Distributed power system and method for controlling distributed power

Abstract

To provide a distributed power supply system and a method for controlling a distributed power supply with which it is possible to control the output change rate of the distributed power supply taking into account the inertia that corresponds to a grid structure or a grid situation and stabilize a power grid.SOLUTION: Provided is a distributed power supply system comprising a distributed power supply 20 that is capable of supplying the electric power generated by a renewable energy power generator such as a solar cell 22 to a power grid 30 and capable of delivering and receiving electric power between the power grid 30 and a power storage device 24 via a PCS 23. The distributed power supply system includes an output detection unit 31 that detects output from the distributed power supply 20 to the power grid 30, and an output monitoring control device 10 that controls the PCS 23 in accordance with the inertia of the power grid 30 on the basis of the output of the PCS 21 (solar cell 22), the detection value by the output detection unit 31, and the inertia of the power grid 30, so that the frequency variation of the power grid 30 falls within a permissible range when the output of the solar cell 22 changes suddenly, thereby adjusting the output change rate of the distributed power supply 20 to a prescribed value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a distributed power source system and a control method for a distributed power source, in which in a power system where a distributed power source including a renewable energy power generation facility and a power storage device is connected, when the output of the renewable energy power generation facility suddenly changes, the output of the power storage device is adjusted according to the inertia of the power system, so as to appropriately control the output change rate of the distributed power source and prevent fluctuations in the system frequency.

Background Art

[0002] Patent Documents 1 to 3 disclose technologies for stabilizing the voltage and frequency of a power system when the output of a distributed power source having a renewable energy power generation facility fluctuates.

[0003] In Patent Document 1, when the time change rate of the output current of a distributed power source exceeds a reference value due to changes in sunlight illumination or significant fluctuations in internal load, a charge / discharge control device and a DC / DC converter charge and discharge a secondary battery to suppress sudden changes in the output current of the distributed power source, thereby suppressing fluctuations in the system voltage. Also, in Patent Document 2, when the generated power of a solar cell panel constituting a distributed power source is below the reference power, a battery and an output-adjustable generator cooperate to compensate for the shortage of the reference power. Furthermore, in Patent Document 3, when the actual generated power of a distributed power source rises steeply, a power storage facility is charged via a power conversion system, or the output of the distributed power source is suppressed to control the change rate of the generated power within a predetermined range. When the actual generated power of the distributed power source drops steeply, the power storage facility is discharged via a power conversion system, or important equipment is operated in an energy-saving manner to control the change rate of the generated power within a predetermined range.

[0004] Here, power companies require power generation companies having a distributed power source equipped with a renewable energy power generation facility and a power storage device to control the charge / discharge amount of the power storage device to mitigate fluctuations in the output of the distributed power source. In other words, Figure 3 is a graph that conceptually illustrates measures to mitigate output fluctuations of distributed power sources, where a shows the output of distributed power sources before implementing output fluctuation mitigation measures, and b shows the output of distributed power sources after implementing output fluctuation mitigation measures. In order to make the fluctuations in the output of distributed power sources behave like b, power generators are required to suppress the rate of change in output (rate of change in output) to, for example, 1% or less per minute. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 3264137 (

[0016] to

[0027] , Figures 1, 3, 4, 6, etc.) [Patent Document 2] Japanese Patent Publication No. 5414082 (

[0051] to

[0056] , Figures 1 to 3, etc.) [Patent Document 3] Japanese Patent Publication No. 2021-136852 (

[0043] ,

[0059] , Figures 1, 2, etc.) [Overview of the project] [Problems that the invention aims to solve]

[0006] The output fluctuation mitigation measures shown in Figure 3 require maintaining a uniform rate of output change regardless of the grid configuration. This can lead to excessive suppression of power generation from distributed power sources, hindering the efficient use of generated electricity and potentially resulting in economic losses. Furthermore, Patent Documents 1 to 3 do not disclose any technology for controlling the output of distributed power sources while considering the system configuration and conditions, such as the inertia which differs depending on the power system configuration, or the case when a system becomes islanded due to a system fault.

