Electric power system and method of operating the same

Abstract

An electric power system includes: a mains grid connected to a first switch; and a microgrid connected to the mains grid via the first switch. The microgrid includes: a converter connected to a busbar; a controller connected to the first switch and the converter for transmitting a first signal; and a load connected to the converter via the busbar. The mains grid is connected to the busbar via the first switch and is used to supply power to the load. The controller is further used to detect a first line connecting the mains grid and the microgrid, and to determine whether the first line is abnormal. When the controller determines that the first line is abnormal, the controller disconnects the first switch and switches a first part of the converter to operate as a voltage source via the first signal.

Description

Technical Field

[0001] This disclosure relates to a power system, and more particularly to a microgrid system with converter equipment for switching power supply operation modes and its operation method. Prior Technology

[0002] In existing power systems, microgrids within a grid or municipal power grid architecture primarily use feeders as their geographical boundaries, with power supplied to the microgrid system from the municipal power grid to power the loads. When an anomaly occurs in the upstream municipal power supply, power can only be supplied to the loads through the downstream microgrid operating off-grid until the anomaly is resolved and it can then reconnect to the municipal power grid. In this case, the power distribution and supply capacity within the off-grid microgrid need further consideration to ensure sufficient power supply. Summary of the Invention

[0003] This disclosure includes a power system comprising: a mains grid connected to a first switch; and a microgrid connected to the mains grid via the first switch, the microgrid including a plurality of converter devices connected to a busbar; a controller connected to each of the first switch and the converter devices and used to transmit a plurality of first signals; and a plurality of loads connected to the converter devices via the busbar, wherein the mains grid is connected to the busbar via the first switch and used to supply power to the loads, the controller further being used to detect a first line connecting the mains grid and the microgrid and to determine whether the first line is abnormal, and when the controller determines that the first line is abnormal, the controller disconnects the first switch and switches a first portion of the converter devices to operate as a voltage source via the first signals.

[0004] This disclosure includes a method for operating a power system, comprising: connecting a mains grid to a plurality of microgrids via a plurality of lines using a plurality of switches; detecting a plurality of voltages on the switches and determining whether the lines are abnormal based on the voltages; when a first line of the lines is determined to be abnormal, disconnecting the first switch of the switches and switching a first portion of a plurality of converter devices in the first microgrid connected to the first line to operate as a voltage source; and when the first line is determined to be normal, maintaining the first switch connected, and each of the converter devices operating as a current source, different from the voltage source mode, wherein when the first line is determined to be abnormal, a second portion of the converter devices operates as a current source, and the second portion is different from the first portion. Simple Explanation of the Diagram

[0005] The nature of this disclosure is best understood when read in conjunction with the accompanying drawings in the following detailed description. It should be noted that, in accordance with industry standard practice, the various features are not drawn to scale. In fact, for clarity of discussion, the dimensions of the various features may be arbitrarily increased or decreased. Figure 1 is a schematic diagram of an electric power system according to some embodiments of the present disclosure. Figure 2 is a schematic diagram of an electric power system according to some embodiments of the present disclosure. Figure 3 is a flowchart illustrating an operation method of a power system according to some embodiments of the present disclosure. Figure 4 is a schematic diagram of an electric power system according to some embodiments of the present disclosure. Figure 5 is a schematic diagram of an electric power system according to some embodiments of the present disclosure. Implementation

[0006] The following disclosure provides numerous different embodiments or examples for implementing various features of the provided subject matter. Specific examples of components and configurations are described below to simplify this disclosure. Of course, these components and configurations are merely examples and are not intended to be limiting. For example, in the following description, forming a first feature on or on a second feature may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which an additional feature is formed between the first and second features such that the first and second features are not in direct contact. Furthermore, reference numerals and / or letters may be repeated in various instances of this disclosure. This repetition is for simplicity and clarity and does not in itself determine the relationship between the various embodiments and / or configurations discussed.

[0007] In this document, when an element is referred to as a "connection" or "coupled," it may mean an "electrical connection" or "electrical coupling." "Connection" or "coupled" can also be used to indicate the operation or interaction between two or more elements. Furthermore, although terms such as "first," "second," etc., are used herein to describe different elements, these terms are merely used to distinguish elements or operations described using the same technical terms. Unless the context clearly indicates otherwise, these terms do not specifically refer to or imply any order or sequence, nor are they intended to limit the invention.

[0008] Additionally, for ease of description, spatial relative terms such as "below," "under," "lower," "above," "upper," "top," "bottom," and similar terms may be used herein to describe the relationship between one element or feature illustrated in the figures and one or more other elements or features. Besides the orientation depicted in the figures, spatial relative terms are intended to cover different orientations of elements in use or operation. Devices may be oriented in other ways (rotated 90 degrees or otherwise), and the spatial relative descriptive terms used herein will be interpreted accordingly.

[0009] Figure 1 is a schematic diagram of a power system 100 according to an embodiment of the present disclosure. As shown in Figure 1, the power system 100 includes a microgrid 110, a power distribution system 120, and a mains grid 130. In some embodiments, the microgrid 110, the power distribution system 120, and the mains grid 130 are separated into a mains end and a grid end by a point of common coupling (PCC).

[0010] As shown in Figure 1, the microgrid 110 includes a controller 111, multiple converter devices 112-116, multiple loads N11 and N12, and multiple switches CB10-CB15, CBN11, and CBN12. In some embodiments, converter device 112 includes a power converter 122 and an energy storage system 132. Converter device 113 includes a power converter 123 and an energy storage system 133. Converter device 114 includes an inverter 124 and a renewable energy device 134. Converter device 115 includes an inverter 125 and a renewable energy device 135. Converter device 116 includes an inverter 126 and a renewable energy device 136.

[0011] As shown in Figure 1, power converter 122 is connected to energy storage system 132 and to busbar BS110 via switch CB11. Power converter 123 is connected to energy storage system 133 and to busbar BS110 via switch CB12. Inverter 124 is connected to renewable energy unit 134 and to busbar BS110 via switch CB13. Inverter 125 is connected to renewable energy unit 135 and to busbar BS110 via switch CB14. Inverter 126 is connected to renewable energy unit 136 and to busbar BS110 via switch CB15. Load N11 is connected to busbar BS110 via switch CBN11. Load N12 is connected to busbar BS110 via switch CBN12.

[0012] In some embodiments, the mains power grid 130 is connected to the power distribution system 120. The power distribution system 120 is connected to the switch CB10 via line L1, and the switch CB10 is connected to the busbar BS110 to distribute power to the microgrid 110. The controller 111 is connected to the switch CB10 to detect the parameters of the mains power supply and to control the switching on and off of the switch CB10. Further details regarding the detection of the mains power supply parameters and the control of the switch CB10 will be described in detail in Figure 3 and the corresponding paragraph.

[0013] In some scenarios, when the mains grid 130 is operating normally and switch CB10 is engaged, the mains grid 130 is used to distribute power to the microgrid 110 and supply power to loads N11 and N12, or to charge energy storage systems 132 and 133. The supply of power to the loads or the charging of the energy storage systems by the mains grid 130 depends on the current operating state of the microgrid 110. In other scenarios, when the mains grid 130 is malfunctioning and switch CB10 is disengaged, the mains grid 130 is disconnected from the microgrid 110, and energy storage systems 132 and 133, as well as renewable energy devices 134-136, are used to supply power to loads N11 and N12. Further details regarding the determination of normal and abnormal operation of the mains grid 130, and the power supply of the microgrid 110 to loads N11 and N12, will be explained in detail in Figure 3 and the corresponding paragraphs.

