Adaptive distributed energy and load plug-and-play DC microgrid grounding fault protection method, system, device and medium

Abstract

The present invention discloses a DC microgrid ground fault protection method, system, device, and medium for adaptive distributed energy and load plug-and-play. The method includes the following steps: real-time calculation of fault area location information; when the regional fault ground current and power change rate meet the protection initiation criteria, determining the fault area based on the fault area location information; sending a trip command to the DC circuit breaker connected to the fault area; and disconnecting the DC circuit breaker after receiving the trip command. Based on the characteristics of the DC microgrid, such as flexible and changeable source-storage-load regional structure, diverse control modes, and easy extraction of high-frequency fault data, the present invention adds a constant power load to the load area to simulate actual scenarios, establishes a universal protection positioning method, realizes the plug-and-play nature of the fault protection positioning method under the conditions of variable DC microgrid source-storage-load structure, and ensures accurate isolation of different fault areas when a ground short circuit fault occurs in the DC microgrid source-storage-load.

Description

Technical Field

[0001] The present invention relates to the field of DC microgrid protection, and in particular to a DC microgrid grounding fault protection method and system with adaptive distributed energy and load plug-and-play. Background Art

[0002] With the continuous increase in energy demand and growing awareness of environmental protection, the application of distributed energy systems and DC microgrids in the energy sector is becoming increasingly prevalent. Today's society faces increasingly severe challenges in energy security and environmental protection, which has driven the widespread application and development of renewable energy. In particular, the rapid development of distributed energy resources such as solar and wind power has led to an increasing prominence for microgrid technology in the energy system. As small-scale power systems, microgrids have the ability to operate autonomously and be isolated from the main grid, providing reliable power supply to areas remote from traditional power grids. Compared to traditional large-scale power grids, microgrids are more flexible and can better adapt to local energy resources and load demands, offering new solutions for sustainable energy system development.

[0003] With the continuous development and application of microgrids, DC microgrids are gaining increasing attention as an emerging form. DC microgrids offer advantages such as low energy loss, fast system response, and easy interface with DC loads and distributed energy resources, making them considered a key development direction for future energy systems. However, unlike AC microgrids, the protection issues of DC microgrids are particularly complex and critical due to their unique operating principles and components. Traditional AC protection schemes cannot be directly applied to DC systems. Therefore, there is an urgent need to develop innovative and adaptable DC microgrid protection methods to address various possible faults and abnormal conditions in the system and ensure its safe operation and stability. Due to the complex topology and dynamic operating characteristics of DC microgrids, their protection issues are becoming increasingly prominent.

[0004] Existing protection methods are often fixed. The transient process of DC microgrids is relatively complex, and dynamic changes make it difficult to apply the protection methods of DC distribution networks to DC microgrid protection. Nowadays, the access of a large number of constant power load devices such as charging piles has further led to a decrease in the stability of DC microgrids. Overcurrent protection and other protections can generally only identify ground faults with small transition resistance. Distance protection cannot adapt to DC microgrids with shorter lines, and cannot adapt to ground fault location with different transition resistances. Therefore, a plug-and-play DC microgrid ground fault location protection method suitable for various occasions is designed to provide new theoretical and technical support for the protection issues of DC microgrids, which is of great significance to promoting the development of DC microgrids. Summary of the Invention

[0005] The present invention addresses the problems faced by the DC microgrid source-storage-load system protection in the prior art, such as constant power load disturbances and small voltage and current changes in ground short-circuit faults that are difficult to distinguish within the DC microgrid. The present invention provides a DC microgrid ground fault protection method and system with adaptive distributed energy and load plug-and-play, thereby realizing the plug-and-play of the DC microgrid source-storage-load protection system.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A DC microgrid ground fault protection method is implemented in a DC microgrid connected to photovoltaic, energy storage, and loads, comprising the following steps:

[0008] The fault area location information is calculated in real time. When the regional fault grounding current and power change rate meet the protection start-up criteria, the fault area is determined based on the fault area location information, and a trip command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker disconnects after receiving the trip command.

[0009] To optimize the above technical solutions, specific measures taken also include:

[0010] Furthermore, the DC microgrid contains X photovoltaic areas, Y energy storage areas and Z constant power loads. The photovoltaic areas, energy storage areas and constant power loads are all connected to the DC bus through DC-DC converters to form a DC microgrid source-storage-load system. The DC microgrid source-storage-load system is connected to the grid through an AC-DC converter. The photovoltaic areas, energy storage areas and load areas are all equipped with DC circuit breakers.

[0011] Furthermore, the real-time calculation of the fault area location information is specifically as follows:

[0012] At each DC circuit breaker, the following calculations are performed based on the collected voltage and current information and the DC circuit breaker's open and closed status:

[0013]

[0014] Where V1 is the state variable of the protection start criterion, and its value is 1 or 0. To protect the startup criteria, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi set Indicates the set value of the current change rate;

[0015] Analyze the harmonic changes before and after the fault and compare them with the setting value of the harmonic change to obtain the status of the protection positioning information:

[0016] ΔE=E(n)-E(m)(2)

[0017]

[0018] Where ΔE is the harmonic change before and after the fault; E(n) is the high-frequency harmonic value after n acquisition points from the start of the fault, and E(m) is the high-frequency harmonic value after m acquisition points from the start of the fault; V2 is the state quantity of the protection location information; when V2 = 1, it means that the harmonic content meets the protection criterion |ΔE|3ΔE set When V2=-1, it means that the harmonic content does not meet the protection criteria, ΔE set is the setting value of harmonic variation;