[0007] Therefore, the problem to be solved by the present invention is to provide a distributed power system and a control method for distributed power sources that enable the stabilization of the power system by appropriately controlling the rate of change of output of distributed power sources, taking into account the inertia according to the system configuration and system conditions. [Means for solving the problem]

[0008] To solve the above problems, the distributed power system according to the present invention is a distributed power system that can supply power generated by a renewable energy power generation device to a power grid connected to a grid power source, and that can exchange power between the power grid and a power storage device via a power converter, An output detection means for detecting the power output from the distributed power source to the power grid, An output monitoring and control means adjusts the rate of change of the output of the distributed power source to a predetermined value by controlling the power converter in accordance with the inertia so that the frequency of the power system remains within an acceptable range when the output of the renewable energy power generation device changes abruptly, based on the output of the renewable energy power generation device, the output detection value by the output detection means, and the inertia of the power system, thereby adjusting the rate of change of the output of the distributed power source to a predetermined value, It is something that is provided.

[0009] Here, it is desirable that the output monitoring and control means control the power converter so that the rate of change of the output of the distributed power source is smaller than that under normal conditions when the grid power source is disconnected from the power grid and the inertia of the power grid decreases compared to normal conditions.

[0010] Furthermore, the distributed power source control method according to the present invention is a distributed power source control method that can supply the power generated by a renewable energy power generation device to a power grid connected to a grid power source, and can exchange power between the power grid and a power storage device via a power converter, Based on the power output from the distributed power source to the power grid, the output of the renewable energy power generation device, and the inertia of the power grid, the power converter is controlled according to the inertia so that the frequency of the power grid remains within an acceptable range when the output of the renewable energy power generation device changes abruptly, thereby adjusting the rate of change of the output of the distributed power source to a predetermined value. [Effects of the Invention]

[0011] According to the present invention, even when the output of renewable energy power generation equipment such as solar cells changes abruptly, the rate of change in the output of distributed power sources can be adjusted by controlling the charging and discharging amount of the energy storage device in accordance with the inertia of the power grid, thereby suppressing the frequency fluctuation amount of the power grid to below an acceptable level. Furthermore, even when the power grid configuration or conditions change, such as when an accident occurs in the power grid and an isolated grid is established, or during recovery from an accident, it is possible to stabilize the grid by appropriately controlling the rate of change in output of distributed power sources. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1(a) shows the overall configuration of the power system under normal conditions, and Figure 1(b) shows the operation of the embodiment of the present invention. [Figure 2] Figure 2(a) shows the overall configuration of the power system when the grid power supply is disconnected, and Figure 2(b) shows the timing chart illustrating the operation of the embodiment of the present invention. [Figure 3] This graph illustrates conventional measures to mitigate output fluctuations in distributed power sources. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described below with reference to the figures. Figure 1 shows the overall configuration of the power system under normal conditions (Figure 1(a)) and a timing chart illustrating the operation of this embodiment (Figure 1(b)).

[0014] In Figure 1(a), a grid power source 51 consisting of large-scale thermal power generators, etc., supplies AC power to the power grid 30 via circuit breakers 32. This power grid 30 has small-scale power sources 52 consisting of small-scale thermal power generators, diesel generators, etc., an AC load 40, and a distributed power source 20 connected in parallel to each other.

[0015] The distributed power source 20 includes a solar cell 22 as a renewable energy power generation facility, a PCS (Power Conditioning System) 21 that converts the DC output thereof into AC power and supplies it to the power grid 30, a power storage device 24, and a PCS 23 that is connected to the power grid 30 and controls the charging and discharging of the power storage device 24. As the renewable energy power generation facility, a wind power generation facility may be used instead of the solar cell 22 and the PCS 21.

[0016] The PCS 21 may be an inverter that converts the DC output of the solar cell 22 into AC power, and the PCS 23 may be an inverter that performs forward and reverse conversion (bidirectional power conversion) between the power storage device 24 and the power grid 30 to transfer power. That is, regardless of the name such as PCS, any power converter having the above functions may be used.

[0017] The AC outputs of the PCSs 21 and 23 are monitored by the output monitoring control device 10, and the operations of the PCSs 21 and 23 can be controlled by this output monitoring control device 10. Also, the output of the distributed power source 20 is detected by an output detection unit 31 provided at the connection point with the power grid 30, and the output detection value is monitored by the output monitoring control device 10. The output monitoring control device 10 may acquire the on / off information of the circuit breaker 32 to detect the occurrence of a system accident, or may acquire the occurrence information of a system accident from a higher-level system monitoring control device (not shown) that monitors and controls the entire power grid including the distributed power source 20.

