TWI867389B - Automatic off-grid power supply method - Google Patents

Abstract

An automatic off-grid power supply method is configured to uninterruptedly supply power to a load inside a micro-grid. The method includes steps of: diagnosing an electrical accident of a mains by a high-voltage digital protective relay connected between the mains and the micro-grid. Afterward, confirming that no abnormal fault occurs in the field inside the micro-grid. Afterward, controlling an energy storage system to operate from a current-source power supply mode to automatically switch to a voltage-source power supply mode when a trip protection of the high-voltage digital protective relay is triggered. Finally, uninterruptedly supplying power to the load under an off-grid state of the micro-grid.

Description

Microgrid off-grid automatic power supply method

The present invention relates to an automatic power supply method, and in particular to an off-grid automatic power supply method for a microgrid.

In response to global energy issues, the global power grid is undergoing relevant technology development and construction. New technologies that enhance the resilience of the power grid while transforming energy will have a huge impact on the future operation of micro-grids. Therefore, strengthening the resilience of regional power grids has become a major goal today and is also the focus of this technology development.

At present, when power accidents occur at the mains in remote islands and remote areas, it takes a long time to confirm the problem and repair it before power can be restored. Therefore, how to design a microgrid off-grid automatic power supply method and propose a countermeasure for the autonomous operation of the microgrid off-grid automatic mode in order to reduce the losses caused by the above situation. In this way, it can be applied to remote islands and remote areas first to solve the power bottleneck problem of small microgrids and improve the stability of load power consumption. In the future, it can be further deployed in microgrids in larger areas and develop further towards the direction of smart grids. This is an important topic in the industry.

The purpose of the present invention is to provide a microgrid off-grid automatic power supply method to solve the problems of the prior art.

To achieve the above-mentioned purpose, the present invention proposes an off-grid automatic power supply method for microgrids, which is used to supply power to the loads in the microgrid without interruption. The method includes diagnosing power accidents in the mains through a high-voltage digital protection switch connected between the mains and the microgrid; confirming that no abnormal faults occur within the microgrid field; when the high-voltage digital protection switch determines that the trip protection condition has been reached, the energy storage system is controlled to automatically switch from the current source power supply mode to the voltage source power supply mode; and the microgrid supplies power to the load without interruption when it is off-grid.

In one embodiment, if the high voltage digital protection stop determines that the trip protection condition has not been reached, the energy storage system operates in the current source power supply mode.

In one embodiment, the power grid includes: at least one load loop and at least one distributed energy resource connected to the at least one load loop connected to at least one first high-voltage loop panel; an energy storage system connected to a second high-voltage loop panel and a low-voltage loop panel; and a microgrid controller connected to a high-voltage main loop panel with a high-voltage digital protection switch, at least one first high-voltage loop panel, a second high-voltage loop panel and a low-voltage loop panel.

In one embodiment, the high voltage main loop disk communicates with the microgrid controller via a high voltage main signal, at least one first high voltage loop disk communicates with the microgrid controller via at least one first high voltage signal, the second high voltage loop disk communicates with the microgrid controller via a second high voltage signal, and the low voltage loop disk communicates with the microgrid controller via a low voltage signal.

In one embodiment, in the step of "controlling the energy storage system to automatically switch from the current source power supply mode to the voltage source power supply mode", the microgrid controller provides a mode conversion signal to switch the power supply mode of the energy storage system.

In one embodiment, in the step of "diagnosing that a power accident has occurred in the mains by the high-voltage digital protection switch", it is determined that the abnormal voltage of the high-voltage digital protection switch is triggered to diagnose that a power accident has occurred in the mains.

In one embodiment, when the distributed energy resources are sufficient to provide the power required by the load loop, the load loop is powered by the distributed energy resources.

In one embodiment, when the distributed energy resources are insufficient to provide the power required by the load loop, the load loop is powered by the energy storage system.

In one embodiment, in the step of “confirming that no abnormal fault occurs in the field of the microgrid”, it is confirmed that no abnormal fault occurs in at least a first high-voltage circuit disk, a second high-voltage circuit disk, and a low-voltage circuit disk.

