Method for controlling charging and discharging of an energy storage system

Abstract

To provide a charge / discharge control method of a power storage system for controlling voltage of a DC link in a power conditioner system including the power storage system having a plurality of battery units.SOLUTION: A power conditioner system includes a power storage system 1 having a plurality of battery units 10-1 to 10-n, and has a power conditioner 2 in which the plurality of battery units are connected to an inverter 22 via a DC link 21. A charge / discharge control method of the plurality of battery units selects at least one first battery unit for performing charge / discharge operation for controlling voltage of the DC link from the plurality of battery units.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technique for controlling charging and discharging of an electricity storage system including a plurality of battery units. [Background technology]

[0002] With the widespread use of distributed power generation devices such as photovoltaic power generation systems and wind power generation systems, power conditioner systems equipped with storage batteries are becoming increasingly popular for stabilizing the grid, adjusting supply and demand, and preparing for long-term power outages due to disasters. Furthermore, as the price of battery units falls, there is an increasing demand for power conditioner systems that include multiple battery units.

[0003] Patent Document 1 discloses a DC power supply system that stabilizes the voltage of a DC bus to which DC power supplies are connected. In this DC power supply system, a controller that controls multiple converters controls the converters so that, when the voltage supplied from a distributed power supply to the DC bus drops below a predetermined voltage, power is supplied from one DC power supply to the DC bus and power is supplied from the DC bus to another DC power supply. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-95418 Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional power conditioner systems, the inverter of the power conditioner controls the voltage of the DC link to which the distributed power source is connected to stabilize it. However, for example, when a power limit command is received from the commercial power grid or when the load power consumption suddenly fluctuates, it can become difficult for the inverter to control the DC link voltage.

[0006] The present invention aims to realize charge / discharge control of a power storage system having a plurality of battery units in a power conditioner system including the power storage system in order to stabilize the voltage of a DC link. [Means for solving the problem]

[0007] An aspect of the present invention is a method for controlling charging and discharging of a power conditioner system including a power storage system having a plurality of battery units, and a power conditioner having a DC link, an inverter, and a controller, wherein the plurality of battery units are each connected to the inverter via the DC link, wherein the controller controls charging and discharging of the plurality of battery units, wherein a distributed power source is connected to the DC link, and the controller calculates a total charging and discharging power of the power storage system based on output power of the distributed power source and output power of the power conditioner, divides and allocates the calculated total charging and discharging power to each of the battery units, selects at least one first battery unit from the plurality of battery units to perform charging and discharging operations for controlling a voltage of the DC link, causes the first battery unit to perform charging and discharging operations for controlling the voltage of the DC link, and causes battery units other than the first battery unit to perform charging and discharging operations with predetermined charging and discharging power. and causing the battery units other than the first battery unit to perform a charge / discharge operation to control the voltage of the DC link when the DC link voltage exceeds a predetermined upper limit value or falls below a predetermined lower limit value. .

[0008] According to this configuration, the power conditioner system includes a power storage system having multiple battery units, and a power conditioner having a DC link, an inverter, and a controller. Each battery unit is connected to the inverter via the DC link. A distributed power source is connected to the DC link. The controller calculates the total charge / discharge power of the power storage system based on the output power of the distributed power source and the output power of the power conditioner, and divides and allocates the calculated total charge / discharge power to each battery unit. Then, a first battery unit is selected from the multiple battery units to perform charge / discharge operations to control the voltage of the DC link. This allows the DC link voltage to be stabilized by the charge / discharge operations of the first battery unit, even if it becomes difficult for the inverter to control the DC link voltage. Furthermore, because the battery units other than the first battery unit can perform charge / discharge operations for power control, the charge / discharge power of the entire power storage system can be appropriately managed. Furthermore, when the DC link voltage exceeds the upper limit value or falls below the lower limit value, the other battery units in addition to the first battery unit perform charging and discharging operations to control the DC link voltage, thereby making it possible to further stabilize the DC link voltage. Therefore, it is possible to realize charge / discharge control for stabilizing the voltage of the DC link in a power storage system including a plurality of battery units.

[0009] In this aspect, the controller may select the first battery unit using at least one parameter related to power or energy of each of the battery units.

