Charge and Discharge Control Method of Energy Storage System and Charge and Discharge Control Device

Abstract

To provide a charge / discharge control method and a charge / discharge control device for a power storage system by which charge / discharge control for stabilizing a voltage of a DC link to the power storage system is realized in a power conditioner system.SOLUTION: A power storage system 1 having storage batteries 11 is connected to an inverter 22 via a DC link 21. A charge / discharge controller 12 measures a voltage VDC of the DC link 21 and performs controlling charge / discharge of the storage batteries 11 based on the measured voltage VDC and a command value of the voltage VDC of the DC link 21.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a technique for controlling charge and discharge of a power storage system.

Background Art

[0002] With the spread of distributed power generation devices such as solar power generation systems and wind power generation systems, the power conditioner system equipped with a storage battery has been increasingly popularized as a means for stabilizing the power grid, adjusting supply and demand, and preparing for long-term power outages due to disasters.

[0003] Patent Document 1 discloses control in a distributed power system in which a storage battery is installed in a power generation device to suppress fluctuations in output power. In this control, the burden on the storage battery is reduced by reducing the frequency of switching between the state of discharging from the storage battery and the state of charging the storage battery, thereby making it possible to extend the life of the storage battery.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In a conventional power conditioner system, an inverter controls so that the voltage of a DC link to which a distributed power source is connected is stabilized. However, for example, when an instruction for power restriction is received from the commercial power grid side, or when the power consumption of a load suddenly changes, it may become difficult to control the voltage of the DC link by the inverter.

[0006] An object of the present invention is to enable a power storage system in a power conditioner system including the power storage system to perform a charge and discharge operation for stabilizing the voltage of a DC link.

Means for Solving the Problem

[0007] A first aspect of the present invention is a method for controlling charging and discharging of a storage battery in a power storage system having a storage battery and connected to an inverter via a DC link, the method measuring a voltage of the DC link and controlling a charging and discharging operation of the storage battery based on the measured voltage of the DC link and a command value of the voltage of the DC link. Then, set an upper limit value higher than the command value and a lower limit value lower than the command value. When the measured voltage of the DC link is higher than the upper limit value, execute a charging operation on the storage battery. When the measured voltage of the DC link is lower than the lower limit value, execute a discharging operation on the storage battery. Further, when the measured voltage of the DC link is between the upper limit value and the lower limit value, execute a charging and discharging operation on the storage battery according to the charge and discharge current command value transmitted from outside the power storage system.

[0008] According to this configuration, in a power storage system connected to an inverter via a DC link, the voltage of the DC link is measured, and the charging and discharging operation of the storage battery is controlled based on the measured voltage of the DC link and the command value of the voltage of the DC link. Thereby, the power storage system can automatically execute a charging and discharging operation for stabilizing the voltage of the DC link. And it is not necessary to send a signal for instructing a charging and discharging operation for stabilizing the voltage of the DC link from the inverter to the power storage system by communication. Therefore, it becomes easy to cope with a sudden change in the voltage of the DC link. Then, When the voltage of the DC link is higher than the upper limit value, the storage battery executes a charging operation so that the voltage of the DC link decreases, and when the voltage of the DC link is lower than the lower limit value, the storage battery executes a discharging operation so that the voltage of the DC link increases. Therefore, the charging and discharging operation for stabilizing the voltage of the DC link is automatically and appropriately performed. Then, When the voltage of the DC link is stable, the storage battery can execute a charging and discharging operation according to a charging and discharging current command value transmitted from outside the power storage system.

[0009] A second aspect of the present invention is an apparatus for controlling charging and discharging of a storage battery in a power storage system having a storage battery and connected to an inverter via a DC link, the apparatus measuring a voltage of the DC link and performing a charging and discharging operation of the storage battery based on the measured voltage of the DC link and a command value of the voltage of the DC link. Then, set an upper limit value higher than the command value and a lower limit value lower than the command value. When the measured voltage of the DC link is higher than the upper limit value, execute a charging operation on the storage battery. When the measured voltage of the DC link is lower than the lower limit value, execute a discharging operation on the storage battery. Further, when the measured voltage of the DC link is between the upper limit value and the lower limit value, execute a charging and discharging operation on the storage battery according to the charge and discharge current command value transmitted from outside the power storage system.

