Microgrid system, energy storage system, and control method

Abstract

Disclosed are a microgrid system, an energy storage system, and a control method. The microgrid system is used for connecting to a mains power system, and is used for operating in a microgrid mode when the mains power system is not supplying power. The microgrid system comprises a renewable energy power generation system and the energy storage system. When the microgrid system operates in the microgrid mode, the energy storage system is used for outputting a control voltage containing a control frequency to the renewable energy power generation system, so that the renewable energy power generation system adjusts, according to the control frequency, the renewable energy output power outputted by the renewable energy power generation system.

Description

Microgrid system, energy storage system and control method Technical Field

[0001] The present disclosure relates to a microgrid system, an energy storage system, and a control method, and more particularly to a microgrid system, an energy storage system, and a control method for power dispatching. Background Art

[0002] Currently, power generation technology is primarily based on centralized power generation, where power companies provide central power generation. However, when a power company's central power generation fails, users are left with no power and can only wait for power to be restored.

[0003] Many technologies have been proposed to address these issues, including energy storage batteries, or using solar generators or other renewable energy auxiliary power generation systems to assist in power generation. However, energy storage batteries will eventually run out of power, so a method of charging energy storage batteries using solar cells has been proposed.

[0004] However, the above method also has its problems. When the energy storage battery and the solar cell cannot communicate with each other, how to control the output power of the solar cell to achieve a balance between the solar cell, the energy storage battery and the load is one of the problems to be solved.

[0005] Summary of the Invention

[0006] To address the aforementioned issues, the present disclosure provides a microgrid system for connecting to a utility power system and operating in microgrid mode when the utility power system is unavailable. The microgrid system includes a renewable energy generation system and an energy storage system. When the microgrid system operates in microgrid mode, the energy storage system outputs a control voltage including a control frequency to the renewable energy generation system, so that the renewable energy generation system adjusts the renewable energy output power according to the control frequency.

[0007] The present disclosure also proposes an energy storage system that, together with a renewable energy generation system, forms a microgrid system. When the mains power system is not supplying power, the microgrid system operates in microgrid mode. The energy storage system includes an energy storage battery and an integration device. The energy storage battery is used to output a DC voltage in microgrid mode. The integration device is coupled to the energy storage battery. The integration device includes a DC-AC converter and a controller. The DC-AC converter is coupled to the energy storage battery to convert the DC voltage into a control voltage and transmit the control voltage to the renewable energy generation system. The control voltage includes a control frequency. The controller is coupled to the DC-AC converter. In microgrid mode, the controller is used to adjust the control frequency so that the renewable energy generation system adjusts the renewable energy output power output by the renewable energy generation system according to the control frequency.

[0008] This disclosure also provides a control method applicable to a microgrid system, connected to a utility power system and configured to operate in microgrid mode when the utility power system is unavailable. The microgrid system includes an energy storage system and a renewable energy generation system. The control method comprises the following steps: the energy storage system outputs a control voltage including a control frequency to the renewable energy generation system; and the renewable energy generation system adjusts the renewable energy output power of the renewable energy generation system based on the control frequency to achieve power balance in the microgrid system.

[0009] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the disclosure as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] To make the above and other objects, features, advantages and embodiments of the present disclosure more apparent and understandable, the following descriptions of the accompanying drawings are provided:

[0011] FIG1 is a schematic diagram of a microgrid system according to some embodiments of the present invention;

[0012] FIG2 is a flow chart of a control method according to some embodiments of the present invention;

[0013] FIG3 is a flow chart showing one of the steps in FIG2 according to some embodiments of the present invention;

[0014] FIG4 is a schematic diagram showing a relationship between a control frequency and a renewable energy output power according to some embodiments of the present invention; and

[0015] FIG5 is a schematic diagram showing the relationship between a control frequency and a renewable energy output power according to some embodiments of the present invention.

