Energy storage system

Abstract

This provides an energy storage system that can suppress fluctuations in the output power of a power conditioner. [Solution] The energy storage system A1 comprises a battery 1, a state monitoring unit 2 that monitors the charge state of the battery 1, and a power conditioner C1 that controls the charging and discharging of the battery 1 according to the magnitude of the charge state. The power conditioner C1 includes an inverter unit 3 to which the battery 1 is connected and which performs charging and discharging of the battery 1, and a control unit 4 that controls the inverter unit 3 so that the charge state is within a predetermined control range. When a predetermined suppression determination condition is met, the control unit 4 performs suppression control that prohibits an increase in the absolute value of the output power of the battery 1 in the change when the magnitude of the charge state changes in a direction that approaches the limit of the control range. The suppression determination condition includes a first condition in which the magnitude of the charge state output by the state monitoring unit 2 is within a charge state determination width set within the control range based on the limit of the control range.

Description

Technical Field

[0001] This disclosure relates to a power storage system.

Background Art

[0002] Conventionally, a power storage system including a storage battery and a power conditioner that charges and discharges the storage battery has been known. In such a power storage system, it is generally performed to control the charge / discharge power of the power conditioner according to the state of charge of the storage battery (for example, the magnitude of the state of charge (SoC)).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a power storage system, for example, as in Patent Documents Nos. 1 and 2, a function of correcting the SoC of a storage battery may be installed. When such an SoC correction function is installed, the SoC may change significantly each time the SoC correction function operates. In this case, a power conditioner that controls the charge / discharge power according to the magnitude of the SoC can significantly change the charge / discharge power (output power). Particularly near the upper limit or lower limit of the charge rate of the storage battery, charge / discharge may be restricted by overcharge protection, over-discharge protection, etc., and there is a risk that the output power of the power conditioner may vibrate. Such fluctuations in the output power of the power conditioner occur not only when controlling the charge / discharge power according to the state of charge (SoC) of the storage battery, but also when controlling the charge / discharge power according to a value corresponding to the state of charge of the storage battery (for example, charge current, charge voltage, etc.).

[0005] This disclosure was conceived in view of the above circumstances, and its purpose is to provide an energy storage system that can suppress fluctuations in the output power of a power conditioner. [Means for solving the problem]

[0006] The energy storage system provided by this disclosure includes a battery, a state monitoring unit for monitoring the charge state of the battery, and a power conditioner for controlling the charging and discharging of the battery according to the magnitude of the charge state, wherein the power conditioner includes an inverter unit to which the battery is connected and which charges and discharges the battery, and a control unit for controlling the inverter unit so that the charge state is within a predetermined control range, wherein the control unit performs suppression control to prohibit an increase in the absolute value of the output power of the battery when the magnitude of the charge state changes in a direction approaching the limit of the control range, and the suppression determination condition includes a first condition that the magnitude of the charge state output by the state monitoring unit is within a charge state determination width set within the control range with respect to the limit of the control range.

[0007] In a preferred embodiment of the energy storage system, the suppression determination condition includes, in addition to the first condition, a second condition that the output power of the storage battery is within a storage battery output determination range provided according to the output power, and the control unit performs the suppression control when both the first and second conditions are met.

[0008] In a preferred embodiment of the energy storage system, the control unit performs the suppression control during at least one of the following: charging operation, where the battery is charged; and discharging operation, where the suppression control during charging operation prohibits an increase in charging power to the battery, with the upper limit of the control range set as the limit of the control range; and during discharging operation, the suppression control prohibits an increase in discharge power from the battery, with the lower limit of the control range set as the limit of the control range.

[0009] In a preferred embodiment of the energy storage system, the charge state is the charge rate of the battery, and the control range is the range between the upper limit of the charge rate and the lower limit of the charge rate.

[0010] In a preferred embodiment of the energy storage system, the state monitoring unit includes a detection unit that detects a value indicating the charging state, a correction unit that corrects the detected value indicating the charging state, and an output unit that outputs a corrected value of the charging state if the correction unit corrects the value indicating the charging state, and outputs a detected value of the charging state detected by the detection unit if the correction unit does not correct the value indicating the charging state. [Effects of the Invention]

[0011] In the energy storage system of this disclosure, when the magnitude of the battery's charge state is within a charge state determination range set within the control range based on the limit value of the control range (for example, the range between the upper and lower limits of the charge state), the control unit prohibits the following: an increase in the absolute value of the battery's output power during a change in which the battery's charge state approaches the limit value of the control range. This makes it possible to suppress fluctuations in the battery's output power near the limit value of the battery's control range. Therefore, according to the energy storage system of this disclosure, fluctuations in the output power of the power conditioner can be suppressed. [Brief explanation of the drawing]

[0012] [Figure 1] A block diagram showing an energy storage system according to one embodiment. [Figure 2] This flowchart shows the charge and discharge control of the energy storage device (battery) performed by the control unit of the power conditioner in the energy storage system shown in Figure 1. [Figure 3] This figure shows the simulation results of suppression control during charging operation. [Figure 4] This figure shows the simulation results of suppression control during discharge operation. [Modes for carrying out the invention]

[0013] Preferred embodiments of the energy storage system of this disclosure will be described below with reference to the drawings. Hereafter, identical or similar components will be denoted by the same reference numerals, and redundant descriptions will be omitted.

[0014] Figure 1 shows an energy storage system A1 according to one embodiment. As shown in Figure 1, the energy storage system A1 comprises an energy storage device B1 and a power conditioner C1.

