Microgrid system, energy storage system, and control method

Abstract

We will disclose a microgrid system. [Solution] A microgrid system used for connection to a commercial power system and configured to operate in microgrid mode when the commercial power system does not supply power, the microgrid system comprising: a renewable energy generation system; and an energy storage system for outputting a control voltage including a control frequency to the renewable energy generation system so as to adjust the renewable energy output power output by the renewable energy generation system according to the control frequency when operating in microgrid mode.

Description

Technical Field

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

Background Art

[0002] Currently, the power generation technology in Taiwan is centered around power companies for power generation, mainly with centralized power generation. However, when problems occur in the centralized power generation of power companies, users have no choice but to wait for power restoration and cannot use power.

[0003] To solve the above problems, many technologies have been proposed that include energy storage batteries or assist power generation by solar power generation devices or other renewable energy auxiliary power generation systems to alleviate the above problems. However, since the power of the energy storage battery may also run out, a form of charging the energy storage battery by solar cells has been proposed.

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, there are also problems with the above method. When communication cannot be established between the energy storage battery and the solar cell, how to control the output power of the solar cell in order to achieve the balance among the solar cell, the energy storage battery, and the load is one of the problems to be solved.

Means for Solving the Problems

[0005] To solve the above problems, this disclosure proposes a microgrid system used for connection to a commercial power system and configured to operate in microgrid mode when the commercial power system does not supply power, comprising: a renewable energy generation system; and an energy storage system for outputting a control voltage including a control frequency to the renewable energy generation system so as to adjust the renewable energy output power output by the renewable energy generation system according to the control frequency when operating in microgrid mode.

[0006] This disclosure further proposes an energy storage system that forms a microgrid system together with a renewable energy generation system, and in the event that a commercial power system does not supply power, the microgrid system is operated in microgrid mode, comprising: an energy storage battery for outputting a DC voltage in microgrid mode; and an integrated device coupled to the energy storage battery, the integrated device comprising: a DC-AC converter coupled to the energy storage battery for converting the DC voltage into a control voltage including a control frequency and transmitting the control voltage to the renewable energy generation system; and a controller coupled to the DC-AC converter for adjusting the control frequency so that, in microgrid mode, the renewable energy generation system adjusts the renewable energy output power output by the renewable energy generation system according to the control frequency.

[0007] This disclosure also proposes a control method applicable to a microgrid system, which is used to connect to a commercial power system and is configured to operate in microgrid mode when the commercial power system does not supply power, and which comprises an energy storage system and a renewable energy generation system, the control method comprising: a step of outputting a control voltage including a control frequency to the renewable energy generation system by the energy storage system; and a step of adjusting the renewable energy output power output by the renewable energy generation system according to the control frequency so that a power balance is achieved in the microgrid system.

[0008] It should be understood that the general statements above and the specific explanations below are merely illustrative and interpretive, and are intended to provide further explanation of the disclosure as required. [Brief explanation of the drawing]

[0009] The following explanation of the attached drawings is intended to make the above and other objectives, features, advantages, and embodiments of the present invention easier to understand. [Figure 1] This is a schematic diagram showing a microgrid system according to several embodiments of the present invention. [Figure 2] This is a flowchart illustrating a control method according to several embodiments of the present invention. [Figure 3] This is a flowchart showing one step in Figure 2 according to several embodiments of the present invention. [Figure 4] This is a schematic diagram showing the relationship between control frequency and renewable energy output power according to several embodiments of the present invention. [Figure 5] This is a schematic diagram showing the relationship between control frequency and renewable energy output power according to several embodiments of the present invention. [Modes for carrying out the invention]

[0010] The following descriptions will elaborate on the embodiments, in accordance with the accompanying drawings. However, the provided embodiments do not limit the scope of this disclosure, nor do the descriptions of the operation of the structures limit their execution order. Any structure reassembled by the components, any device that produces an equivalent effect, is included within the scope of this disclosure. Furthermore, the drawings are for illustrative purposes only and are not drawn to their original dimensions. For ease of understanding, identical or similar parts will be denoted by the same reference numerals in the following description.

[0011] Please refer to Figure 1, a schematic diagram showing a microgrid system 100 according to several embodiments of the present invention. In Figure 1, the microgrid system 100 comprises an energy storage system 110 and a renewable energy generation system 130.

[0012] The microgrid system 100 is used to connect to the commercial power system 800. In some embodiments, the microgrid system 100 includes switches (relays) C1 to C4 that work in conjunction with no-fuse circuit breakers B1 to B3 to control the connection and power supply relationships between the energy storage system 110, the renewable energy generation system 130, and the commercial power system 800.