[0010] This allows the first battery unit to be appropriately selected to perform the charge / discharge operation for controlling the voltage of the DC link. 。 [Effects of the Invention]

[0011] According to the present invention, it is possible to realize charge / discharge control for stabilizing the voltage of a DC link in a power storage system including a plurality of battery units. [Brief explanation of the drawings]

[0012] [Figure 1] Example of the overall configuration of a power conditioner system including a power storage system [Figure 2] An image diagram showing the role of the battery unit in the embodiment. [Figure 3] Control block diagram showing an example of a scheme in which a battery unit controls the DC link voltage. [Figure 4] FIG. 4 is a diagram illustrating control for charging and discharging a predetermined power in the control scheme of FIG. 3. [Figure 5] 10 is a flowchart showing an example of a process performed by a controller. [Figure 6] Graph showing the results of an experiment using the method of the embodiment [Figure 7] Flowchart showing an example of the operation of the unit controller DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the present invention, its scope of application, or its uses.

[0014] (Embodiment) FIG. 1 shows an example of the overall configuration of a power conditioner system including a power storage system. In FIG. 1, the power storage system 1 includes n (n is a positive integer) battery units 10-1, 10-2, ..., 10-n that can be charged and discharged. Note that hereinafter, the battery units 10-1, 10-2, ..., 10-n may be collectively referred to as battery units 10. Each battery unit 10 includes a storage battery 11 and a unit controller 12. The power conditioner 2 includes a DC link 21 connected to each battery unit 10 of the power storage system 1, an inverter 22 that converts DC power from the DC link 21 to AC power, and a controller 23 that controls the charging and discharging operations of the battery units 10 of the power storage system 1. The controller 23 is implemented, for example, by a microcomputer including a processor and memory. The unit controller 12 of each battery unit 10 includes a bidirectional DC / DC converter (not shown) and charges and discharges the storage battery 11 in accordance with signals transmitted from the controller 23 of the power conditioner 2. Furthermore, the unit controller 12 of each battery unit 10 is provided with a voltage sensor that measures the voltage VDC of the DC link.

[0015] The distributed power source 4 is, for example, a solar power generation system, a hydroelectric power generation system, a wind power generation system, etc. The distributed power source 4 is connected to a DC link 21 and outputs electric power PDER. The output electric power PAC of the power conditioner 2 is supplied to a commercial power system and a load.

[0016] The controller 3 of the power conditioner 2 calculates the charge / discharge power Pstorage of the power storage system 1 for each predetermined cycle. For example, when the output power PDER of the distributed power source 4 is greater than the output power PAC of the power conditioner 2, the surplus power is used as the charge power Pstorage of the power storage system 1. Furthermore, when the output power PDER of the distributed power source 4 decreases due to weather conditions or the like and falls short of the output power PAC of the power conditioner 2, the shortfall in power is used as the discharge power Pstorage of the power storage system 1.

[0017] Furthermore, the inverter 22 of the power conditioner 2 performs control to stabilize the voltage VDC of the DC link 21. However, for example, when a power limit command is received from the commercial power grid or when the power consumption of the load suddenly fluctuates, it may become difficult to control the voltage VDC of the DC link 21.

[0018] Therefore, in this embodiment, the energy storage system 1 including the multiple battery units 10 controls the voltage VDC of the DC link 21. This makes it possible to further stabilize the voltage VDC of the DC link 21 even when it is difficult for the inverter 22 of the power conditioner 2 to appropriately control the voltage VDC of the DC link 21.

[0019] However, if all the battery units 10 included in the power storage system 1 are caused to control the voltage VDC of the DC link 21, the following problem occurs: The voltage VDC measured by each battery unit 10 may differ slightly, and the voltage sensor of each battery unit 10 may have measurement errors. As a result, some battery units 10 attempt to increase the voltage VDC of the DC link 21 and others attempt to decrease it may coexist, which may result in charging and discharging occurring between the battery units 10.

[0020] Furthermore, in order for the power storage system 1 having a plurality of battery units 10 to stably demonstrate its charge / discharge capacity for a longer period of time, it is necessary to appropriately manage the charge / discharge power allocated to each battery unit 10. For example, when the SOC (State Of Charge) of each battery unit 10 is different, it is preferable to allocate charge / discharge power to each battery unit 10 so that the SOC converges at the same time.

