Microgrid short-circuit fault protection method and device based on current rate of change difference
By suppressing current ripple and noise through polynomial fitting and using the difference in current change rate to form the differential protection action quantity, the problem of excessively long detection time of longitudinal differential protection is solved, rapid fault detection and isolation are achieved, and the operational stability of the ship's power system is improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TAN KAH KEE INNOVATION LAB
- Filing Date
- 2023-05-09
- Publication Date
- 2026-08-04
AI Technical Summary
The existing longitudinal differential protection method has the problem of excessively long detection time when detecting short-circuit faults with large transition resistance, and it is difficult to be compatible with the range of transition resistance changes, which affects the rapid fault detection and isolation of the ship's power system.
A polynomial fitting method is used to suppress current ripple and sampling noise. The operating quantity of the differential protection is constructed by the difference in the rate of change of current. Taking advantage of the characteristic that the rate of change of current at the time of fault occurrence is not greatly affected by the value of the transition resistor, a sliding window and low-pass filter are set to extract the rate of change of current, and the operating quantity and braking quantity of the longitudinal differential protection are calculated.
While expanding the compatibility range of longitudinal differential protection with changes in transition resistance, it shortens the fault detection time and improves the fault detection speed and selectivity of ship power systems.
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Figure CN116599008B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of relay protection technology for tugboat DC power grids, and in particular to a microgrid short-circuit fault protection method and device based on the difference in current change rate. Background Technology
[0002] Compared to AC power grids, tugboat DC power grids offer advantages such as improved fuel efficiency, convenient access to other energy units or energy storage units, and flexible electrical equipment layout, attracting widespread attention. However, when a short-circuit fault occurs in a DC power grid, the fault develops very rapidly. If the fault is not isolated in time, it will affect the normal operation of the entire system, and in severe cases, lead to system collapse. This is especially true for shipboard electrical systems, where cable lengths are limited by the ship's hull, resulting in low line impedance and a low short-circuit power factor. Under bipolar short-circuit fault conditions, the current is extremely high. If the faulty line is not isolated in time, it will cause various malfunctions or abnormal operations on the ship, affecting combat effectiveness and navigation safety. Therefore, it is essential to quickly detect and isolate faulty lines to ensure the continuous operation of the tugboat DC power grid.
[0003] With the continuous increase in the capacity of shipboard power systems, shipboard power grid relay protection technology has also developed rapidly. New technologies such as three-stage protection, differential protection, adaptive protection, and modular power electronic protection are gradually being researched and applied. Among them, differential protection has gradually gained recognition in the field of shipboard power systems in recent years due to its excellent speed and selectivity. Longitudinal differential protection can achieve complete selectivity for short circuits in transmission lines and busbars of complex shipboard power systems.
[0004] Current longitudinal differential protection methods mainly employ low cutoff frequency filtering schemes to suppress the influence of current ripple and cable distributed parameters as much as possible. However, this results in a longer detection time for short-circuit faults with large transition resistance, creating a contradiction between the compatibility range of transition resistance changes and shortening the fault detection time.
[0005] It should be noted that the information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention, and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention
[0006] To address the challenges of existing technologies, this invention utilizes the characteristic that the rate of change of current at the moment of a fault is minimally affected by the value of the transition resistance. It employs a polynomial fitting method to suppress the influence of current ripple and sampling noise, thereby effectively extracting the rate of change of current. The rate of change of current is then used to construct the operating quantity of the differential protection, thus resolving the contradiction between expanding the compatibility range of longitudinal differential protection with changes in transition resistance and shortening the fault detection time.
[0007] An embodiment of the present invention provides a microgrid short-circuit fault protection method based on the difference in current change rate, comprising the following steps: continuously collecting current data; setting a first sliding window and a second sliding window to record the historical current information at both ends of the cable; fitting the current data of the first sliding window according to a fitting formula; calculating the current change rate at the window boundary of the first sliding window using the fitting formula; obtaining the difference in current change rate at both ends of the cable based on the current change rate at the window boundary of the first sliding window; obtaining the operating quantity of the longitudinal differential protection from the difference in current change rate; calculating the sum of the maximum value of the differential current and the average value of the absolute current at both ends of the cable based on the current data in the second sliding window; obtaining the restraining quantity of the longitudinal differential protection from the sum of the maximum value of the differential current and the average value of the absolute current at both ends of the cable; and determining that a bipolar short-circuit fault has occurred in the cable and disconnecting the faulty line when the operating quantity and the restraining quantity meet predetermined conditions.
[0008] In some embodiments, during the continuous acquisition of current data, the acquired current data is low-pass filtered to suppress current sampling noise.