The proposed microgrid off-grid automatic power supply method can achieve the following features and advantages: The microgrid off-grid automatic power supply method can quickly diagnose the information and signals sent back by each digital protection switch in the microgrid, and at the moment when the abnormal voltage triggers the protection, based on these information and signals, the controller sends a mode switching command to the energy storage system, so that the energy storage system can automatically switch to the voltage source mode in an instant when operating in the current source mode, and use the voltage loop and power loop calculation to automatically switch the energy storage system so that the load power supply is not interrupted, so as to achieve the purpose of off-grid automatic operation of the microgrid.

In order to further understand the technology, means and effects adopted by the present invention to achieve the intended purpose, please refer to the following detailed description and drawings of the present invention. It is believed that the purpose, features and characteristics of the present invention can be understood in depth and in detail. However, the attached drawings are only provided for reference and explanation, and are not used to limit the present invention.

The technical content and detailed description of the present invention are described as follows with reference to the accompanying drawings.

The microgrid is equipped with an energy storage system (Energy Management System, EMS) and many distributed energy resources (Distributed Energy Resource, DER), such as solar energy, wind energy, charging piles, diesel generators and other energy resources, as well as load power. When a power accident occurs at the mains end, the grid controller can quickly diagnose the conditions of various parts of the microgrid through digital protection pole information at the moment of disconnection from the mains, and after applying the method developed by the present invention to confirm that the status is safe, quickly issue instructions to switch the energy storage system to the voltage source mode, and use the voltage loop and power loop of the energy storage system to stabilize the internal voltage of the microgrid, so that the internal microgrid will not be interrupted due to the loss of voltage. At this time, the distributed energy resources in the microgrid still have the ability to continue to supply electricity in the microgrid, and make the best adjustment with the energy storage system's energy storage and power consumption, and assist the energy storage system in providing load power, achieving a new technology of automatic off-grid operation of the microgrid and seamless switching of load power sources.

Please refer to Figure 1, which is a block diagram of the microgrid with energy storage system and protection switch operating under normal power supply. The present invention is a technology that combines energy storage system with digital protection switch to realize off-grid automatic operation in microgrid. Specifically, as shown in FIG. 1 , each protection bus in the microgrid 20, in this embodiment, includes a digital protection bus #M (21) in the high-voltage main circuit board, a digital protection bus #H1 (22-1) in the high-voltage circuit board 1, a digital protection bus #H2 (22-2) in the high-voltage circuit board 2, a digital protection bus #H3 (22-3) in the high-voltage circuit board 3, and a digital protection bus #L (24) in the low-voltage circuit board, all of which transmit digital and analog information to the microgrid controller 28, as described in detail below. Therefore, the microgrid controller 28 can obtain the operation status and fault status of each circuit in the microgrid 20 in real time based on the digital protection relay signal, and determine whether the status of each circuit is normal.

As shown in FIG1 (or FIG2, FIG3), the mains 10 is connected to the microgrid 20 through a high-voltage parallel-connected circuit breaker switch 30 (hereinafter referred to as switch 30). When the switch 30 is in a bridged state (i.e., in a conductive state), the mains 10 can supply power to the load loop 1 and/or the load loop 2 in the microgrid 20. On the contrary, when the switch 30 is disconnected or tripped (i.e., in a non-conductive state), the load loop 1 and/or the load loop 2 cannot be supplied with power by the mains 10. The load loop is used to represent a residential power load or a factory power load, but is not limited thereto and is not limited to the two loops shown in FIG1.

One side of the digital protection relay #M(21) in the high voltage main circuit panel is directly connected to the mains 10 through the switch 30, and the other side is connected to the load circuit 1 through the digital protection relay #H1(22-1) in the high voltage circuit panel 1 and the transformer 1(23-1), and the digital protection relay #H1(22-1) in the high voltage circuit panel 2 is directly connected to the mains 10 through the switch 30. The protection bus #H2 (22-2) and the transformer 2 (23-2) are connected to the load circuit 2, and are connected to the energy storage system 27 through the digital protection bus #H3 (22-3) in the high-voltage circuit board 3, the transformer 3 (23-3) and the digital protection bus #L (24) in the low-voltage circuit board. In this embodiment, the energy storage system 27 needs to convert the high voltage into a low voltage through the transformer 3 (23-3), and then store energy through the digital protection bus #L (24) in the low-voltage circuit board.

