Power grid system, and method for controlling power grid system

Abstract

Provided in the present disclosure are a power grid system, and a method for controlling the power grid system. In the present invention, a power grid system is provided. The power grid system is applicable to providing power to at least one load unit, and the power grid system comprises a busbar, a switch module, and an energy storage system which is coupled to the busbar. The at least one load unit is coupled to the busbar. The switch module comprises a switch apparatus, which is connected between the busbar and a backbone power grid. The energy storage system is configured to operate in a current source mode and a voltage source mode, and is configured to receive a trip signal from the switch module. The energy storage system is configured to switch to the voltage source mode when the energy storage system has received the trip signal.

Description

Power grid system and method for controlling the same Technical Field

[0001] The technical field of the present invention relates to a power grid system and a method for controlling the power grid system; more particularly, to a power grid system that achieves a grid-connected mode and a standalone mode and a method for controlling the power grid system. Background Art

[0002] A microgrid is a grid system that includes a set of loads and distributed energy sources located in a specific area and can operate as a single, controllable entity. The loads can be utility "customers," a group of several sites, or dispersed sites operating in a coordinated manner. Distributed energy sources can include reciprocating engine generators, microturbines, fuel cells, photovoltaic / solar energy, and other small-scale renewable energy generation devices.

[0003] Microgrids can operate in either grid-connected or off-grid mode. Under normal circumstances, microgrids operate in grid-connected mode. In grid-connected mode, the microgrid is connected to the main grid, which serves as the microgrid's voltage source. If a main grid fault occurs, the microgrid can be disconnected from the main grid and switch to off-grid mode. In this case, backup voltage supply equipment must replace the main grid and serve as the voltage supply source to stabilize the microgrid's voltage.

[0004] In some cases, when switching to off-grid mode, a generator can serve as a backup voltage supply. However, the startup of the generator can cause a delay in switching the voltage source. This time delay can lead to terminal load tripping or failure due to a sudden voltage drop. Therefore, an improved power grid system with shorter time delays and a method for operating the same are desirable.

[0005] Summary of the Invention

[0006] The present invention provides a power grid system suitable for providing power to at least one load unit. The power grid system includes a busbar, a switch module, and an energy storage system coupled to the busbar. At least one load unit is coupled to the busbar. The switch module includes a switching device connected between the busbar and a main power grid. The energy storage system is configured to operate in a current source mode and a voltage source mode and is configured to receive a trip signal from the switch module. The energy storage system is configured to switch to a voltage source mode upon receiving the trip signal.

[0007] In one embodiment, the trip signal is a feedback signal from the switching device.

[0008] In one embodiment, the energy storage system and the switch module are coupled by one or more cables, and the trip signal is transmitted to the energy storage system via the one or more cables.

[0009] In one embodiment, the energy storage system is configured to receive a closing signal from the switch module and is configured to switch from the voltage source mode to the current source mode when the energy storage system receives the closing signal.

[0010] In one embodiment, the closing signal is a feedback signal from the switching device.

[0011] In one embodiment, the energy storage system and the switch module are coupled by one or more cables, and the closing signal is transmitted to the energy storage system via the one or more cables.

[0012] In one embodiment, the energy storage system is configured to receive a multiplexing instruction signal from the control system and is configured to synchronize the power grid system with the main power grid when the energy storage system receives the multiplexing instruction signal.

[0013] In one embodiment, the grid system further includes a voltage sensing unit configured to measure the voltage of the main grid and provide a voltage signal to the energy storage system.

[0014] In one embodiment, the energy storage system is configured to determine whether the power grid system is synchronized with the main power grid based on the voltage signal.

[0015] In one embodiment, the energy storage system is configured to send a switching instruction signal when the energy storage system determines that the power grid system is synchronized with the main power grid.

[0016] In one embodiment, the energy storage system is configured to send a switching instruction signal to the switch module.

[0017] In one embodiment, the switch module further includes an intelligent electronic device (IED) coupled to the switch device and configured to initiate a switching operation of the switch device, and the energy storage system is configured to send a switching instruction signal to the intelligent electronic device.

[0018] In an embodiment, the intelligent electronic device is configured to trip the switching device.

[0019] In an embodiment, the switch device comprises a contact switch.