[0009] In some embodiments, the cutoff frequency of the low-pass filter is greater than or equal to half the operating frequency of the converter in the microgrid, so that the acquired current data includes the current ripple generated by the converter.
[0010] In some embodiments, the window duration of the first sliding window is T1, and T1 is configured to be 10ms or more, so that the current change trend can be extracted during the acquisition of the action quantity without being affected by the current ripple and output power change of the converter.
[0011] In some embodiments, the window duration of the second sliding window is T2, which is configured to be more than 5 times the converter duty cycle, and T1 > T2, so as to identify whether the current changes rapidly during the acquisition of braking amount.
[0012] In some embodiments, the fitting formula is as follows:
[0013]
[0014] Among them, i (1) and i (2) The current is the collected current, t is the time corresponding to the current data in the first and second sliding windows, and t ranges from 0 to T1. T1 is the window length of the first sliding window, and a, b, and c are the coefficients of the quadratic polynomial.
[0015] In some embodiments, the rate of change of current at the window boundary of the first sliding window is as follows:
[0016]
[0017] The operating parameters of the longitudinal differential protection are as follows:
[0018]
[0019] In some embodiments, the sum of the maximum value of the differential current and the average of the absolute values of the currents at both ends of the cable is as follows:
[0020]
[0021] Among them, i d For differential current, i d =i (1) -i (2) Δi is the maximum value of the differential current, I ave The sum of the mean values is n, where n is the number of current data points in the second sliding window.
[0022] The braking amount of the longitudinal differential protection is as follows:
[0023]
[0024] In some embodiments, the predetermined conditions are as follows:
[0025]
[0026] Where (di / dt)limit is the threshold value of the action quantity of the longitudinal differential protection mode, k limit This is the braking coefficient.
[0027] An embodiment of the present invention also provides an apparatus including a memory and a processor. The memory is used to store embedded software programs; the processor is used to execute the embedded software programs stored in the memory, and when the embedded programs are executed, they implement the steps of the microgrid short-circuit fault protection method based on the difference in current change rate as described in any of the foregoing embodiments.
[0028] In summary, an embodiment of the present invention provides a microgrid short-circuit fault protection method and device based on the difference in current change rate. By utilizing the characteristic that the current change rate at the time of fault occurrence is less affected by the value of the transition resistance, a polynomial fitting method is used to suppress the influence of current ripple and sampling noise, thereby effectively extracting the current change rate. The current change rate is then used to constitute the operating quantity of the differential protection, thus resolving the contradiction between expanding the compatibility range of the longitudinal differential protection for changes in transition resistance and shortening the fault detection time. This allows for both expanding the compatibility range for changes in transition resistance and shortening the fault detection time.
[0029] Other features and beneficial effects of the invention will be set forth in the following description, and some of these features and beneficial effects may be apparent from the description or learned by practicing the invention. The objects of the invention and other beneficial effects may be realized and obtained through the structures specifically pointed out in the description and other contents. Attached Figure Description
[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, some of the drawings in the following description are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0031] Figure 1 This is a schematic diagram of a traditional longitudinal differential protection method;
[0032] Figure 2 This is a schematic flowchart of a microgrid short-circuit fault protection method based on the difference in current change rate provided in an embodiment of the present invention;
[0033] Figure 3 This is a schematic diagram of a tugboat DC power grid model that uses a short-circuit fault protection method based on the difference in the rate of change of current.
[0034] Figure 4 This is a schematic diagram of the equivalent capacitance model for a short-circuit fault in a tugboat's DC power grid;
[0035] Figure 5 This is a schematic diagram of polynomial fitting for the action threshold of longitudinal differential protection based on the difference in current change rate;
[0036] Figure 6 This is a schematic diagram showing the threshold values for the action quantity of longitudinal differential protection based on the difference in current change rate. Detailed Implementation
[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. The technical features designed in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.
[0038] In the description of this invention, it should be understood that the terms "center," "lateral," "upper," "lower," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more. Additionally, the term "comprising" and any variations thereof mean "at least comprising."
[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integrally formed connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0040] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms “a” and “an” as used herein are also intended to include the plural. It should also be understood that the terms “comprising” and / or “including” as used herein specify the presence of the stated features, integers, steps, operations, units, and / or components, without excluding the presence or addition of one or more other features, integers, steps, operations, units, components, and / or combinations thereof.