[0014] In some embodiments, when the mains grid 130 is operating normally, each of the converter devices 112-116 operates in grid-following (GFL) mode. Specifically, when the converter devices 112-116 operate in GFL mode, they function as current sources. At this time, the power converters 122-123 and the inverters 124-126 operate according to the voltage and frequency provided by the mains grid 130.

[0015] In some embodiments, when the mains grid 130 malfunctions, or when the microgrid 110 is off-grid, a portion of the inverter devices 112-116 switch to grid-forming (GFM) mode. Specifically, when one or more of the inverter devices 112-116 operate in GFM mode, they function as voltage sources. In this case, power converters 122-123 and inverters 124-126 independently generate voltage and frequency to supply power to each of loads N11 and N12. In some embodiments, off-grid operation refers to the independent operation of the microgrid 110 to supply power to each of loads N11 and N12 when the switch CB10 connecting the microgrid 110 and the mains grid 130 is disconnected.

[0016] As shown in Figure 1, controller 111 controls converter devices 112-116 via signals S1-S5, respectively, to switch the operating modes of converter devices 112-116. Specifically, controller 111 switches converter devices 112-116 from GFL mode to GFM mode and / or from GFM mode to GFL mode via signals S1-S5. In some embodiments, each of signals S1-S5 can be implemented via a fiber optic network or cable, and controller 111 transmits signals S1-S5 to power converters 122-123 and inverters 124-126 via a virtual channel for power interconnection. In some embodiments disclosed herein, signals S1-S5 can be implemented using GOOSE (Generic Object Oriented Substation Event) virtual channel communication technology.

[0017] In some embodiments, the power distribution system 120, the mains power grid 130, the controller 111, the converter devices 112-116, the loads N11 and N12, and each of the multiple switches CB10-CB15, CBN11, and CBN12 in the power system 100 are interconnected via power lines. In some embodiments, the controller 111 transmits signals S1-S5 to the converter devices 112-116 via GOOSE communication lines.

[0018] In the embodiments disclosed herein, each of switches CB11-CB15, CBN11, and CBN12 is in the ON state. In other words, when the microgrid 110 is operating, each of switches CB11-CB15, CBN11, and CBN12 is ON.

[0019] In some embodiments, converter devices 112-116 may be implemented using inverter-based power resources (IBRs). Power converters 122-123 may be implemented using a power conversion system (PCS). Energy storage systems 132-133 may be implemented using a battery energy storage system (BESS). Inverters 124-126 may be implemented using a solar photovoltaic inverter (PV inverter). Renewable energy devices 134-136 may be implemented using a solar photovoltaic array (PV array). In some embodiments, renewable energy devices 134-136 may also be implemented using generators or renewable energy sources, such as solar power systems, wind power systems, hydropower systems, and geothermal power systems; however, this disclosure is not limited to the aforementioned power generation systems.

[0020] In some embodiments, the power distribution system 120 may be located in a substation or related facility and is used to distribute the power provided by the mains power grid 130 to multiple different microgrids.

[0021] In some embodiments, loads N11-N12 may be general-purpose power supplies with low instantaneous power withdrawal. In other embodiments, loads N11-N12 may be power supplies for electric vehicles (EVs) with higher instantaneous power withdrawal. For example, general-purpose power supplies may have an instantaneous power withdrawal of 0.05-5.0 kWh, while electric vehicle power supplies may have an instantaneous power withdrawal of 20-400 kWh.

[0022] Figure 2 is a schematic diagram of a power system 200 according to some embodiments of the present disclosure. As shown in Figure 2, the power system 200 includes various devices found in the power system 100. The power system 200 further includes a microgrid 210.

[0023] In some embodiments, power system 200 is another variation of power system 100. In various embodiments, power systems 100 and 200 may include one or more microgrids, such as microgrids 110 and 210, however, this disclosure is not limited thereto.

[0024] As shown in Figure 2, microgrid 210 includes a controller 211, multiple converter devices 212-216, multiple loads N21 and N22, and multiple switches CB20-CB25, CBN21, and CBN22. In some embodiments, converter device 212 includes a power converter 222 and an energy storage system 232. Converter device 213 includes a power converter 223 and an energy storage system 233. Converter device 214 includes an inverter 224 and a renewable energy device 234. Converter device 215 includes an inverter 225 and a renewable energy device 235. Converter device 216 includes an inverter 226 and a renewable energy device 236. In some embodiments, the connection relationships and operation modes of the various devices in microgrid 210 are similar to those in microgrid 110. For the sake of brevity, some similarities between microgrids 210 and 110 will not be repeated.

[0025] As shown in Figure 2, power converter 222 is connected to energy storage system 232 and then to busbar BS210 via switch CB21. Power converter 223 is connected to energy storage system 233 and then to busbar BS210 via switch CB22. Inverter 224 is connected to renewable energy unit 234 and then to busbar BS210 via switch CB23. Inverter 225 is connected to renewable energy unit 235 and then to busbar BS210 via switch CB24. Inverter 226 is connected to renewable energy unit 236 and then to busbar BS210 via switch CB25. Load N21 is connected to busbar BS210 via switch CBN21. Load N22 is connected to busbar BS210 via switch CBN22.

[0026] In some embodiments, the power distribution system 120 is connected to switch CB20 via line L2, and switch CB20 is connected to busbar BS210 to distribute power to microgrid 210. Controller 211 is connected to switch CB20 to detect parameters of the mains power supply and control the switching of switch CB20. Further details regarding the detection of mains power parameters and the control of switch CB20 will be described in detail in Figure 3 and the corresponding paragraph. In some embodiments, the independent operation of microgrid 210 is similar to that of microgrid 110. For simplicity, the similarities in operation between microgrids 210 and 110 will not be repeated.

[0027] In some scenarios, when the mains power grid 130 is operating normally and each of switches CB10 and CB20 is engaged, the mains power grid 130 is used to distribute power to each of microgrids 110 and 210 and to supply power to loads N11, N12, N21 and N22.

[0028] In other scenarios, when the mains power grid 130 malfunctions and either switch CB10 or CB20 is disconnected, the mains power grid 130 is disconnected from each of the microgrids 110 and 210. Energy storage systems 132 and 133, and renewable energy devices 134-136, are used to supply power to loads N11 and N12. Energy storage systems 232 and 233, and renewable energy devices 234-236, are used to supply power to loads N21 and N22.

[0029] In other scenarios, when the mains grid 130 is operating normally and one of the switches CB10 and CB20 is disconnected, the microgrid corresponding to the disconnected switch operates off-grid. The microgrid corresponding to the one with switches CB10 and CB20 still connected is powered by the mains grid 130. For example, when the mains grid 130 is operating normally, switch CB10 is disconnected, and switch CB20 is engaged, the mains grid 130 is used to distribute power to the microgrid 210 and to power loads N21 and N22. Simultaneously, the mains grid 130 is disconnected from the microgrid 110, and the microgrid 110 operates off-grid. Energy storage systems 132 and 133 and renewable energy devices 134-136 are used to power loads N11 and N12.