[0013] When commercial power is supplied, the microgrid system 100 operates in commercial power mode. In this case, the commercial power system 800 operates as a voltage source, the energy storage system 110 and the renewable energy generation system 130 operate as current sources, and the commercial power system 800 supplies power to load 900A, which in turn is powered by the commercial power system 800 via a path consisting of no-fuse circuit breaker B1, switch (relay) C1, switch (relay) C2, switch (relay) C3, and no-fuse circuit breaker B3. On the other hand, when commercial power is not supplied, the microgrid system 100 operates in microgrid mode, in which case the energy storage system 110 operates as a voltage source, the renewable energy generation system 130 operates as a current source, and the energy storage system 110 and the renewable energy generation system are connected in parallel to supply power to a specific load 900B. In one embodiment, if the output power of the renewable energy generation system 130 is greater than the load power of load 900B, the renewable energy generation system 130 further supplies power to the specific load 900B while simultaneously charging the energy storage system 110.

[0014] In some embodiments, load 900A is a general load, and load 900B is a specific load. In one embodiment, the specific load may be an emergency power source, such as an emergency lighting system, which must be used when the commercial power system 800 does not supply power.

[0015] The detailed operation of the microgrid system 100 shown in Figure 1 will be explained in detail below with reference to Figure 2.

[0016] Please refer to Figure 1. In Figure 1, the energy storage system 110 comprises an energy storage battery 112 and an integration device 114. The energy storage battery 112 is coupled to the integration device 114. The renewable energy generation system 130 includes a solar cell 132 and a solar inverter 134. The solar cell 132 is coupled to the solar inverter 134.

[0017] In some embodiments, the integrated device 114 includes a DC-AC converter 115 and a controller 117. The DC-AC converter 115 is coupled to the controller 117. The DC-AC converter 115 is coupled to the energy storage battery 112 and is used to convert the DC voltage output by the energy storage battery 112 in microgrid mode into a control voltage VC. The controller 117 is used 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 according to the control frequency FC.

[0018] Please refer to Figure 2. Figure 2 is a flowchart showing a control method 200 according to several embodiments of the present invention. The control method 200 is applied to being performed in microgrid mode by the microgrid system 100 in Figure 1. The control method 200 comprises steps S210 to S230.

[0019] 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.

[0020] In process 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, a power balance can be achieved between the renewable energy generation system 130, the load 900B, and the energy storage system 110.

[0021] Please also refer to Figure 3. Figure 3 is a flowchart showing step S210 in Figure 2 according to several embodiments of the present invention. Step S210 includes steps S305 to S390. The following explanation will also refer to Figure 1.

[0022] In step S305, the energy storage system 110 operates in the microgrid mode and outputs a control voltage VC having a control frequency FC as a fundamental frequency FB to the renewable energy power generation system 130. Thereby, the renewable energy power generation system 130 outputs a renewable energy output power POUT according to the fundamental frequency FB of the control voltage VC.

[0023] Refer to FIG. 4 in combination. FIG. 4 is a schematic diagram showing the relationship P(f) between the control frequency FC and the renewable energy output power POUT according to some embodiments of the present invention. As shown in FIG. 4, the fundamental frequency FB is a frequency located in the buffer frequency section Fbuffer. When the control frequency FC is higher than the buffer frequency section Fbuffer, as the control frequency FC increases, the renewable energy output power POUT gradually decreases.

[0024] It should be noted that the relationship between the control frequency FC and the renewable energy output power POUT shown in FIG. 4 is linear, but the embodiments of the present application are not limited thereto. In some other embodiments, the relationship between the control frequency FC and the renewable energy output power POUT may decrease stepwise.

[0025] Also refer to FIG. 3. In step S305, when the control frequency FC is the fundamental 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.

[0026] Refer to FIG. 5 in combination. FIG. 5 is a schematic diagram showing the relationship between the control frequency FC and the renewable energy output power POUT according to some embodiments of the present invention. As shown in FIG. 5, at time t0, the control frequency FC is the fundamental frequency FB. In this case, the renewable energy output power POUT is the basic power PB. In one embodiment, the basic power PB corresponds to 100% power shown in FIG. 4.

