Control device for battery unit

Abstract

To make a battery unit execute charge and discharge operations for stabilizing a DC link voltage and charge and discharge operations of prescribed charge and discharge power with a simple structure.SOLUTION: A current determination section 121 determines a current value for controlling a DC link voltage VDC according to a command value and a measured value thereof. The current restriction section 122 applies restriction on the current value determined by the current determination section 121 between an upper limit value and a lower limit value applied. By using the same value in the upper limit value and the lower limit value of the current, it is possible to output a current corresponding to prescribed charge and discharge power from a battery unit 10.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a control device for controlling charge and discharge, which is included in a battery unit.

Background Art

[0002] With the spread of distributed power generation devices such as solar power generation systems and wind power generation systems, the spread of power conditioner systems equipped with storage batteries has been progressing as a means for stabilizing the system and adjusting supply and demand, and also for preparing for long-term power outages due to disasters. And with the price reduction of battery units, the demand for using power conditioner systems including a plurality of battery units is increasing.

[0003] Patent Document 1 discloses a DC power supply system that stabilizes the voltage of a DC bus to which a DC power supply device is connected. In this DC power supply system, when the voltage supplied from a distributed power generation device to the DC bus drops from a predetermined voltage, a controller that controls a plurality of converters supplies power from one DC power supply device to the DC bus and supplies power from the DC bus to other DC power supply devices, and controls the converters.

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, the inverter of the power conditioner controls so that the voltage of the 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 system side, or when the power consumption of the load suddenly changes, it may become difficult to control the voltage of the DC link by the inverter.

[0006] To solve this problem, for example, the battery unit may be made to perform a charge / discharge operation for stabilizing the voltage of the DC link. However, in order to make the battery unit perform a charge / discharge operation for stabilizing the voltage of the DC link in addition to the charge / discharge operation of a predetermined charge / discharge power, its control becomes complicated.

[0007] An object of the present invention is to enable a battery unit to perform a charge / discharge operation for stabilizing a DC link voltage and a charge / discharge operation of a predetermined charge / discharge power by means of a control device having a simple configuration.

Means for Solving the Problem

[0008] In an aspect of the present invention, In a power conditioner system including a DC link, an inverter provided between the DC link and a commercial power system, and a controller, the a control device of a battery unit connected to a DC link includes performs charging and discharging of the battery unit according to a signal transmitted from the controller, and receives from the controller a current determination unit that determines a current value for controlling the DC link voltage based on a command value of the DC link voltage and a measured value of the DC link voltage, and a current limiting unit that receives an upper limit value and a lower limit value of the current and applies a limit between the received upper limit value and lower limit value to the current value determined by the current determination unit a limit value conversion unit that converts the upper and lower limit values of the charging and discharging power of the battery unit received from the controller into upper and lower limit values of current and sends them to the current limiting unit and is provided with.

[0009] According to this configuration, the current value for controlling the DC link voltage is determined by the current determination unit based on the command value and the measured value of the DC link voltage. Therefore, the battery unit can realize a charge / discharge operation for stabilizing the DC link voltage. Further, the current limiting unit applies a limit between the received upper limit value and lower limit value to the current value determined by the current determination unit. For this reason, for example, by using the current value corresponding to the charge / discharge power of the battery unit for both the upper limit value and the lower limit value of the current, a current corresponding to a predetermined charge / discharge power can be output from the battery unit. Therefore, with a simple configuration, the battery unit can be made to perform a charge / discharge operation for stabilizing the DC link voltage and a charge / discharge operation of a predetermined charge / discharge power. . In addition, when the same value is transmitted from the controller as the upper and lower limit values of the charging and discharging power of the battery unit, the current value corresponding to the charging and discharging power of the same value is used for both the upper limit value and the lower limit value in the current limiting unit. That is, the battery unit can output a current corresponding to a predetermined charging and discharging power.

Effect of the Invention

[0010] According to the present invention, with a simple configuration, it is possible to cause a battery unit to perform a charge / discharge operation for stabilizing a DC link voltage and a charge / discharge operation with a predetermined charge / discharge power.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2

Figure 3

Figure 4

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Figure 6

Figure 7

Modes for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail based on the drawings. The following description of the preferred embodiments is merely illustrative in nature and is not intended to limit the present invention, its scope of application, or its use.