[0030] As shown in Figure 2, controller 211 controls converter devices 212-216 via signals S6-S10, respectively, to switch the operating modes of converter devices 212-216. Specifically, controller 211 switches converter devices 212-216 from GFL mode to GFM mode and / or from GFM mode to GFL mode via signals S6-S10. In some embodiments, signals S6-S10 can be implemented using GOOSE virtual channel communication technology.

[0031] In some embodiments, when the mains power grid 130 is operating normally, each of the converter devices 112-116 and 212-216 operates in GFL mode. At this time, each of the converter devices 112-116 and 212-216 operates as a current source.

[0032] In other embodiments, when the mains power grid 130 malfunctions, a portion of converter devices 112-116 and 212-216 switches to GFM mode. At this time, converter devices 112-116 and 212-216 operate as voltage sources. In some embodiments, a portion of converter devices 112-116 and 212-216 includes one or more of converter devices 112-116 and / or one or more of converter devices 212-216.

[0033] In some embodiments, the controller 211, the converter devices 212-216, the loads N21 and N22, and each of the multiple switches CB20-CB25, CBN21, and CBN22 are interconnected via power lines. In some embodiments, the controller 211 transmits signals S6-S10 to the converter devices 212-216 via GOOSE communication lines.

[0034] In the embodiments disclosed herein, each of switches CB21-CB25, CBN21, and CBN22 is in the active state. In other words, when the microgrid 210 is operating, each of switches CB21-CB25, CBN21, and CBN22 is turned on.

[0035] In some embodiments, converter devices 212-216 may be implemented using an IBR. Power converters 222-223 may be implemented using a PCS. Energy storage systems 232-233 may be implemented using a BESS. Inverters 224-226 may be implemented using solar photovoltaic inverters. Renewable energy devices 234-236 may be implemented using solar cell arrays.

[0036] In some embodiments, loads N21-N22 may be general power supplies with low instantaneous power withdrawal. In other embodiments, loads N11-N12 may be power supplies for electric vehicles (EVs) with higher instantaneous power withdrawal.

[0037] Figure 3 is a flowchart illustrating an operation method 300 of power systems 100 and 200 according to some embodiments of the present disclosure. As shown in Figure 3, the operation method 300 includes operations 301-312. In some embodiments, the operation method 300 can be applied to power systems 100 and 200, and the following various embodiments will use power system 200 as an example to illustrate the operation method 300.

[0038] In operation 301, when the power system 200 is running, the municipal power grid 130 is connected to each of the microgrids 110 and 210.

[0039] Specifically, when the power system 200 is operating, microgrids 110 and 210 respectively switch CB10 and CB20. At this time, the mains power grid 130 distributes power to each of microgrids 110 and 210 through the power distribution system 120 to supply power to loads N11, N12, N21, and N22. After completing operation 301, the power system 200 proceeds to operation 302.

[0040] In operation 302, controllers 111 and 211 measure and calculate the parameters of the mains terminals of lines L1 and L2, respectively.

[0041] Specifically, controller 111 measures multiple parameters between power distribution system 120 and switch CB10 via line L1. Controller 211 measures multiple parameters between power distribution system 120 and switch CB20 via line L2. These parameters include voltages V_CB10 and V_CB20, currents I_CB10 and I_CB20, and frequencies F_CB10 and F_CB20 between switches CB10 and CB20 and power distribution system 120, respectively. However, this disclosure is not limited to the parameters described above.

[0042] In some embodiments, controllers 111 and 211 can measure multiple parameters of lines L1 and L2 using relays and voltmeters. Power system 200 performs operation 303 after completing operation 302.

[0043] In operation 303, controllers 111 and 211 monitor multiple initial state parameters of converter devices 112~116 and 212~216, respectively.

[0044] Specifically, converter devices 112-116 transmit their initial state parameters to controller 111 via signals S1-S5 respectively. Converter devices 212-216 transmit their initial state parameters to controller 211 via signals S6-S10 respectively.

[0045] In some embodiments, the initial state parameters of converter devices 112-116 include the operating state of converter devices 112-116 and the capacities S112_GFL to S116_GFL of converter devices 112-116 operating in GFL mode. The initial state parameters of converter devices 212-216 include the operating state of converter devices 212-216 and the capacities S212_GFL to S216_GFL of converter devices 212-216 operating in GFL mode. In some embodiments, each of the capacities S112_GFL to S116_GFL and S212_GFL to S216_GFL may have a capacity unit of kilowatt-hours (kWh) or megawatt-hours (MWh). Power system 200 performs operation 304 after completing operation 303.

[0046] In operation 304, controllers 111 and 211 calculate the total capacity of microgrids 110 and 210, respectively.

[0047] Specifically, controller 111 calculates the total capacity ST1_GFL of microgrid 110 when converter devices 112-116 operate in GFL mode, and the capacity S1_GFM of microgrid 110 when converter devices 112-116 operate in GFM mode. Similarly, controller 211 calculates the total capacity ST2_GFL of microgrid 210 when converter devices 212-216 operate in GFL mode, and the capacity S2_GFM of microgrid 210 when converter devices 212-216 operate in GFM mode.

[0048] In some embodiments, the total capacities ST1_GFL and ST2_GFL can be calculated according to the following formula. Where Ni, Nj, i, and j are positive integers greater than zero.

[0049] In formula (1), the total capacity ST_GFL(t) is used to represent the total capacity of the microgrid at time t and when it is operating in GFL mode, for example, the total capacity ST1_GFL and ST2_GFL.

[0050] In formula (1), the capacity S_PCS_GFL_i(t) represents the total capacity of the PCS-implemented converter devices in the microgrid at time t, operating in GFL mode. The positive integer Ni represents the number of PCS-implemented converter devices in the microgrid, such as converter devices 112 and 113. The positive integer i represents the i-th converter device; for example, i equals 1 to represent converter device 112, and i equals 2 to represent converter device 113.

[0051] In formula (1), the capacity S_PV_GFL_j(t) represents the total capacity of inverter-implemented converter devices in the microgrid at time t, operating in GFL mode. The positive integer Nj represents the number of inverter-implemented converter devices in the microgrid, for example, converter devices 114~116. The positive integer j represents the j-th inverter-implemented converter device; for example, j equals 1 to represent converter device 114, j equals 2 to represent converter device 115, and j equals 3 to represent converter device 116. In some embodiments, the capacity S_PV_GFL_j can be used to represent the capacity of the solar photovoltaic inverter.

[0052] In some embodiments, the parameter B_j(t) in formula (1) is used to indicate the maximum power percentage capacity of the j-th solar photovoltaic inverter at time t. In some embodiments, the parameter B_j can be expressed as a percentage value or a decimal, such as 20% or 0.2. However, this disclosure is not limited to this value or representation.

[0053] In some embodiments, the capacities S1_GFM and S2_GFM can be calculated based on the total capacities ST1_GFL and ST2_GFL. Specifically, the capacities S1_GFM and S2_GFM are calculated using the following formulas.

[0054] In formula (2), the capacity S_GFM(t) is used to represent the capacity of the microgrid at time t and when it is operating in GFM mode, for example, the capacities S1_GFM and S2_GFM.

