Power control device, power control system, and power control method

Abstract

To provide a power control device, a power control system, and a power control method which can restrict or stop output of a power generator to a power line by satisfying an output restriction condition under which a system voltage rise suppression function or overvoltage protection function of the power generator is actuated.SOLUTION: A power control device 10 controls a power storage device 20 which is connected in parallel with a power line 70 with a power generator 40 and a load 30. The power control device 10 controls a voltage value of a reference voltage waveform which is output to the power line 70 by the power storage device 20 so that an output restriction condition under which the power generator 40 restricts or stops output to the power line 70 is satisfied when a value representing a chargeable idle capacity of the power storage device 20 is a first threshold or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a power control device, a power control system, and a power control method.

Background Art

[0002] There is known a power generation system that coordinately controls both power conditioners so as to prioritize the output voltage suppression process by either the power conditioner of a photovoltaic power generation device or a fuel cell power generation device (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When operating power generation devices in coordination, surplus power may be charged to a power storage device for load following. It is required to control the output of the power generation devices.

[0005] An object of the present disclosure is to provide a power control device, a power control system, and a power control method that can limit or stop the output to a power line of a power generation device by satisfying output limit conditions under which a system voltage rise suppression function or an overvoltage protection function of the power generation device is activated.

Means for Solving the Problems

[0006] A power control device according to one embodiment of the present disclosure controls a power storage device connected in parallel to a power line together with a power generator and a load. When the value representing the rechargeable free capacity of the power storage device is less than or equal to a first threshold, the power control device controls the voltage value of the reference voltage waveform output by the power storage device to the power line so as to satisfy an output limiting condition that limits or stops the output of the power generator to the power line.

[0007] A power control system according to one embodiment of the present disclosure comprises a power control device, a power storage device, a power generation device, and a load. The power storage device, the power generation device, and the load are connected in parallel to a power line. The power control device controls the voltage value of a reference voltage waveform output by the power storage device to the power line. The power generation device is configured to limit or stop its output based on the voltage value of the reference voltage waveform. The power storage device charges surplus power when the power output by the power generation device is greater than the power consumed by the load.

[0008] In one embodiment of the present disclosure, a power control device that controls a power storage device connected in parallel to a power line together with a power generator and a load controls the voltage value of a reference voltage waveform output by the power storage device to the power line when the value representing the rechargeable available capacity of the power storage device is less than or equal to a first threshold, such that an output limiting condition is met for the power generator to limit or stop outputting to the power line. [Effects of the Invention]

[0009] According to a power control device, power control system, and power control method according to one embodiment of the present disclosure, the output of a power generator to the power line is limited or stopped by satisfying the output limiting conditions that trigger the grid voltage rise suppression function or overvoltage protection function of the power generator. [Brief explanation of the drawing]

[0010] [Figure 1] This block diagram shows an example configuration of a power control system according to one embodiment. [Figure 2] This graph shows an example of a reference voltage waveform. [Figure 3] This graph shows an example of the time variation of the amplitude of a reference voltage waveform. [Figure 4] This flowchart shows an example procedure for a power control method according to one embodiment. [Figure 5] This block diagram shows an example configuration of a power control system according to another embodiment. [Modes for carrying out the invention]

[0011] As shown in Figure 1, a power control system 1 according to one embodiment of the present disclosure comprises a power control device 10, a power storage device 20, a load 30, and a power generation device 40. The power control system 1 is connected to a power grid 80 and supplies power from the power grid 80 to the load 30 through a power line 70. The power storage device 20 and the power generation device 40 are connected in parallel to the power line 70. The power storage device 20 or the power generation device 40 may supply power to the load 30 when power is not supplied to the load 30 from the power grid 80. The power storage device 20 comprises a battery 22. The power control device 10 is included in the power storage device 20. The power control device 10 may be configured separately from the power storage device 20, as described in other embodiments below (see Figure 5). The power generation device 40 includes a photovoltaic power generation device. The power generation device 40 may include a fuel cell.