[0020] In one embodiment, the power grid system further includes at least one distributed power generation device coupled to the busbar.

[0021] In one embodiment, the power grid system further includes a transformer, wherein the transformer includes a first coil coupled to the switch device and a second coil coupled to the busbar.

[0022] The present invention provides a method for operating a power grid system. The power grid system includes a switch module and an energy storage system, and is adapted to supply power to at least one load unit via a busbar. The switch module includes a switching device connected between the busbar and an external main power grid. The energy storage system is coupled to the busbar. The method includes tripping the switching device, wherein the energy storage system receives a trip signal from the switch module; and switching the operating mode of the energy storage system from a current source mode to a voltage source mode upon receipt of the trip signal.

[0023] In one embodiment, the trip signal is a feedback signal from the switching device.

[0024] In one embodiment, the energy storage system and the switch module are coupled by one or more cables, and the method includes transmitting a trip signal to the energy storage system via the one or more cables.

[0025] In one embodiment, the method further includes turning on the switch device, receiving a closing signal from the switch module by the energy storage system, and switching the operation mode of the energy storage system from the voltage source mode to the current source mode when the energy storage system receives the closing signal.

[0026] In one embodiment, the closing signal is a feedback signal from the switching device.

[0027] In one embodiment, the energy storage system and the switch module are coupled by one or more cables, and the method includes transmitting a closing signal to the energy storage system via the one or more cables.

[0028] In one embodiment, the method further includes synchronizing the power grid system with the main power grid when the energy storage system receives a reconnection instruction signal from the control system.

[0029] In one embodiment, the method further includes measuring the voltage of the main grid using a voltage sensing unit and providing a voltage signal to the energy storage system.

[0030] In one embodiment, the method further includes using the energy storage system to determine whether the main power grid has been repaired based on the voltage signal.

[0031] In one embodiment, the method further includes using the energy storage system to determine whether the power grid system is synchronized with the main power grid based on the voltage signal.

[0032] In one embodiment, switching on the switch device includes sending a switching instruction signal from the energy storage system to the switch module.

[0033] In one embodiment, the method includes sending a startup instruction signal when the energy storage system determines that the power grid system is synchronized with the main power grid.

[0034] In one embodiment, the switch module includes an intelligent electronic device (IED) coupled to the switch device, and switching on the switch device includes sending a switching command signal from the energy storage system to the IED and initiating a switching operation of the switch device using the IED.

[0035] In one embodiment, tripping the switching device includes opening contacts of the switching device. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a block diagram of a power grid system according to an embodiment of the present disclosure;

[0037] FIG2 is a block diagram of a power grid system switched to an off-grid mode according to an embodiment of the present disclosure;

[0038] FIG3 is a flow chart of a method for controlling a power grid system according to an embodiment of the present disclosure;

[0039] FIG4 is a block diagram of a power grid system switched to a grid-connected mode according to an embodiment of the present disclosure;

[0040] FIG5 is a flowchart of a method for controlling a power grid system according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0041] The following examples are described in detail with accompanying drawings. However, the examples provided are not intended to limit the scope of the present invention, and the description of operations is not intended to limit the order of execution. Any structure resulting from the recombination of components with equivalent functionality is within the scope of this disclosure. Furthermore, the drawings are for illustrative purposes only and are not drawn to scale. To facilitate understanding, identical or similar components will be designated with the same reference numerals throughout the following description.

[0042] Throughout the specification and claims, unless otherwise noted, terms used generally have their ordinary meanings in the art, in the context of the present disclosure, and in the specific context in which they are used. Certain terms used to describe the present disclosure are discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art regarding the description of the present disclosure.

[0043] In addition, the terms "include," "comprising," "having," "containing," etc. used herein are open-ended terms, meaning "including but not limited to." Furthermore, "and / or" used herein includes any one or more of the listed items and all combinations thereof.

[0044] As used herein, when an element is referred to as being "coupled," it may refer to being "electrically coupled," and when referred to as being "connected," it may refer to being "electrically connected." "Connected" and "coupled" may also refer to two or more elements operating in conjunction with or interacting with each other. Furthermore, while terms such as "first," "second," etc. are used herein to describe various elements, such terms are used solely to distinguish one element from another and are not intended to limit the present invention. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element without departing from the scope of the embodiments.