[0016] Explanation of reference numerals: 100: Microgrid system 110: Energy storage system 112: Energy storage battery 114: Integration device 115: DC / AC converter 117: Controller 130: Renewable energy generation system 132: Solar cell 134: Solar inverter B1, B2, B3: No-fuse switches C1, C2, C3, C4: Switches (relays) VC: Control voltage FC: Control frequency POUT: Renewable energy output power 900A, 900B: Load 800: Mains power system 200: Control method S210, S230: Steps S305, S310, S320, S330, S350, S360: Steps S370, S390: Step Fbuffer: Buffer frequency interval FB: Basic frequency PB: Basic power P1, P2: Power F1, F2, F3, F4: Frequency t0, t1, t2, t3, t4, t5: Time point t6, t7, t8, t9, t10, t11, t12: Time point ta1, ta2, ta3, ta4: Time interval tb1, tb2: Time interval DETAILED DESCRIPTION

[0017] The following examples are described in detail with accompanying drawings. However, the examples provided are not intended to limit the scope of this disclosure, and the description of the structure and operation is not intended to limit the order of execution. Any device that produces an equivalent technical effect by recombining the components is within the scope of this disclosure. Furthermore, the drawings are for illustrative purposes only and are not drawn to scale. To facilitate understanding, identical or similar components will be designated with the same reference numerals in the following description.

[0018] Please refer to Figure 1 , which is a schematic diagram of a microgrid system 100 according to some embodiments of the present invention. In Figure 1 , the microgrid system 100 includes an energy storage system 110 and a renewable energy generation system 130 .

[0019] The microgrid system 100 is configured to connect to the mains power system 800. In some embodiments, the microgrid system 100 further includes switches (relays) C1 to C4, which, in conjunction with the no-fuse switches B1 to B3, control the connection and power supply between the energy storage system 110, the renewable energy generation system 130, and the mains power system 800.

[0020] When the utility is supplying power, microgrid system 100 operates in utility mode. At this time, utility system 800 operates as a voltage source, while energy storage system 110 and renewable energy generation system 130 operate as current sources. Load 900A is powered by utility system 800, while load 900B is powered by utility system 800 via a path consisting of no-fuse switch B1, switch (relay) C1, switch (relay) C2, switch (relay) C3, and no-fuse switch B3. On the other hand, when the utility is not supplying power, microgrid system 100 operates in microgrid mode, with energy storage system 110 operating as a voltage source and renewable energy generation system 130 operating as a current source. Energy storage system 110 and renewable energy generation system 130 operate in parallel to supply power to specific attached load 900B. In one embodiment, when the output power of the renewable energy generation system 130 is greater than the load power of the load 900B, the renewable energy generation system 130 is further configured to supply power to the load 900B while charging the energy storage system 110 .

[0021] In some embodiments, the load 900A is a general load, and the load 900B is a specific load. In one embodiment, the specific load may be an emergency load that needs to be used when the mains power system 800 is not supplying power, such as an emergency lighting lamp.

[0022] The detailed operation of the microgrid system 100 in FIG. 1 will be described in detail below with reference to FIG. 2 .

[0023] Please continue to refer to Figure 1. In Figure 1, energy storage system 110 includes energy storage battery 112 and integration device 114. Energy storage battery 112 and integration device 114 are coupled together. Renewable energy generation system 130 includes solar cells 132 and solar inverter device 134. Solar cells 132 and solar inverter device 134 are coupled together.

[0024] In some embodiments, the integrated device 114 includes a DC / AC converter 115 and a controller 117. The DC / AC converter 115 and the controller 117 are coupled to each other. The DC / AC converter 115 is also coupled to the energy storage battery 112 and is configured to convert the DC voltage output by the energy storage battery 112 in microgrid mode into a control voltage VC. The controller 117 is configured to adjust the control frequency FC included in the control voltage VC so that the renewable energy generation system 130 adjusts the renewable energy output power POUT output by the renewable energy generation system 130 based on the control frequency FC.

[0025] Please refer to Figure 2. Figure 2 is a flow chart of a control method 200 according to some embodiments of the present invention. The control method 200 is suitable for execution by the microgrid system 100 in Figure 1 in microgrid mode. The control method 200 includes steps S210 to S230.

[0026] In step S210 , the energy storage system 110 outputs a control voltage VC including a control frequency FC to the renewable energy generation system 130 .

[0027] In step S230, the renewable energy generation system 130 adjusts the renewable energy output power POUT output by the renewable energy generation system 130 according to the control frequency FC. By adjusting the renewable energy output power POUT output by the renewable energy generation system 130, power balance can be achieved among the renewable energy generation system 130, the load 900B, and the energy storage system 110.

[0028] Please refer to FIG3 . FIG3 is a flowchart of step S210 in FIG2 according to some embodiments of the present invention. Step S210 includes steps S305 to S390 . The following description will be made with reference to FIG1 .