[0012] The power control system 1 continues to supply power to the load 30 by performing independent operation using the energy storage device 20 and the power generation device 40 when the power grid 80 experiences a power outage or when it is disconnected from the power grid 80 by the switch 82 and is unable to receive power from the power grid 80. The switch 82 may be actually installed between the power grid 80 and the power line 70, or it may be virtually installed.

[0013] When standalone operation is performed in the power control system 1, it is necessary to synchronize the frequency or phase of the terminal voltages of the energy storage device 20 and the power generation device 40 so that crosscurrents do not occur between the energy storage device 20 and the power generation device 40, or between multiple power generation devices 40. When the power generation device 40 is connected to the grid in synchronization with the standalone operation of the energy storage device 20, load tracking control becomes difficult. For example, when the solar power generation device, which is the power generation device 40, is performing MPPT (Maximum Power Point Tracking) operation, the power consumption of the load 30 may decrease. In other words, the power load may become lighter. When the power load becomes lighter, surplus power is generated in the power control system 1. However, when standalone operation is performed in the power control system 1, reverse power flow of the surplus power toward the power grid 80 is not performed. As a result, the power line 70 becomes overvoltage due to the surplus power. When the power line 70 becomes overvoltage, the power conditioner of the power generation device 40, such as the solar power generation device or fuel cell, connected to the power line 70 shuts down due to the overvoltage protection function. For example, if the voltage setting for the fuel cell's overvoltage protection function is lower than that of the solar power generation system, the fuel cell will also shut down even if the overvoltage is caused by the solar power generation system. Similarly, if the voltage setting for the energy storage device 20's overvoltage protection function is lower than that of the power generation device 40, the energy storage device 20 will also shut down. Furthermore, the power outage will cause the load 30 to shut down due to insufficient power.

[0014] The power control system 1 reduces surplus power to prevent overvoltage in the power line 70 during independent operation. For example, if the power generation device 40 is a fuel cell, the power control system 1 could reduce surplus power by controlling the fuel cell in load-following mode. However, it is desirable for fuel cells to operate at a constant output. Therefore, fuel cells are not suitable for load-following operation. Also, if the power generation device 40 is a solar power generation device, the power line 70 is prone to overvoltage when the load 30 is light, making it unsuitable for load-following operation. Alternatively, the power control system 1 can reduce surplus power by charging the energy storage device 20 with the surplus power from the power generation device 40. However, if there is little available capacity to charge the energy storage device 20, or if the energy storage device 20 is fully charged, the power control system 1 cannot charge the surplus power and therefore cannot reduce the surplus power.

[0015] Therefore, the power control system 1 according to this embodiment controls the power generator 40 based on the available capacity that the energy storage device 20 can charge, before the power generator 40 or the energy storage device 20 stops due to the overvoltage protection function. Specifically, during independent operation, the energy storage device 20 outputs a reference voltage waveform to the power line 70 that the power generator 40, which is connected to the power line 70, refers to. The reference voltage waveform is a waveform that the power generator 40 refers to so that it can synchronize its output. The power generator 40 is configured to output power to the power line 70 in synchronization with the reference voltage waveform. Furthermore, the power generator 40 is configured to suppress the rise in voltage of the power line 70 before the available capacity that the energy storage device 20 can charge becomes low by reducing the power output or stopping the power output based on the amplitude of the reference voltage waveform.

[0016] Hereinafter, as one embodiment of the present disclosure, a power control system 1 is described that can suppress or stop the output of the power generator 40 to the power line 70 by satisfying the output limiting conditions that activate the grid voltage rise suppression function or overvoltage protection function of the power generator 40.

[0017] (Example configuration of power control system 1) The following describes an example configuration of a power control system 1 according to one embodiment.