[0013] (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 n rechargeable battery units 10-1, 10-2, …, 10-n (n is a positive integer). Hereinafter, the battery units 10-1, 10-2, …, 10-n may be collectively referred to as the battery unit 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 the DC power of the DC link 21 into AC power, and a controller 23 that controls the charge and discharge operations of the battery units 10 of the power storage system 1. The controller 23 is realized by, for example, a microcomputer including a processor and a memory. The unit controller 12 of each battery unit 10 includes a bidirectional DC / DC converter (not shown) and performs charge and discharge of the storage battery 11 according to a signal transmitted from the controller 23 of the power conditioner 2. Further, the unit controller 12 of each battery unit 10 includes a voltage sensor that measures the voltage VDC of the DC link.

[0014] 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 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.

[0015] The controller 3 of the power conditioner 2 calculates the charge and discharge power Pstorage of the power storage system 1 every 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 set as the charge power Pstorage of the power storage system 1. Also, when the output power PDER of the distributed power source 4 decreases due to the influence of weather conditions, etc., and is insufficient with respect to the output power PAC of the power conditioner 2, the insufficient power is set as the discharge power Pstorage of the power storage system 1.

[0016] Further, the inverter 22 of the power conditioner 2 controls the voltage VDC of the DC link 21 so as to be stabilized. However, for example, when receiving an instruction of power limitation from the commercial power system side or when the power consumption of the load suddenly fluctuates, it may be difficult to control the voltage VDC of the DC link 21.

[0017] Therefore, in this embodiment, the power storage system 1 including a plurality of battery units 10 is configured to control the voltage VDC of the DC link 21. Thereby, 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, the voltage VDC of the DC link 21 can be made more stable.

[0018] However, if the voltage VDC of the DC link 21 is controlled for all the battery units 10 included in the power storage system 1, the following problems occur. That is, the values of the voltage VDC measured by each battery unit 10 may be slightly different, and there may be a measurement error in the voltage sensor of each battery unit 10. For this reason, there may be a situation where the battery units 10 that try to increase the voltage VDC of the DC link 21 and the battery units 10 that try to decrease it are mixed, and charge and discharge may occur between the battery units 10.

[0019] Also, regarding the power storage system 1 having a plurality of battery units 10, in order to stably exhibit its charge and discharge capacity for a longer period, it is necessary to appropriately manage the charge and discharge power assigned to each battery unit 10. For example, when the SOC (State Of Charge) of each battery unit 10 is different, it is preferable to assign the charge and discharge power to each battery unit 10 so that the SOC converges at the same timing.

[0020] Therefore, in the present embodiment, as shown in FIG. 2, at least one battery unit 10 for controlling the voltage VDC of the DC link 21 is selected from among the plurality of battery units 10. In FIG. 2, the battery unit 10-1 is selected as the battery unit for controlling 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, when the voltage VDC of the DC link 21 is higher than a predetermined reference value, the battery unit 10-1 performs a charging operation, and when the voltage VDC of the DC link 21 is lower than the predetermined reference value, the battery unit 10-1 performs a discharging operation. On the other hand, predetermined charge / discharge power is assigned to the other battery units 10-2 to 10-n.

[0021] Thereby, the voltage VDC of the DC link 21 can be made more stable, and for the power storage system 1 having a plurality of battery units 10, the charge / discharge ability can be stably exhibited for a longer period. Such charge / discharge control of the battery unit 10 is executed by the controller 23 every cycle in which the charge / discharge power Pstorage of the power storage system 1 is calculated.

[0022] 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 in 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 from this comparison result. The current value represented by the current command X indicates a discharging operation for a positive value and a charging operation for a negative value. The measured value is obtained by a voltage sensor provided in the unit controller 12. The command value is transmitted from the controller 23.

[0023] The current limiting unit 122 applies limits to this current command X on the discharge side (upper limit) and the charge side (lower limit) respectively. The charge and discharge current of the battery unit 10 is controlled by the current command K after being limited by the current limiting unit 122. The limit value conversion unit 123 converts the upper limit value and the lower limit value of the charge and discharge power of the battery unit 10 received from the outside into the upper limit value and the lower limit value of the current, and supplies them to the current limiting unit 122. Here, the upper limit value and the lower limit value of the charge and discharge power of the battery unit 10 are transmitted from the controller 23.

[0024] The control scheme of FIG. 3 can easily realize not only the control of the voltage VDC of the DC link 21 but also the control of charging and discharging a predetermined power to and from the battery unit 10. That is, as shown in FIG. 4, by setting the upper limit value and the lower limit value in the current limiting unit 122 to the same current value, the current command K after being limited can be set to that current value. Specifically, (a) when discharging to the battery unit 10, the upper limit value and the lower limit value in the current limiting unit 122 are set to the same positive value, and (b) when charging the battery unit 10, the upper limit value and the lower limit value in the current limiting unit 122 may be set to the same negative value.