[0045] FIG1 is a block diagram of a power grid system according to an embodiment of the present disclosure. Referring to FIG1 , a power grid system 100 is provided. The power grid system 100 may be a microgrid system, which is a regionalized grouping of power generation, energy storage, and loads. The power grid system 100 may include a bus 102 (e.g., an AC bus), a switch module 104, and an energy storage system 106. The bus 102 may be coupled to a main power grid 50, such as a traditional centralized power grid, a "macrogrid," or a distribution grid, so that the power grid system 100 may be connected to the main power grid 50 and powered by the main power grid 50. The power grid system 100 is suitable for supplying power to at least one load unit, such as a load unit L1, a load unit L2, a load unit L3, and a load unit L4. Each of the load units L1, L2, L3, and L4 may be directly or indirectly coupled to the bus 102. The load unit L1 , the load unit L2 , the load unit L3 and the load unit L4 can be general loads or critical loads. The number of the load units is only an example and is not limiting.

[0046] Grid system 100 may also include at least one distributed power generation device. The distributed power generation device may be a photovoltaic / solar power generation device 108A or a diesel power generation device 108B. The distributed power generation device may also be a reciprocating engine power generation device, a microturbine power generation device, a fuel cell, a wind turbine power generation device, a hydroelectric power generation device, other small-scale renewable energy power generation devices, and the like. As shown in FIG1 , distributed power generation devices 108A and 108B are coupled to bus 102 and can provide power to load units L1, L2, L3, and L4 via bus 102. The number of distributed power generation devices is merely illustrative and not limiting.

[0047] The energy storage system 106 may include a direct current to alternating current (DC / AC) converter and a plurality of storage cells, such as lead-acid batteries, nickel-cadmium batteries, nickel-metal hydride batteries, sodium-sulfur batteries, lithium batteries, or fuel cells. The types of batteries are not limited to those listed in this embodiment. The energy storage system 106 may also include a supercapacitor or a flywheel. In some embodiments, at least one of the DC / AC converters may be a three-phase converter. The energy storage system 106 may be coupled to the bus 102. The energy storage system 106 may be used to provide stable power to the load units L1, L2, L3, and L4. For example, during periods of excess power generation, the energy storage system 106 can be charged by the distributed power generation device 108A, and can provide additional power when the power generation from the distributed power generation device 108A (and the distributed power generation device 108B) is low, such as at night or on cloudy days (in the case of solar energy), or when the power demand from the load units L1, L2, L3 and L4 is high.

[0048] The energy storage system 106 may further include processing circuitry (which may include digital and / or analog circuitry, such as one or more controllers, processors, application-specific integrated circuits (ASICs), etc.) to execute program code that implements one or more of the processes described herein. The energy storage system 106 may also include one or more storage media, such as random access memory (RAM), read-only memory (ROM), hard drive storage, temporary storage, volatile memory, flash memory, optical storage, or any other suitable memory for storing program code and related data processed and accessed by the processing circuitry during execution of the program code. The storage media may also store results generated by the energy storage system 106.

[0049] The switch module 104 may include a switch device 1042. In some embodiments, the switch device 1042 may include a contactor, such as a circuit breaker, such as an oil circuit breaker, a gas-blast circuit breaker, a sulfur hexafluoride (SF6) circuit breaker, a vacuum circuit breaker, a miniature circuit breaker (MCB), a molded case circuit breaker (MCCB), or the like. The switch device 1042 may also include an operating mechanism for closing and tripping the switch device 1042. However, the present disclosure is not limited thereto. As shown in FIG1 , the switch device 1042 is connected between the bus 102 and the main power grid 50. As shown in FIG1 , the switch device 1042 can be connected to the high-voltage feeder 105 of the main power grid 50. The switch device 1042 can be configured to selectively allow current to flow between the bus 102 and the main power grid 50, so that the power grid system 100 can be separated from the main power grid 50 by opening at least the switch device 1042.

[0050] Specifically, the power grid system 100 is configured to connect to the main power grid 50 in the on-grid mode and to disconnect from the main power grid 50 (or, in some cases, from the main power grid 50 and other power grids) in the off-grid mode. The power grid system 100 can achieve the on-grid mode and the off-grid mode by connecting / disconnecting the switching device 1042.