[0029] In step S305 , the energy storage system 110 operates in the microgrid mode and outputs a control voltage VC having a control frequency FC equal to the basic frequency FB to the renewable energy generation system 130 , so that the renewable energy generation system 130 outputs a renewable energy output power POUT according to the basic frequency FB of the control voltage VC.

[0030] Please also refer to Figure 4 . Figure 4 is a schematic diagram illustrating the relationship P(f) between control frequency FC and renewable energy output power POUT according to some embodiments of the present invention. As shown in Figure 4 , the fundamental frequency FB is a frequency within the buffer frequency range Fbuffer . When the control frequency FC is higher than the buffer frequency range Fbuffer , the renewable energy output power POUT gradually decreases as the control frequency FC increases.

[0031] It should be noted that the relationship between the control frequency FC and the renewable energy output power POUT shown in FIG4 is linear, however, the embodiments of the present disclosure are not limited thereto. In other embodiments, the relationship between the control frequency FC and the renewable energy output power POUT may be a step-down relationship.

[0032] Please refer back to Figure 3. In step S305, when the control frequency FC is the basic frequency FB, the renewable energy output power POUT is the maximum power that the renewable energy power generation system 130 can output, that is, 100% power.

[0033] Please also refer to Figure 5 . Figure 5 illustrates a relationship between control frequency FC and renewable energy output power POUT according to some embodiments of the present invention. As shown in Figure 5 , at time t0, control frequency FC is at base frequency FB, and renewable energy output power POUT is at base power PB. In one embodiment, base power PB corresponds to 100% of the power shown in Figure 4 .

[0034] In some embodiments, when the microgrid system 100 is operating in microgrid mode, the controller 117 of the energy storage system 110 is further configured to adjust the control frequency FC so that the control frequency FC periodically decreases from a first frequency to a second frequency and then increases back to the first frequency. As shown in FIG5 , at time t1, the controller 117 adjusts the control frequency FC so that the control frequency FC gradually decreases from a base frequency FB to a frequency F1 within a time interval ta1, reaching frequency F1 at time t2. Next, at time t2, the controller 117 adjusts the control frequency FC so that the control frequency FC gradually increases from a frequency F1 to a base frequency FB within a time interval ta2, reaching frequency base FB at time t3. During a time interval tb1 between time t3 and time t4, the control frequency FC remains at the base frequency FB. Next, at time t4, the controller 117 adjusts the control frequency FC so that the control frequency FC gradually decreases to a frequency F1 within a time interval ta3, reaching frequency F1 at time t5. Next, at time point t5 , the controller 117 adjusts the control frequency FC so that the control frequency FC gradually increases from the frequency F1 to the frequency FB within the time interval ta4 , and reaches the frequency FB at time point t6 .

[0035] In one embodiment, the time intervals ta1 , ta2 , ta3 , and ta4 shown in FIG. 5 have the same length, and the time intervals tb1 and tb2 have the same length.

[0036] The control frequency FC, which periodically decreases from a first frequency to a second frequency and then increases back to the first frequency, can be considered a password in the control frequency FB. This password allows the renewable energy generation system 130 to determine whether the microgrid system 100 is currently operating in microgrid mode. If the renewable energy generation system 130 does not receive the password within a certain period of time, the renewable energy generation system 130 determines that the microgrid system 100 is currently operating in utility mode.

[0037] In step S310, the controller 117 of the energy storage system 110 determines whether the renewable energy output power POUT is greater than the load power of the load 900B. If the renewable energy output power POUT is not greater than the load power of the load 900B, step S320 is executed. If the renewable energy output power POUT is greater than the load power of the load 900B, step S330 is executed.

[0038] In step S320, when the renewable energy output power POUT is less than the load power of load 900B, the renewable energy generation system 130 and the energy storage system 110 are connected in parallel to supply power to load 900B, thereby simultaneously outputting power to load 900B. When the renewable energy output power POUT is equal to the load power of load 900B, the renewable energy generation system 130 outputs the renewable energy output power POUT to load 900B, thereby supplying power to load 900B.

[0039] In step S330, the renewable energy generation system 130 simultaneously provides load power to the load 900B and charges the energy storage battery 112 in the energy storage system 110 with charging power. In some embodiments, the charging power is the power obtained by increasing the renewable energy output power POUT over the load power of the load 900B. Specifically, the charging power is the renewable energy output power POUT minus the load power of the load 900B.