[0027] In some embodiments, when the microgrid system 100 operates in microgrid mode, the controller 117 of the energy storage system 110 is further used 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 Figure 5, at time t1, the controller 117 adjusts the control frequency FC so that the control frequency FC gradually decreases from the fundamental frequency FB to frequency F1 within time interval ta1 and reaches 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 frequency F1 to the fundamental frequency FB within time interval ta2 and reaches the fundamental frequency FB at time t3. During the time interval tb1 between time t3 and time t4, the control frequency FC is maintained at the fundamental frequency FB. Next, at time t4, the controller 117 adjusts the control frequency FC so that the control frequency FC gradually decreases to frequency F1 within the time interval ta3 and reaches frequency F1 at time t5. Next, at time t5, the controller 117 adjusts the control frequency FC so that the control frequency FC gradually increases from frequency F1 to the fundamental frequency FB within the time interval ta4 and reaches the fundamental frequency FB at time t6.

[0028] In one embodiment, the time lengths of time intervals ta1, ta2, ta3, and ta4 shown in Figure 5 are the same, and the time lengths of time intervals tb1 and tb2 are the same.

[0029] The periodic decrease of the control frequency FC from the first frequency to the second frequency, followed by an increase back to the first frequency, can be considered a passcode for controlling the fundamental frequency FB. This passcode allows the renewable energy generation system 130 to understand that the microgrid system 100 is currently operating in microgrid mode. If the renewable energy generation system 130 does not receive such a passcode within a certain time period, it determines that the microgrid system 100 is currently operating in commercial power mode.

[0030] 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 load 900B. If the renewable energy output power POUT is not greater than the load power of load 900B, step S320 is executed. If the renewable energy output power POUT is greater than the load power of load 900B, step S330 is executed.

[0031] In process S320, if 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, and the power is output to load 900B simultaneously. If the renewable energy output power POUT becomes equal to the load power of load 900B, the renewable energy generation system 130 outputs the renewable energy output power POUT to load 900B, and the power is supplied to load 900B.

[0032] In step S330, the renewable energy generation system 130 provides load power to the load 900B, while simultaneously charging the energy storage battery 112 in the energy storage system 110 with the charging power. In some embodiments, the charging power is the amount by which the renewable energy output power POUT exceeds the load power of the load 900B. That is, the charging power is the renewable energy output power POUT minus the load power of the load 900B.

[0033] 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 rechargeable power of the energy storage battery 112. That is, it determines whether the charging power of the energy storage battery 112 is greater than the rechargeable power of the energy storage battery 112.

[0034] If the renewable energy output power POUT is greater than the sum of the load power of load 900B and the rechargeable power of energy storage battery 112, that is, if the charging power is greater than the rechargeable power, then 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 rechargeable power of energy storage battery 112, that is, if the charging power is not greater than the rechargeable power, then step S370 is executed.

[0035] In step S360, the controller 117 of the energy storage system 110 increases the control frequency FC, thereby reducing the renewable energy output power POUT output by the renewable energy generation system 130 until the renewable energy output power POUT becomes equal to the sum of the load power of the load 900B and the rechargeable power of the energy storage battery 112.

[0036] In some embodiments, in step S360, the controller 117 of the energy storage system 110 is further used to raise 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 rechargeable power of the energy storage battery 112, and to lower 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 rechargeable power of the energy storage battery 112.

[0037] Please also refer to Figure 5. At time t8, the controller 117 of the energy storage system 110 gradually increases the control frequency FC from the fundamental frequency FB to frequency F3. As the control frequency FC gradually increases from the fundamental frequency FB to frequency F3, the renewable energy output power POUT gradually decreases from the fundamental power PB to power P1.

[0038] At time t9, the renewable energy output power POUT is P1, in which case the renewable energy output power POUT is slightly lower than the sum of the load power of the load 900B and the rechargeable power of the energy storage battery 112. That is, at time t9, the charging power is slightly less than the rechargeable power. In this case, the controller 117 of the energy storage system 110 also gradually lowers 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. In this case, the renewable energy output power POUT is equal to the sum of the load power of the load 900B and the rechargeable power of the energy storage battery 112. That is, at time t10, the charging power is equal to the rechargeable power.

[0039] As shown in Figure 5, after time t10, the charging power is equal to the rechargeable power, so there is no need to raise or lower the control frequency FC. At this time, the controller 117 of the energy storage system 110 adjusts the control frequency FC again, periodically decreasing it from frequency F2 to frequency F4, and then increasing it from frequency F4 to frequency F2. That is, the controller 117 of the energy storage system 110 adjusts the control frequency FC again to form a passcode signal, which is output to the renewable energy generation system 130. This allows the renewable energy generation system 130 to understand that the microgrid system 100 is currently operating in microgrid mode.

[0040] 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 rechargeable power of the energy storage battery 112. That is, it determines whether the charging power of the energy storage battery 112 is less than the rechargeable power of the energy storage battery 112.