[0018] <Load 30> When power is supplied from the power grid 80 to the power line 70, Load 30 operates by the power supplied from the power grid 80. When power is not supplied from the power grid 80 to the power line 70, Load 30 operates by the power supplied from the power storage device 20 or the power generation device 40. When Load 30 operates with DC power, it may include a converter that converts the AC power supplied from the power line 70 into DC power.

[0019] <Power storage device 20> The power storage device 20 includes a storage battery 22. The storage battery 22 may be configured to include a secondary battery such as a lithium ion battery. The power storage device 20 includes a power conditioner (PCS: Power Conditioning System). It is assumed that the power conditioner of the power storage device 20 is a bidirectional inverter that converts DC power and AC power bidirectionally.

[0020] The power conditioner of the power storage device 20 draws in the AC power from the power line 70, converts it into DC power, and charges the storage battery 22. Also, the power conditioner of the power storage device 20 converts the discharge current of the storage battery 22 into AC power and supplies power to Load 30 through the power line 70. The power conditioner of the power storage device 20 may convert the discharge current of the storage battery 22 into AC power and perform reverse power flow to the power grid 80.

[0021] The power conditioner of the power storage device 20 has a terminal connected to the power line 70 and can control the waveform of the voltage output to the terminal. The voltage output by the power conditioner to the terminal is also referred to as the output voltage or terminal voltage of the power storage device 20. During independent operation when power is not supplied from the power grid 80 to the power line 70, the power generation device 40 controls its output to synchronize with the waveform of the output voltage of the power storage device 20. That is, the waveform of the output voltage of the power storage device 20 is used as the reference voltage waveform.

[0022] <Power generation device 40> In the power control system 1 according to this embodiment, the power generation device 40 includes a photovoltaic power generation device. The photovoltaic power generation device comprises a photovoltaic panel and a power conditioner. The power conditioner of the photovoltaic power generation device converts the DC power output by the photovoltaic panel into AC power and supplies power to the load 30 through the power line 70.

[0023] The power generation device 40 may include power generation devices that utilize other renewable energy sources such as wind power generation devices. The power generation device 40 may also include power generation devices such as fuel cells. The power generation device includes a power conditioner. The power conditioner of the power generation device converts the DC power output by the power generation device into AC power and supplies power to the load 30 through the power line 70.

[0024] Any surplus power output from the power generator 40 in excess of the power consumption of the load 30 may be output to the energy storage device 20 to charge it, or it may be reverse-flowed into the power grid 80.

[0025] The number of power generation devices 40 is not limited to one, but may be two or more. The number of power generation devices included in one power generation device 40 is not limited to one, but may be two or more.

[0026] The power generator 40 controls its output to prevent the power line 70 from becoming overvoltage. In the power control system 1 according to this embodiment, the power generator 40 has a voltage rise suppression function that suppresses the power output from the power generator 40 to the power line 70 in order to suppress a rise in the voltage of the power line 70. The power generator 40 also has an overvoltage detection function that stops the output of power to the power line 70 when it detects that the power line 70 has become overvoltage.

[0027] <Power control device 10> The power control device 10 obtains a value representing the available capacity that the energy storage device 20 can charge. This value is also called the available capacity value. The available capacity value may be expressed as, for example, the amount of energy that the energy storage device 20 can actually charge. The available capacity value may also be expressed as, for example, the remaining capacity percentage obtained by subtracting the State of Charge (SOC) of the energy storage device 20 from 100%. The available capacity value is not limited to these examples and may be expressed in various forms. During standalone operation, the power control device 10 controls the reference voltage waveform that the energy storage device 20 outputs to the power line 70 based on the available capacity value.

[0028] The power control device 10 may include at least one processor. The processor may include a CPU (Central Processing Unit). The processor can execute a program for controlling the energy storage device 20. The processor may be implemented as a single integrated circuit. An integrated circuit is also called an IC (Integrated Circuit). The processor may be implemented as a plurality of communicably connected integrated circuits and discrete circuits. The processor may be implemented based on various other known technologies.