[0040] In step S350 , the controller 117 of the energy storage system 110 determines whether the renewable energy output power POUT is greater than the sum of the load power of the load 900B and the charging power capacity of the energy storage battery 112 . In other words, the controller 117 determines whether the charging power of the energy storage battery 112 is greater than the charging power capacity of the energy storage battery 112 .

[0041] If the renewable energy output power POUT is greater than the sum of the load power of load 900B and the charging power capacity of energy storage battery 112, that is, the charging power is greater than the charging power capacity, step S360 is executed. If the renewable energy output power POUT is not greater than the sum of the load power of load 900B and the charging power capacity of energy storage battery 112, that is, the charging power is not greater than the charging power capacity, step S370 is executed.

[0042] In step S360 , the controller 117 of the energy storage system 110 increases the control frequency FC to reduce the renewable energy output power POUT output by the renewable energy power generation system 130 until the renewable energy output power POUT is equal to the sum of the load power of the load 900B and the charging power capacity of the energy storage battery 112 .

[0043] In some embodiments, in step S360, the controller 117 of the energy storage system 110 is further configured to increase the control frequency FC until the renewable energy output power POUT is slightly lower than the sum of the load power of the load 900B and the charging power capacity of the energy storage battery 112, and then decrease the control frequency FC until the renewable energy output power POUT is equal to the sum of the load power of the load 900B and the charging power capacity of the energy storage battery 112.

[0044] Please refer to Figure 5. At time t8, the controller 117 of the energy storage system 110 gradually increases the control frequency FC from frequency FB to frequency F3. As the control frequency FC gradually increases from frequency FB to frequency F3, the renewable energy output power POUT gradually decreases from power PB to power P1.

[0045] At time t9, the renewable energy output power POUT is P1. At this time, the renewable energy output power POUT is slightly lower than the sum of the load power of the load 900B and the charging power capacity of the energy storage battery 112. That is, at time t9, the charging power is slightly less than the charging power capacity. At this time, the controller 117 of the energy storage system 110 gradually adjusts the control frequency FC from frequency F3 to frequency F2. As the control frequency FC gradually decreases from frequency F3 to frequency F2, the renewable energy output power POUT gradually increases from power P1 to power P2. At time t10, the control frequency FC is frequency F2, and the renewable energy output power POUT is power P2. At this time, the renewable energy output power POUT is equal to the sum of the load power of the load 900B and the charging power capacity of the energy storage battery 112. That is, at time t10, the charging power is equal to the charging power capacity.

[0046] As shown in Figure 5 , after time t10, since the charging power is equal to the charging power capacity, the control frequency FC does not need to be increased or decreased. The controller 117 of the energy storage system 110 adjusts the control frequency FC again, causing the control frequency FC to periodically decrease from frequency F2 to frequency F4 and then increase from frequency F4 to frequency F2. In other words, the controller 117 of the energy storage system 110 adjusts the control frequency FC again, causing the control frequency FC to output a code to the renewable energy generation system 130, thereby informing the renewable energy generation system 130 that the microgrid system 100 is currently operating in microgrid mode.

[0047] In step S370 , the controller 117 of the energy storage system 110 determines whether the renewable energy output power POUT is less than the sum of the load power of the load 900B and the charging power capacity of the energy storage battery 112 . In other words, the controller 117 determines whether the charging power of the energy storage battery 112 is less than the charging power capacity of the energy storage battery 112 .

[0048] If the renewable energy output power POUT is not less than the sum of the load power of load 900B and the charging power capacity of energy storage battery 112, that is, the charging power is not less than the charging power capacity, the process returns to step S330. The load power is simultaneously output to load 900B using the current renewable energy output power POUT, and the energy storage battery 112 is charged with the charging power. On the other hand, if the renewable energy output power POUT is less than the sum of the load power of load 900B and the charging power capacity of energy storage battery 112, that is, the charging power is less than the charging power capacity, the process returns to step S330.

[0049] In step S390 , the controller 117 of the energy storage system 110 reduces the control frequency FC to the base frequency FB, so that the renewable energy output power POUT output by the renewable energy power generation system 130 increases to the base power PB.

[0050] Please also refer to Figure 5. At time t11, controller 117 of energy storage system 110 gradually decreases control frequency FC from frequency F2 to frequency FB, causing renewable energy output power POUT to gradually increase from power P2 to base power PB. At time t12, control frequency FC reaches base frequency FB, and renewable energy output power POUT reaches base power PB. After step S390, the process returns to step S310.