[0015] As shown in Figure 1, the energy storage system A1 may be connected to, for example, a power grid K and a load L. Unlike the illustrated example, the energy storage system A1 does not necessarily have to have a load L connected to it. The energy storage system A1 discharges the energy storage device B1 (battery 1 described later) by outputting the power stored in the storage device B1 (battery 1 described later) to at least one of the power grid K and the load L via the power conditioner C1. The energy storage system A1 also charges the energy storage device B1 (battery 1 described later) by outputting the power supplied from the power grid K to the storage device B1 (battery 1 described later) via the power conditioner C1. In the illustrated example, the power grid K is a three-phase AC power source. The load L consumes power supplied from the power conditioner C1 or the power grid K. The type of load L is not limited in any way. In a different example in Figure 1, the energy storage system A1 may be connected to a power generation system such as a solar power generation system.

[0016] The energy storage device B1 is connected to the power conditioner C1. The energy storage device B1 is capable of storing and releasing electricity. As shown in Figure 1, the energy storage device B1 includes a battery 1 and a state monitoring unit 2.

[0017] The storage battery 1 is a secondary battery that can perform repeated charge and discharge. The storage battery 1 is, for example, a lithium-ion battery, a nickel-hydrogen battery, a nickel-cadmium battery, a lead storage battery, or the like. The storage battery 1 may be a capacitor such as an electric double layer capacitor instead of a secondary battery. The storage battery 1 may be installed alone or may be mounted on an electric vehicle or the like. The storage battery 1 discharges (releases) the stored power and supplies DC power to the power conditioner C1. Further, the storage battery 1 stores (accumulates) the power supplied from the power conditioner C1.

[0018] The state monitoring unit 2 outputs the charging state of the storage battery 1 to the power conditioner C1. In the present embodiment, the state monitoring unit 2 monitors the state of charge (SoC) of the storage battery 1 as the charging state of the storage battery 1 and outputs it to the power conditioner C1. The state of charge is an index indicating the charging state of the storage battery 1, and is a percentage showing the ratio of the remaining charge to the capacity at full charge. The state of charge is calculated, for example, by integrating the charging current and the discharging current of the storage battery 1. Note that the calculation method of the state of charge is not limited. An upper limit value (for example, 95%, but not limited to this) and a lower limit value (for example, 5%, but not limited to this) are set for the state of charge. As shown in FIG. 1, the state monitoring unit 2 includes a detection unit 21, a correction unit 22, and an output unit 23.

[0019] The detection unit 21 detects a value indicating the charging state of the storage battery 1. In the present embodiment, the detection unit 21 detects the state of charge [%] of the storage battery 1 as a value indicating the charging state of the storage battery 1.

[0020] The correction unit 22 corrects the value (detection value) indicating the charging state detected by the detection unit 21. In the present embodiment, the correction unit 22 corrects the detection value of the state of charge of the storage battery 1 detected by the detection unit 21. The correction method by the correction unit 22 is not limited in any way, and well-known techniques (for example, the techniques described in Patent Documents 1 and 2) can be appropriately adopted.

[0021] The output unit 23 outputs a value indicating the state of charge of the storage battery 1. When correction is performed by the correction unit 22, the output unit 23 outputs the corrected value of the charge rate to the power conditioner C1. On the other hand, when correction by the correction unit 22 is not performed, the output unit 23 outputs the detected value of the charge rate detected by the detection unit 21 to the power conditioner C1.

[0022] The power conditioner C1 can be connected between the power storage device B1, the power system K, and the load L. The power conditioner C1 controls the charge and discharge of the storage battery 1 according to the state of charge of the storage battery 1. The power conditioner C1 performs power conversion between the power storage device B1, the power system K, and the load L. In this embodiment, conversion is performed between the DC power handled by the power storage device B1 (storage battery 1) and the three-phase AC power handled by the power system K and the load L. As shown in FIG. 1, the power conditioner C1 includes an inverter unit 3, a control unit 4, and a power sensor 5.

[0023] The inverter unit 3 is connected between the storage battery 1, the power system K, and the load L. The inverter unit 3 converts the AC power input from the power system K into DC power and outputs it to the storage battery 1. Thereby, the storage battery 1 is charged. Also, the inverter unit 3 converts the DC power input from the storage battery 1 into AC power and outputs it to the power system K or the load L. Thereby, the storage battery 1 is discharged.

[0024] The inverter unit 3 is composed of, for example, a PWM-controlled inverter. In this example, the inverter unit 3 is, for example, a full-bridge circuit including six switching elements. Transistors such as IGBTs (Insulated-Gate Bipolar Transistors), MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), and bipolar transistors are used as each switching element. The inverter unit 3 receives drive signals from the control unit 4 to each switching element, and each switching element switches (switches between on and off) in response to these drive signals, thereby converting between DC power and AC power. The inverter unit 3 may be a half-bridge circuit, for example, instead of a full-bridge circuit. The configuration of the inverter unit 3 is not limited to those described above.