[0029] The power control device 10 may include a storage unit. The storage unit may store various information or programs, etc. The storage unit may be composed of, for example, semiconductor memory. The storage unit may function as the processor's work memory. The storage unit may be included in the processor.

[0030] (Example of operation of power control system 1) In the event of a power outage in the power grid 80, or if the power grid 80 is not connected, the power control system 1 performs independent operation. The power control device 10 controls the energy storage device 20 to change the amplitude of the reference voltage waveform according to the available capacity that can be charged into the battery 22. As illustrated in Figure 2, the reference voltage waveform is output as a sine wave. The vertical axis in Figure 2 represents the voltage of the reference voltage waveform. The horizontal axis represents time. Figure 2 illustrates three types of reference voltage waveforms, each denoted as W0, W1, and W2. The amplitude of each reference voltage waveform is set to V0, V1, and V2. The amplitude of the waveform denoted as W0 and represented by a solid line is V0. The amplitude of the waveform denoted as W1 and represented by a dashed line is V1. The amplitude of the waveform denoted as W2 and represented by a dashed line is V2.

[0031] The power control device 10 does not need to limit the output from the generator 40 to the power line 70 when there is sufficient available capacity to charge the battery 22. In this case, the power control device 10 controls the energy storage device 20 so that it outputs a waveform with the sign W0 to the power line 70. In other words, the power control device 10 controls the energy storage device 20 so that the amplitude of the reference voltage waveform is V0 under normal circumstances. V0 is set to 101±6V when the standard voltage applied to the load 30 is 100V. V0 is set to 202±20V when the standard voltage applied to the load 30 is 200V.

[0032] <Output Limitations> When the available capacity of the energy storage device 20 is below a first threshold, the power control device 10 controls the voltage value of the amplitude of the reference voltage waveform output by the energy storage device 20 to the power line 70 so that the output limiting condition that the power generator 40 uses to limit output to the power line 70 is met. The output limiting by the power generator 40 may include setting the output to zero, i.e., stopping the output.

[0033] The output limiting condition includes the voltage value of the reference voltage waveform being equal to or greater than a first voltage value. The first voltage value is represented as V1 in the reference voltage waveform illustrated in Figure 2. The power control device 10 satisfies the output limiting condition by causing the energy storage device 20 to output a reference voltage waveform denoted as W1, thereby limiting the output of the power generator 40. That is, at the first voltage value (V1), the output is suppressed by the operation of the grid voltage rise suppression function. V1 is set as appropriate as part of the specifications of the power generator 40.

[0034] When the standard voltage applied to the load 30 is 100V, the power generator 40 is configured to limit its output when the voltage of the power line 70 exceeds the setting range of V0, which is 101±6V. Therefore, the first voltage value (V1) required to satisfy the output limiting condition is set to a value higher than the setting range of V0, which is 101±6V. Also, if the power generator 40 is equipped with an overvoltage relay (OVR), V1 is set to a value lower than the 110V to 120V range that is generally set as the voltage at which the OVR operates. Therefore, V1 may be set to, for example, 108V. Specifically, if the power generator 40 is a solar power generation system, setting the reference voltage waveform to W1 makes the first voltage value (V1) 108V, thus satisfying the output limiting condition. When the output limiting condition is met, the power conditioner of the solar power generation system activates the grid voltage rise suppression function and performs output suppression such as reducing the output power. Even when the standard voltage applied to the load 30 is 200V, V1 can be set appropriately.

[0035] The first threshold may be set, for example, as the lower limit of the region in which rapid charging of the battery 22 should be avoided. The first threshold may be set to any other value.

[0036] <Stop output> The power control device 10 controls the voltage value of the amplitude of the reference voltage waveform output by the energy storage device 20 to the power line 70 when the available capacity of the energy storage device 20 is below the second threshold, so that the output stop condition for the power generator 40 to stop outputting to the power line 70 is met. The second threshold is a lower value than the first threshold.