[0021] Therefore, in this embodiment, as shown in Fig. 2, at least one battery unit 10 is selected from the plurality of battery units 10 to control the voltage VDC of the DC link 21. In Fig. 2, the battery unit 10-1 is selected as the battery unit to control the voltage VDC of the DC link 21. The selected battery unit 10-1 performs a charge / discharge operation to stabilize the voltage VDC of the DC link 21. For example, the battery unit 10-1 performs a charge operation when the voltage VDC of the DC link 21 is higher than a predetermined reference value, and performs a discharge operation when the voltage VDC of the DC link 21 is lower than the predetermined reference value. On the other hand, predetermined charge / discharge power is allocated to the other battery units 10-2 to 10-n.

[0022] This makes it possible to further stabilize the voltage VDC of the DC link 21, and to stably demonstrate the charge / discharge capability for a longer period of time in the power storage system 1 having a plurality of battery units 10. Such charge / discharge control of the battery units 10 is performed in each cycle in which the controller 23 calculates the charge / discharge power Pstorage of the power storage system 1.

[0023] FIG. 3 is a control block diagram showing an example of a scheme for controlling the voltage VDC of the DC link 21 in the unit controller 12. The control scheme of FIG. 3 is provided for each battery unit 10. As shown in FIG. 3, in this control scheme, the current determination unit 121 compares the measured value of the voltage VDC of the DC link 21 with a command value, and generates a current command X representing the charge / discharge current value of the battery unit 10 based on the comparison result. A positive value of the current value represented by the current command X indicates a discharging operation, and a negative value indicates a charging operation. The measured value is obtained by a voltage sensor provided in the unit controller 12. The command value is transmitted from the controller 23.

[0024] The current limiting unit 122 imposes limits on this current command X on both the discharge side (upper limit) and the charge side (lower limit). The charge / discharge current of the battery unit 10 is controlled by the current command K after limiting by the current limiting unit 122. The limit value conversion unit 123 converts the upper and lower limit values ​​of the charge / discharge power of the battery unit 10 received from the outside into upper and lower limit values ​​of current, and provides them to the current limiting unit 122. Here, the upper and lower limit values ​​of the charge / discharge power of the battery unit 10 are transmitted from the controller 23.

[0025] The control scheme in Fig. 3 can easily realize not only control of the voltage VDC of the DC link 21 but also control of charging and discharging a predetermined amount of power to and from the battery unit 10. That is, as shown in Fig. 4, by setting the upper and lower limit values ​​in the current limiting unit 122 to the same current value, the limited current command K can be set to that current value. Specifically, (a) when discharging the battery unit 10, the upper and lower limit values ​​in the current limiting unit 122 can be set to the same positive value, and (b) when charging the battery unit 10, the upper and lower limit values ​​in the current limiting unit 122 can be set to the same negative value.

[0026] That is, for a battery unit 10 that controls the voltage VDC of the DC link 21, the controller 23 transmits a positive power value as the upper limit of the power value to the unit controller 12, and transmits a negative power value as the lower limit of the power value. The limit conversion unit 123 converts the received upper and lower limits of the power value into upper and lower limits of the current value, and provides them to the current limiting unit 122. On the other hand, for the other battery units 10, the controller 23 transmits the same positive power values ​​as the upper and lower limits of the power value when discharging, and transmits the same negative power values ​​as the upper and lower limits of the power value when charging. The limit conversion unit 123 converts the received power value into a current value and provides it to the current limiting unit 122. As a result, a current command K indicating a current corresponding to the same power value is output from the current limiting unit 122. That is, the other battery units 10 can be charged or discharged with a predetermined amount of power.

[0027] Therefore, the control scheme of FIG. 3 allows the battery unit 10 to perform charging and discharging operations for controlling the voltage VDC of the DC link 21 and charging and discharging operations of a predetermined charging and discharging power with a simple configuration.

[0028] Fig. 5 is a flowchart showing an example of the processing of the controller 23. The controller 23 executes the processing of Fig. 5 for each predetermined cycle. First, the total charge / discharge power PSTORAGE of the power storage system 1 is calculated (S11). This calculation may be performed, for example, by taking the sum of the current charge / discharge power of each battery unit 10 included in the power storage system 1.

[0029] Then, the controller 23 divides and allocates the total charge / discharge power PSTORAGE of the power storage system 1 to each battery unit 10 (S12). Here, the allocated power is referred to as Passign-i (i is an integer from 1 to n corresponding to the battery units 10-1 to 10-n).