[0025] The power sensor 5 detects the power output from the battery 1 to the inverter unit 3, that is, the output power of the battery 1. Hereinafter, the output power of the battery 1 may be referred to as "battery output". This battery output corresponds to the output power of the inverter unit 3 to the battery 1 (the output power of the power conditioner C1 to the battery 1). In this embodiment, when the detected value of the power sensor 5 (detected value of battery output) is positive, it is assumed that power is being supplied from the battery 1 to the inverter unit 3 (i.e., the battery 1 is discharging). On the other hand, when the detected value of the power sensor 5 (detected value of battery output) is negative, it is assumed that power is being supplied from the inverter unit 3 to the battery 1 (i.e., the battery 1 is charging). When the detected value of the power sensor 5 (detected value of battery output) is 0 (zero), the battery 1 is neither charging nor discharging. Note that the positive and negative signs of this battery output may be reversed. The power sensor 5 outputs the detected battery output value to the control unit 4. Hereafter, the absolute value of the battery output when it is a negative value will be referred to as "charging power," and the absolute value of the battery output when it is a positive value will be referred to as "discharging power." In other words, the magnitude of the charging power corresponds to the negative sign of the battery output value; for example, when the battery output is "-1kW," the charging power is "1kW."

[0026] The control unit 4 controls the inverter unit 3 so that the charge level of the battery 1 falls within a predetermined control range. The predetermined control range is defined as the range between the upper and lower limits of the charge level of the battery 1. In other words, the control unit 4 controls the inverter unit 3 so that the charge level of the battery 1 falls between the upper and lower limits of the charge level. The control unit 4 generates a drive signal to control the inverter unit 3 (the switching operation of each switching element). Then, by outputting the generated drive signal to the inverter unit 3 (the corresponding switching element), the control unit 4 controls the power conversion of the inverter unit 3. The control unit 4 controls the charging and discharging of the battery 1 by controlling the inverter unit 3 (controlling the power conversion). Hereinafter, the time when the battery 1 is being charged will be referred to as "charging operation," and the time when the battery 1 is being discharged will be referred to as "discharging operation."

[0027] In the energy storage system A1, the control unit 4 performs output control according to the charge level of the battery 1. In this output control, the control unit 4 receives the charge level of the battery 1 from the state monitoring unit 2 and sets a target value for the battery output according to the input charge level. Then, it controls the inverter unit 3 so that the battery output reaches the set target value. However, in this output control, if the suppression judgment conditions described later are met, the control unit 4 performs suppression control to limit the charging and discharging of the battery 1. This suppression control is a control that prohibits an increase in the absolute value of the output power of the battery 1 when the charge level (charge state) of the battery 1 changes in a direction that approaches the limit value of the control range. In this embodiment, the control unit 4 performs suppression control both during charging operation, when charging the battery 1, and during discharging operation, when discharging the battery 1. In the suppression control during charging operation, the control unit 4 uses the upper limit of the control range (i.e., the upper limit of the charge rate) as the limit of the control range, and when the charge rate of the battery 1 changes in a direction approaching the upper limit of the control range (i.e., a change that charges the battery 1), it prohibits an increase in the charging power to the battery 1 (power supplied to the battery 1). However, in the suppression control during charging operation, a decrease in the charging power to the battery 1 (power supplied to the battery 1) is not prohibited. On the other hand, in the suppression control during discharge operation, the control unit 4 uses the lower limit of the control range (i.e., the lower limit of the charge rate) as the limit of the control range, and when the charge rate of the battery 1 changes in a direction approaching the lower limit of the control range (i.e., a change that discharges the battery 1), it prohibits an increase in the discharge power from the battery 1 (power released from the battery 1). Furthermore, in the suppression control during discharge operation, a reduction in the discharge power from battery 1 (power released from battery 1) is not prohibited.

[0028] In this embodiment, the above-described suppression determination conditions include a first condition based on the charge rate (charge state) of the storage battery 1 and a second condition based on the output power of the storage battery 1. The control unit 4 determines that the suppression determination conditions have been met when both the first and second conditions are met, and executes suppression control.

[0029] The first condition is that the magnitude of the charge rate of the battery 1 input from the state monitoring unit 2 is within the range of the charge state determination width. The charge state determination width is set within the control range based on the limit value of the charge rate of the battery 1, and is defined, for example, between the limit value of the charge rate of the battery 1 and a limit threshold obtained by taking a predetermined margin from that limit value. Hereinafter, the charge state determination width during charging operation will be referred to as the "upper limit determination width," and the charge state determination width during discharging operation will be referred to as the "lower limit determination width." Also below, the limit threshold during charging operation will be referred to as the "upper limit charge state threshold," and the limit threshold during discharging operation will be referred to as the "lower limit charge state threshold."

[0030] In the suppression control during charging operation, the limit value of the control range is the upper limit of the control range (upper limit of the charge rate), and the aforementioned limit threshold (upper limit of the charge state threshold) is a value smaller by a predetermined margin from the upper limit of the charge rate. Therefore, the upper limit determination range (charge state determination range during charging operation) is the range defined between the upper limit of the charge rate and the upper limit of the charge state threshold. In other words, during charging operation, the first condition is satisfied if the magnitude of the charge rate of the battery 1 is between the upper limit of the charge rate and the upper limit of the charge state threshold. In this embodiment, the control unit 4 determines that the first condition is satisfied if the magnitude of the charge rate of the battery 1 is greater than or equal to the upper limit of the charge state threshold during charging operation.

[0031] In the suppression control during discharge operation, the limit value of the control range is the lower limit of the control range (lower limit of the charge rate), and the aforementioned limit threshold (lower limit threshold of the charge state) is a value that is larger than the lower limit of the charge rate by a predetermined margin. Therefore, the lower limit judgment range (charge state judgment range during discharge operation) is the range defined between the lower limit of the charge rate and the lower limit threshold of the charge state. In other words, during discharge operation, the first condition is satisfied if the magnitude of the charge rate of the battery 1 is between the lower limit of the charge rate and the lower limit threshold of the charge state. In this embodiment, the control unit 4 determines that the first condition is satisfied if the magnitude of the charge rate of the battery 1 is less than or equal to the lower limit threshold of the charge state during discharge operation.