[0037] The output stop condition includes the voltage value of the reference voltage waveform becoming equal to or greater than the second voltage value. The second voltage value is represented as V2 in the reference voltage waveform illustrated in Figure 2. The power control device 10 satisfies the output stop condition by outputting a reference voltage waveform labeled W2 to the energy storage device 20, and can stop the output from the power generation device 40. In other words, at the second voltage value (V2), the output is stopped due to the activation of the overvoltage protection function. Note that in some cases, such as when a voltage rise occurs in a short period of time, the overvoltage protection function may activate before the grid voltage rise suppression function activates. V2 is set appropriately as per the specifications of the power generation device 40. V2 is set to a value higher than V1. Specifically, if the power generation device 40 is a solar power generation device, setting the reference voltage waveform to W2 results in a second voltage value (V2) of 111V, satisfying the output stop condition. The power conditioner of the solar power generation device, having satisfied the output stop condition, activates the overvoltage protection function and stops the output.

[0038] The power generator 40 is configured to shut down its output when the voltage of the power line 70 exceeds an overvoltage detection threshold higher than 107V, which is the upper limit of the setting range of V0. The overvoltage detection threshold is set to 110V, for example, the voltage at which the OVR operates. Therefore, the second voltage value (V2) required to satisfy the output shutdown condition is set to a value higher than the overvoltage detection threshold. Thus, V2 may be set to 111V, for example. Specifically, if the power generator 40 is a solar power generation system, setting the reference voltage waveform to W2 makes the second voltage value V2 111V, thus satisfying the output shutdown condition. The power conditioner of the solar power generation system, having satisfied the output shutdown condition, activates its overvoltage protection function and shuts down the output. Even when the standard voltage applied to the load 30 is 200V, V2 can be set appropriately.

[0039] The second threshold may be set to, for example, the value at which the battery 22 is fully charged. The second threshold may be set to any other value.

[0040] <Recovery of output> As described above, when the available capacity of the energy storage device 20 falls below the first threshold, the power control device 10 controls the voltage value of the reference voltage waveform output by the energy storage device 20 to the power line 70 so that the output limiting condition is met. After the output limiting condition is met, if the available capacity of the energy storage device 20 returns to a third threshold or higher, which is higher than the first threshold, the power control device 10 may return the amplitude of the voltage value of the reference voltage waveform output by the energy storage device 20 to V0 so that the output limiting condition is not met. When the output limiting condition is no longer met, the power generator 40 may output power without limiting the output according to the capacity of the power generator 40.

[0041] Furthermore, when the available capacity of the energy storage device 20 falls below the second threshold, the power control device 10 controls the voltage value of the reference voltage waveform output by the energy storage device 20 to the power line 70 so that the output stop condition is met. After the output stop condition is met, when the available capacity of the energy storage device 20 returns to above the fourth threshold, the power control device 10 may return the amplitude of the voltage value of the reference voltage waveform output by the energy storage device 20 to V0 so that the output limiting condition and the output stop condition are not met. The fourth threshold only needs to be less than the second threshold, and may be less than the first threshold or the third threshold, or may include the first threshold and the third threshold. When the output limiting condition and the output stop condition are no longer met, the power generator 40 may release the output stop and output according to the capacity of the power generator 40. The power generator 40 may restart when recovering output after stopping output due to the output stop condition being met.

[0042] The third threshold may be set such that the difference between the first threshold and the third threshold is greater than or equal to a predetermined value. If the third threshold is set to a value close to the first threshold, the output limiting and recovery based on the available capacity of the energy storage device 20 may be repeated frequently. Repeated limiting and recovery of the output destabilizes the operation of the power control system 1. By having the difference between the first threshold and the third threshold be greater than or equal to a predetermined value, the frequency of repeated limiting and recovery of the output is reduced. As a result, the operation of the power control system 1 can be made more stable.