[0051] As shown in FIG1 , when the power grid system 100 operates in the grid-connected mode, the switch device 1042 is in the turned-on state. In this case, the energy storage system 106 can be charged by at least one of the distributed power generation devices (e.g., the distributed power generation device 108A) and / or the main grid 50; or, in some cases, the energy storage system 106 can operate in a current source mode, in which the energy storage system 106 operates similarly to a current source. The energy storage system 106 can refer to the voltage and frequency of the power grid system 100 (e.g., the voltage and frequency of the bus 102) or the voltage and frequency of the main grid 50, and the power generated by the energy storage system 106 is supplied to the power grid system 100 to supply power to the load units L1, L2, L3, and L4.

[0052] In the grid-connected mode, when an incident occurs in the main grid 50 or another regional grid connected to the main grid 50, the switch device 1042 can trip. The switch device 1042 is thus in a turned-off state, and the power grid system 100 can operate in the off-grid mode. In this case, the energy storage system 106 can operate in a voltage source mode, in which the energy storage system 106 serves as a voltage source for the power grid system 100. The energy storage system 106 can supply power to the load units L1, L2, L3, and L4 and can establish the bus voltage on the bus 102 for the distributed power generation devices 108A and 108B.

[0053] The switch module 104 may further include an intelligent electronic device (IED) 1044 coupled to the switch device 1042. The IED 1044 may be configured to measure electrical characteristics of the power flowing through the switch device 1042 and use the measured results to determine whether an incident has occurred. In some embodiments, the IED 1044 is configured to trip the switch device 1042.

[0054] As shown in FIG1 , the power grid system 100 may further include a voltage sensing unit 1046. The voltage sensing unit 1046 is configured to measure the voltage of the main grid 50 and provide a voltage signal VS to the energy storage system 106. In one embodiment, the voltage sensing unit 1046 may be a voltmeter or a potential transformer (PT), wherein the high-voltage side of the PT is connected to the main grid 50 (e.g., the high-voltage feeder 105 of the main grid 50) and the voltmeter is connected to the low-voltage side of the PT to measure the proportional voltage of the main grid 50.

[0055] As shown in FIG1 , power grid system 100 may further include a transformer 109. For example, switch module 104 may be located within a substation, and the substation may include a transformer 109 that steps down the voltage to a distribution voltage. One or more distribution buses (e.g., bus 102) may distribute this stepped-down distribution voltage in multiple directions. Switch device 1042 may be configured to disconnect the substation (or portions thereof) and the remainder of power grid system 100 from the main grid 50 or to disconnect one or more distribution lines from the substation. Transformer 109 may include a first coil 1092 and a second coil 1094. As shown in FIG1 , first coil 1092 is coupled to switch device 1042, and second coil 1094 is coupled to bus 102. Switch device 1042 may be configured to isolate the remainder of power grid system 100 from the main grid 50 to initiate an off-grid mode of power grid system 100. However, the present disclosure is not limited in this manner.

[0056] Although the power grid system 100 of FIG1 is shown as a single-line diagram, the power grid system 100 can be configured to transmit single-phase or multi-phase power. Although the power grid system 100 is an AC power system, other embodiments may include a DC power system, such as a DC distribution system. Furthermore, it should be understood that the layout of the power grid system 100 is shown for illustrative purposes and is not intended to be a limitation of the present disclosure.

[0057] FIG2 is a block diagram of a power grid system switched to off-grid mode according to an embodiment of the present disclosure. As shown in FIG2 , switch device 1042 is tripped. As previously described, switch device 1042 may be tripped by intelligent electronic device 1044. In some embodiments, switch device 1042 may be remotely controlled by a control system (e.g., a Supervisory Control and Data Acquisition (SCADA) system). In some embodiments, switch device 1042 may be tripped due to an incident in main grid 50 or another grid connected to main grid 50.