Since each circuit board (whether high-voltage or low-voltage) has its own digital protection busbar, the protection logic planning of the digital protection busbar can be set to provide complete protection functions for the circuits they are responsible for, or to coordinate the protection between digital protection busbars.

Specifically, each loop panel is connected to the microgrid controller 28 and communicates with the microgrid controller 28 in both directions through corresponding signals. For example, the communication signal between the digital protection relay #M (21) in the high-voltage main loop panel and the microgrid controller 28 is the high-voltage main signal _SM . The communication signals between the digital protection motor #H1 (22-1) in the high-voltage circuit board 1, the digital protection motor #H2 (22-2) in the high-voltage circuit board 2, the digital protection motor #H3 (22-3) in the high-voltage circuit board 3 and the microgrid controller 28 are respectively the first high-voltage signal S _H1 , the second high-voltage signal S _H2 and the third high-voltage signal S _H3 . The communication signal between the digital protection motor #L (24) in the low-voltage circuit board and the microgrid controller 28 is the low-voltage signal SL.

In this embodiment, the distributed energy resource 1 or distributed energy resource 2 shown in FIG. 1 may be a solar energy system, but it is not limited thereto. Existing renewable energy sources, such as wind energy, geothermal energy, biomass energy, etc., can all be included in the scope of the distributed energy resources in this case. The energy storage system 27 is connected to the microgrid controller 28, and the power supply mode of the energy storage system 27 is switched through the mode conversion signal S _ES provided by the microgrid controller 28, which will be described in detail later.

In digital protection relays, the protection logic judgments of overvoltage, undervoltage, overcurrent, etc. all have two levels: pickup and trip. Taking undervoltage as an example, when the undervoltage pickup is triggered, it means that the mains 10 is abnormal, but has not yet reached the tripping circuit breaker to isolate the mains 10; when the undervoltage trip is triggered, it means that the voltage abnormality of the mains 10 has triggered the tripping threshold. At this time, the protection relay will trip the corresponding circuit breaker to isolate the fault area.

Power accidents on the mains side or equipment abnormalities inside the microgrid may cause the high-voltage side protection stop of the microgrid to operate, thereby causing the microgrid to disconnect. Under normal circumstances, after the high-voltage side protection stop is tripped, the voltage provided by the mains will be lost; and if the low-voltage side circuit protection stops are equipped with undervoltage protection, the protection stops will also be triggered and tripped, causing the microgrid to lose power completely. If a protection trip occurs on the high-voltage side and there is no safety risk inside the microgrid, the controller can quickly switch the energy storage system 27 operation mode through the energy storage system 27 voltage ring to support the internal voltage of the microgrid so that it will not go completely black due to the undervoltage protection trip. Since the microgrid includes the energy storage system 27 and other various distributed energy resources (or distributed power resources) that can provide electricity, the energy storage system 27 power ring is seamlessly connected to allow these power resources to continue to provide power to the load when off-grid.

Please refer to FIG. 2, which is a block diagram of the microgrid with energy storage system and protection post in the first scenario of abnormal power supply of the mains. The first scenario refers to the mains 10 being abnormal, but the microgrid 20 is still in the grid-connected state. When the voltage of the mains 10 begins to be abnormal, the microgrid controller 28 will receive the start signal returned by each high-voltage digital protection post in the microgrid, such as a voltage drop that enables the return of the start signal, so the digital protection post #M (21) in the high-voltage main circuit board returns the high-voltage main signal _SM to the microgrid controller 28. At this time, because the protection trip signal of the digital protection motor has not been activated, the microgrid is still in the grid-connected mode. The microgrid controller 28 is based on the digital protection motor signal, that is, the microgrid controller 28 receives the first high-voltage signal S _H1 returned by the digital protection motor #H1 (22-1) in the high-voltage loop panel 1, the second high-voltage signal S _H2 returned by the digital protection motor #H2 (22-2) in the high-voltage loop panel 2, the third high-voltage signal S _H3 returned by the digital protection motor #H3 (22-3) in the high-voltage loop panel 3, and the low-voltage signal S _L returned by the digital protection motor #L (24) in the low-voltage loop panel. , confirm whether there is an abnormal fault overcurrent trip signal inside the microgrid field: if there is, it means that there may be a cable or equipment failure inside the field; otherwise, it can be preliminarily determined that there is no abnormality in the circuits inside the power grid.