[0051] In some embodiments, the integrated device 114 and the solar inverter device 134 may include a central processing unit (CPU), a microprocessor (MCU), a server, or other computing circuits or elements having data access, data calculation, data storage, data transmission and reception, or similar functions, and may be used to execute the control method 200.

[0052] In some embodiments, the integrated device 114 and the solar inverter device 134 may further include other components required for operation and application. For example, the integrated device 114 and the solar inverter device 134 may also include an output interface (for example, a display panel for displaying information), an input interface (for example, a touch panel, a keyboard, a scanner or a flash memory reader) and an internal communication circuit (for example, a WiFi communication model, a Bluetooth communication model, a wireless telecommunications network communication model, etc.), a DC-to-DC converter, a switch, a switch driving circuit, a power detection circuit, a feedback circuit, a storage element, etc.

[0053] In some embodiments, the integrated device 114 further includes a battery management circuit for managing the status of the energy storage battery 112 and charging and discharging the energy storage battery 112 .

[0054] In summary, the disclosed embodiments provide a microgrid system, an energy storage system, and a control method. By changing the control frequency FC input to the renewable energy generation system 130, the renewable energy output power POUT of the renewable energy generation system 130 is controlled to achieve power balance between the energy storage system 110, the renewable energy generation system 130, and the load 900B. Furthermore, by setting a password in the control frequency FC, the renewable energy generation system 130 can determine whether the microgrid 100 is currently operating in microgrid mode or mains mode without a communication connection with the energy storage system 110. In this way, the renewable energy generation system 130 can operate in different islanding parameters, power boost parameters, P(F) parameters, etc., in both microgrid mode and mains mode, respectively, providing greater operational flexibility.

[0055] In addition, it should be noted that, unless otherwise specified, there is no particular order requirement for the steps in the control method 200. In addition, these steps may also be executed simultaneously, or their execution time may at least partially overlap.

[0056] The terms used herein generally have their ordinary meanings in the art, in the context of this disclosure, and in the specific context, unless otherwise noted. Certain terms used to describe the present disclosure are discussed elsewhere in this specification to provide additional guidance to those skilled in the art in describing the present disclosure.

[0057] Although specific embodiments of the present disclosure have been disclosed with respect to the above-described embodiments, these embodiments are not intended to limit the present disclosure. Various substitutions and modifications may be made by those skilled in the relevant art without departing from the principles and concepts of the present disclosure. Therefore, the scope of protection of the present disclosure is determined by the appended claims.

Claims

1. A microgrid system, for connecting to a mains power system and for operating in a microgrid mode when the mains power system is not supplying power, wherein the microgrid system comprises: A renewable energy power generation system; and An energy storage system, wherein when the microgrid system operates in the microgrid mode, the energy storage system is used to output a control voltage including a control frequency to the renewable energy power generation system, so that the renewable energy power generation system adjusts a renewable energy output power output by the renewable energy power generation system according to the control frequency.

2. The microgrid system as described in claim 1, wherein when the renewable energy output power output by the renewable energy power generation system is greater than a load power, the renewable energy power generation system charges a storage battery of the energy storage system with a charging power, wherein the charging power is the difference between the renewable energy output power and the load power.

3. The microgrid system as described in claim 2, wherein when the charging power is greater than a charging power capacity of the energy storage battery, the energy storage system increases the control frequency from a first frequency to a second frequency, so that the renewable energy output power output by the renewable energy power generation system decreases from a first power to a second power, so that the renewable energy output power is equal to the charging power plus the load power.

4. The microgrid system as described in claim 3, wherein when the charging power is greater than the charging power capacity of the energy storage battery, the energy storage system is further used to increase the control frequency from the first frequency to a third frequency until the output power of the renewable energy is less than the charging power capacity plus the load power, and then reduce the control frequency from the third frequency to the second frequency.

5. The microgrid system as claimed in claim 2, wherein when the charging power is less than a charging power capacity of the energy storage battery, the energy storage system is further configured to reduce the control frequency to a basic frequency.

6. The microgrid system as claimed in claim 1, wherein when the renewable energy output power output by the renewable energy power generation system is greater than a load power, the energy storage system is further used to supply power in parallel with the renewable energy power generation system.