[0058] The energy storage system 106 described herein may be configured to receive a trip signal DS1 from the switch module 104. In some embodiments, the trip signal DS1 is a feedback signal from the switch device 1042. Specifically, the switch device 1042 may be configured to output a status signal. The status signal may be a feedback signal, such as a trip feedback signal (TRIPPED), an on / off feedback signal (On / Off), a closed feedback signal (CLOSED), or a combination thereof, indicating the operating status of the switch device (e.g., a circuit breaker). In some embodiments, the switch device 1042 may include a control finite state machine (control FSM) configured to output the feedback signal. The feedback signal may be a digital signal. However, the present disclosure is not limited thereto. In some embodiments, the trip signal may be a signal from the intelligent electronic device 1044. The energy storage system 106 may be configured to receive a signal from the switch module 104. The energy storage system 106 may include a receiving card so that the energy storage system 106 can receive the signal from the switch module 104 and operate accordingly. For example, the energy storage system 106 may be configured to receive a trip feedback signal (TRIPPED) and / or an on / off feedback signal (On / Off). However, the present disclosure is not limited thereto.

[0059] The energy storage system 106 described herein may be further configured to switch to a voltage source mode when the energy storage system 106 receives the trip signal DS1. As previously described, the energy storage system 106 is configured to operate in a current source mode and a voltage source mode. For example, when the power grid system 100 operates in a grid-connected mode, the energy storage system 106 may operate in a current source mode. The energy storage system 106 described herein may be configured to switch from a current source mode to a voltage source mode when the energy storage system 106 receives the trip signal DS1, for example, through a processing circuit and / or a switch module in the energy storage system 106.

[0060] Through the configuration described herein, energy storage system 106 can complete the switchover to voltage source mode and provide bus voltage to load units L1, L2, L3, and L4 and distributed power generation devices 108A and 108B in a relatively short period of time. Thus, load units L1, L2, L3, and L4 can be continuously powered by grid system 100. Furthermore, since distributed power generation devices 108A and 108B can also be continuously powered by grid system 100, distributed power generation devices 108A and 108B can continue to generate electricity for grid system 100. Therefore, even during the transition from grid-connected mode to off-grid mode, grid system 100 can continue to provide power without interruption. Furthermore, energy storage system 106 described herein can be configured to operate based on feedback signals from switching device 1042, eliminating the need for additional computation or signal processing, and transitions in energy storage system 106 can be performed without further delay. It should be noted that during the conversion of the energy storage system 106 , the residual voltage on the bus 102 can continue to supply power to the load units L1 , L2 , L3 and L4 and the distributed power generation devices 108A and 108B for a certain period of time.

[0061] As shown in FIG2 , in some embodiments, the energy storage system 106 and the switch module 104 are coupled by one or more cables. The cables may include electrical cables, optical fiber cables, power lines, or a combination thereof. In some embodiments, the trip signal DS1 may be transmitted to the energy storage system 106 via the one or more cables (e.g., cable 107A). Through the configuration described herein, the energy storage system 106 can directly receive the trip signal DS1 from the switch device 1042 without transmitting the signal to a third device (e.g., a control system such as a SCADA system) and / or having the third device process the signal. Therefore, the receipt of the trip signal DS1 and the switching of the operating mode can be performed without further delay.

[0062] FIG3 is a flow chart of a method for operating a power grid system (e.g., power grid system 100 shown in FIG1 and FIG2 ) according to an embodiment of the present disclosure. Referring to FIG2 and FIG3 , power grid system 100 may include a switch module 104 and an energy storage system 106. Power grid system 100 may be adapted to supply power to at least one load unit (e.g., load units L1, L2, L3, and L4) via busbar 102. Switch module 104 may include a switch device 1042. Switch device 1042 may be connected between busbar 102 and main grid 50. Energy storage system 106 is coupled to busbar 102.

[0063] Method 300 includes tripping switching device 1042 (step 310). In some embodiments, switching device 1042 may be a contactor switch, and tripping switching device 1042 may include opening contacts of switching device 1042. Method 300 includes receiving a trip signal (e.g., trip signal DS1) from switch module 104 by energy storage system 106 if switching device 1042 trips (e.g., due to an event in main power grid 50) (step 320). Method 300 includes switching an operating mode of energy storage system 106 from a current source mode (or, in some cases, from another operating mode) to a voltage source mode when energy storage system 106 receives trip signal DS1 (step 330). Method 300 may also include supplying power to at least one load unit (e.g., load units L1, L2, L3, and L4) in an off-grid mode of power grid system 100 (step 340). In the method 300 , if the switch device 1042 has not tripped, the energy storage system 106 may not receive the trip signal DS1 , and the energy storage system 106 maintains its current operation mode (step 350 ).