[0032] The second condition is that the power (battery output) value detected by the power sensor 5 is within the range of the battery output determination range. The battery output determination range is set with 0 (zero) as the base value, and corresponds to the range defined between 0 (zero) and a set value obtained by taking a predetermined margin from 0 (zero). Hereinafter, the battery output determination range during charging operation will be referred to as the "charging power determination range," and the battery output determination range during discharging operation will be referred to as the "discharging power determination range." Also below, the set value during charging operation will be referred to as the "charging set value," and the set value during discharging operation will be referred to as the "discharging set value."

[0033] In the suppression control during charging operation, the aforementioned set value (charging set value) is a value smaller than 0 (zero) by a predetermined margin. Therefore, the charging power determination range (battery output determination range during charging operation) is defined as the range between 0 (zero) and the charging set value. In other words, during charging operation, the second condition is satisfied if the magnitude of the charging power is between 0 (zero) and the charging set value. In this embodiment, the control unit 4 determines that the second condition is satisfied when the magnitude of the charging power is greater than or equal to the charging set value (the magnitude of the battery output is greater than or equal to the charging set value and less than or equal to 0 (zero)) during charging operation.

[0034] In the suppression control during discharge operation, the aforementioned set value (referred to as the discharge set value) is a value greater than 0 (zero) by a predetermined margin. Therefore, the discharge power determination range (battery output determination range during discharge operation) is defined as the range between 0 (zero) and the discharge set value. In other words, during discharge operation, the second condition is satisfied if the magnitude of the discharge power is between 0 (zero) and the discharge set value. In this embodiment, the control unit 4 determines that the second condition is satisfied when the magnitude of the discharge power during discharge operation is less than or equal to the discharge set value (i.e., the magnitude of the battery output is greater than or equal to 0 (zero) and less than or equal to the discharge set value).

[0035] In addition to the inverter unit 3 and the control unit 4, the power conditioner C1 may also include a DC capacitor connected between the inverter unit 3 and the battery 1 to stabilize the battery output, a DC / DC converter connected between the inverter unit 3 and the battery 1, and a filter circuit connected between the inverter unit 3 and the power system K and the load L. It may also include a power sensor that detects the output power of the inverter unit 3 to the power system K and the load L.

[0036] Figure 2 is a flowchart showing the charge and discharge control of the energy storage device B1 (battery 1) performed by the control unit 4. The control unit 4 performs this repeatedly while the energy storage system A1 (power conditioner C1) is in operation.

[0037] First, the control unit 4 determines whether the energy storage system A1 is in charging or discharging operation (S101). For example, based on the detected value of the battery output input from the power sensor 5, the control unit 4 determines that it is in discharging operation when the battery output is a positive value, and determines that it is in charging operation when the battery output is a negative value. However, the method for determining whether it is in charging or discharging operation is not limited to this.

[0038] If it is determined in step S101 that charging is in progress, the control unit 4 then determines whether the charge rate of the battery 1 input from the state monitoring unit 2 is equal to or greater than the upper limit threshold for the charge state (S102). In other words, the control unit 4 determines whether the charge rate of the battery 1 is within the upper limit determination range and satisfies the first condition. If it is determined in step S102 that the charge rate of the battery 1 is equal to or greater than the upper limit threshold for the charge state (S102:YES), the control unit 4 then determines whether the battery output is equal to or greater than the charging set value (S103). In other words, the control unit 4 determines whether the battery output is within the charging power determination range and satisfies the second condition. If it is determined in step S103 that the battery output is equal to or greater than the charging set value (S103:YES), the control unit 4 determines that the suppression determination conditions during charging (both the first and second conditions) are met and executes suppression control during charging (S104). In the suppression control in step S104, the control unit 4 prohibits an increase in charging power (decrease in battery output) but does not prohibit a decrease in charging power (increase in battery output). If, in step S102, it is determined that the charge rate of battery 1 is below the upper limit threshold of the charge state (S102:NO), or if, in step S103, it is determined that the battery output is below the charging set value (S103:NO), the control unit 4 determines that the suppression judgment condition is not met and executes output control according to the charge rate of battery 1 (S105).

[0039] If it is determined in step S101 that discharge operation is in progress, the control unit 4 then determines whether the charge rate of the battery 1 input from the state monitoring unit 2 is below the lower limit threshold of the charge state (S106). In other words, the control unit 4 determines whether the charge rate of the battery 1 is within the lower limit determination range and satisfies the first condition. If it is determined in step S106 that the charge rate of the battery 1 is below the lower limit threshold of the charge state (S106:YES), the control unit 4 then determines whether the battery output is below the discharge setting value (S107). In other words, the control unit 4 determines whether the battery output is within the discharge power determination range and satisfies the second condition. If it is determined in step S107 that the battery output is below the discharge setting value (S107:YES), the control unit 4 determines that the suppression determination conditions during discharge operation (both the first and second conditions) are met and executes suppression control during discharge operation (S108). In the suppression control in step S108, the control unit 4 prohibits an increase in discharge power (an increase in battery output), but does not prohibit a decrease in discharge power (a decrease in battery output). If, in step S106, it is determined that the charge level of battery 1 is greater than the lower limit threshold of the charge state (S106:NO), or if, in step S107, it is determined that the battery output is greater than the discharge setting value (S107:NO), the control unit 4 determines that the suppression judgment condition is not met and executes output control according to the charge level of battery 1 (S109).