[0055] In some embodiments, parameter A(t) indicates the percentage of multiple converter devices that can switch from GFL mode to GFM mode at time t. In some embodiments, parameter A may be expressed as a percentage value or a decimal, such as 20% or 0.2. However, this disclosure is not limited to this value or representation.

[0056] In some embodiments, the percentage value of parameter A is directly proportional to the number of converter devices operating in GFM mode. Specifically, when the number of converter devices switching from GFL mode to GFM mode increases, the percentage value of parameter A increases. When the number of converter devices switching from GFL mode to GFM mode decreases, the percentage value of parameter A decreases.

[0057] For example, in formula (2), when each of the converter devices 112-116 operates in GFL mode, the total capacity ST1_GFL of the microgrid 110 is 50 MWh. In some scenarios, when one of the converter devices 112-116 switches from GFL mode to GFM mode, parameter A has a conversion percentage of 20%. In this case, the capacity S1_GFM of the microgrid 110 is equal to 50 MWh multiplied by 20%, which is 10 MWh. In other scenarios, when multiple of the converter devices 112-116 switch from GFL mode to GFM mode, parameter A has a conversion percentage of 90%. In this case, the capacity S1_GFM of the microgrid 110 is equal to 50 MWh multiplied by 90%, which is 45 MWh.

[0058] In some embodiments, the calculation methods for the total capacity ST2_GFL and capacity S2_GFM of microgrid 210, and the relationship between the operating modes of converter devices 212-216 and the calculation of the total capacity ST2_GFL and capacity S2_GFM, are similar to those of microgrid 110. For the sake of simplicity, the calculation of the total capacity ST2_GFL and capacity S2_GFM will not be described again with examples. After completing operation 304, power system 200 performs operation 305.

[0059] In operation 305, controllers 111 and 211 calculate the capacity of converter devices 112~116 and 212~216 in GFM mode and GFL mode, respectively.

[0060] Specifically, controller 111 calculates the capacity S1_GFM of a portion of the converter devices 112-116 operating in GFM mode, and the capacity S1_GFL of another portion of the converter devices 112-116 maintaining in GFL mode. Controller 211 calculates the capacity S2_GFM of a portion of the converter devices 212-216 operating in GFM mode, and the capacity S2_GFL of another portion of the converter devices 212-216 maintaining in GFL mode.

[0061] In some embodiments, the capacities S1_GFM and S2_GFM can be calculated using formula (2). The capacities S1_GFL and S2_GFL can be calculated using the following formula.

[0062] In formula (3), the capacity S_GFL(t) is used to represent the capacity of the microgrid at time t, when one or more of the converter devices are still operating in GFL mode, for example, the capacities S1_GFL and S2_GFL.

[0063] In some embodiments, the operating modes of multiple converter devices can be switched according to the required load capacity S_Load. Specifically, when a portion of the multiple converter devices operates in GFL mode, the microgrid has a capacity S_GFL. When another portion of the multiple converter devices operates in GFM mode, the microgrid has a capacity S_GFM. In this case, the sum of the capacities S_GFL and S_GFM must be greater than or equal to the load capacity S_Load and satisfy the following formula. As shown in formula (4), the sum of the capacities S_GFL and S_GFM at time t is greater than or equal to the load capacity S_Load required by the load at time t.

[0064] For example, at time t, loads N11 and N12 have withdrawn capacities S_N11 and S_N12, respectively. When a portion of converter devices 112-116 operates in GFL mode and another portion operates in GFM mode, microgrid 110 has capacities S1_GFL and S1_GFM. In this case, the sum of each of the capacities S1_GFL and S1_GFM must be greater than or equal to the sum of each of the withdrawn capacities S_N11 and S_N12. Microgrid 210 operates similarly to microgrid 110; for simplicity, the withdrawn capacity of microgrid 210 will not be described again.

[0065] In some embodiments, a portion of the multiple loads may be further divided into critical loads, and another portion may be further divided into non-shutdown loads. Accordingly, the load capacity S_Load of the multiple loads may be further divided into critical load capacity SC_Load of critical loads and non-critical load capacity SNC_Load of non-critical loads, satisfying the following formula. As shown in formula (5), the load capacity S_Load required by the load in the microgrid at time t is equal to the sum of the critical load capacity SC_Load and the non-critical load capacity SNC_Load at time t.

[0066] For example, in microgrids 110 and 210, a portion of loads N11, N12, N21, and N22 can be classified as critical loads, such as loads N11 and N21. Another portion of loads N11, N12, N21, and N22 can be classified as non-critical loads, such as loads N12 and N22. However, this disclosure is not limited to this example.

[0067] In some embodiments, the critical load capacity SC_Load represents the load capacity required for a critical load. Critical loads may include hospitals, city centers, military facilities, banks, or other similar electrical installations; however, this disclosure is not limited to these critical installations. The non-critical load capacity SNC_Load represents the load capacity required for a non-critical load. Non-critical loads may include general household electricity, charging stations, or other similar electrical installations; however, this disclosure is not limited to these non-critical installations. After completing operation 305, the power system 200 proceeds to operation 306.

[0068] In operation 306, controllers 111 and 211 determine whether the mains power grid 130 and the lines L1 and L2 connected to the mains power grid are abnormal.

[0069] Specifically, controller 111 determines whether line L1 is abnormal based on voltage V_CB10, current I_CB10, and frequency F_CB10. Similarly, controller 211 determines whether line L2 is abnormal based on voltage V_CB20, current I_CB20, and frequency F_CB20.

[0070] In some embodiments, when the voltage level of voltage V_CB10 is less than or equal to the lower voltage level V_limL, or when the voltage level of voltage V_CB10 is greater than or equal to the upper voltage level V_limH, the controller 111 determines that line L1 is abnormal. When the current level of current I_CB10 is greater than the threshold current level I_lim, the controller 111 determines that line L1 is abnormal. When the frequency F_CB10 is less than or equal to the lower frequency F_limL, or when the frequency F_CB10 is greater than or equal to the upper frequency F_limH, the controller 111 determines that line L1 is abnormal.

[0071] Correspondingly, when the voltage level of voltage V_CB20 is less than or equal to the lower limit voltage level V_limL, or when the voltage level of voltage V_CB20 is greater than or equal to the upper limit voltage level V_limH, controller 211 determines that line L2 is abnormal. When the current level of current I_CB20 is greater than the threshold current level I_lim, controller 211 determines that line L2 is abnormal. When the frequency F_CB20 is less than or equal to the lower limit frequency F_limL, or when the frequency F_CB20 is greater than or equal to the upper limit frequency F_limH, controller 211 determines that line L2 is abnormal.

[0072] In some embodiments, when controllers 111 and 211 determine that lines L1 and L2 are abnormal, controllers 111 and 211 determine that the mains power grid 130 is operating abnormally, and the power system 200 performs operation 307 after completing operation 306.

[0073] In some embodiments, when controllers 111 and 211 determine that lines L1 and L2 are normal, controllers 111 and 211 determine that the mains power grid 130 is operating normally, and the power system 200 repeats operation 302 after completing operation 306.

[0074] In operation 307, controllers 111 and 211 disconnect switches CB10 and CB20 connected to the mains power grid 130 and transmit commands to multiple converter devices.