When the distributed energy resource 1 is sufficient to provide the power required by the load loop 1, or when the distributed energy resource 2 is sufficient to provide the power required by the load loop 2, the load loop 1 and the load loop 2 are powered by the distributed energy resource 1 and the distributed energy resource 2 respectively. Even the redundant power of the distributed energy resources can be stored in the energy storage system 27. On the contrary, if the distributed energy resource 1 is insufficient to provide the power required by the load loop 1, or the distributed energy resource 2 is insufficient to provide the power required by the load loop 2, the energy storage system 27 is used for power supply and power regulation, and the energy storage system 27 operates in the current source power supply mode. Incidentally, when the energy storage system 27 is sufficient to provide the power required by the load loop, it is no longer necessary to supply power through the mains 10. The aforementioned information on power supply and power consumption (the amount of power required by each loop) is collected and coordinated by the microgrid controller 28. Incidentally, in this embodiment, both the load loop 1 and the load loop 2 are connected to important power loads.

Please refer to FIG3, which is a block diagram of the microgrid with energy storage system and protection switch in the second scenario of abnormal power supply of the mains. The so-called first scenario refers to the mains 10 being abnormal, but the microgrid 20 is off-grid. When the abnormal voltage of the mains 10 triggers the tripping of the high-voltage side digital protection switch (linked tripping of the high voltage and the circuit breaker switch 30), the microgrid controller 28 will receive the digital protection switch tripping signal and confirm whether there is an abnormal condition inside the field of the microgrid 20 according to the above-mentioned pre-completed judgment mechanism. The purpose of the switch 30 tripping is to prevent excessive fault current generated by an abnormality in the mains 10 from entering the microgrid 20, causing damage to the equipment and devices in the microgrid 20 or casualties of personnel. If there is no abnormality in the internal circuits of the microgrid 20, the microgrid controller 28 will send a mode conversion signal S _ES to the energy storage system 27, so that the energy storage system 27 can seamlessly switch from the current source mode to the voltage source mode and automatically operate in the microgrid off-grid mode (that is, automatically switch from the current source mode to the voltage source mode). Under this approach, the distributed energy resources (DER) in the microgrid still have the ability to continue to supply electricity in the microgrid, and make the best adjustment with the energy storage system 27 to assist the energy storage system 27 in providing electricity for the load (load loop 1, load loop 2), thereby achieving the goal of uninterrupted power supply to the load.

There are more than one reason for the disconnection of the microgrid 20 from the mains 10. If the field fault conditions are not determined and a safety judgment mechanism is not established, the energy storage system 27 is switched from the current source mode to the voltage source mode without any warning, which may cause a secondary accident when the microgrid 20 supplies power to the load without clearing the internal fault circuit. Therefore, the safety judgment mechanism is particularly important, and this is also the focus of the development of the present invention.

The present invention combines a digital protection switch with a controller to diagnose the internal status of the field. When a power accident occurs in the mains, it can respond quickly according to the internal status of the microgrid. If there is no safety concern, a control command is instantly issued to the energy storage system, causing it to immediately convert into a voltage source for autonomous operation to support the voltage inside the microgrid, thereby preventing the microgrid from going completely black due to the loss of the mains voltage and ensuring that the power consumption of the loads in the microgrid is not interrupted.