[0041] Please see Figure 2 , Figure 2 This is a schematic flowchart of a microgrid short-circuit fault protection method based on the difference in current change rate provided in an embodiment of the present invention. An embodiment of the present invention provides a microgrid short-circuit fault protection method based on the difference in current change rate. As shown in the figure, the method includes the following steps:
[0042] S1. Continuously collect current data;
[0043] S2. Set up a first sliding window and a second sliding window to record the historical current information at both ends of the cable;
[0044] S3. Fit the current data of the first sliding window according to the fitting formula;
[0045] S4. Calculate the rate of change of current at the window boundary of the first sliding window using the fitting formula;
[0046] S5. Obtain the difference in the rate of change of current at both ends of the cable based on the rate of change of current at the window boundary of the first sliding window.
[0047] S6. Obtain the operating quantity of the longitudinal differential protection from the difference in current change rate;
[0048] S7. Based on the current data in the second sliding window, calculate the sum of the maximum value of the differential current and the average value of the absolute values of the currents at both ends of the cable.
[0049] S8. The braking amount of the longitudinal differential protection is obtained by summing the maximum value of the differential current and the average value of the absolute values of the currents at both ends of the cable.
[0050] S9. When the action amount and braking amount meet the predetermined conditions, it is determined that a double-pole short circuit fault has occurred in the cable, and the faulty line is disconnected.
[0051] In step S1, during the continuous acquisition of current data, the acquired current data is low-pass filtered to suppress current sampling noise. The cutoff frequency of the low-pass filter is greater than or equal to half the operating frequency of the converter in the microgrid, so that the acquired current data includes the current ripple generated by the converter.
[0052] In step S2, the window duration of the first sliding window is set to T1, which is configured to be 10ms or more, so that the current change trend can be extracted during the acquisition of the action quantity without being affected by the current ripple and output power changes of the converter. The window duration of the second sliding window is set to T2, which is configured to be 5 times or more the duration of the converter's duty cycle, and T1 > T2, so that the rapid change of current can be identified during the acquisition of the braking quantity.
[0053] The fitting formula in step S3 is as follows:
[0054]
[0055] Among them, i (1) and i (2) The current is the collected current, t is the time corresponding to the current data in the first and second sliding windows, and t ranges from 0 to T1. T1 is the window length of the first sliding window, and a, b, and c are the coefficients of the quadratic polynomial.
[0056] In step S4, the rate of change of current at the window boundary of the first sliding window is as follows:
[0057]
[0058] In step S6, the operating parameters of the longitudinal differential protection are as follows:
[0059]
[0060] In step S7, the sum of the maximum value of the differential current and the average absolute value of the current at both ends of the cable is as follows:
[0061]
[0062] Among them, i d For differential current, i d =i (1) -i (2) Δi is the maximum value of the differential current, I ave The sum of the mean values is n, where n is the number of current data points in the second sliding window.
[0063] In step S8, the braking amount of the longitudinal differential protection is as follows:
[0064]
[0065] The predetermined conditions in step S9 are as follows:
[0066]
[0067] Where (di / dt)limit is the threshold value of the action quantity of the longitudinal differential protection mode, k limit This is the braking coefficient.
[0068] Please see Figures 3 to 6 , Figure 3 This is a schematic diagram of a tugboat DC power grid model that employs a short-circuit fault protection method based on the difference in the rate of change of current. Figure 4 This is a schematic diagram of the equivalent capacitance model for a short-circuit fault in a tugboat's DC power grid. Figure 5 This is a schematic diagram of polynomial fitting for the operating threshold of longitudinal differential protection based on the difference in current change rate. Figure 6 This is a schematic diagram illustrating the threshold values for the longitudinal differential protection action quantity based on the difference in current change rate. The following will use a tugboat DC power grid as an example to illustrate the microgrid short-circuit fault protection method based on the difference in current change rate of this invention.
[0069] like Figure 3As shown, the power supply side consists of an engine, a motor G, and a battery pack. The engine drives the generator G to produce AC power, which is rectified and boosted by a rectifier before being connected to the busbar. The battery pack is boosted by a bidirectional DC-DC converter before being connected to the busbar. The power load side consists of a propulsion turbine M and other daily loads. The propulsion motor is connected to the busbar via an inverter; other loads are connected to the busbar via a buck converter. The busbar is connected to the rectifier, bidirectional DC-DC converter, inverter, and buck converter via cables, and each cable is equipped with a solid-state circuit breaker CB at both ends for quickly disconnecting faulty lines. The protection method includes low-pass filtering, sliding window configuration, polynomial fitting-based action quantity calculation, braking quantity calculation, and fault protection output stage. Low-pass filtering is used to suppress current sampling noise; sliding window is used to record historical information of cable current changes; polynomial fitting is used to extract the current change rate, and then calculate the action quantity of the protection mode; braking quantity calculation is used to prevent protection maloperation.