[0010] Accordingly, in a power storage system connected to an inverter via a DC link, the voltage of the DC link is measured, and based on the measured voltage of the DC link and the command value of the voltage of the DC link, the charge and discharge operations of the storage battery are controlled. Thereby, the power storage system can automatically execute a charge and discharge operation for stabilizing the voltage of the DC link. And it is not necessary to send a signal for instructing a charge and discharge operation for stabilizing the voltage of the DC link from the inverter to the power storage system by communication. Therefore, it becomes easy to cope with sudden fluctuations in the voltage of the DC link. Then, when the voltage of the DC link is higher than the upper limit value, the storage battery executes a charging operation so that the voltage of the DC link decreases. When the voltage of the DC link is lower than the lower limit value, the storage battery executes a discharging operation so that the voltage of the DC link increases. Therefore, the charging and discharging operations for stabilizing the voltage of the DC link are automatically and appropriately performed. And when the voltage of the DC link is stable, the storage battery can execute a charging and discharging operation according to the charge and discharge current command value transmitted from outside the power storage system.

Advantages of the Invention

[0011] According to the present invention, in a power conditioner system including a power storage system, the power storage system can execute a charge and discharge operation for stabilizing the DC link voltage.

Brief Description of the Drawings

[0012]

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Mode for Carrying Out the Invention

[0013] Hereinafter, embodiments of the present invention will be described in detail with reference to the 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 is 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 a rechargeable battery 11 and a charge / discharge controller 12. In FIG. 1, a single charge / discharge controller 12 is provided for four batteries 11. However, a unit controller may be provided for each battery 11. The power conditioner 2 includes a DC link 21 connected to the power storage system 1, an inverter 22 that converts the DC power of the DC link 21 into AC power, and a controller 23 that transmits charge / discharge command values and the like to the charge / discharge controller 12 of the power storage system 1. The controller 23 is realized by, for example, a microcomputer including a processor and a memory. The charge / discharge controller 12 of the power storage system 1 includes a bidirectional DC / DC converter (not shown) and executes the charge / discharge of the battery 11 according to a signal transmitted from the controller 23. Further, the charge / discharge controller 12 of the power storage system 1 includes a voltage sensor (not shown) that measures the voltage VDC of the DC link 21.

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

[0016] In the normal state, the inverter 22 of the power conditioner 2 exchanges power with the grid to maintain the power balance of the DC link 21. That is, the inverter 22 adjusts the power PINV quickly and accurately by controlling the voltage VDC of the DC link 21 to a constant level.

[0017] The controller 23 of the power conditioner 2 calculates the charge-discharge power PES of the energy storage system 1 every predetermined cycle. The calculated value of the charge-discharge power PES is transmitted to the charge-discharge controller 12 of the energy storage system 1. For example, when the output power PDER of the distributed power source 4 is greater than the output power PINV of the power conditioner 2, the surplus power is used as the charging power PES of the energy storage system 1. Also, when the output power PDER of the distributed power source 4 decreases due to the influence of weather conditions or the like and is insufficient compared to the output power PINV of the power conditioner 2, the shortage power is used as the discharging power PES of the energy storage system 1.

[0018] However, for example, when receiving an instruction for power limitation from the commercial power grid side or when the power consumption of the load suddenly changes, it may become difficult for the inverter 22 to maintain the power balance of the DC link 21.

[0019] Figure 2 shows an example of the control scheme of the inverter 22. The control scheme in Figure 2 includes a power control block 222. Here, the power control block 222 has a level limitation function 222a, a rate-of-change limitation function 222b, and a determined power control function 222c. When this power control block 222 operates, regardless of the current command value for controlling the voltage VDC of the DC link 21, the output voltage PINV of the inverter 22 is controlled by the power control block 222.

[0020] Figure 3 shows the level limiting function 222a. The inverter 22 can only handle a limited amount of power due to its own limitations or system-side requirements. Therefore, the level limiting function 222a limits the level of the inverter power PINV. When the level limiting function 222a operates, a power difference occurs between the generated power PDER of the distributed power source 4 and the inverter power PINV.

[0021] Figure 4 shows the rate-of-change limiting function 222b. When the generated power PDER of the distributed power source 4 fluctuates, the inverter power PINV fluctuates. However, when the fluctuation of the inverter power PINV is severe, there is a risk of problems occurring on the system side. Therefore, the rate-of-change limiting function 222b limits the rate of change of the inverter power PINV. When the generated power PDER suddenly increases due to the rate-of-change limiting function 222b, surplus power is generated, and when the generated power PDER suddenly decreases, there is a power shortage.

[0022] Figure 5 shows the determined power control function 222c. When the determined power control function 222c receives a power command value determined from the system side, it outputs the inverter power PINV according to that command value. When the determined power control function 222c operates, even if the generated power PDER is stable, a power difference occurs between the generated power PDER and the inverter power PINV.