The biggest feature of the present invention is that the energy storage system 27 has real-time information of the high-voltage panel and the low-voltage panel protection relay. Before the high-voltage shunt panel circuit breaker switch trips, the voltage analog signal, undervoltage signal, fault current signal and other data of each digital protection relay are used as the basis to determine whether the disconnection is an internal accident of the microgrid through the algorithm in the controller of the present invention. If so, the energy storage system should not be started rashly before the fault is eliminated or the faulty equipment is isolated to avoid the occurrence of a secondary accident; on the contrary, if the controller determines that it is a power accident on the mains side and there is no abnormal situation in the circuit within the microgrid 20 field, the controller can issue a control command to instantly switch the energy storage system 27 to the voltage source mode. This is different from the previous practice of manually restarting the energy storage system and various equipment after manually inspecting the abnormal situation and eliminating the fault. This method can prevent the loss of power in the microgrid 20 and ensure that the load power supply is not interrupted.

In summary, please refer to FIG4, which is a flow chart of the microgrid off-grid automatic power supply method of the present invention. The microgrid off-grid automatic power supply method of the present invention is used to supply power to the loads in the microgrid without interruption (continuously). The microgrid off-grid automatic power supply method includes the following steps: First, diagnose the occurrence of a power accident in the mains through a high-voltage digital protection switch connected between the mains and the microgrid (S10). Then, confirm that no abnormal fault occurs within the microgrid field (S20). Then, when the high-voltage digital protection switch determines that the trip protection condition is reached, the energy storage system is controlled to operate from the current source power supply mode and automatically switch to the voltage source power supply mode (S30). Finally, the microgrid supplies power to the load without interruption in an off-grid state (S40).

Specifically, please refer to FIG. 5, which is a detailed flow chart of the off-grid automatic power supply method of the microgrid of the present invention. First, determine whether the abnormal voltage start of the high-voltage digital protection motor is triggered (S111). If "yes", it means that the abnormal voltage start of the digital protection motor #M (21) in the high-voltage main circuit board is triggered, and the microgrid status is determined according to the signal of each digital protection motor (S112). If "no", continue to execute step (S111) or end the determination.

After step (S112), it is determined whether all digital protection switches have no fault current tripping signal (S113). If "yes", the microgrid controller issues an instruction to prepare to switch the power supply mode of the energy storage system (S114). If "no", it means that an abnormal fault has occurred inside the field of the microgrid, and the fault range needs to be isolated (S115), and the automatic power supply is terminated. After step (S114), it is determined whether the abnormal voltage protection of the high-voltage digital protection switch is triggered (S116). If "yes", the energy storage system automatically switches to the voltage source power supply mode (S117). If "No", the process returns to step (S111), that is, the judgment process is restarted. After step (S117), the microgrid supplies power to the load without interruption in the off-grid state (S118).

In summary, the present invention has the following features and advantages: The microgrid off-grid automatic power supply method of the present invention can quickly diagnose with the information and signals sent back by each digital protection switch in the microgrid, and at the moment when the abnormal voltage triggers the protection, based on these information and signals, the controller sends a mode switching instruction to the energy storage system, so that the energy storage system can automatically switch to the voltage source mode in an instant when operating in the current source mode, and use the voltage loop and power loop calculation to make the energy storage system automatically switch so that the load power consumption is not interrupted, so as to achieve the purpose of the microgrid off-grid automatic operation. In other words, when a power accident occurs in the mains, if the conditions for the microgrid to operate off-grid are met, the controller of this technology can quickly switch the energy storage system to a power supply mode to avoid the loss of load power in the microgrid, so that the remaining power resources in the grid can continue to supply power to the load in the microgrid, solving the problem of load power interruption when the microgrid loses mains power, and achieving the microgrid's off-grid automatic and autonomous operation mode.

The above description is only a detailed description and drawings of the preferred specific embodiments of the present invention, but the features of the present invention are not limited thereto and are not intended to limit the present invention. The entire scope of the present invention shall be subject to the following patent application scope. All embodiments that conform to the spirit of the patent application scope of the present invention and similar variations thereof shall be included in the scope of the present invention. Any changes or modifications that can be easily thought of by anyone familiar with the art within the field of the present invention shall be covered by the following patent scope of the present case.