[0030] Various methods of power allocation are possible. For example, power is allocated so that the SOC (State Of Charge) of each battery unit 10 gradually becomes more equal. That is, when PSTORAGE is a positive value, i.e., discharging power, a large amount of discharging power is allocated to the battery unit 10 with a large SOC, and a small amount of discharging power is allocated to the battery unit 10 with a small SOC. Also, when PSTORAGE is a negative value, i.e., charging power, a small amount of charging power is allocated to the battery unit 10 with a large SOC, and a large amount of charging power is allocated to the battery unit 10 with a small SOC. Other possible power allocation methods include a method using the SOH (State Of Health) of each battery unit 10, a method using the current charging / discharging power of each battery unit 10, or a method using a combination of the SOC, SOH, and current charging / discharging power.

[0031] Then, the controller 23 selects a battery unit (battery unit k) that controls the voltage VDC of the DC link 21 from among the battery units 10 (S13). This selection may be performed using at least one of the parameters related to the power or energy of each battery unit 10. Here, the parameter related to power refers to, for example, a power value related to a requested command value (a set power value), and the parameter related to energy refers to, for example, the SOC.

[0032] Various methods for this selection are possible. For example, the power capacity of each battery unit 10 may be used, the SOC of each battery unit 10 may be used, or both the power capacity and the SOC may be used. Specifically, for example, the battery unit 10 with the largest power capacity may be selected as battery unit k. Alternatively, the battery unit 10 with an SOC close to 50%, i.e., a battery unit 10 with a remaining capacity that is neither too large nor too small, may be selected as battery unit k. Alternatively, the power Passign-i allocated in step S12 may be used. Specifically, for example, the battery unit 10 with the smallest absolute value of the power Passign-i allocated in step S12 may be selected as battery unit k.

[0033] Alternatively, the battery unit k may be prevented from being changed frequently. Specifically, for example, the battery unit k may be selected every several cycles.

[0034] Then, the controller 23 transmits the upper and lower limits of the rated power to the selected battery unit k (S14). The unit controller 12 of the battery unit k converts the upper and lower limits of the rated power transmitted from the controller 23 into upper and lower limit values ​​of the current using the limit conversion unit 123. Using these upper and lower limit values ​​of the current, the current limiting unit 122 imposes a limit on the current command. This allows the battery unit k to perform charging and discharging operations for controlling the voltage VDC of the DC link 21.

[0035] Furthermore, the controller 23 transmits the power Passign-i allocated in step S12 to the battery units 10 other than the battery unit k as the upper and lower limit values ​​of the power (S15). When the power Passign-i is a positive value, i.e., when discharging, the positive current value obtained by converting the power Passign-i is set as the upper and lower limit values ​​of the current in the current limiting unit 122. This allows the battery unit 10 to discharge the allocated power Passign-i. When the power Passign-i is a negative value, i.e., when charging, the negative current value obtained by converting the power Passign-i is set as the upper and lower limit values ​​of the current in the current limiting unit 122. This allows the battery unit 10 to charge the allocated power Passign-i.

[0036] FIG. 6 is a graph showing the results of an experiment using the method of this embodiment. In this experiment, a power storage system equipped with two battery units (unit 1 and unit 2) was used. Unit 1 was selected as the battery unit that controls the voltage VDC of the DC link 21, and the load power consumption Pload was varied to plot the changes in the power Punit-1 and Punit-2 of units 1 and 2. It can be seen from FIG. 6 that when the load power consumption Pload changes, the power Punit-1 of unit 1 changes sharply. This sharp change corresponds to the sudden change in the voltage VDC of the DC link 21.

[0037] As described above, according to the present embodiment, the power conditioner system includes the power storage system 1 having a plurality of battery units 10. Each battery unit 10 is connected to the inverter 22 via the DC link 21. Then, for example, the battery unit 10-1 among the plurality of battery units 10 is caused to perform a charge / discharge operation for controlling the voltage VDC of the DC link 21. As a result, even if it becomes difficult for the inverter 22 to control the voltage VDC of the DC link 21, the charge / discharge operation of the battery unit 10-1 can stabilize the voltage VDC of the DC link 21. Furthermore, predetermined charge / discharge power is allocated to the other battery units 10-2 to 10-n. As a result, the charge / discharge power of the entire power storage system 1 can be appropriately managed. Therefore, for the power storage system 1 including a plurality of battery units 10, charge / discharge control for stabilizing the voltage VDC of the DC link 22 can be realized.