[0023] In the cases of Figures 3 to 5, it becomes difficult for the inverter 22 alone to control the voltage VDC of the DC link 21 at a constant level. That is, when surplus power is generated, the voltage VDC of the DC link 21 rises, and when there is a power shortage, the voltage VDC of the DC link 21 drops. In order to control the voltage VDC of the DC link 21 at a constant level, it is preferable that the power storage system 1 quickly and accurately absorbs the power difference between the generated power PDER and the inverter power PINV caused by the operation of the power control block 22. That is, when surplus power is generated, it is preferable that the power storage system 1 quickly performs a charging operation, and when there is a power shortage, it is preferable that the power storage system 1 quickly performs a discharging operation.

[0024] In this embodiment, the charge / discharge controller 12 of the power storage system 1 monitors the voltage VDC of the DC link 21 and automatically controls the charge / discharge of the storage battery 11. Thereby, the power storage system 1 can stabilize the voltage VDC of the DC link 21 without requiring a signal from other components.

[0025] FIG. 6 is an example of the control scheme of the charge / discharge controller 12 of the power storage system 1. FIG. 7 shows the setting of the dead band of the DC link voltage VDC used in the control scheme of FIG. 6. As shown in FIG. 7, dead bands (hysteresis bands) are set on the high voltage side and the low voltage side of the command value with respect to the DC link voltage VDC. Note that the sizes of the dead bands may be the same or different between the high voltage side and the low voltage side.

[0026] The control scheme of FIG. 6 includes current determination units 121a and 121b, current limit units 122a and 122b, and a current control unit 123. The current determination unit 121a compares the value obtained by adding the dead band to the command value of the DC link voltage VDC with the measured value of the DC link voltage VDC. Then, according to the deviation (= command value + dead band - measured value), the current value is determined. When the deviation is positive, the current value is increased; when the deviation is negative, the current value is decreased; and when the deviation is zero, the current value is not changed. The current limit unit 122a applies a limit to the current value determined by the current determination unit 121a. Here, the upper limit is set to 0.5×ID, and the lower limit is set to (maximum charge current - 0.5×ID). Note that ID is the command value of the charge / discharge current and is transmitted from the controller 23. The discharge current is represented by a positive value, and the charge current is represented by a negative value.

[0027] The current determination unit 121b compares a value obtained by subtracting a dead band from the command value of the DC link voltage VDC with the measured value of the DC link voltage VDC. Then, it determines the current value according to the deviation (= command value - dead band - measured value). When the deviation is positive, it increases the current value; when the deviation is negative, it decreases the current value; and when the deviation is zero, it does not change the current value. The current limiting unit 122b applies a limit to the current value determined by the current determination unit 121b. Here, the upper limit is set to (maximum discharge current - 0.5×ID), and the lower limit is set to 0.5×ID.

[0028] Figure 8 shows the operation of the control scheme of Figure 6 when the DC link voltage VDC rises. When the DC link voltage VDC rises and exceeds the value obtained by adding the dead band to the command value, the deviation (= command value + dead band - measured value) in the current determination unit 121a changes from positive to negative. As a result, the current value determined by the current determination unit 121a decreases. Due to the current limiting unit 122a, the current value finally becomes (maximum charge current - 0.5×ID). On the other hand, the deviation (= command value - dead band - measured value) in the current determination unit 121b is a negative value, and due to the current limiting unit 122b, the current value becomes 0.5×ID. As a result, the current value given to the current control unit 123 becomes the maximum charge current. Therefore, the power storage system 1 executes a charging operation with the maximum charge current.

[0029] Figure 9 shows the operation of the control scheme of Figure 6 when the DC link voltage VDC drops. When the DC link voltage VDC drops and is lower than the value obtained by subtracting the dead band from the command value, the deviation (= command value - dead band - measured value) in the current determination unit 121b changes from negative to positive. As a result, the current value determined by the current determination unit 121b increases. Due to the current limiting unit 122b, the current value finally becomes (maximum discharge current - 0.5×ID). On the other hand, the deviation (= command value + dead band - measured value) in the current determination unit 121a is a positive value, and due to the current limiting unit 122a, the current value becomes 0.5×ID. As a result, the current value given to the current control unit 123 becomes the maximum discharge current. Therefore, the power storage system 1 executes a discharging operation with the maximum discharge current.

[0030] FIG. 10 shows the operation of the control scheme when the DC link voltage VDC is within the normal range. Here, the normal range refers to the range from the value obtained by subtracting the dead band from the command value to the value obtained by adding the dead band to the command value. In this case, the deviation (= command value + dead band - measured value) in the current determination unit 121a is a positive value, the current value determined by the current determination unit 121a increases, and the current value finally becomes 0.5×ID by the current limit unit 122a. On the other hand, the deviation (= command value - dead band - measured value) in the current determination unit 121b is a negative value, the current value determined by the current determination unit 121b decreases, and the current value finally becomes 0.5×ID by the current limit unit 122b. As a result, the current value given to the current control unit 123 becomes the command value of ID, that is, the charge / discharge current. Therefore, the power storage system 1 executes a charge / discharge operation according to the charge / discharge current command value ID transmitted from the controller 23.