[0025] That is, the controller 23 transmits a positive power value as the upper limit of the power value and a negative power value as the lower limit of the power value to the unit controller 12 of the battery unit 10 that controls the voltage VDC of the DC link 21. The limit conversion unit 123 converts the received upper limit and lower limit of the power value into the upper limit and lower limit of the current value, and supplies 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 value as the upper limit and lower limit of the power value when discharging, and the same negative power value as the upper limit and lower limit of the power value when charging. The limit conversion unit 123 converts the received power value into a current value and supplies it to the current limiting unit 122. Thereby, a current command K indicating the current corresponding to the same power value is output from the current limiting unit 122. That is, a predetermined power can be charged and discharged to and from the other battery units 10.

[0026] Therefore, according to the control scheme of FIG. 3, with a simple configuration, the battery unit 10 can be made to perform a charge / discharge operation for stabilizing the voltage VDC of the DC link 21 and a charge / discharge operation with a predetermined charge / discharge power.

[0027] FIG. 5 is a flowchart showing an example of the processing of the controller 23. The controller 23 executes the processing of FIG. 5 every 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 powers of each battery unit 10 included in the power storage system 1.

[0028] 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, let the allocated power be Passign-i (where i is an integer from 1 to n and corresponds to the battery units 10-1 to 10-n).

[0029] As methods for this power allocation, various methods can be considered. For example, power is allocated so that the SOC (State Of Charge) of each battery unit 10 gradually approaches equality. That is, when PSTORAGE is a positive value, i.e., discharge power, a large discharge power is allocated to the battery unit 10 with a large SOC, and a small discharge power is allocated to the battery unit 10 with a small SOC. Also, when PSTORAGE is a negative value, i.e., charge power, a small charge power is allocated to the battery unit 10 with a large SOC, and a large charge power is allocated to the battery unit 10 with a small SOC. Also, as other power allocation methods, a method using the SOH (State Of Health) of each battery unit 10, a method using the current charge / discharge power of each battery unit 10, or a method using a combination of SOC, SOH, and the current charge / discharge power can be considered.

[0030] 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). Various selection methods can be considered for this. 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 the battery unit k. Alternatively, a battery unit 10 with an SOC close to 50%, that is, a remaining capacity that is not too large and not too small, may be selected as the battery unit k. Alternatively, the power Passign-i assigned in step S12 may be used. Specifically, for example, the battery unit 10 with the smallest absolute value of the power Passign-i assigned in step S12 may be selected as the battery unit k.

[0031] Alternatively, it may be configured to avoid frequent changes to the battery unit k. Specifically, for example, the selection of the battery unit k may be performed every multiple cycles.

[0032] 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 the upper and lower limit values of the current by the limit conversion unit 123. Using these upper and lower limit values of the current, the current command is limited in the current limiting unit 122. As a result, the battery unit k can perform a charge / discharge operation for controlling the voltage VDC of the DC link 21.

[0033] Further, the controller 23 transmits the power Passign-i assigned in step S12 to the battery unit 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., during 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. Thereby, the battery unit 10 can discharge the assigned power Passign-i. When the power Passign-i is a negative value, i.e., during 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. Thereby, the battery unit 10 can charge the assigned power Passign-i.

[0034] Figure 6 is a graph showing the results of an experiment using the method of this embodiment. In this experiment, a power storage system including two battery units (unit 1, unit 2) was used. Unit 1 was selected as the battery unit for controlling the voltage VDC of the DC link 21, and the load consumption power Pload was varied to plot the changes in the powers Punit-1 and Punit-2 of units 1 and 2. From Figure 6, it can be seen that when the load consumption power Pload changes, the power Punit-1 of unit 1 changes steeply. This steep change corresponds to the rapid change in the voltage VDC of the DC link 21.

[0035] As described above, according to this 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 made to execute a charge / discharge operation for stabilizing the voltage VDC of the DC link 21. Thereby, even when it becomes difficult to control the voltage VDC of the DC link 21 by the inverter 22, the voltage VDC of the DC link 21 can be stabilized by the charge / discharge operation of the battery unit 10-1. Also, a predetermined charge / discharge power is assigned to the other battery units 10-2 to 10-n. Thereby, the charge / discharge power of the entire power storage system 1 can be appropriately managed. Therefore, for the power storage system 1 including the plurality of battery units 10, charge / discharge control for stabilizing the voltage VDC of the DC link 22 can be realized.