[0041] If the renewable energy output power POUT is not less than the sum of the load power of load 900B and the rechargeable power of energy storage battery 112, that is, if the charging power is not less than the rechargeable power, the process returns to step S330. The current renewable energy output power POUT is used to simultaneously output load power to load 900B and charge energy storage battery 112 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 rechargeable power of energy storage battery 112, that is, if the charging power is less than the rechargeable power, the process returns to step S330.

[0042] In step S390, the controller 117 of the energy storage system 110 lowers the control frequency FC to the fundamental frequency FB so that the renewable energy output power POUT output by the renewable energy generation system 130 rises to the fundamental power PB.

[0043] Please also refer to Figure 5. At time t11, the controller 117 of the energy storage system 110 gradually lowers the control frequency FC from frequency F2 to the fundamental frequency FB, so that the renewable energy output power POUT gradually increases from power P2 to the fundamental power PB. At time t12, the control frequency FC is the fundamental frequency FB, and the renewable energy output power POUT is the fundamental power PB. After step S390, the process returns to step S310.

[0044] In some embodiments, the integrated device 114 and the solar inverter 134 may include a central processor unit (CPU), a microprocessor (MCU), a server, or other arithmetic circuits or elements having data access, data calculation, data storage, data transmission / reception, or similar functions, and may be used to execute the control method 200.

[0045] In some embodiments, the integrated device 114 and the solar inverter 134 may further include other elements necessary for operation and application, for example, the integrated device 114 and the solar inverter 134 may further include an output interface (e.g., a display panel for information display), an input interface (e.g., a touch panel, a keyboard, a scanner, or a flash memory reader), and internal communication circuits (e.g., a WiFi® communication module, a Bluetooth® communication module, a wireless communication network communication module, etc.), a DC-DC converter, a switch, a switch drive circuit, a power detection circuit, a feedback circuit, a memory element, etc.

[0046] In some embodiments, the integrated device 114 further includes a battery management circuit for managing the state of the energy storage battery 112 and for charging and discharging the energy storage battery 112.

[0047] In summary, the embodiments of this disclosure provide a microgrid system, an energy storage system, and a control method, which further control the renewable energy output power POUT of the renewable energy generation system 130 by modifying the control frequency FC input to the renewable energy generation system 130, thereby achieving a power balance between the energy storage system 110, the renewable energy generation system 130, and the load 900B. Furthermore, by setting a passcode in the control frequency FC, if the renewable energy generation system 130 is not communicatively connected to the energy storage system 110, it is possible to determine whether the microgrid system 100 is currently operating in microgrid mode or commercial power mode. Thus, the renewable energy generation system 130 can operate with different isolated island parameters, power rise parameters, P(F) parameters, etc., in microgrid mode and commercial power mode, respectively, providing greater operational flexibility.

[0048] Furthermore, it should be explained that, unless otherwise specified, no special order is required in the steps of the control method 200 described above. Also, these steps may be executed simultaneously, and their execution times may overlap, at least partially.

[0049] Unless otherwise noted, the terms used herein have the meanings that they commonly have in the art, within the content of this disclosure, and in specific contexts. Some terms used to describe this disclosure are discussed elsewhere in this specification to provide additional guidance to those skilled in the art.

[0050] With respect to the embodiments described above, specific embodiments of this disclosure have been disclosed, but these embodiments are not intended to limit this disclosure. Those skilled in the art can make various substitutions and improvements within this disclosure without departing from the principles and spirit of this disclosure. Accordingly, the scope of protection of this disclosure is determined by the appended claims. [Explanation of Symbols]

[0051] 100: Microgrid Systems 110: Energy storage systems 112: Energy storage batteries 114: Integration device 115: DC-AC converter 117: Controller 130: Renewable energy power generation systems 132: Solar Cells 134: Solar Inverter B1, B2, B3: No-fuse circuit breaker C1, C2, C3, C4: Switches (relays) VC: Control Voltage FC: Control frequency POUT: Renewable energy output power 900A, 900B: Load 800: Commercial power systems 200: Control Method S210, S230: Process S305, S310, S320, S330, S350, S360: Process S370, S390: Process Fbuffer: Buffer frequency interval FB: Fundamental frequency PB: Basic power P1, P2: Power F1, F2, F3, F4: Frequency t0, t1, t2, t3, t4, t5: time points t6, t7, t8, t9, t10, t11, t12: time point ta1, ta2, ta3, ta4: Time intervals tb1, tb2: Time intervals

Claims

1. A microgrid system used for connection to a commercial power system and configured to operate in microgrid mode when the commercial power system does not supply power, Renewable energy power generation systems, When the microgrid system operates in the microgrid mode, an 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 output by the renewable energy generation system according to the control frequency. A microgrid system equipped with [the following features].