[0038] Furthermore, in this embodiment, the total charge / discharge power PSTORAGE to be allocated to the power storage system 1 is calculated, and this total charge / discharge power PSTORAGE is divided and allocated to each battery unit 10. Then, from among the plurality of battery units 10, a battery unit 10 that performs a charge / discharge operation for controlling the voltage VDC of the DC link 21 is selected. Through such processing, the charge / discharge power of the entire power storage system 1 can be appropriately managed, while stabilizing the voltage VDC of the DC link 21.

[0039] In addition, in this embodiment, the battery units 10 that perform the charge / discharge operation to control the voltage VDC of the DC link 21 are selected using at least one of the power capacity and SOC of each battery unit. This allows the battery units 10 that perform the charge / discharge operation to control the voltage VDC of the DC link 21 to be appropriately selected.

[0040] Furthermore, the control scheme of FIG. 3 allows the battery unit 10 to perform charging and discharging operations for controlling the voltage VDC of the DC link 21 and charging and discharging operations of a predetermined charging and discharging power with a simple configuration.

[0041] Furthermore, when the voltage VDC of the DC link 21 changes significantly, it may be impossible to adequately control the voltage VDC only with the selected battery unit 10. In consideration of such a case, when the voltage VDC of the DC link 21 changes significantly, the non-selected battery unit 10 may be configured to control the voltage VDC.

[0042] Fig. 7 is a flowchart showing an example of the operation of the unit controller 12. As shown in Fig. 7, the unit controller 12 receives the allocated power Passign-i from the controller 23 as upper and lower limit values ​​of power (S21). Then, the unit controller 12 converts the power Passign-i into upper and lower limit values ​​of current value (S22). These operations have already been described.

[0043] The unit controller 12 then determines whether the voltage VDC of the DC link 21 exceeds a predetermined upper limit or falls below a predetermined lower limit (S23). If the voltage VDC is between the upper limit and the lower limit (NO in S23), the settings of the upper and lower limits of the current value are not changed. On the other hand, if the voltage VDC exceeds the upper limit or falls below the lower limit (YES in S23), the upper and lower limits of the rated current are set as the upper and lower limits of the current value (S24). This setting change allows the battery unit 10 to perform charging and discharging operations to control the voltage VDC of the DC link 21, even though the power Passign-i has been allocated to it. This makes it possible to further stabilize the voltage VDC of the DC link 21.

[0044] In the above description, the battery unit 10 that performs charging and discharging operations to control the voltage VDC of the DC link 21 is one, but this is not limited to one. Two or more battery units 10 may be selected to perform charging and discharging operations to control the voltage VDC of the DC link 21.

[0045] The technology described here can be applied to VtoH (Vehicle to Home), VtoG (Vehicle to Grid), etc. The battery unit of the present disclosure can be applied not only to home use, but also to industrial equipment and automotive batteries (for powertrains). [Industrial Applicability]

[0046] INDUSTRIAL APPLICABILITY The present invention is useful for further stabilizing the DC link voltage in a power conditioner system that uses a power storage system including a plurality of battery units. [Explanation of symbols]

[0047] 1. Energy storage system 10, 10-1, 10-2, ..., 10-n battery unit 11 Storage battery 12 Unit controller (control device) 21 DC link 22 Inverter 23 Controller 121 Current determination unit 122 Current limiter 123 Restriction conversion section

Claims

1. A method for controlling charging and discharging of the battery units in a power conditioner system including a power storage system having a plurality of battery units, and a power conditioner having a DC link, an inverter, and a controller, wherein the battery units are each connected to the inverter via the DC link, the method comprising: a distributed power source connected to the DC link; The controller calculating a total charge / discharge power of the power storage system based on the output power of the distributed power source and the output power of the power conditioner; Dividing and allocating the calculated total charge / discharge power to each of the battery units; selecting at least one first battery unit from the plurality of battery units to perform a charging / discharging operation for controlling a voltage of the DC link; causing the first battery unit to perform a charging / discharging operation to control a voltage of the DC link; causing a battery unit other than the first battery unit to perform a charging / discharging operation with a predetermined charging / discharging power; When the DC link voltage exceeds a predetermined upper limit value or falls below a predetermined lower limit value, the battery units other than the first battery unit are caused to perform a charge / discharge operation to control the DC link voltage. A charge / discharge control method comprising:

2. 2. The charge / discharge control method according to claim 1, The controller The selection of the first battery unit is performed using at least one parameter related to power or energy of each of the battery units. A charge / discharge control method comprising:

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