[0075] Specifically, when controllers 111 and 211 disconnect switches CB10 and CB20 connected to the mains power grid 130, microgrids 110 and 210 operate off-grid. At this time, controller 111 transmits commands to converter devices 112-116 via signals S1-S5 respectively. Controller 211 transmits commands to converter devices 212-216 via signals S6-S10 respectively.

[0076] In some embodiments, the above instructions may include switching converter devices 112-116 and 212-216 from GFL mode to GFM mode, and setting converter devices 112-116 and 212-216 to the corresponding rated output voltage level V_DEF. However, the instructions may include other similar parameters and settings, and this disclosure is not limited to the above instructions. After completing operation 307, the power system 200 performs operation 308.

[0077] In operation 308, controllers 111 and 211 switch a portion of the converter equipment to GFM mode and GFL mode.

[0078] Specifically, controller 111 switches one or more of converter devices 112-116 from GFL mode to GFM mode via signals S1-S5 respectively. Controller 211 switches one or more of converter devices 212-216 from GFL mode to GFM mode via signals S6-S10 respectively.

[0079] In some embodiments, due to differences in the modules or configurations of the converter devices, the capacity that the converter devices can supply under GFM mode varies. Therefore, the capacity S_GFM that the microgrid can provide to the loads also differs. For example, in some scenarios, the capacity S1_GFM that microgrid 110 can provide under GFM mode is less than the required load capacity S1_Load for loads N11 and N12. In other scenarios, the capacity S2_GFM of microgrid 210 is greater than the capacity that microgrid 210 can provide to loads N21 and N22 under GFM mode.

[0080] In the above scenario, the controllers 111 and 211 disclosed herein can switch a portion of the converter devices 112-116 and 212-216 from GFL mode to GFM mode to supply power to loads N11, N12, N21 and N22 through the methods of total load determination, critical load determination in GFM mode, and critical load determination in both GFM and GFL modes.

[0081] In the method for determining the total load, when the controller's calculated capacity S_GFM is greater than the load's required tap-through capacity S_Load, one or more of the converter devices switch to GFM mode and are used to supply power to the load. The method for determining the total load satisfies the following formula. Specifically, when the microgrid's capacity S_GFM at time t is greater than the load-discharge capacity S_Load, the converter's capacity S_GFM operating in GFM mode can supply the load within the microgrid. At this time, the converter's capacity S_GFL operating in GFL mode is equal to the total capacity ST_GFL minus the capacity switched to GFM mode, i.e., the total capacity ST_GFL multiplied by parameter A.

[0082] For example, when controller 111 calculates that the capacity S1_GFM of microgrid 110 at time t is greater than the required load capacity S_Load of each of loads N11 and N12, a portion of converter devices 112-116 operates in GFM mode to supply power to each of loads N11 and N12.

[0083] In the method for determining the critical load supply in GFM mode, when the controller's calculated capacity S_GFM is greater than the critical load's critical load capacity SC_Load, one or more converter devices switch to GFM mode operation and are used to supply power to the critical load. The method for determining the critical load supply in GFM mode satisfies the following formula. Specifically, when the microgrid's capacity S_GFM at time t is greater than the critical load capacity SC_Load, the capacity S_GFM of one or more converter devices operating in GFM mode can supply the critical load within the microgrid. At this time, the capacity S_GFL of the converter devices operating in GFL mode is equal to the total capacity ST_GFL minus the capacity switched to GFM mode, i.e., the total capacity ST_GFL multiplied by parameter A.

[0084] For example, when load N11 is a critical load and load N12 is a non-critical load, and when controller 111 calculates that the capacity S1_GFM of microgrid 110 at time t is greater than the critical load capacity SC_Load required by load N11, a portion of converter devices 112-116 switches to GFM mode, and another portion of converter devices 112-116 operates in GFL mode to jointly supply power to loads N11 and N12. In the above example, when the capacity required by load N11 changes (e.g., the required capacity increases), the converter devices operating in GFM mode output power according to the changed capacity required by load N11 to absorb the change in the required capacity of load N11. At this time, the converter devices operating in GFM and GFL modes maintain joint power supply to loads N11 and N12.

[0085] In some scenarios, when microgrid 110 is operating, converter devices 112-114 operate in GFM mode, and their capacity is sufficient to cover load variations in load N11. Conversely, converter devices 115-116 operate in GFL mode. In this mode, converter devices 115-116 operate in maximum power point tracking (MPPT), and their output power can also be scheduled according to the converter devices operating in GFM mode.

[0086] In other scenarios, when microgrid 110 is operating and the capacity of converter devices 112-114 operating in GFM mode is insufficient to cover load changes in load N11, converter devices 115-116 can further switch to GFM mode operation to absorb load changes in load N11. In the method for determining critical load in GFM mode, converter devices 112-116 are used together to supply power to each of loads N11 and N12.

[0087] In some embodiments, whether a converter device (e.g., converter devices 112-116) can switch to GFM mode operation depends on the actual device function.

[0088] In the method for determining the critical load supply in GFM and GFL modes, when the controller-calculated capacity S_GFM is less than the critical load's critical load capacity SC_Load, but the sum of the capacities S_GFM and S_GFL is greater than the critical load's critical load capacity SC_Load, each of the converter devices switches to GFM or GFL mode to supply power to the critical load. The method for determining the critical load supply in GFM mode satisfies the following formula. Specifically, when the sum of the microgrid's capacity S_GFM and capacity S_GFL at time t exceeds the critical load capacity SC_Load, each converter device operates in both GFM and GFL modes, jointly supplying power to the critical load within the microgrid. In this case, the converter device's capacity S_GFL operating in GFL mode is equal to the total capacity ST_GFL minus the capacity switched to GFM mode, i.e., the total capacity ST_GFL multiplied by parameter A.

[0089] For example, when load N11 is a critical load and load N12 is a non-critical load, and when controller 111 calculates that the capacity S1_GFM of microgrid 110 at time t is less than the critical load capacity SC_Load required by load N11, a portion of converter devices 112-116 operates in GFM mode, while another portion of converter devices 112-116 maintains GFL mode to provide capacity S1_GFL to jointly power loads N11 and N12. In some embodiments, since the capacities S1_GFM and S1_GFL are only sufficient to provide power to loads N11 and N12, when the power required by critical load N11 changes, the change in the power required by load N11 cannot be absorbed by converter devices 112-114.

[0090] In some situations, when the change in the amount of electricity required by the load N11 cannot be absorbed by the converter devices 112~114 operating in GFM mode, and the converter devices 112~114 cannot adjust the output voltage in a timely manner according to the change in electricity, the bus BS110 may experience voltage imbalance.

[0091] In other scenarios, when the power required by the changes in loads N11 and N12 exceeds the power that converter devices 112-116 can provide, the microgrid 110 can also maintain a stable power supply from converter devices 112-116 to critical load N11 by unloading the non-critical load N12. However, this disclosure is not limited to the above-mentioned operating scenarios.

[0092] In some embodiments, the above-described discrimination method only provides some implementations of the operation of microgrids 110 and 210 disclosed herein; however, the content of this disclosure is not limited thereto. In various embodiments, microgrids 110 and 210 can still control the operating mode of converter devices using different discrimination methods. Power system 200 performs operation 309 after completing operation 308.

[0093] In operation 309, each of the multiple converter devices 112~116 and 212~216 sends back the status parameters after switching to GFM mode and GFL mode to controllers 111 and 211.