[0064] FIG4 is a block diagram of a power grid system switched to grid-connected mode according to one embodiment of the present disclosure. As shown in FIG4 , power grid system 100 is still operating in off-grid mode, and switch device 1042 is in the off state. Switch device 1042 may be in a ready-to-close state. In some embodiments, energy storage system 106 may receive a ready-to-close (RTC) feedback signal from switch device 1042. However, the present disclosure is not limited thereto.

[0065] Energy storage system 106 may be configured to receive a reconnection command signal DS2 from control system 60. Specifically, in some embodiments, control system 60 may perform a restoration switching analysis (RSA) to determine a service restoration switching plan. Control system 60 may then send one or more command signals (e.g., reconnection command signal DS2) to activate switch device 1042 to reconnect power grid system 100 to main grid 50.

[0066] In some embodiments, the energy storage system 106 is configured to synchronize the power grid system 100 (or the energy storage system 106) with the main power grid 50. Specifically, in the off-grid mode, the power grid system 100 may operate at a frequency and voltage different from that of the main power grid. The energy storage system 106 may be configured to control and adjust the frequency, voltage, and phase angle of the power grid system 100 to match the frequency, voltage, and phase angle of the main power grid 50. The energy storage system 106 may be configured to synchronize the power grid system 100 with the main power grid 50 when the energy storage system 106 receives the multiplexing instruction signal DS2.

[0067] In some embodiments, the energy storage system 106 is configured to determine whether the power grid system 100 is synchronized with the main power grid 50. As described above with respect to FIG. 1 , the power grid system 100 may further include a voltage sensing unit 1046 that measures the voltage of the main power grid 50 and provides a voltage signal VS to the energy storage system 106. The energy storage system 106 may be configured to receive the voltage signal VS and, based on the voltage signal VS, determine whether the power grid system 100 is synchronized with the main power grid 50. When the power grid system 100 is synchronized with the main power grid 50, the energy storage system 106 may perform phase lock.

[0068] As shown in FIG4 , the energy storage system 106 can be further configured to send a closing command signal DS3 when the energy storage system 106 determines that the power grid system 100 is synchronized with the main power grid 50. The energy storage system 106 can be configured to send the closing command signal DS3 to the switch module 104. In an embodiment where the switch module 104 further includes an intelligent electronic device 1044, the intelligent electronic device 1044 can be configured to initiate a closing operation of the switch device 1042, and the energy storage system 106 can be configured to send the closing command signal DS3 to the intelligent electronic device 1044 (e.g., via cable 107B). Specifically, in some embodiments, when the intelligent electronic device 1044 is configured to output an enable signal from the digital output port 1044O of the intelligent electronic device 1044 to initiate the activation of the switching device 1042, the energy storage system 106 is configured to send the enable command signal DS3 to the digital input port 1044I of the intelligent electronic device 1044, rather than directly sending the enable command signal DS3 to the switching device 1042. In the case where the switching device 1042 is a high-voltage circuit breaker, the configuration described herein enables the energy storage system 106 to control the activation of the switching device 1042. However, the present disclosure is not limited thereto. In some other embodiments, the enable command signal DS3 can be sent to the switching device 1042 to initiate the activation of the switching device 1042.

[0069] Similar to the above description with respect to FIG. 2 , the energy storage system 106 may be configured to receive a closed signal DS4 from the switch module 104. Specifically, the switch device 1042 may be configured to output a closed signal DS4, such as a closed feedback signal (CLOSED) and / or an on / off feedback signal (On / Off). The closed signal DS4 may be a feedback signal from the switch device 1042. The energy storage system 106 may include a receiving card to receive the closed signal DS4. The closed signal DS4 may be a digital signal. However, the present disclosure is not limited thereto. The energy storage system 106 may be further configured to switch from a voltage source mode to a current source mode when the energy storage system 106 receives the closed signal DS4.

[0070] In the embodiment of FIG4 , the power grid system 100 operates in an off-grid mode, and the energy storage system 106 can operate in a voltage source mode. The energy storage system 106 described herein can be configured to switch from the voltage source mode to the current source mode, for example, via a processing circuit and / or a switch module within the energy storage system 106, upon receiving the closing signal DS4.