[0043] <Switching between independent operation and grid-connected operation> As described above, the power control system 1 operates independently when the power grid 80 experiences a power outage or when it is not connected to the power grid 80. The power control system 1 may switch to grid-connected operation when the power grid 80 is restored or when it is connected to the power grid 80. The power control device 10 may be restarted when switching to grid-connected operation.

[0044] <Rate of change in the voltage value of the reference voltage waveform> The power control device 10 may change the amplitude of the voltage value of the reference voltage waveform over time, for example, as shown in Figure 3. In the graph in Figure 3, the vertical axis represents the amplitude of the voltage value of the reference voltage waveform, and the horizontal axis represents time.

[0045] In the graph of Figure 3, the amplitude of the reference voltage waveform changes from time T1, T2, and T3. The amplitude of the reference voltage waveform changes over a time represented by ΔT1 when changing from V0 to V1. The rate of change in amplitude when changing from V0 to V1 is represented by (V1-V0) / ΔT1. The amplitude of the reference voltage waveform also changes over a time represented by ΔT2 when changing from V1 to V2. The rate of change in amplitude when changing from V1 to V2 is represented by (V2-V1) / ΔT2. Furthermore, the amplitude of the reference voltage waveform changes over a time represented by ΔT3 when changing from V2 to V0. The rate of change in amplitude when changing from V2 to V0 is represented by (V0-V2) / ΔT3.

[0046] The power control device 10 may determine the rate at which it changes the amplitude of the voltage value of the reference voltage waveform based on the available capacity of the energy storage device 20. The power control device 10 may determine the rate at which it changes the amplitude of the voltage value of the reference voltage waveform according to the rate at which the available capacity of the energy storage device 20 changes after the available capacity of the energy storage device 20 falls below a first threshold or a second threshold. For example, when the battery 22 is being rapidly charged, the power control device 10 may suppress the decrease in the available capacity of the energy storage device 20 by rapidly increasing the amplitude of the voltage value of the reference voltage waveform.

[0047] <Example of a power control procedure> The power control device 10 may execute a power control method that includes, as an example, the procedure shown in the flowchart of Figure 4. The power control method may be executed as a power control program by the processor of the power control device 10. The power control program may be stored on a non-temporary computer-readable medium.

[0048] The power control device 10 obtains the available capacity value of the energy storage device 20 (step S1). The power control device 10 determines whether the available capacity value of the energy storage device 20 is less than or equal to a first threshold (step S2). If the available capacity value of the energy storage device 20 is not less than or equal to the first threshold (step S2: NO), the power control device 10 repeats the procedure for obtaining the available capacity value of the energy storage device 20 in step S1.

[0049] If the available capacity of the energy storage device 20 is below the first threshold (step S2: YES), the power control device 10 determines whether the available capacity of the energy storage device 20 is below the second threshold (step S3). If the available capacity of the energy storage device 20 is not below the second threshold (step S3: NO), the power control device 10 controls the amplitude of the voltage value of the reference voltage waveform so that the output limiting condition is met (step S4). If the available capacity of the energy storage device 20 is below the second threshold (step S3: YES), the power control device 10 controls the amplitude of the voltage value of the reference voltage waveform so that the output stop condition is met (step S5).

[0050] The power control device 10 may terminate the execution of the steps in the flowchart of Figure 4 after executing the procedure in step S4 or S5. After executing the procedure in step S4 or S5, the power control device 10 may return to the procedure in step S1 for obtaining the available capacity value of the energy storage device 20 and determine whether the available capacity value has returned to the third threshold or higher.

[0051] (summary) As described above, the power control device 10 according to this embodiment can limit or stop the output of the power generator 40 by controlling the energy storage device 20 to change the amplitude of the reference voltage waveform that the energy storage device 20 outputs to the power line 70. In this embodiment, the power control device 10 does not need to communicate with the power generator 40. Therefore, regardless of whether the power generator 40 has the capability to communicate with the power control device 10, the power control device 10 can limit or stop the output of the power generator 40. As a result, the functions of the power control device 10 according to this embodiment can be easily added to an existing power control system 1.