[0031] FIG. 11 is a graph showing the results of an experiment using the method according to this embodiment. In this experiment, it is assumed that the variability limiting function 22b of the inverter 2 is operating. That is, when the output power PDER of the distributed power source 4 changes rapidly, the power PINV of the inverter 2 does not change rapidly but changes gradually. For this reason, when the power PDER drops rapidly, the power storage system 1 performs a discharge operation to supplement the insufficient power, and the power PES rises rapidly from zero. On the other hand, when the power PDER rises rapidly, the power storage system 1 performs a charge operation to supplement the excess power, and the power PES drops rapidly from zero. As a result, significant fluctuations in the voltage VDC of the DC link 2 are suppressed.

[0032] As described above, according to this embodiment, in the power storage system 1 connected to the inverter 22 via the DC link 2, the voltage VDC of the DC link 2 is measured, and based on the measured voltage VDC and its command value, the charge and discharge operation of the storage battery 11 is controlled. Thereby, the power storage system 1 can automatically execute the charge and discharge operation for stabilizing the voltage VDC of the DC link 21. And it is not necessary to send a signal for instructing the charge and discharge operation for stabilizing the voltage VDC of the DC link 21 from the inverter 22 to the power storage system 1 by communication. Therefore, it becomes easy to cope with sudden fluctuations in the voltage VDC of the DC link 21.

[0033] Also, according to this embodiment, a dead band is provided on the high voltage side and the low voltage side of the command value with respect to the voltage VDC of the DC link 21. When the measured voltage VDC of the DC link 21 is higher than (command value + dead band), the storage battery 11 executes a charging operation so that the voltage VDC decreases. When the measured voltage VDC of the DC link 21 is lower than (command value - dead band), the storage battery 11 executes a discharging operation so that the voltage VDC increases. Thereby, the charge and discharge operation for stabilizing the voltage VDC of the DC link 21 is automatically and appropriately performed by the power storage system 1.

[0034] When the voltage VDC of the DC link 21 is within the dead band, the storage battery 11 executes the charge and discharge operation according to the charge and discharge current command value transmitted from outside the power storage system 1. Thereby, when the voltage VDC of the DC link 21 is stable, the storage battery 11 can execute the charge and discharge operation according to the charge and discharge current command value.

[0035] Note that the control scheme of the charge and discharge controller 12 of the power storage system 1 is not limited to that shown in FIG. 6. For example, it may be a control without providing a dead band with respect to the command value, or a control with a dead band provided only on either the high voltage side or the low voltage side of the command value.

[0036] Note that the battery unit 10 that performs the charge and discharge operation to control the voltage VDC of the DC link 21 is not limited to one, and two or more may be used.

Industrial Applicability

[0037] The present invention is useful for stabilizing the DC link voltage in a power conditioner system including a power storage system.

Explanation of Signs

[0038] 1 Power storage system 11 Storage battery 12 Charge and discharge controller (charge and discharge control device) 21 DC link 22 Inverter

Claims

1. In a power storage system having a storage battery and connected to an inverter via a DC link, a method for controlling charging and discharging of the storage battery, comprising: measuring the voltage of the DC link; controlling the charging and discharging operations of the storage battery based on the measured voltage of the DC link and a command value of the voltage of the DC link; setting an upper limit value higher than the command value and a lower limit value lower than the command value; when the measured voltage of the DC link is higher than the upper limit value, causing the storage battery to perform a charging operation; when the measured voltage of the DC link is lower than the lower limit value, causing the storage battery to perform a discharging operation; when the measured voltage of the DC link is between the upper limit value and the lower limit value, causing the storage battery to perform a charging and discharging operation according to a charging and discharging current command value transmitted from outside the power storage system. A method for controlling charging and discharging of a power storage system, characterized by the above.

2. In a power storage system having a storage battery and connected to an inverter via a DC link, an apparatus for controlling charging and discharging of the storage battery, comprising: measuring the voltage of the DC link; performing the charging and discharging operations of the storage battery based on the measured voltage of the DC link and a command value of the voltage of the DC link; setting an upper limit value higher than the command value and a lower limit value lower than the command value; when the measured voltage of the DC link is higher than the upper limit value, causing the storage battery to perform a charging operation; when the measured voltage of the DC link is lower than the lower limit value, causing the storage battery to perform a discharging operation; when the measured voltage of the DC link is between the upper limit value and the lower limit value, causing the storage battery to perform a charging and discharging operation according to a charging and discharging current command value transmitted from outside the power storage system. A charging and discharging control apparatus, characterized by the above.

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