[0094] Specifically, the aforementioned state parameters include the output voltages V112~V116 and V212~V216 of each of the converter devices 112~116 and 212~216, the actual power P112~P116 and P212~P216, the virtual power Q112~Q116 and Q212~Q216, and the operating mode. The converter devices 112~116 and 212~216 respectively transmit their respective output voltages V112~V116 and V212~V216 back to the controllers 111 and 211. The converter devices 112~116 and 212~216 further transmit their respective operating modes back to the controllers 111 and 211. After completing operation 309, the power system 200 performs operation 310.

[0095] In operation 310, controllers 111 and 211 determine whether the status parameters of converter devices 112~116 and 212~216 after switching operating modes are the same as the instructions.

[0096] Specifically, controller 111 determines whether the voltage levels of output voltages V112~V116 are equal to the rated output voltage level V_DEF, whether the real power P112~P116 and virtual power Q112~Q116 are the same as the power output command values, and whether the operating modes of converter devices 112~116 and 212~216 are the same as the command. Controller 211 determines whether the voltage levels of output voltages V212~V216 are equal to the rated output voltage level V_DEF, and whether the operating modes of converter devices 112~116 and 212~216 are the same as the command.

[0097] In some embodiments, when controllers 111 and 211 determine that the output voltages V112~V116 and V212~V216 of converter devices 112~116 and 212~216, the actual power P112~P116 and P212~P216, the virtual power Q112~Q116 and Q212~Q216, and the operating mode of the converter devices 112~116 and 212~Q216 are the same as the command, the power system 200 performs operation 311. When controllers 111 and 211 determine that the output voltages V112~V116 and V212~V216 of converter devices 112~116 and 212~216, and the operating mode of the converter devices 212~216 are different from the command, the power system 200 performs operation 312.

[0098] For example, when controller 111 sends a command to converter device 112 in operation 307 that includes the rated output voltage level V_DEF and GFM mode, and the rated output voltage level V_DEF is 50 volts, controller 111 determines whether the voltage level of output voltage V112 is equal to 50 volts, and whether the real power P112 and virtual power Q112 are the same as the command values, and whether converter device 112 is operating in GFM mode. When controller 111 determines that the voltage level of output voltage V112 is equal to 50 volts and converter device 112 is operating in GFM mode, controller 111 determines that the output voltage V112 and operating mode of converter device 112 are the same as the command. Conversely, when the controller 111 determines that the voltage level of the output voltage V112 is not equal to 50 volts, and / or the converter device 112 is not operating in GFM mode, the controller 111 determines that the output voltage V112 and / or the operating mode of the converter device 112 are different from the command.

[0099] In operation 311, microgrids 110 and 210 operate off-grid and supply power to loads N11, N12, N21 and N22.

[0100] Specifically, when controller 111 determines that the output voltages V112~V116 of converter devices 112~116 and the operating mode are the same as the command, switch CB10 remains disconnected, and microgrid 110 is used to supply power to loads N11 and N12. When controller 211 determines that the output voltages V212~V216 of converter devices 212~216 and the operating mode are the same as the command, switch CB20 remains disconnected, and microgrid 210 is used to supply power to loads N21 and N22. After completing operation 311, power system 200 completes operation method 300.

[0101] In operation 312, the converter devices 112~116 and 212~216 perform parameter compensation.

[0102] Specifically, when controller 111 determines that the output voltage V112~V116, actual output power P112~P116, virtual output power Q112~Q116, and operating mode of converter devices 112~116 are different from the command, controller 111 retransmits the command to converter devices 112~116 via signals S1~S5 respectively. When controller 211 determines that the output voltage V212~V216 and operating mode of converter devices 212~216 are different from the command, controller 211 retransmits the command to converter devices 212~216 via signals S6~S10 respectively. After completing operation 312, power system 200 repeats operation 309.

[0103] In some methods, the architecture of the mains grid and microgrid primarily uses feeders as the power supply and distribution path for the microgrid. Power is typically supplied to the microgrid from the mains grid to power the loads. When an anomaly occurs in the upstream line or the mains power, power can only be supplied to the loads through the downstream microgrid operating off-grid until the anomaly is resolved and it can then be reconnected to the mains grid. However, when the capacity provided by the off-grid microgrid is insufficient, the only way to reduce power demand is to offload the load. This can lead to power outages for some emergency or critical facilities.

[0104] Compared to the methods described above, in the embodiments disclosed herein, power systems 100 and 200 can control converter devices 112-116 and 212-216 to switch operating modes via signals S1-S10 using the GOOSE communication protocol. When lines L1 and L2 connected to the mains power grid 130 experience an anomaly, converter devices 112-116 and 212-216 switch from GFL mode to GFM mode according to signals S1-S10, enabling microgrids 110 and 210 to continuously supply power to loads N11, N12, N21, and N22 during off-grid operation. The power systems 100 and 200 disclosed herein further prevent emergency or critical facilities from being unable to obtain power due to mains power anomalies.

[0105] Figure 4 is a schematic diagram of a power system 200 according to some embodiments of the present disclosure. As shown in Figure 4, switch CB10 in microgrid 110 is in the off state, and switch CB20 in microgrid 210 is in the on state.

[0106] Referring to Figures 4 and 3, in the scenario shown in Figure 4, controller 111 determines that line L1 is abnormal during operation 306 and disconnects switch CB10. At this time, controller 111 transmits commands to converter devices 112-116 via signals S1-S5, switching each of converter devices 112-114 to GFM mode and maintaining each of converter devices 115-116 in GFL mode. When converter devices 112-114 operate in GFM mode, microgrid 110 has the capacity S1_GFM provided by converter devices 112-114. When converter devices 115-116 operate in GFL mode, microgrid 110 has the capacity S1_GFL provided by converter devices 115-116.

[0107] In some scenarios, when load N11 is a critical load and load N12 is a non-critical load, load N11 has a critical load withdrawal capacity SC_Load, and load N12 has a non-critical load withdrawal capacity SNC_Load. In this case, when the capacity S1_GFM is greater than the sum of the critical load withdrawal capacity SC_Load and the non-critical load withdrawal capacity SNC_Load, converter devices 112-114 are used to supply power to each of loads N11 and N12. Specifically, the capacity S1_GFM provided by converter devices 112-114 is used to supply power to each of loads N11 and N12.

[0108] In some embodiments, when the capacity S1_GFM is greater than the critical load removal capacity SC_Load and less than the load removal capacity S_Load, converter devices 112-114 operate in GFM mode, and converter devices 115-116 operate in GFL mode to supply power to loads N11 and N12. Converter devices 112-114 can absorb changes in the capacity required by load N11. Specifically, when converter devices 112-114 operate in GFM mode, the capacity S1_GFM provided by microgrid 110 is greater than the capacity required by load N11. At this time, converter devices 112-116 jointly supply power to each of loads N11 and N12. When the capacity required by load N11 changes, converter devices 112-114 can absorb the changing capacity of load N11.