[0040] The control unit 4 controls the charging and discharging of the storage battery 1 by repeatedly performing the above processes. Note that the process shown in Figure 2 is just one example and is not limited thereto.

[0041] Next, the suppression control performed by the control unit 4 will be explained with reference to Figures 3 and 4. Figure 3 shows the simulation results of suppression control during charging operation, and Figure 4 shows the simulation results of suppression control during discharge operation. Figures 3(a) and 4(a) show the time change in the charge rate of the battery 1, with the horizontal axis being time and the vertical axis being the charge rate of the battery 1. Figures 3(b) and 4(b) show the time change in the battery output (output power of the battery 1), with the horizontal axis being time and the vertical axis being the battery output (output power of the power conditioner C1). In Figures 3(b) and 4(b), the thick dashed line represents the actual battery output, and the solid line represents the target value of the battery output set by output control according to the charge rate of the battery 1. Furthermore, in Figures 3(b) and 4(b), when the output power (battery output) of battery 1 is a positive value, battery 1 is discharging, and when the output power (battery output) of battery 1 is a negative value, battery 1 is charging. In the following explanation, the absolute value of the battery output when the battery output is a positive value is called "discharge power," and the absolute value of the battery output when the battery output is a negative value is called "charging power."

[0042] First, with reference to Figure 3, let's explain the suppression control during charging operation. As shown in Figure 3, from the start of the simulation until time t101, the charge rate of battery 1 is outside the range of the upper limit determination width (see Figure 3(a)), and the battery output is outside the range of the charging power determination width (see Figure 3(b)). In other words, neither the first nor the second condition is met (the suppression determination condition is not met), and suppression control is not executed. Therefore, from the start of the simulation until time t101, the control unit 4 sets a target for the battery output by output control according to the charge rate of battery 1 and charges battery 1. Here, from the start of the simulation until time t101, as battery 1 is charged, the charge rate of battery 1 gradually increases, so the battery output gradually increases (the charging power gradually decreases). Then, at time t101, as shown in Figure 3(b), the battery output falls within the range of the charging power determination width. On the other hand, at time t101, the charge level of battery 1 is still outside the upper limit judgment range, so the first condition is not met, and suppression control is not executed.

[0043] From time t101 to time t102, as shown in Figure 3(a), the charge level of battery 1 is outside the upper limit determination range. Therefore, suppression control is not performed, and the control unit 4 controls the battery output by output control according to the charge level of battery 1. Subsequently, at time t102, the charge level of battery 1 becomes within the upper limit determination range. However, the battery output has decreased compared to time t101 (although it has increased in terms of charging power), and is outside the charging power determination range. Therefore, at time t102, although the first condition is met, the second condition is not met, and thus suppression control is not performed here either.

[0044] Subsequently, at time t103, as shown in Figure 3(a), the charge level of battery 1 is within the upper limit determination range, and as shown in Figure 3(b), the battery output is within the charging power determination range. In other words, both the first and second conditions are met (the suppression determination conditions are met). Therefore, the suppression control prohibits an increase in the absolute value of the battery output when the charge level of battery 1 changes in a direction that brings it closer to the upper limit of the charge level. In other words, the suppression control prohibits an increase in charging power (decrease in battery output) when charging battery 1. However, from time t103 to time t104, as shown in Figure 3(b), the battery output is increasing (charging power is decreasing), so this change is not restricted by the suppression control. In other words, the battery output is controlled by output control according to the charge level of battery 1.

[0045] Subsequently, at time t104, as shown by the solid line in Figure 3(b), the output control according to the charge rate of battery 1 sets a target for battery output to reduce the battery output. However, at time t104, the first and second conditions are met (the suppression judgment conditions are met), so suppression control prevents the battery output from decreasing (the charging power from increasing). Note that between time t104 and time t106, as shown by the solid line in Figure 3(b), if only output control according to the charge rate of battery 1 is performed, there is a period when the battery output falls outside the range of the charging power judgment range (for example, at time t105). However, due to the suppression control at time t104, the battery output maintains the value at time t104 and is therefore within the range of the charging power judgment range. In other words, suppression control continues between time t104 and time t106.

[0046] Subsequently, from time t106 to time t107, the output control according to the charge rate of battery 1 targets increasing the battery output (decreasing the charging power) compared to the battery output at time t104. Therefore, the control unit 4 increases the battery output (decreases the charging power) according to this target. Thus, the battery output shown by the dashed line in Figure 3(b) changes in line with the target value of the battery output shown by the solid line in Figure 3(b). Then, at time t107, the charge rate of battery 1 reaches the upper limit of the charge rate of battery 1, so the battery output becomes 0 (zero).

[0047] Subsequently, as shown in Figure 3(a), when the charge rate of the battery 1 is corrected by the correction unit 22 at time t108, the charge rate of the battery 1 input to the control unit 4 changes instantaneously and significantly. Even after this charge rate correction, the charge rate of the battery 1 remains within the upper limit determination range, and the battery output remains within the charging power determination range. On the other hand, because the charge rate of the battery 1 has fallen from the upper limit of the charge rate, the output control according to the charge rate of the battery 1 changes its target to decrease the battery output (increase the charging power). However, from time t108 to time t109, both the first and second conditions are met, so suppression control prevents the change in the direction of decreasing the battery output (increasing the charging power). In other words, the state at time t108 continues, and the battery output is fixed as shown by the dashed line in Figure 3(b). Furthermore, from time t109 to time t110, the output control according to the charge rate of battery 1 changes the target to increase the battery output (decrease the charging power), but due to the suppression control, the battery output is greater than the target value in the output control according to the charge rate of battery 1 (the charging power is less than the target value in the output control according to the charge rate of battery 1), so the state at time t108 continues.