[0036] Also, in this embodiment, the total charge / discharge power PSTORAGE to be assigned to the power storage system 1 is calculated, and this total charge / discharge power PSTORAGE is divided and assigned to each battery unit 10. Then, a battery unit 10 that executes a charge / discharge operation for stabilizing the voltage VDC of the DC link 21 is selected from among the plurality of battery units 10. By such processing, while appropriately managing the charge / discharge power of the entire power storage system 1, the voltage VDC of the DC link 21 can be stabilized.

[0037] Also, in this embodiment, a battery unit 10 that executes a charge / discharge operation for stabilizing the voltage VDC of the DC link 21 is selected using at least one of the power capacity or the SOC of each battery unit. Thereby, a battery unit 10 that executes a charge / discharge operation for stabilizing the voltage VDC of the DC link 21 can be appropriately selected.

[0038] Also, according to the control scheme of FIG. 3, the battery unit 10 can perform a charge / discharge operation for stabilizing the voltage VDC of the DC link 21 and a charge / discharge operation with a predetermined charge / discharge power with a simple configuration.

[0039] Also, when the voltage VDC of the DC link 21 changes significantly, it may not be possible to appropriately control the voltage VDC only with the selected battery unit 10. Considering such a case, when the change in the voltage VDC of the DC link 21 is drastic, the unselected battery unit 10 may be made to control the voltage VDC.

[0040] FIG. 7 is a flowchart showing an operation example of the unit controller 12. As shown in FIG. 7, the unit controller 12 receives the assigned power Passign-i from the controller 23 as the upper limit value and the lower limit value of the power (S21). Then, the power Passign-i is converted into the upper limit and the lower limit of the current value (S22). These operations are as described above.

[0041] Then, the unit controller 12 determines whether the voltage VDC of the DC link 21 exceeds a predetermined upper limit value or is below a predetermined lower limit value (S23). And when the voltage VDC is between the upper limit value and the lower limit value (NO in S23), the setting of the upper limit and the lower limit of the current value is not changed. On the other hand, when the voltage VDC exceeds the upper limit value or is below the lower limit value (YES in S23), the upper limit and the lower limit of the rated current are set as the upper limit and the lower limit of the current value (S24). By this setting change, the battery unit 10 can perform a charge / discharge operation for controlling the voltage VDC of the DC link 21 despite being assigned the power Passign-i. Therefore, the voltage VDC of the DC link 21 can be made more stable.

[0042] In the above description, the battery unit 10 that performs the charge and discharge operation to control the voltage VDC of the DC link 21 is assumed to be one, but this is not limited to one. Two or more battery units 10 may be selected to perform the charge and discharge operation to control the voltage VDC of the DC link 21.

[0043] (Modification example) In the control scheme shown in FIG. 3, the limit value conversion unit 123 may be omitted. In this case, the controller 23 provided in the power conditioner 2 may have a function corresponding to the limit value conversion unit 123. That is, the controller 23 converts the upper limit value and the lower limit value of the charge and discharge power of the battery unit 10 into the upper limit value and the lower limit value of the current, and transmits them to the unit controller 12. The unit controller 12 receives the upper limit value and the lower limit value of the current, and the current limiting unit 122 uses the received upper limit value and the lower limit value of the current to limit the current command X.

[0044] Also according to this modification example, by using the current value corresponding to the charge and discharge power of the battery unit 10 for both the upper limit value and the lower limit value of the current value, a current corresponding to a predetermined charge and discharge power can be output from the battery unit 10. Therefore, with a simple configuration, the battery unit 10 can be made to execute the charge and discharge operation for stabilizing the voltage VDC of the DC link 21 and the charge and discharge operation with a predetermined charge and discharge power.

Industrial applicability

[0045] The present invention is useful for making the DC link voltage more stable in a power conditioner system including a battery unit.

Explanation of symbols

[0046] 1 Power 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 Limitation Unit 123 Limitation Conversion Unit

Claims

In a power conditioner system including a DC link, an inverter provided between the DC link and a commercial power system, and a power conditioner having a controller, a control device for a battery unit connected to the DC link, wherein the control device executes charging and discharging of the battery unit according to a signal transmitted from the controller; a current determination unit that determines a current value for controlling the DC link voltage based on a commanded value of the DC link voltage received from the controller and a measured value of the DC link voltage; a current limiting unit that receives an upper limit value and a lower limit value of the current and applies a limit between the received upper limit value and lower limit value to the current value determined by the current determination unit; and a limit value conversion unit that converts an upper limit value and a lower limit value of the charging and discharging power of the battery unit received from the controller into an upper limit value and a lower limit value of the current and sends them to the current limiting unit. A control device for a battery unit, characterized by the above.

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