[0109] In other embodiments, when the capacity S1_GFM is less than the critical load capacity SC_Load, each of the converter devices 112-116 supplies power to loads N11 and N12. When the power required by the loads N11 and N12 changes exceeds the power that the converter devices 112-116 can provide, a voltage drop occurs. The controller 111 disconnects the switch CBN12, causing the microgrid 110 to stop supplying power to load N12, ensuring that the capacity generated by each of the converter devices 112-116 is sufficient to supply power to load N11. Specifically, the capacity S1_GFM provided by converter devices 112-114 operating in GFM mode and the capacity S1_GFL provided by converter devices 115-116 operating in GFL mode are used to supply power to each of loads N11 and N12. When the capacity required by load N11 changes, converter devices 112-114 cannot adjust the provided capacity S1_GFM to absorb the change in the capacity required by load N11. At this time, the controller 111 unloads the load N12, so that the capacity S1_GFM is sufficient to power the critical load N11.

[0110] In other scenarios, when load N11 is a non-critical load and load N12 is a critical load, load N12 has a critical load withdrawal capacity SC_Load, and load N11 has a non-critical load withdrawal capacity SNC_Load. In this case, the operation of microgrid 110 is similar to the previous scenario, only requiring the replacement of loads N11 and N12. Therefore, for the sake of brevity, the similarities will not be repeated.

[0111] Referring to Figures 4 and 3, in the scenario shown in Figure 4, controller 211 determines that line L2 is normal during operation 306. At this time, switch CB20 remains engaged, and the mains power grid 130 continues to supply power to microgrid 210 to supply power to loads N21 and N22.

[0112] Figure 5 is a schematic diagram of a power system 200 according to some embodiments of the present disclosure. As shown in Figure 5, each of the switches CB10 in microgrid 110 and CB20 in microgrid 210 is in a disconnected state.

[0113] Referring to Figures 5 and 3, in the scenario shown in Figure 5, controller 111 determines that line L1 is abnormal in operation 306 and disconnects switch CB10. Controller 211 determines that line L2 is abnormal in operation 306 and disconnects switch CB20.

[0114] At this time, controller 111 transmits commands to converter devices 112-116 via signals S1-S5 respectively, switching each of converter devices 112-114 to GFM mode and maintaining each of converter devices 115-116 in GFL mode. Correspondingly, controller 211 transmits commands to converter devices 212-216 via signals S6-S10 respectively, switching each of converter devices 212-214 to GFM mode and maintaining each of converter devices 215-216 in GFL mode.

[0115] In some embodiments, when each of inverter devices 112-114 and 212-214 operates in GFM mode, microgrid 110 has the capacity S1_GFM provided by inverter devices 112-114, and microgrid 210 has the capacity S2_GFM provided by inverter devices 212-214. When each of inverter devices 115-116 and 215-216 operates in GFL mode, microgrid 110 has the capacity S1_GFL provided by inverter devices 115-116, and microgrid 210 has the capacity S2_GFL provided by inverter devices 215-216.

[0116] In some scenarios, when loads N11 and N21 are critical loads and loads N12 and N22 are non-critical loads, loads N11 and N21 have critical load capacity SC1_Load and SC2_Load respectively, and loads N12 and N22 have non-critical load capacity SNC1_Load and SNC2_Load respectively.

[0117] At this time, when the capacity S1_GFM is greater than the sum of the critical load capacity SC1_Load and the non-critical load capacity SNC1_Load, converter devices 112-114 supply power to each of loads N11 and N12. Specifically, the capacity S1_GFM provided by converter devices 112-114 is used to supply power to each of loads N11 and N12. Correspondingly, when the capacity S2_GFM is greater than the sum of the critical load capacity SC2_Load and the non-critical load capacity SNC2_Load, converter devices 212-214 supply power to each of loads N21 and N22. Specifically, the capacity S2_GFM provided by converter devices 212-214 is used to supply power to each of loads N21 and N22.

[0118] In some embodiments, when the capacity S1_GFM is greater than the critical load extraction capacity SC1_Load but less than the load extraction capacity S1_Load, converter devices 112-114 operate in GFM mode, and converter devices 115-116 operate in GFL mode, jointly supplying power to loads N11 and N12. Specifically, the capacity S1_GFM provided by converter devices 112-114 and the capacity S1_GFL provided by converter devices 115-116 are jointly supplied to loads N11 and N12. In this case, when the required capacity of load N11 changes, the operation of converter devices 112-114 in GFM mode can further absorb the change in the required capacity of load N11. Correspondingly, when the capacity S2_GFM is greater than the critical load extraction capacity SC2_Load but less than the load extraction capacity S2_Load, converter devices 212-214 operate in GFM mode, and converter devices 215-216 operate in GFL mode to jointly supply power to loads N21 and N22. Specifically, the capacity S2_GFM provided by converter devices 212-214 and the capacity S2_GFL provided by converter devices 215-216 are jointly supplied to loads N21 and N22. At this time, when the capacity required by load N21 changes, the operation of converter devices 212-214 in GFM mode can further absorb the change in the capacity required by load N21.

[0119] In other embodiments, when the capacity S1_GFM is less than the critical load capacity SC1_Load, each of the converter devices 112-116 supplies power to loads N11 and N12. When the power required by the changes in loads N11 and N12 exceeds the power that the converter devices 112-116 can provide, a voltage drop occurs, and the controller 111 disconnects the switch CBN12, causing the microgrid 110 to stop supplying power to load N12. Specifically, the capacity S1_GFM provided by converter devices 112-114 and the capacity S1_GFL provided by converter devices 115-116 are used to supply power to loads N11 and N12. When the capacity S1_GFM provided by converter devices 112-114 is insufficient to absorb the changes in the capacity required by load N11, the controller 111 unloads load N12, allowing the microgrid 110 to maintain power supply to load N11. Correspondingly, when the capacity S2_GFM is less than the critical load capacity SC2_Load, each of the converter devices 212-216 is used to supply power to loads N21 and N22. At this time, if the converter devices 212-214 operating in GFM mode are insufficient to absorb changes in the capacity required by load N21, the controller 211 will disconnect the switch CBN22, causing the microgrid 210 to stop supplying power to load N22. Specifically, the capacity S2_GFM provided by converter devices 212-214 and the capacity S2_GFL provided by converter devices 215-216 are used to supply power to loads N21 and N22. When the capacity S2_GFM provided by converter devices 212-214 is insufficient to absorb changes in the capacity required by load N21, the controller 211 will unload load N22, allowing the microgrid 210 to maintain power supply to load N21.

[0120] In other scenarios, when loads N11 and N21 are non-critical loads, and loads N12 and N22 are critical loads, loads N12 and N22 have critical load removal capacities SC1_Load and SC2_Load, respectively, while loads N11 and N21 have non-critical load removal capacities SNC1_Load and SNC2_Load, respectively. In this case, the operation of microgrids 110 and 210 is similar to the previous scenario, only requiring the replacement of loads N11 and N21 with loads N12 and N22, respectively. Therefore, the similarities will not be repeated.

[0121] Referring also to Figures 5 and 4, in the embodiments disclosed herein, the switching of converter devices 112-114 and 212-214 to GFM mode is not limited to this. In various variations, each of converter devices 112-116 and 212-216 can switch between GFM mode and GFL mode.

[0122] Unless otherwise specified, the terms used herein generally have their ordinary meaning in the context of this art, the content of this disclosure, and the specific content thereof. Certain terms used to describe this disclosure will be discussed elsewhere in this specification to provide additional guidance to those skilled in the art in describing this disclosure.