10: Mains 20: Microgrid 30: High voltage parallel circuit breaker switch 21: High voltage main circuit digital protection motor #M 22-1: High voltage circuit 1 digital protection motor #H1 22-2: High voltage circuit 2 digital protection motor #H2 22-3: High voltage circuit 3 digital protection motor #H3 23-1: Transformer 1 23-2: Transformer 2 23-3: Transformer 3 24: Low voltage circuit digital protection motor #L 25-1: Load circuit 1 25-2: Load circuit 2 26-1: Distributed energy resource 1 26-2: Distributed energy resource 2 27: Energy storage system 28: Microgrid controller S _M : High voltage total signal S _H1 : First high voltage signal S _H2 : Second high voltage signal S _H3 : Third high voltage signal S _L : Low voltage signal S _ES : Mode conversion signal

FIG. 1 is a block diagram of a microgrid with an energy storage system and a protection switch operating under normal power supply.

FIG. 2 is a block diagram of the microgrid with an energy storage system and a protection switch of the present invention operating in a first scenario of abnormal city power supply.

FIG3 is a block diagram of the microgrid with an energy storage system and a protection switch of the present invention operating in the second scenario of abnormal city power supply.

FIG4 is a flow chart of the microgrid off-grid automatic power supply method of the present invention.

FIG5 is a detailed flow chart of the microgrid off-grid automatic power supply method of the present invention.

S10~S40: Steps

Claims (9)

A microgrid off-grid automatic power supply method is used to supply power to a load in a microgrid without interruption. The method includes: diagnosing a power accident of the mains through a high-voltage digital protection switch connected to a high-voltage main circuit board between the mains and the microgrid; confirming that no abnormal fault occurs within the field of the microgrid; when the high-voltage digital protection switch determines that a trip protection condition has been reached, controlling an energy storage system to automatically switch from a current source power supply mode to a voltage source power supply mode; and the microgrid supplies power to the load without interruption in an off-grid state. As described in claim 1, in the off-grid automatic power supply method for microgrids, if the high-voltage digital protection stop determines that the trip protection condition has not been reached, the energy storage system operates in the current source power supply mode. The microgrid off-grid automatic power supply method as described in claim 1, wherein the microgrid comprises: at least one load loop and at least one distributed energy resource connected to the at least one load loop, connected to at least one first high-voltage circuit board; the energy storage system, connected to a second high-voltage circuit board and a low-voltage circuit board; and a microgrid controller, connected to the high-voltage main circuit board having the high-voltage digital protection switch, the at least one first high-voltage circuit board, the second high-voltage circuit board and the low-voltage circuit board. As described in claim 3, the microgrid off-grid automatic power supply method, wherein the high-voltage main circuit plate communicates with the microgrid controller via a high-voltage main signal, the at least one first high-voltage circuit plate communicates with the microgrid controller via at least one first high-voltage signal, the second high-voltage circuit plate communicates with the microgrid controller via a second high-voltage signal, and the low-voltage circuit plate communicates with the microgrid controller via a low-voltage signal. As described in claim 3, in the step of "controlling an energy storage system to automatically switch from a current source power supply mode to a voltage source power supply mode", the microgrid controller provides a mode conversion signal to switch the power supply mode of the energy storage system. As described in claim 1, in the step of "a high-voltage digital protection switch diagnoses a power accident in the mains", it is determined that the abnormal voltage of the high-voltage digital protection switch is triggered to diagnose a power accident in the mains. As described in claim 3, the microgrid off-grid automatic power supply method, wherein when the distributed energy resource is sufficient to provide the power required by the load loop, the load loop is powered by the distributed energy resource. As described in claim 3, the microgrid off-grid automatic power supply method, wherein when the distributed energy resources are insufficient to provide the power required by the load loop, the load loop is powered by the energy storage system. As described in claim 3, in the step of "confirming that no abnormal fault occurs within the field of the microgrid", it is confirmed that no abnormal fault occurs in the at least one first high-voltage circuit plate, the second high-voltage circuit plate, and the low-voltage circuit plate.

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