unit 60 may calculate the current command value using the droop characteristic representing the relationship between DC current and DC voltage, or may calculate the power command value using the droop characteristic representing the relationship between DC power and DC voltage. As described above, the present modified example can also achieve the same effects as the above-described embodiment and modified example.

[0111] B4: Fourth variant In the above-described embodiment and modified example, the case where the SOC of the DC power supply 20 is used as the remaining energy amount of the DC power supply 20 has been exemplified, but the present invention is not limited to such an embodiment. For example, the integral of the input / output power of the DC power supply 20, the voltage of the DC power supply 20, or the like may be used as the remaining energy amount of the DC power supply 20. For example, the voltage of the DC power supply 20 decreases as the SOC decreases. Furthermore, if the DC power supply 20 is a fuel cell that uses hydrogen as fuel, the remaining amount of hydrogen in the fuel cell (e.g., the remaining amount of hydrogen in a hydrogen tank) may be used as the remaining energy amount of the DC power supply 20. Furthermore, if the DC power supply 20 is a flywheel, the rotation speed of the flywheel may be used as the remaining energy amount of the DC power supply 20. As described above, in this modified example, the same effects as those of the above-described embodiment and modified example can be obtained.

[0112] B5: Fifth variant In the above-described embodiment and modified example, the droop characteristics are changed by changing the droop gain K. However, the present invention is not limited to such an embodiment. For example, the power control unit 60 may change the droop characteristics by changing the initial voltage value Vint (initial voltage value Vint in FIG. 2 ) corresponding to the voltage when the measured current value IM is “0.” That is, the power control unit 60 may change the droop characteristics by changing the intercept of the droop characteristics based on the remaining energy of the DC power supply 20. Furthermore, the power control unit 60 may change the droop characteristics by changing both the slope and the intercept of the droop characteristics based on the remaining energy of the DC power supply 20. As described above, the present modified example can also achieve the same effects as those of the above-described embodiment.

[0113] B6: 6th variant In the above-described embodiment, for ease of understanding, an example has been given in which power control unit 60 includes characteristic adjustment unit 620 and command value calculation unit 640, but the present invention is not limited to this aspect. For example, as long as power control unit 60 can change the droop characteristic based on the difference between a representative differential value representing a plurality of individual differential values ​​SOCDi(t) corresponding to a plurality of DC power supplies 20 and the individual differential value SOCDi(t) of DC power supply 20i, characteristic adjustment unit 620 and command value calculation unit 640 do not need to be strictly separated. As described above, in this modified example, the same effects as those of the above-described embodiment can be obtained.

[0114] B7: 7th variant In the above-described embodiment and modifications, the command value calculation unit 640 may be provided in each controller 32.

[0115] FIG. 10 is an explanatory diagram for explaining an example of a DC power supply system 1 according to a seventh modification. The DC power supply system 1 according to the seventh modification is similar to the DC power supply system 1 shown in FIG. 1 except that it has a power control unit 60A instead of the power control unit 60 shown in FIG. 1 and a controller 32A instead of the controller 32 shown in FIG. 1. Note that, as in FIG. 4, FIG. 10 shows the DC power supply system 1 when focusing on an arbitrary DC power supply 20i among the multiple DC power supplies 20, and uses the subscript i instead of the subscripts a and b. Also, in FIG. 10, a calculation formula for the droop gain Ki(t) when the DC power supply 20i is charged is shown in a characteristic adjustment unit 620.

[0116] Power control unit 60A is similar to power control unit 60 shown in Fig. 4 etc., except that command value calculation unit 640 shown in Fig. 4 etc. is omitted. That is, power control unit 60A has characteristic adjustment unit 620 described in Fig. 4 etc.

[0117] Each controller 32Ai includes a gate signal generator 322i and a command value calculator 324i. The command value calculator 324i is similar to the command value calculator 640 shown in FIG. 4 and other figures. For example, the command value calculator 324i acquires a measured current value IMi(t) from a current measuring unit 40i corresponding to the power conversion device 30i. The command value calculator 324i then calculates a voltage command value VCi(t) based on the measured current value IMi(t) and the droop gain Ki(t) adjusted by the characteristic adjusting unit 620, and notifies the gate signal generator 322i of the calculated voltage command value VCi(t). The gate signal generator 322i controls the switching operation of the power conversion device 30i based on, for example, the voltage command value VCi(t) from the command value calculator 324i. For example, the gate signal generating unit 322i generates a gate signal, which is a control signal for controlling the switching operation of the power conversion device 30i, based on the voltage command value VCi(t) from the command value calculating unit 324i.