[0052] (Other embodiments) The following describes an example configuration of the power control system 1 according to another embodiment.

[0053] <Limitations due to insufficient voltage> In the embodiments described above, the power generator 40 is configured to limit its output when the amplitude of the voltage value of the reference voltage waveform becomes equal to or greater than a first voltage value, and to stop its output when the amplitude of the voltage value of the reference voltage waveform becomes equal to or greater than a second voltage value. In other words, the output limiting condition is that the amplitude of the voltage value of the reference voltage waveform becomes equal to or greater than a first voltage value. The output stopping condition is that the amplitude of the voltage value of the reference voltage waveform becomes equal to or greater than a second voltage value.

[0054] In another embodiment, the power generator 40 may be configured to stop outputting when the amplitude of the voltage value of the reference voltage waveform falls below a voltage drop threshold. In other words, the output stop condition may be that the amplitude of the voltage value of the reference voltage waveform falls below a voltage drop threshold. The voltage drop threshold is a threshold determined based on the specifications of the power generator 40.

[0055] The power generator 40 may be configured to shut down its output when the voltage of the power line 70 falls below an undervoltage detection threshold that is lower than 93V, which is the lower limit of the set range of V0. The undervoltage detection threshold is set to, for example, 90V, which is the voltage at which the UVR operates. Therefore, the voltage drop threshold (VL) required to satisfy the output shutdown condition is set to a value lower than the undervoltage detection threshold. Thus, VL may be set to, for example, 88V. Even when the standard voltage applied to the load 30 is 200V, VL can be set appropriately.

[0056] <Arrangement of power control device 10> As illustrated in Figure 5, the power control device 10 may be installed independently and not included in the energy storage device 20. The power control device 10 is communicated with the energy storage device 20 by wired or wireless communication, as shown by the dashed lines. The power control device 10 may also be communicated with the load 30 or the power generator 40. Even if the power control device 10 is not communicated with the load 30 and the power generator 40, it can prevent the power line 70 from becoming overvoltage by controlling the basic voltage waveform output by the energy storage device 20.

[0057] The diagrams illustrating the embodiments described herein are schematic. Dimensions and proportions shown in the drawings do not necessarily correspond to actual dimensions.

[0058] While embodiments relating to this disclosure have been described based on the drawings and examples, it should be noted that those skilled in the art can make various modifications or alterations based on this disclosure. Therefore, it should be noted that these modifications or alterations are within the scope of this disclosure. For example, the functions included in each component can be rearranged in a logically consistent manner, and multiple components can be combined into one or separated.

[0059] In one embodiment, (1) the power control device controls a power storage device connected in parallel to the power line together with the power generator and the load. When the value representing the rechargeable free capacity of the power storage device is less than or equal to a first threshold, the power control device controls the voltage value of the reference voltage waveform output by the power storage device to the power line so that the output limiting condition is met, which causes the power generator to limit or stop outputting to the power line.

[0060] (2) In the power control device described in (1) above, the output limiting condition may include the voltage value of the reference voltage waveform being equal to or greater than the first voltage value.

[0061] (3) The power control device described in (1) above may control the voltage value of the reference voltage waveform output by the energy storage device to the power line when the value representing the rechargeable available capacity of the energy storage device is less than or equal to the second threshold which is less than the first threshold, so that the output stop condition for the power generation device to stop outputting to the power line is met.

[0062] (4) In the power control device described in (3) above, the output stop condition may include the voltage value of the reference voltage waveform being equal to or greater than the voltage drop threshold.

[0063] (5) In the power control device described in (3) above, the output limiting condition may include the voltage value of the reference voltage waveform being less than or equal to a voltage drop threshold. The output stopping condition may include the voltage value of the reference voltage waveform being less than or equal to a second voltage value which is lower than the first voltage value.