[0048] Subsequently, at time t110, the battery output falls outside the range of the charging power determination range. Therefore, since the second condition is not met after time t110, suppression control is not executed, and the battery output shown by the dashed line in Figure 3(b) changes in accordance with the target value of the battery output shown by the solid line in Figure 3(a). Note that after time t110, since the battery output is a positive value, battery 1 is being discharged, and the charge level of battery 1 is gradually decreasing. As described above, suppression control can be executed during charging operation.

[0049] Next, with reference to Figure 4, the suppression control during discharge operation will be explained. As shown in Figure 4, from the start of the simulation until time t201, the charge level of battery 1 is outside the lower limit judgment range (see Figure 4(a)), and the battery output is outside the discharge power judgment range (see Figure 4(b)). In other words, neither the first nor the second condition is met (the suppression judgment condition is not met), and suppression control is not executed. Therefore, from the start of the simulation until time t201, the control unit 4 sets a target for the battery output by output control according to the charge level of battery 1 and discharges battery 1. Here, from the start of the simulation until time t201, as the battery discharges, the charge level of battery 1 gradually decreases, so the battery output gradually decreases (the discharge power gradually decreases). Then, at time t201, as shown in Figure 4(b), the battery output becomes within the discharge power judgment range. On the other hand, at time t201, the charge level of battery 1 is still outside the lower limit of the judgment range, so the first condition is not met, and suppression control is not executed.

[0050] From time t201 to time t202, as shown in Figure 4(a), the charge level of battery 1 is outside the lower limit determination range. Therefore, suppression control is not performed, and the control unit 4 controls the battery output by output control according to the charge level of battery 1. Subsequently, at time t202, the charge level of battery 1 comes within the lower limit determination range. However, the battery output has increased compared to time t201 (it has increased in terms of discharge power), and is outside the discharge power determination range. Therefore, at time t202, although the first condition is met, the second condition is not met, and thus suppression control is not performed here either.

[0051] Subsequently, at time t203, as shown in Figure 4(a), the charge level of battery 1 is within the lower limit of the judgment range, and as shown in Figure 4(b), the battery output is within the discharge power judgment range. In other words, both the first and second conditions are met (the suppression judgment conditions are met). Therefore, the suppression control prohibits an increase in the absolute value of the battery output when the charge level of battery 1 changes in a direction that brings it closer to the lower limit of the charge level. In other words, the suppression control prohibits an increase in discharge power (increase in battery output) when discharging to battery 1. However, from time t203 to time t204, as shown in Figure 4(b), the battery output decreases (discharge power decreases), so this change is not restricted by the suppression control. In other words, the battery output is controlled by output control according to the charge level of battery 1.

[0052] Subsequently, at time t204, as shown by the solid line in Figure 4(b), the output control according to the charge level of battery 1 sets a target for battery output to increase the battery output. However, at time t204, the first and second conditions are met (the suppression judgment conditions are met), so the suppression control prevents the battery output from increasing (the discharge power from increasing). Note that between time t204 and time t206, as shown by the solid line in Figure 4(b), if only output control according to the charge level of battery 1 is performed, there is a period when the battery output falls outside the discharge power judgment range (for example, at time t205). However, due to the suppression control at time t204, the battery output maintains the value at time t204 and is therefore within the discharge power judgment range. In other words, the suppression control continues between time t204 and time t206.

[0053] Subsequently, from time t206 to time t207, the output control according to the charge rate of battery 1 targets a decrease in battery output (reduces discharge power) compared to the battery output at time t204. Therefore, the control unit 4 reduces the battery output (reduces discharge power) according to this target. Thus, the battery output shown by the dashed line in Figure 4(b) changes in line with the target value of battery output shown by the solid line in Figure 4(b). Then, at time t207, the charge rate of battery 1 reaches the lower limit of the charge rate of battery 1, so the battery output becomes 0 (zero).

[0054] Subsequently, as shown in Figure 4(a), at time t208, when the charge rate of battery 1 is corrected by the correction unit 22, the charge rate of battery 1 input to the control unit 4 changes instantaneously and significantly. Even after this charge rate correction, the charge rate of battery 1 remains within the lower limit determination range, and the battery output remains within the discharge power determination range. On the other hand, because the charge rate of battery 1 has risen above the lower limit of the charge rate, the output control according to the charge rate of battery 1 changes its target to increase the battery output (increase the discharge power). However, from time t208 to time t209, both the first and second conditions are met, so suppression control prevents the change in the direction of increasing the battery output (increasing the discharge power). In other words, the state at time t208 continues, and the battery output is fixed as shown by the dashed line in Figure 4(b). Furthermore, from time t209 to time t210, the output control according to the charge rate of battery 1 changes the target to reduce the battery output (reduce discharge power), but due to the suppression control, the battery output is smaller than the target value in the output control according to the charge rate of battery 1 (the discharge power is smaller than the target value in the output control according to the charge rate of battery 1), so the state at time t208 continues.