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

3. The microgrid system according to claim 2, wherein if the charging power is greater than the rechargeable power 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 is equal to the sum of the charging power and the load power, thereby reducing the renewable energy output power output by the renewable energy generation system from a first power to a second power.

4. If the charging power is greater than the rechargeable power of the energy storage battery, the energy storage system is further used to raise the control frequency from the first frequency to the third frequency and then to the second frequency until the renewable energy output power is less than the rechargeable power plus the load power.

5. If the charging power is less than the rechargeable power of the energy storage battery, the energy storage system is further used to lower the control frequency to the fundamental frequency, according to claim 2 of the microgrid system.

6. The microgrid system according to claim 1, wherein, when the renewable energy output power output by the renewable energy generation system is less than the load power, the energy storage system is further connected in parallel to the renewable energy generation system and used to supply power.

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

8. An energy storage system that forms a microgrid system together with a renewable energy generation system, and in the event that the commercial power system does not supply power, the microgrid system is operated in microgrid mode, An energy storage battery for outputting a DC voltage in the aforementioned microgrid mode, An integrated device coupled to the aforementioned energy storage battery, Equipped with, The aforementioned integrated device is A DC-AC converter coupled to the energy storage battery converts the DC voltage into a control voltage including a control frequency and transmits the control voltage to the renewable energy generation system, A controller coupled to the DC-AC converter, which adjusts the control frequency in the microgrid mode so as to adjust the renewable energy output power output by the renewable energy generation system according to the control frequency, Energy storage systems including

9. The energy storage system according to claim 8, wherein, when the renewable energy output power output by the renewable energy generation system is greater than the load power, the renewable energy generation system charges the energy storage battery of the energy storage system with the charging power which is the difference between the renewable energy output power and the load power, and, when the charging power is greater than the rechargeable power of the energy storage battery, the controller further increases the control frequency from a first frequency to a second frequency so that the renewable energy output power becomes equal to the sum of the charging power and the load power, thereby reducing the renewable energy output power output by the renewable energy generation system from a first power to a second power.

10. If the charging power is greater than the rechargeable power of the energy storage battery, the controller is further used to raise the control frequency from the first frequency to the third frequency and then to the second frequency until the renewable energy output power is less than the rechargeable power plus the load power.

11. If the charging power is less than the rechargeable power of the energy storage battery, the controller is further used to lower the control frequency to the fundamental frequency.

12. The energy storage system according to claim 8, wherein, if the renewable energy output power output by the renewable energy generation system is less than the load power, the controller is further connected in parallel to the renewable energy generation system and used to supply power.

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

14. A control method applicable to a microgrid system that is used to connect to a commercial power system and is configured to operate in microgrid mode when the commercial power system does not supply power, and which comprises an energy storage system and a renewable energy generation system, The process involves outputting a control voltage, including a control frequency, to the renewable energy generation system using the energy storage system, The process of adjusting the renewable energy output power output by the renewable energy generation system according to the control frequency so that power balance is achieved in the microgrid system by the renewable energy generation system, A control method including

15. If the renewable energy output power generated by the renewable energy generation system is greater than the load power, the process further includes charging the energy storage battery of the energy storage system with the power generated by the renewable energy generation system. The control method according to claim 14, wherein the charging power is the difference between the renewable energy output power and the load power.

16. If the charging power is greater than the rechargeable power of the energy storage battery, the energy storage system raises the control frequency from a first frequency to a second frequency. The renewable energy power generation system includes a step of adjusting 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 sum of the charging power and the load power, The control method according to claim 15, further comprising:

17. The control method according to claim 16, further comprising the steps of raising the control frequency from the first frequency to the third frequency and then lowering the control frequency from the third frequency to the second frequency by the energy storage system until the renewable energy output power becomes less than the sum of the rechargeable power and the load power, if the charging power is greater than the rechargeable power of the energy storage battery.

18. The control method according to claim 15, further comprising the step of reducing the control frequency to the fundamental frequency by the energy storage system when the charging power is less than the rechargeable power of the energy storage battery.

19. The control method according to claim 14, further comprising the step of supplying power to the renewable energy generation system by connecting the energy storage system in parallel to the renewable energy generation system if the renewable energy output power output by the renewable energy generation system is less than the load power.

20. The control method according to claim 14, further comprising the step of adjusting the control frequency so that the energy storage system can determine that the renewable energy generation system is currently operating in the microgrid mode, by periodically decreasing the control frequency from a first frequency to a second frequency and increasing it from the second frequency to the first frequency.

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