[0064] (6) The power control device described in any one of (1) to (5) above may, after the output limiting condition has been met, control the voltage value of the reference voltage waveform output by the energy storage device to the power line so as not to satisfy the output limiting condition when the value representing the rechargeable free capacity of the energy storage device returns to a third threshold or greater than the first threshold.

[0065] (7) The power control device described in any one of (1) to (6) above may determine the rate at which the energy storage device changes the voltage value of the reference voltage waveform output to the power line based on a value representing the rechargeable available capacity of the energy storage device.

[0066] In one embodiment, (8) the power control system comprises a power control device described in any one of (1) to (7) above, a power storage device, a power generation device, and a load. The power storage device, the power generation device, and the load are connected in parallel to a power line. The power control device controls the voltage value of a reference voltage waveform output by the power storage device to the power line. The power generation device is configured to limit or stop its output based on the voltage value of the reference voltage waveform. The power storage device charges surplus power when the power output by the power generation device is greater than the power consumed by the load.

[0067] In one embodiment, (9) the power control method includes a power control device that controls a power storage device connected in parallel to the power line together with the power generator and the load, and when the value representing the rechargeable available capacity of the power storage device is less than or equal to a first threshold, the power control device controls the voltage value of the reference voltage waveform output by the power storage device to the power line so that an output limiting condition is met for the power generator to limit or stop outputting to the power line. [Explanation of Symbols]

[0068] 1. Power control system 10 Power control device 20. Energy storage devices (22: batteries) 30 load 40 Power generation equipment 70 Power lines 80 Power grid (82: Switches)

Claims

1. A power control device that controls a power storage device connected in parallel to the power line together with a power generator and a load, A power control device that, when the value representing the rechargeable available capacity of the energy storage device is less than or equal to a first threshold, controls the voltage value of the reference voltage waveform output by the energy storage device to the power line so as to satisfy the output limiting conditions that cause the power generator to limit or stop outputting to the power line.

2. The power control device according to claim 1, wherein the output limiting condition includes the voltage value of the reference voltage waveform being equal to or greater than a first voltage value.

3. The power control device according to claim 1, wherein when the value representing the rechargeable free capacity of the energy storage device is less than or equal to a second threshold which is less than the first threshold, the power control device controls the voltage value of the reference voltage waveform output by the energy storage device to the power line so that the output stop condition for the power generation device to stop outputting to the power line is met.

4. The output limiting condition includes the voltage value of the reference voltage waveform being equal to or greater than the first voltage value, The power control device according to claim 3, wherein the output stop condition includes the voltage value of the reference voltage waveform becoming a second voltage value or higher than the first voltage value.

5. The power control device according to claim 3, wherein the output stop condition includes the voltage value of the reference voltage waveform becoming less than or equal to a voltage drop threshold.

6. A power control device according to any one of claims 1 to 5, wherein, after the output limiting condition has been met, if the value representing the rechargeable free capacity of the energy storage device returns to a third threshold greater than the first threshold, the voltage value of the reference voltage waveform output by the energy storage device to the power line is controlled so that the output limiting condition is not met.

7. The power control device according to any one of claims 1 to 5, wherein the rate at which the energy storage device changes the voltage value of the reference voltage waveform output to the power line is determined based on a value representing the rechargeable available capacity of the energy storage device.

8. A power control device according to any one of claims 1 to 5, a power storage device, a power generation device, and a load, The energy storage device, the power generation device, and the load are connected in parallel to the power line. The power control device controls the voltage value of the reference voltage waveform output by the energy storage device to the power line. The power generation device is configured to limit or stop its output based on the voltage value of the reference voltage waveform. The energy storage device charges surplus power when the power output by the power generator is greater than the power consumed by the load. Power control system.

9. A power control method comprising: a power control device that controls a power storage device connected in parallel to a power line together with a power generator and a load, which controls the voltage value of a reference voltage waveform output by the power storage device to the power line when the value representing the rechargeable available capacity of the power storage device is less than or equal to a first threshold, such that an output limiting condition is met for the power generator to limit or stop outputting to the power line.

Images