[0018] The output monitoring control device 10 includes an arithmetic processing device such as a CPU that executes a predetermined program including the control program of the PCS 23, a memory, a communication interface, a display device, etc., based on the outputs of the PCSs 21 and 23, the output detection value by the output detection unit 31, the on / off information of the circuit breaker 32, etc. Note that the output monitoring control device 10 may be installed along with the power generation business operator having the distributed power source 20, or the higher-level system monitoring control device described above may be provided with the functions of the output monitoring control device 10.

[0019] Here, the output monitoring and control device 10 constantly monitors the output of the solar cell 22 (output of the PCS 21), and in the event of a sudden change in its output, it adjusts the charge and discharge amount of the energy storage device 24 in accordance with the inertia of the power grid 30 to appropriately control the rate of change of the output of the distributed power source 20, thereby suppressing fluctuations in the frequency of the power grid 30.

[0020] Next, the operation of this embodiment will be described. Figure 1(b) shows the operation under normal conditions when the power system 30 is healthy. As shown in Figure 1(b), for example, the output monitoring and control device 10 detects that the output of PCS21 has decreased sharply at time t1 due to a sudden decrease in solar radiation. In this case, the output monitoring and control device 10 recognizes that the power grid 30, which is supplied by the grid power 51 and the small-scale power 52, has a large inertia, and determines that even if the overall output of the distributed power 20 is rapidly reduced, the impact on the power grid 30 will be small.

[0021] Therefore, the output monitoring and control device 10 controls the PCS 23 so that the rate of change of the output detected by the output detection unit 31 is relatively large (allowing a sharp decrease in output), causing the output to rise linearly at time t1, and then sharply decrease to become 0 at time t2. During the period from time t1 to t2, the energy storage device 24 is discharged and the PCS 23 supplies AC power to the power grid.

[0022] Due to this operation, even if the output rate of the distributed power source 20 is large and decreases sharply during the period from time t1 to t2, the power system frequency will not fluctuate significantly due to the inertia of the power system 30 and will be suppressed to a value below the permissible level, thus there is no risk of the system becoming unstable. Needless to say, when adjusting the output rate of the distributed power source 20, a rate of change that can be achieved within the State of Charge (SOC) range of the energy storage device 24 should be considered. Furthermore, if the output of the distributed power supply 20 decreases linearly at time t1, but the grid frequency remains below an acceptable level, the output of the PCS 23 may be kept at 0 without changing it during the period from time t1 to t2.

[0023] Next, Figure 2 shows the overall configuration of the power system when the grid power supply is disconnected (Figure 2(a)) and a timing chart showing the operation of this embodiment (Figure 2(b)).

[0024] As shown in Figure 2(a), when an accident such as a ground fault occurs in the power system 30 and the circuit breaker 32 is turned off, the system power supply 51 is disconnected and the power system 30 becomes an islanding system, and its inertia decreases compared to normal conditions. In this state, for example, if the output monitoring and control device 10 detects that the output of PCS21 has decreased sharply at time t1 due to a sharp decrease in solar radiation, it is expected that a large voltage fluctuation will occur in the power system 30 in a short period of time, and the system frequency will fluctuate significantly, given the low inertia of the power system 30.

[0025] Therefore, the output monitoring and control device 10 monitors the values ​​detected by the output detection unit 31 and controls the output of the PCS 23 to rise linearly at time t1 and then gradually decrease to 0 at time t3, so that the rate of change of the output of the distributed power supply 20 becomes relatively small (gradually decreases) compared to normal conditions. In this case as well, during the period from time t1 to t3, the energy storage device 24 is discharged and AC power is supplied to the power grid by the PCS 23.

[0026] As a result of the above operation, even if the inertia of the power system 30 from which the grid power supply 51 has been disconnected is small, the output of the distributed power supply 20 decreases gradually during the period from time t1 to t3, as shown in Figure 2(b). Therefore, although the grid frequency fluctuates slightly, it is suppressed to a value below the permissible level, and there is no risk of the grid becoming unstable.

[0027] In Figures 1(b) and 2(b), the rate of change of output of the distributed power source 20 after time t1 may be calculated in advance and stored according to the inertia of the power system 30 during normal operation and when the grid power is disconnected, as well as the type and capacity of the distributed power source 20. If the output of the PCS 21 changes abruptly at time t1, the stored rate of change of output may be selected.