[0070] Let i be the current at both ends of the L2 branch cable. (1) and i (2) For example, consider a double-pole short-circuit fault in cable L2: when i (1) and i (2) When the action and braking quantities obtained from the sampled data reach the fault protection conditions, the fault protection output issues a protection command through the solid-state circuit breaker CB. 2(1) and CB 2(2) Disconnect the faulty line.
[0071] The specific process of the bipolar short-circuit fault longitudinal differential protection is as follows:
[0072] During ship operation, i is continuously collected (1) and i (2) The data is then low-pass filtered to suppress current sampling noise. The cutoff frequency of the low-pass filter is no less than half the operating frequency of each converter in the tugboat's DC power grid, so that i (1) and i (2) The data includes the current ripple generated by the converter. Subsequently, two sliding windows of different lengths are set to record the current history information. The length of the first sliding window, T1, can be configured to be greater than 10 ms, so that the action calculation section can reliably extract the current change trend without being affected by converter current ripple and output power changes; the length of the second sliding window is T2, where T1 is greater than T2, and T2 can be configured to be greater than 5 times the converter duty cycle, so that the action calculation section can identify whether the current has changed rapidly.
[0073] The current data of the first sliding window are fitted using a quadratic polynomial, as shown in equation (1):
[0074]
[0075] The rate of change of current at the boundary of the first sliding window is calculated from the coefficients of equation (1), as shown in equation (2):
[0076]
[0077] From equation (2), the action quantity of the longitudinal differential protection can be obtained as follows:
[0078]
[0079] Then, based on the n current data points in the second sliding window, calculate the maximum value of the differential current id and the current i at both ends of cable L2. (1) i (2) The sum of the mean of the absolute values is shown in equation (4):
[0080]
[0081] From equation (4), the braking amount of the longitudinal differential protection can be obtained as:
[0082]
[0083] When the action amount and braking amount satisfy equation (6), it is determined that the cable has a double-pole short-circuit fault. The fault protection output circuit outputs a control signal to turn off the solid-state circuit breaker and disconnect the faulty line.
[0084] Equation (6) is as follows:
[0085]
[0086] The (di / dt)limit is determined using the equivalent capacitance model of a bipolar short-circuit fault in a tugboat DC power grid. The equivalent capacitance model is as follows: Figure 4 As shown. Figure 4 In the diagram, C1 and C2 are respectively Figure 3 The output capacitors of the rectifier and bidirectional DC-DC converter on the power supply side of the power grid are shown; R1 to R4 and L1 to L4 are the parasitic resistance and parasitic inductance of each cable, respectively; C3 and C4 are the input capacitors of the inverter and buck converter on the power load side, and R3 and R4 are the equivalent resistance of the load; R f This is the transition resistor for the bipolar short-circuit fault location. Set the expected maximum R... f By simulating the equivalent capacitance model, the current curves at both ends of the cable after a fault can be obtained, for example... Figure 4 The i of the L2 cable (1) and i (2) Curve, according to i (1) and i (2) The curve can then be further used to determine (di / dt). limit .
[0087] Figure 5 and Figure 6 For the obtained i (1) and i (2) Curve and motion threshold (di / dt) limit A schematic diagram of the adjustment. (See example.) Figure 5 As shown, when the i values before and after the fault are obtained... (1) and i (2) After the data is processed, the first sliding window with a window length of T1 is used. Figure 5 (The first sliding window in the image is 1) Scan i (1) and i (2) Curve; according to equation (1), the current data within the fitting window is fitted to obtain the fitted curve; according to equation (2), the rate of change of current at the window boundary is obtained, i.e., the tangent di of the fitted curve. (1) / dt and di (2) / dt. During the first sliding window scan, by di (1) / dt and di (2) / dt gives the motion quantity (di / dt). op Curves that change over time (e.g.) Figure 6 As shown). According to Figure 6 (di / dt) op The changing pattern of (di / dt) can be used to determine the expected protection output time after a fault. op The value serves as a threshold for the amount of motion (di / dt). limit .
[0088] For k limit The ripple coefficient of the converter's output current can then be adjusted. Ideally, during stable operation of the tugboat's DC grid, the currents at both ends of the cable are in the same direction and equal, meaning Δi is zero. However, due to the influence of cable distributed parameters, the current ripples at both ends of the cable exhibit a phase difference, causing Δi to not be continuously zero; the maximum offset is the current ripple amplitude. When Δi equals the current ripple amplitude, the braking amount k is the ripple coefficient of the electronic power converter's output current. Considering that the output current of the electronic power converter will change during the tugboat's DC grid power dispatching process, k... limit The value can be slightly larger than the output current ripple coefficient of the electronic power converter.