[0071] Similar to the above description with respect to FIG. 2 , in some embodiments, the energy storage system 106 and the switch module 104 are coupled by one or more cables. In some embodiments, the closing signal DS4 can be transmitted to the energy storage system 106 via the one or more cables, such as cable 107A. In some embodiments, the closing signal DS4 can be transmitted via the same cable as the tripping signal DS1. However, the closing signal DS4 can be transmitted via a different cable than the tripping signal DS1. With the configuration described herein, the reception of the closing signal DS4 and the switching of the operating mode can be performed without further delay.

[0072] FIG5 is a flow chart of a method for controlling a power grid system (e.g., the power grid system 100 shown in FIG1 , FIG2 , and FIG4 ) according to an embodiment of the present disclosure. Referring to FIG4 and FIG5 , in method 500 , the main power grid 50 may be in a repaired state (step 510 ). The energy storage system 106 receives a reconnection instruction signal DS2 from the control system 60 (step 520 ). The method 500 further includes synchronizing the power grid system 100 with the main power grid 50 when the energy storage system 106 receives the reconnection instruction signal DS2 from the control system 60 (step 530 ).

[0073] Method 500 may further include determining whether power grid system 100 is synchronized with main grid 50 (step 540). In some embodiments, method 500 further includes measuring the voltage of main grid 50 using voltage sensing unit 1046 and providing voltage signal VS to energy storage system 106. Whether power grid system 100 is synchronized with main grid 50 may be determined based on voltage signal VS.

[0074] Method 500 further includes enabling switching device 1042. Enabling switching device 1042 may include energy storage system 106 sending an enabling command signal DS3 to switch module 104. When energy storage system 106 determines that power grid system 100 is synchronized with main power grid 50, energy storage system 106 may send enabling command signal DS3. In embodiments where switch module 104 further includes an intelligent electronic device (IED) 1044 coupled to switching device 1042, enabling switching device 1042 may include energy storage system 106 sending an enabling command signal to IED 1044 and initiating enabling operation of switching device 1042 using IED 1044.

[0075] In some embodiments, the method 500 further includes receiving, by the energy storage system 106, a closing signal DS4 from the switch module 104, wherein the closing signal is a feedback signal from the switch device 1042. The method 500 may further include switching the operation mode of the energy storage system 106 from the voltage source mode to the current source mode when the energy storage system 106 receives the closing signal DS4 (step 550).

[0076] In method 500, if the main grid 50 is not repaired, the energy storage system 106 maintains its current operating mode (step 560). In some embodiments, method 500 may further include using the energy storage system 106 to determine whether the main grid 50 is repaired based on the voltage signal VS. In method 500, if the energy storage system 106 does not receive the reconnection instruction signal DS2 from the control system 60, the energy storage system 106 maintains its current operating mode (step 560). In method 500, if the energy storage system 106 determines that the power grid system 100 is not synchronized with the main grid 50, the method 500 continues to synchronize the power grid system 100 with the main grid 50 (step 530).

[0077] The description of the above embodiments provides a basis for those skilled in the art to implement the subject matter of the invention. Various modifications to the embodiments will be apparent to those skilled in the art, and the novel principles and subject matter of the invention identified herein may be applied to other embodiments without inventive step. Therefore, the subject matter described in the claims is not limited to the embodiments shown herein, but is to be applied to the widest scope consistent with the principles and novel features disclosed herein. Other embodiments are contemplated that are also within the spirit and scope of the disclosed subject matter. Therefore, the present disclosure is intended to cover modifications and variations within the scope of the appended claims and their equivalents.

Claims

1. A power grid system, adapted to provide power to at least one load unit, the power grid system comprising: a bus bar, the at least one load unit being coupled to the bus bar; A switch module, comprising a switch device, wherein the switch device is connected between the busbar and the main power grid; and An energy storage system coupled to the bus, the energy storage system being configured to operate in a current source mode and a voltage source mode, and being configured to receive a trip signal from the switch module; The energy storage system is configured to switch to the voltage source mode when the energy storage system receives the trip signal. 2 . The power grid system according to claim 1 , wherein the tripping signal is a feedback signal from the switching device. 3 . The power grid system according to claim 1 , wherein the energy storage system and the switch module are coupled by one or more cables, and the trip signal is transmitted to the energy storage system via the one or more cables. 4 . The power grid system according to claim 1 , wherein the energy storage system is configured to receive a closing signal from the switch module and is configured to switch from the voltage source mode to the current source mode when the energy storage system receives the closing signal.