7. The microgrid system as described in claim 1, wherein the energy storage system is further used to periodically reduce the control frequency from a first frequency to a second frequency, and then increase from the second frequency to the first frequency, so that the renewable energy generation system knows that it is currently operating in the microgrid mode.

8. An energy storage system, together with a renewable energy power generation system, forms a microgrid system, wherein when a mains power system is not supplying power, the microgrid system operates in a microgrid mode, wherein the energy storage system comprises: an energy storage battery for outputting a DC voltage in the microgrid mode; and An integrated device, coupled to the energy storage battery, comprising: a DC-AC converter, coupled to the energy storage battery, for converting the DC voltage into a control voltage and transmitting the control voltage to the renewable energy generation system, wherein the control voltage includes a control frequency; and A controller is coupled to the DC / AC converter, wherein in the microgrid mode, the controller is used to adjust the control frequency so that the renewable energy generation system adjusts the output of the renewable energy generation system according to the control frequency. The output power of renewable energy.

9. The energy storage system as described in claim 8, wherein when the renewable energy output power output by the renewable energy power generation system is greater than a load power, the renewable energy power generation system charges a storage battery of the energy storage system with a charging power, wherein the charging power is the difference between the renewable energy output power and the load power, and when the charging power is greater than a charging power capacity of the energy storage battery, the controller is further used to increase the control frequency from a first frequency to a second frequency, so that the renewable energy output power output by the renewable energy power generation system decreases from a first power to a second power, so that the renewable energy output power is equal to the charging power plus the load power.

10. The energy storage system as claimed in claim 9, wherein when the charging power is greater than the charging power capacity of the energy storage battery, the controller is further configured to increase the control frequency from the first frequency to a third frequency until the output power of the renewable energy is less than the charging power capacity plus the load power, and then reduce the control frequency from the third frequency to the second frequency. 11 . The energy storage system as claimed in claim 9 , wherein when the charging power is less than a charging power capability of the energy storage battery, the controller is further configured to reduce the control frequency to a basic frequency. 12 . The energy storage system as claimed in claim 8 , wherein when the renewable energy output power output by the renewable energy power generation system is greater than a load power, the controller is further configured to supply power in parallel with the renewable energy power generation system.

13. The energy storage system as claimed in claim 8, wherein the controller is further used to periodically reduce the control frequency from a first frequency to a second frequency, and then increase from the second frequency to the first frequency, so that the renewable energy power generation system knows that it is currently operating in the microgrid mode.

14. A control method, applicable to a microgrid system, used to connect to a mains power system and to operate in a microgrid mode when the mains power system is not supplying power, wherein the microgrid system includes an energy storage system and a renewable energy generation system, wherein the control method includes: Outputting a control voltage including a control frequency from the energy storage system to the renewable energy power generation system; and The renewable energy power generation system adjusts a renewable energy output power output by the renewable energy power generation system according to the control frequency, so that the microgrid system achieves power balance.

15. The control method according to claim 14, further comprising: When the renewable energy output power output by the renewable energy power generation system is greater than a load power, the renewable energy power generation system charges an energy storage battery of the energy storage system with a charging power; The charging power is the difference between the output power of the renewable energy and the load power.

16. The control method according to claim 15, further comprising: When the charging power is greater than a charging power capacity of the energy storage battery, the energy storage system increases the control frequency from a first frequency to a second frequency; The renewable energy power generation system adjusts the renewable energy output power from a first power to a second power according to the control frequency, so that the renewable energy output power is equal to the charging power plus the load power.

17. The control method according to claim 16, further comprising: When the charging power is greater than the charging power capacity of the energy storage battery, the energy storage system controls the frequency from The first frequency is increased to a third frequency until the output power of the renewable energy is less than the charging power capacity plus the load power, and then the control frequency is decreased from the third frequency to the second frequency.

18. The control method according to claim 15, further comprising: When the charging power is less than a charging power capacity of the energy storage battery, the energy storage system adjusts the control frequency down to a basic frequency.

19. The control method according to claim 14, further comprising: When the renewable energy output power output by the renewable energy power generation system is greater than a load power, the energy storage system and the renewable energy power generation system are connected in parallel to supply power.

20. The control method of claim 14, further comprising: The energy storage system adjusts the control frequency so that the control frequency periodically decreases from a first frequency to a second frequency and then increases from the second frequency to the first frequency, so that the renewable energy generation system knows that it is currently operating in the microgrid mode.

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