[0028] Furthermore, even if the output of PCS21 suddenly decreases and the system selects to reduce the rate of change of the output of the distributed power source 20 as shown in Figure 2(b), the output monitoring and control device 10 may switch to controlling the system to increase the rate of change of the output of the distributed power source 20 as shown in Figure 1(b) if the inertia of the power system subsequently recovers in a direction that increases (for example, if the circuit breaker 32 recloses after recovery from a system fault, or if the amount of energy stored in other energy storage devices connected to the power system 30 or the amount of power generated by pumped-storage hydroelectric generators, thermal power generators, etc. increases), or if it is confirmed that the deviation from the rated value of the system frequency or the rate of change of frequency has decreased and the fluctuation of the system frequency has fallen below an acceptable level. [Explanation of Symbols]

[0029] 10: Output monitoring and control device 20: Distributed power supply 21,23: PCS (Power Conditioning System) 22: Solar cells 24: Energy storage device 30: Power system 31: Output detection unit 32: Circuit breaker 40: Load 51: Grid power supply 52: Small-scale power supply

Claims

1. In a distributed power system comprising a distributed power source capable of supplying electricity generated by a renewable energy power generation device to a power grid connected to a grid power source, and capable of exchanging power between the power grid and a power storage device via a power converter, An output detection means for detecting the power output from the distributed power source to the power grid, An output monitoring and control means that recognizes the inertia according to the grid configuration and grid conditions of the power grid, and adjusts the output of the energy storage device via the power converter according to the inertia when the output of the renewable energy power generation device changes abruptly, based on the output of the renewable energy power generation device and the output detection value by the output detection means, thereby adjusting the rate of change of the output of the distributed power source to a predetermined value. A distributed power system characterized by having the following features.

2. In the distributed power supply system described in claim 1, The output monitoring and control means is A distributed power system characterized by controlling the power converter in accordance with the inertia so that the frequency of the power grid falls within an acceptable range when the output of the renewable energy power generation device drops sharply.

3. In the distributed power supply system described in claim 1 or 2, The output monitoring and control means is A distributed power system characterized by controlling the power converter so that the rate of change of the output of the distributed power source is smaller than that under normal conditions when the grid power source is disconnected from the power grid and the inertia of the power grid decreases compared to normal conditions.

4. In the distributed power supply system described in claim 3, The output monitoring and control means is A distributed power system characterized by controlling the power converter so as to restore the output rate of the distributed power source to its normal value when the inertia of the power system increases after the output rate of the distributed power source has been reduced to a normal value.

5. In the distributed power supply system described in claim 4, The output monitoring and control means is A distributed power system characterized by detecting an increase in the inertia of the power grid based on the restoration of the grid power supply, or an increase in the amount of energy stored in other energy storage devices connected to the power grid, or an increase in the amount of energy generated by a power generation means.

6. In the distributed power supply system described in claim 3, The output monitoring and control means is A distributed power system characterized by controlling the power converter to restore the output rate of the distributed power source to its normal value when the frequency of the power system falls within an acceptable range after the output rate of the distributed power source has been reduced to a value lower than that of the normal state.

7. A control method for a distributed power source that can supply the power generated by a renewable energy power generation device to a power grid connected to a grid power source, and can exchange power between the power grid and a power storage device via a power converter, A method for controlling a distributed power source, characterized by recognizing the inertia according to the grid configuration and grid conditions of the power grid, and adjusting the output of the energy storage device via the power converter according to the inertia when the output of the renewable energy power generation device changes abruptly, based on the power output from the distributed power source to the power grid and the output of the renewable energy power generation device, thereby adjusting the rate of change of the output of the distributed power source to a predetermined value.

8. In the method for controlling a distributed power source described in claim 7, A control method for a distributed power source, characterized by controlling the power converter in accordance with the inertia so that the frequency of the power grid falls within an acceptable range when the output of the renewable energy power generation device decreases sharply.

9. In the method for controlling a distributed power source according to claim 7 or 8, A method for controlling a distributed power source, characterized in that when the grid power source is disconnected from the power grid and the inertia of the power grid decreases compared to normal, the power converter is controlled to make the rate of change of the output of the distributed power source smaller than that of normal.

Images