5. The power grid system according to claim 4, wherein the closing signal is a feedback signal from the switching device. 6 . The power grid system according to claim 4 , wherein the energy storage system and the switch module are coupled by one or more cables, and the closing signal is transmitted to the energy storage system via the one or more cables.

7. The power grid system according to claim 1, wherein the energy storage system is configured to receive a multiplexing instruction signal from a control system and is configured to synchronize the power grid system with the main power grid when the energy storage system receives the multiplexing instruction signal. 8 . The power grid system according to claim 1 , further comprising a voltage sensing unit configured to measure a voltage of the main power grid and provide a voltage signal to the energy storage system. 9 . The power grid system according to claim 8 , wherein the energy storage system is configured to determine whether the power grid system is synchronized with the main power grid based on the voltage signal. 10 . The power grid system according to claim 1 , wherein the energy storage system is configured to send a startup instruction signal when the energy storage system determines that the power grid system is synchronized with the main power grid.

11. The power grid system according to claim 1, wherein the energy storage system is configured to send a switching instruction signal to the switch module.

12. The power grid system according to claim 11, wherein the switch module further comprises an intelligent electronic device, the intelligent electronic device is coupled to the switch device and is configured to initiate a start-up operation of the switch device, and the energy storage system is configured to send the start-up instruction signal to the intelligent electronic device.

13. The power grid system according to claim 12, wherein the intelligent electronic device is configured to trip the switch device.

14. The power grid system of claim 1, wherein the switch device comprises a contactor switch.

15. The power grid system according to claim 1, further comprising at least one distributed power generation device, wherein the distributed power generation device is coupled to the bus.

16. The power grid system of claim 1, further comprising a transformer, wherein the transformer comprises a first coil coupled to the switch device and a second coil coupled to the bus.

17. A method for controlling a power grid system, the power grid system comprising a switch module and an energy storage system and being adapted to supply power to at least one load unit via a bus, the switch module comprising a switch device connected between the bus and a main power grid, the energy storage system being coupled to the bus, the method comprising: causing the switch device to trip; The energy storage system receives a trip signal from the switch module; and When the energy storage system receives the trip signal, the operation mode of the energy storage system is switched from the current source mode to the voltage source mode.

18. The method of claim 17, wherein the trip signal is a feedback signal from the switching device.

19. The method of claim 17, wherein the energy storage system and the switch module are coupled by one or more cables, and the method comprises transmitting the trip signal to the energy storage system via the one or more cables.

20. The method according to claim 17, further comprising: Putting the switch device into operation; The energy storage system receives a closing signal from the switch module; and When the energy storage system receives the closing signal, the operation mode of the energy storage system is switched from the voltage source mode to the current source mode.

21. The method of claim 20, wherein the closing signal is a feedback signal from the switching device.

22. The method of claim 20, wherein the energy storage system and the switch module are coupled by one or more cables, and the method includes transmitting the closing signal to the energy storage system via the one or more cables.

23. The method according to claim 17, further comprising synchronizing the power grid system with the main power grid when the energy storage system self-control system receives a reconnection instruction signal. 24 . The method according to claim 17 , further comprising using a voltage sensing unit to measure a voltage of the main grid and provide a voltage signal to the energy storage system.

25. The method according to claim 24, further comprising using the energy storage system to determine whether the main power grid has been repaired based on the voltage signal.

26. The method according to claim 24, further comprising using the energy storage system to determine whether the power grid system is synchronized with the main power grid based on the voltage signal.

27. The method according to claim 20, wherein switching on the switch device comprises sending a switching command signal from the energy storage system to the switch module.

28. The method according to claim 27, comprising sending the input instruction signal when the energy storage system determines that the power grid system is synchronized with the main power grid.

29. The method according to claim 20, wherein the switch module comprises an intelligent electronic device, the intelligent electronic device is coupled to the switch device, and switching on the switch device comprises the energy storage system sending a switching command signal to the intelligent electronic device and using the intelligent electronic device to start the switching device switching operation.

30. The method of claim 17, wherein tripping the switching device comprises opening contacts of the switching device.

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