[0123] While specific embodiments of the present disclosure have been disclosed in relation to the above embodiments, these embodiments are not intended to limit the present disclosure. Various alternatives and modifications can be made by those skilled in the art in accordance with the present disclosure without departing from the principles and spirit of the present disclosure. Therefore, the scope of protection of the present disclosure is determined by the appended claims.

[0124] 100: Power System 110: Microgrid 111: Controller 112~116: Converter equipment 120: Power Distribution System 122, 123: Power converter 124, 125, 126: Inverters 130: Municipal power grid 132, 133: Energy storage system 134, 135, 136: Renewable Energy Devices 200: Power System 210: Microgrid 211: Controller 212~216: Converter Equipment 222, 223: Power converters 224, 225, 226: Inverters 232, 233: Energy storage system 234, 235, 236: Renewable Energy Devices 300: Operating Instructions 301~312: Operation A, A(t): parameters BS110, BS210: Busbars B_j, B_j(t): Parameters CB10~CB15: Switches CB20~CB25: Switches CBN11, CBN12: Switches CBN21, CBN22: Switches F_CB10, F_CB20: Frequency F_limL: Lower frequency limit F_limH: Upper limit frequency I_CB10, I_CB20: Current I_lim: Threshold current level i: a positive integer j: a positive integer L1, L2: Lines N11, N12: Load N21, N22: Load Ni, Nj: Positive integers PCC: Common Coupling Point P112~P116, P212~P216: Actual power Q112~Q116, Q212~Q216: Virtual power S1~S10: Signals ST_GFL, ST_GFL(t): Total capacity S_PCS_GFL_i(t): Capacity S_PV_GFL_j(t): Capacity S_GFM, S_GFM(t): Capacity S_GFL, S_GFL(t): Capacity S_Load, S_Load(t): Loading capacity SC_Load, SC_Load(t): Critical load extraction capacity SNC_Load, SNC_Load(t): Non-critical load capacity ST1_GFL, ST2_GFL: Total capacity S1_GFM, S2_GFM: Capacity S1_GFL, S2_GFL: Capacity S1_Load, S2_Load: Load extraction capacity SC1_Load, SC2_Load: Critical load extraction capacity SNC1_Load, SNC2_Load: Non-critical load extraction capacity S_N11, S_N12: Loading capacity S112_GFL~S116_GFL: Capacity S212_GFL~S216_GFL: Capacity t: time V112~V116: Output voltage V212~V216: Output voltage V_DEF: Rated output voltage level V_limL: Low-limit voltage level V_limH: Upper voltage level V_CB10, V_CB20: Voltage

[0125] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. An electric power system comprising: a mains power grid connected to a first switch; and a microgrid connected to the mains power grid via the first switch, the microgrid comprising: a plurality of converter devices connected to a bus; a controller connected to the first switch and each of the converter devices and for transmitting a plurality of first signals; and a plurality of loads connected to the converter devices via the bus, wherein... The city power grid is connected to the bus via the first switch and is used to supply power to these loads. The controller is further used to detect a first line connecting the city power grid and the microgrid, and to determine whether the first line is abnormal. When the controller determines that the first line is abnormal, the controller disconnects the first switch and switches a first part of the converter equipment to operate as a voltage source through the first signals.

2. The power system as claimed in claim 1, wherein when the controller determines that the first line is normal, the controller keeps the first switch on, and each of the converter devices operates as a current source different from the voltage source, and when the controller determines that the first line is abnormal, a second part of the converter devices operates as the current source, and the second part is different from the first part.

3. The power system as described in claim 2, wherein the converter equipment comprises: a plurality of converters connected to the bus; and a plurality of energy storage systems, respectively connected to the converters, wherein, When the first part of the converter equipment operates as a voltage source, the energy storage systems corresponding to the first part of the converter are used to supply power to the loads.

4. The power system as claimed in claim 2, wherein the controller is further configured to: calculate a first capacity of the first portion of the converter equipment when the first portion operates in voltage source mode, and calculate a second capacity of the second portion of the converter equipment when the second portion operates in current source mode.

5. The power system as claimed in claim 4, wherein when the first capacity is greater than a third capacity of the loads, the first portion of the converter devices is used to supply power to each of the loads; when the first capacity is less than the third capacity and the first capacity is greater than a fourth capacity of a third portion of the loads, the first portion and the second portion of the converter devices are used to supply power to the fourth capacity of the loads; and when a capacity change occurs in the fourth capacity, the first portion of the converter devices is used to absorb the capacity change; and when the first capacity is less than the fourth capacity and the sum of the first capacity and the second capacity is greater than the fourth capacity, each of the first portion and the second portion of the converter devices supplies power to the third capacity of the loads.

6. The power system as claimed in claim 4, wherein when a voltage level of a voltage of the first switch is less than a lower voltage level or higher than an upper voltage level, the controller determines that the first line is abnormal, and when the first part of the converter equipment switches to the voltage source mode, each of the first parts sends back a plurality of status parameters to the controller, the status parameters including at least an output voltage of each of the first parts.

7. The power system as claimed in claim 2, wherein the converter equipment further comprises: a plurality of inverters connected to the bus; and a plurality of renewable energy devices, respectively connected to the inverters, wherein, When the first part of the converter equipment operates as the voltage source, the regenerative energy devices corresponding to the first part of the inverter are used to supply power to the loads.

8. A method of operating a power system, comprising: connecting a mains power grid to a plurality of microgrids via a plurality of lines using a plurality of switches; detecting a plurality of voltages on the switches and determining whether the lines are abnormal based on the voltages; when a first line of the lines is determined to be abnormal, disconnecting a first switch of the switches and switching a first portion of a plurality of converter devices in a first microgrid connected to the first line to operate as a voltage source; and when the first line is determined to be normal, maintaining the first switch connected, and each of the converter devices operating as a current source different from the voltage source, wherein... When the first line is determined to be abnormal, a second part of the converter equipment operates as the current source, and the second part is different from the first part.

9. The method of operating a power system as described in claim 8, further comprising: when it is determined that a second line of the lines is abnormal and the first line is normal, disconnecting a second switch of the switches and switching a third portion of a plurality of converter devices in a second microgrid of the microgrids connected to the second line to operate in the form of a voltage source; and when it is determined that the second line is normal, maintaining the second switch connected, and each of the converter devices operating in the form of a current source different from the voltage source form, wherein... When the second line is determined to be abnormal, a fourth part of the converter equipment operates as a current source, and the fourth part is different from each of the first part, the second part and the third part; and when the second line is determined to be abnormal and the first line is normal, each of the first part and the second part of the converter equipment operates as a current source.

10. The method of operating a power system as described in claim 9, further comprising calculating a first capacity of the first portion operating in the form of a voltage source, and a second capacity of the second portion operating in the form of a current source; calculating a third capacity of the third portion operating in the form of a voltage source, and a fourth capacity of the fourth portion operating in the form of a current source, wherein, When the first capacity is greater than a fifth capacity of a plurality of loads of the first microgrid, the first portion is used to supply power to each of those loads. When the third capacity is less than a sixth capacity of a plurality of loads of the second microgrid, and the third capacity is greater than a seventh capacity of a seventh portion of those loads of the second microgrid, each of those converter devices is used to supply power to each of those loads.

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