[0089] An embodiment of the present invention also provides an apparatus including a memory and a processor. The memory is used to store embedded software programs; the processor is used to execute the embedded software programs stored in the memory, and when the embedded programs are executed, they implement the steps of the microgrid short-circuit fault protection method based on the difference in current change rate as described in any of the foregoing embodiments.
[0090] In summary, an embodiment of the present invention provides a microgrid short-circuit fault protection method and device based on the difference in current change rate. By utilizing the characteristic that the current change rate at the time of fault occurrence is less affected by the value of the transition resistance, a polynomial fitting method is used to suppress the influence of current ripple and sampling noise, thereby effectively extracting the current change rate. The current change rate is then used to constitute the operating quantity of the differential protection, thus resolving the contradiction between expanding the compatibility range of the longitudinal differential protection for changes in transition resistance and shortening the fault detection time. This allows for both expanding the compatibility range for changes in transition resistance and shortening the fault detection time.
[0091] Furthermore, those skilled in the art should understand that although many problems exist in the prior art, each embodiment or technical solution of the present invention can be improved in only one or a few aspects, without necessarily solving all the technical problems listed in the prior art or the background art simultaneously. Those skilled in the art should understand that any content not mentioned in a claim should not be construed as a limitation on that claim.
[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A microgrid short-circuit fault protection method based on the difference in current change rate, characterized in that: The microgrid short-circuit fault protection method includes the following steps: Continuously collect current data; Set up a first sliding window and a second sliding window to record the historical current information at both ends of the cable; The current data of the first sliding window is fitted according to the fitting formula; The rate of change of current at the window boundary of the first sliding window is calculated using a fitting formula; The difference in the rate of change of current at both ends of the cable is obtained based on the rate of change of current at the window boundary of the first sliding window. The operating quantity of the longitudinal differential protection is obtained from the difference in the rate of change of the current; Based on the current data in the second sliding window, calculate the sum of the maximum value of the differential current and the average absolute value of the current at both ends of the cable; The braking amount of the longitudinal differential protection is obtained by summing the maximum value of the differential current and the average value of the absolute values of the currents at both ends of the cable. When the action amount and the braking amount meet the predetermined conditions, it is determined that a double-pole short-circuit fault has occurred in the cable, and the faulty line is disconnected. The window duration of the first sliding window is T1, and T1 is configured to be more than 10ms, so that the current change trend can be extracted during the acquisition of the action quantity without being affected by the current ripple and output power change of the converter. The window duration of the second sliding window is T2, which is configured to be more than 5 times the duration of the converter's working cycle, and T1 > T2, so as to identify whether the current changes rapidly during the process of acquiring the braking amount. The fitting formula is as follows: （1） Among them, i (1) and i (2) The current is the collected current, t is the time corresponding to the current data in the first sliding window and the second sliding window, t ranges from 0 to T1, T1 is the window length of the first sliding window, and a, b, and c are the coefficients of the quadratic polynomial. The rate of change of current at the window boundary of the first sliding window is as follows: （2） The operating parameters of the longitudinal differential protection are as follows: （3） The sum of the maximum value of the differential current and the average of the absolute values of the currents at both ends of the cable is as follows: （4） Among them, i d Let i be the differential current. d =i (1) i (2) , This is the maximum value of the differential current. The sum of the averages, where n is the number of current data points in the second sliding window; The braking amount of the longitudinal differential protection is as follows: （5）。 2. The microgrid short-circuit fault protection method based on the difference in current change rate according to claim 1, characterized in that: During the continuous acquisition of current data, the acquired current data is low-pass filtered to suppress current sampling noise.
3. The microgrid short-circuit fault protection method based on the difference in current change rate according to claim 2, characterized in that: The cutoff frequency of the low-pass filter is greater than or equal to half the operating frequency of the converter in the microgrid, so that the acquired current data includes the current ripple generated by the converter.
4. The microgrid short-circuit fault protection method based on the difference in current change rate according to claim 1, characterized in that: The predetermined conditions are as follows: （6） Where (di / dt)limit is the threshold value of the action quantity of the longitudinal differential protection, k limit This is the braking coefficient.
5. A device, characterized in that: The device includes: Memory, used to store embedded software programs; A processor is configured to execute an embedded software program stored in the memory, wherein the embedded software program, when executed, implements the steps of the microgrid short-circuit fault protection method based on the difference in current change rate as described in any one of claims 1 to 4.