[0055] Subsequently, at time t210, the battery output falls outside the range of the discharge power determination range. Therefore, since the second condition is not met after time t210, suppression control is not executed, and the battery output shown by the dashed line in Figure 4(b) changes in accordance with the target value of the battery output shown by the solid line in Figure 4(a). Note that after time t210, since the battery output is a negative value, battery 1 is being charged, and the charge rate of battery 1 is gradually increasing. As described above, suppression control can be executed during discharge operation.

[0056] The operation and effects of energy storage system A1 are as follows:

[0057] In the energy storage system A1, the control unit 4 performs suppression control to prevent an increase in the absolute value of the battery output when the magnitude of the charge state of the battery 1 changes in a direction approaching the limit value of the charge state, provided that predetermined suppression determination conditions are met. The suppression determination conditions include a first condition in which the magnitude of the charge state of the battery 1 output by the state monitoring unit 2 is within the range of the charge state determination width set within the control range based on the limit value of the charge state. In the energy storage system A1 of this embodiment, the charge state of the battery 1 is the charge rate (SoC) of the battery 1. With this configuration, when the magnitude of the charge state (charge rate) of the battery 1 is within the range of the charge state determination width (charge rate determination width) set within the control range based on the limit value of the charge state (charge rate), the control unit 4 prevents an increase in the absolute value of the battery output when the charge state of the battery 1 changes in a direction approaching the limit value of the charge state. For example, in this embodiment, as described above, the charge rate of the battery 1 is used as the charge state of the battery 1. Therefore, when the charge rate of the battery 1 changes in a direction approaching the limit value (upper or lower limit) of the charge rate, an increase in the absolute value of the battery output during that change is prohibited. As a result, even when the charge state (charge rate) of the battery 1 is corrected, fluctuations in the battery output (output power of the battery 1) near the limit value (upper or lower limit) of the charge state of the battery 1 can be suppressed. Therefore, the energy storage system A1 can suppress fluctuations in the output power of the power conditioner C1. For this reason, the energy storage system A1 can reduce degradation associated with unnecessary fluctuations in the output power of the battery 1 or the power conditioner C1.

[0058] In the energy storage system A1, the suppression determination conditions include a first condition and a second condition in which the output power of battery 1 (battery output) is within the range of the battery output determination range established according to the battery output. Therefore, the control unit 4 determines that the suppression determination conditions are met and performs suppression control when both the first and second conditions are met. With this configuration, the second condition is met when the absolute value of the battery output (charging power or discharging power) is smaller than the size defined by the battery output determination range. Therefore, it is possible to suppress abrupt fluctuations in the absolute value of the battery output (charging power or discharging power) from a small state to a large state. For example, during charging operation, if the charge rate of battery 1 is near the upper limit (within the range of the upper limit determination range), and the charge rate of battery 1 is corrected downward, the control unit 4 sets a target value to rapidly increase the charging power by output control according to the charge rate. Even if the battery output is to be controlled by this target value, there is a possibility that the charging and discharging of battery 1 may be restricted for purposes such as overcharge protection of battery 1. In this case, the output power of power conditioner C1 may fluctuate. This is also true during discharge operation. Therefore, by adding the second condition as described above, fluctuations in the battery output near the limit value (upper or lower limit) of the charge state of battery 1 can be suppressed, and thus the energy storage system A1 can further suppress fluctuations in the output power of power conditioner C1.

[0059] In the energy storage system A1, suppression control is performed during both charging and discharging operations. With this configuration, fluctuations in output power that may occur when the charge level of battery 1 is corrected downwards near the upper limit, and fluctuations in output power that may occur when the charge level of battery 1 is corrected upwards near the lower limit, can be suppressed.

[0060] In the energy storage system A1, the state monitoring unit 2 includes a detection unit 21 that detects a value indicating the charging state, a correction unit 22 that corrects the detected value indicating the charging state, and an output unit 23 that outputs the corrected value of the charging state to the power conditioner C1 if the correction unit 22 corrects the value indicating the charging state, and outputs the detected value of the charging state detected by the detection unit 21 to the power conditioner C1 if the correction unit 22 does not correct the value indicating the charging state. With this configuration, in the energy storage device B1 (state monitoring unit 2), the detected value of the charge rate of the battery 1 is corrected, and the corrected charge rate of the battery 1 is output to the power conditioner C1. In other words, even if the charge rate of the battery 1 input to the power conditioner C1 changes abruptly, the above suppression control can suppress fluctuations in the output power of the power conditioner C1.

[0061] In the energy storage system A1, even if the suppression judgment condition is met, the control unit 4 does not prohibit (permits) the absolute value of the battery output changing in a direction that moves the magnitude of the charge rate (charge state) of the battery 1 away from the limit value of the charge rate (charge state). The magnitude of the charge rate (charge state) of the battery 1 tends to be corrected in a direction that moves away from the limit value of the charge rate (charge state) when it is near the limit value of the charge rate (charge state). Specifically, the charge rate of the battery 1 tends to be corrected downwards when it is near its upper limit, and upwards when it is near its lower limit. Therefore, when the magnitude of the charge rate (charge state) of the battery 1 is corrected, the output power of the power conditioner C1 may be changed in a direction that moves the charge rate (charge state) of the battery 1 closer to the limit value of the charge rate. Consequently, in suppression control, it is not necessary to prohibit the absolute value of the battery output changing in a direction that moves the magnitude of the charge state of the battery 1 away from the limit value of the charge state. In other words, the energy storage system A1 can avoid unnecessary limitations on the battery output. As a result, the energy storage system A1 can control the output according to the charge state of battery 1 while suppressing fluctuations in the output power of power conditioner C1.