[0118] As described above, this modification can also achieve the same effects as the above-described embodiment and modification. Furthermore, in this modification, the controller 32Ai located closest to the power electronics device 30i includes a command value calculation unit 324i. Therefore, in this modification, even when the power electronics device 30i and the power control unit 60A are far apart, as in a DC microgrid, it is possible to prevent the communication path between the current measurement value IMi(t) and the voltage command value VCi(t) from becoming long. For example, if the communication path between the current measurement value IMi(t) and the voltage command value VCi(t) is long, there is a risk of signal delays, interruptions, and the like. In this modification, the controller 32Ai (more specifically, the command value calculation unit 324i) located closest to the power electronics device 30i calculates the voltage command value VCi(t), thereby reducing the risk of communication delays, interruptions, and the like between the current measurement value IMi(t) and the voltage command value VCi(t). [Explanation of symbols]

[0119] 1...DC power supply system, 2...load, 3...power supply device, 10...DC bus, 20, 20a, 20b, 20i...DC power supply, 22, 22a, 22b, 22i...BMS, 30, 30a, 30b, 30i...power conversion device, 32, 32a, 32b, 32i, 32Ai...controller, 40, 40a, 40b, 40i...current measurement unit, 50, 50a, 50b, 50i...voltage measurement unit, 60, 60A...power control unit, 322i...gate signal generation unit, 324i...command value calculation unit, 620...characteristic adjustment unit, 640...command value calculation unit.

Claims

1. A DC power control method for a DC power supply system having a plurality of DC power sources that perform at least one of outputting power to a DC bus and inputting power from the DC bus, and a plurality of power conversion devices that are provided corresponding to the plurality of DC power sources and perform power conversion between a corresponding one of the plurality of DC power sources and the DC bus, comprising: controlling the power output by each of the plurality of power conversion devices based on each of a plurality of droop characteristics corresponding to the plurality of power conversion devices and representing a relationship between a DC current or a DC power and a DC voltage; acquiring remaining energy information indicating remaining energy amounts of the DC power sources; calculating an individual difference value for each of the plurality of DC power supplies based on a difference between the remaining energy amount indicated by the remaining amount information and a remaining energy amount target value; identifying a representative difference value that represents a plurality of individual difference values ​​corresponding to the plurality of DC power supplies; changing each of the plurality of droop characteristics based on a difference between the individual difference value and the representative difference value of the DC power supply corresponding to the droop characteristic; the remaining energy target value is a target value of the remaining energy that is individually set for each of the plurality of DC power sources. A DC power control method comprising:

2. calculating an average value of the plurality of individual difference values ​​as the representative difference value; calculating a control value for each of the plurality of droop characteristics based on a difference between the individual difference value and the representative difference value; changing each of the plurality of droop characteristics based on the nth power (n is a real number equal to or greater than 1) of the control value; 2. The DC power control method according to claim 1.

3. a plurality of DC power sources that perform at least one of outputting power to a DC bus and inputting power from the DC bus; a plurality of power conversion devices provided corresponding to the plurality of DC power sources, the power conversion devices performing power conversion between corresponding DC power sources among the plurality of DC power sources and the DC bus; a control unit that corresponds to the plurality of power conversion devices and controls power output by each of the plurality of power conversion devices based on each of a plurality of droop characteristics that represent a relationship between a DC current or a DC power and a DC voltage; Equipped with a remaining energy amount target value that is a target value of a remaining energy amount is individually set for each of the plurality of DC power sources, The control unit acquiring remaining amount information indicating the remaining amount of energy of each of the plurality of DC power sources; calculating an individual difference value for each of the plurality of DC power supplies based on a difference between the remaining energy amount indicated by the remaining amount information and the remaining energy amount target value; identifying a representative difference value that represents a plurality of individual difference values ​​corresponding to the plurality of DC power supplies; changing each of the plurality of droop characteristics based on a difference between the individual difference value and the representative difference value of the DC power supply corresponding to the droop characteristic; A DC power supply system characterized by:

4. The control unit calculating an average value of the plurality of individual difference values ​​as the representative difference value; calculating a control value for each of the plurality of droop characteristics based on a difference between the individual difference value and the representative difference value; changing each of the plurality of droop characteristics based on the nth power (n is a real number equal to or greater than 1) of the control value; 4. The DC power supply system according to claim 3.

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