[0062] In the above embodiment, an example was shown in which the charge rate of the battery 1 was used as the charge state of the battery 1. Unlike this example, in the energy storage system of this disclosure, information other than the charge rate, such as the voltage of the battery 1 (battery voltage) or the current of the battery 1 (battery current), may be used as the charge state of the battery 1, or multiple detection elements (such as charge rate, battery voltage, and battery current) may be combined. Since the battery voltage and battery current change according to the charge rate of the battery 1, these can also be used as the charge state of the battery 1. Note that the battery voltage increases as the charge rate of the battery 1 increases and decreases as the charge rate of the battery 1 decreases. The battery current decreases as the charge rate of the battery 1 increases and increases as the charge rate of the battery 1 decreases. In this configuration, the state monitoring unit 2 of the energy storage device B1 detects and corrects the battery voltage, battery current, etc., as the charging state and outputs it to the power conditioner C1. The control unit 4 of the power conditioner C1 then performs output control or suppression control according to the battery voltage, battery current, etc. In other words, in the energy storage system of this disclosure, the indicator showing the charging state of the battery 1 is not limited to the charge rate, but may be other indicators such as battery voltage or battery current. Furthermore, by combining multiple indicators such as the charge rate, battery voltage, and battery current as indicators showing the charging state of the battery 1, it becomes possible to further suppress fluctuations in the output power of the power conditioner C1 through more precise control.

[0063] In the above embodiment, the control unit 4 is shown to perform suppression control during both charging and discharging operations. Unlike this example, in the energy storage system of this disclosure, suppression control may be performed during either charging or discharging operations, but not both.

[0064] In the above embodiment, the suppression determination condition for executing suppression control includes a first condition and a second condition, and the control unit 4 is shown to execute suppression control when both the first and second conditions are met. Unlike this example, in the energy storage system of the present disclosure, the suppression determination condition may include only the first condition. In other words, in the energy storage system of the present disclosure, the control unit 4 may execute suppression control when the first condition is met. However, it is preferable for the suppression determination condition to include both the first and second conditions in order to suppress fluctuations in the output power of the power conditioner C1.

[0065] In the above embodiment, an example was shown in which the energy storage device B1 is equipped with a status monitoring unit 2. However, the status monitoring unit 2 may be provided in the power conditioner C1, or it may be provided in a device other than the energy storage device B1 and the power conditioner C1.

[0066] In the above embodiment, an example was shown where the power system K is a three-phase AC power source, but it is not limited to this, and the power system K may also be a single-phase AC power source. In this case, the power conditioner C1 performs the conversion between the DC power handled by the energy storage device B1 (storage battery 1) and the single-phase AC power handled by the power system K.

[0067] In the above embodiment, an example was shown in which the power conditioner C1 converts DC power from the energy storage device B1 (battery 1) side to AC power from the power system K side. However, the embodiment is not limited to this, and it is also possible to convert DC power to DC power. In this case, the power system K may be a DC power source, or a device that converts DC power to AC power may be provided between the power system K and the power conditioner C1.

[0068] The energy storage system relating to this disclosure is not limited to the embodiments described above. The specific configuration of each part of the energy storage system relating to this disclosure can be modified in various ways. [Explanation of symbols]

[0069] A1: Energy storage system, B1: Energy storage device, C1: Power conditioner, 1: Battery, 2: Status monitoring unit, 21: Detection unit, 22: Correction unit, 23: Output unit, 3: Inverter unit, 4: Control unit, 5: Power sensor

Claims

1. Storage batteries and A status monitoring unit that monitors the charging status of the aforementioned storage battery, A power conditioner controls the charging and discharging of the battery according to the magnitude of the charge state, Equipped with, The power conditioner includes an inverter unit to which the battery is connected and which charges and discharges the battery, and a control unit that controls the inverter unit so that the charging state is within a predetermined control range. The control unit, when a predetermined suppression determination condition is met, performs suppression control to prohibit an increase in the absolute value of the output power of the storage battery during a change in which the magnitude of the charge state changes in a direction approaching the limit of the control range. The suppression determination condition includes a first condition that the magnitude of the charge state output by the state monitoring unit is within a charge state determination width set within the control range based on the limit value of the control range, in an energy storage system.

2. The suppression determination condition includes, in addition to the first condition, a second condition that the output power of the storage battery is within a storage battery output determination range provided according to the output power. The energy storage system according to claim 1, wherein the control unit performs the suppression control when both the first and second conditions are met.

3. The control unit performs the suppression control during at least one of the following: charging operation for charging the battery and discharging operation for discharging the battery. In the suppression control during the charging operation, the upper limit of the control range is set as the limit of the control range, and the increase in charging power to the storage battery is prohibited. The energy storage system according to claim 1 or claim 2, wherein in the suppression control during the discharge operation, the lower limit of the control range is set as the limit of the control range, and an increase in the discharge power from the storage battery is prohibited.

4. The aforementioned charging state is the charge rate of the storage battery, The energy storage system according to claim 1 or claim 2, wherein the control range is the range between the upper limit of the charge rate and the lower limit of the charge rate.

5. The energy storage system according to claim 1 or 2, wherein the state monitoring unit includes a detection unit for detecting a value indicating the charging state, a correction unit for correcting the detected value indicating the charging state, and an output unit that outputs a corrected value of the charging state if the correction unit corrects the value indicating the charging state, and outputs a detected value of the charging state detected by the detection unit if the correction unit does not correct the value indicating the charging state.

Images