[0019] Calculate fault judgment information for each of the photovoltaic area, energy storage area, and load area:

[0020] V b =V1*V2*S v (4)

[0021] Where S v V is the information indicating whether the DC circuit breaker is in the open or closed state. Its value is 1 or 0, 0 indicates the open state and 1 indicates the closed state. b It is the regional fault judgment information, and its value is 1, 0 or -1, indicating that a DC circuit breaker performs real-time calculation based on the collected information to determine whether a fault has occurred, and then decides whether to start the protection tripping circuit breaker based on the starting criteria. b =0 or -1 indicates that no fault has occurred in the area, V b =1 indicates that a fault has occurred in the area;

[0022] For a total of X photovoltaic areas, the calculation method for determining the ground fault status of the area is:

[0023]

[0024] Where V f1 is the ground fault state of the photovoltaic area, 1 indicates a fault occurs within the photovoltaic area, -1 indicates a fault occurs outside the photovoltaic area, where V bx 1 Indicates the fault judgment information of the xth photovoltaic area after the ground fault occurs; V bx 1 The calculation method of is formula (4);

[0025] For a total of Y energy storage areas, the calculation method for determining the ground fault state of the area is:

[0026]

[0027] Where V f2is the ground fault state variable of the energy storage area, 1 indicates a fault occurs within the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Indicates the fault judgment information of the yth energy storage area after the ground fault occurs; V by 2 The calculation method of is formula (4);

[0028] For a total of Z load areas, the calculation method for determining the ground fault state of the area is:

[0029]

[0030] Where V f3 is the load area ground fault state quantity, 1 indicates a fault occurs within the load area, -1 indicates a fault occurs outside the area, where V bz 3 Indicates the fault judgment information of the zth load area after the ground fault occurs;

[0031] The directed edge structure matrix of the DC microgrid source-storage-load area is A, where the i-row vector represents the number of DC microgrid source-storage-load areas, and the j-column vector represents the number of DC circuit breakers. After a ground fault occurs, the fault information vectors of the photovoltaic area, energy storage area, and load area are subjected to matrix operations with the structure matrix A to obtain the positioning information. The formula is as follows:

[0032] W=A[v pv v bat v load ] (8)

[0033] Where W represents the fault area location information, and its value is the representative value of the DC microgrid source-storage fault area, v pv 、v bat 、v load Represents the photovoltaic area V b1～X , energy storage area V b1～Y , load area V b1～Z Fault information vector.

[0034] Furthermore, the fault information vector calculation method of the photovoltaic area, energy storage area, and load area is:

[0035]

[0036] Where V a1～X 、V b1～Y 、V c1～Z It is the comprehensive judgment information value of whether a fault occurs in the area, and its value is 1 or -1; 1 means a fault occurs within the area, and -1 means a fault occurs outside the area.

[0037] Furthermore, the calculation method of the harmonic high frequency amount is:

[0038]

[0039] Where P(m) represents the power variation collected at the DC circuit breaker, E(n) represents the high-frequency harmonics generated by the ground fault, and H(nm) represents the rectangular window function with a window length of l.

[0040] Furthermore, the power change is calculated by performing Fourier transform analysis on the voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-storage-load system, converting the time domain information into frequency domain information, extracting the frequency information where the power transient change is greater than the set threshold based on the number of power electronic equipment in the DC microgrid source-storage-load system and the line inductance and resistance values, and then calculating it through the protection comprehensive judgment device.

[0041] Furthermore, the high-frequency harmonic quantity is filtered by a Chebyshev filter based on the voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-storage system, and the double frequency, triple frequency and higher frequency harmonic frequency values ​​are set, and then calculated by the protection comprehensive judgment device.

[0042] Furthermore, the protection start criterion is:

[0043]

[0044] Where, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi set Indicates the set value of the current change rate.

[0045] Furthermore, the protection initiation criterion is as follows: by comparing the fault status of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas with the local stable operating status, the power change rate and the regional fault grounding current change rate are detected to determine whether the transient change exceeds the set value and thus determine whether the protection is activated.

[0046] Furthermore, the setting value of the power change rate and the setting value of the current change rate are both in the range of 1.2 to 1.5 times the rated value.

[0047] Furthermore, the setting value of the power change rate is in the range of 1.2 to 1.5 times the rated value. The setting value of the current change rate is in the range of 1.2 to 1.5 times the rated value. The setting value of the harmonic variation ΔE set The value range is 1.5 to 1.6 times the rated value.

[0048] The present invention also proposes a DC microgrid ground fault protection system, comprising: a protection comprehensive judgment device, a protection communication device and a DC circuit breaker;

[0049] The DC circuit breaker corresponds to each photovoltaic area, energy storage area and load area, is used to collect high-frequency information, regional power and current, and isolate the fault area by disconnecting itself;

[0050] The protection comprehensive judgment device communicates with the DC circuit breaker via the protection communication device. When a fault occurs, the protection comprehensive judgment device collects and analyzes the results of the high-frequency harmonic changes of each DC circuit breaker, and calculates the fault area location information in real time. When the regional fault grounding current and power change rate meet the protection start-up judgment criteria, the fault area is determined based on the fault area location information, and a trip command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker disconnects after receiving the trip command.

[0051] To optimize the above technical solutions, specific measures taken also include:

[0052] Furthermore, the DC microgrid contains X photovoltaic areas, Y energy storage areas and Z constant power loads. The photovoltaic areas, energy storage areas and constant power loads are all connected to the DC bus through DC-DC converters to form a DC microgrid source-storage-load system. The DC microgrid source-storage-load system is connected to the grid through an AC-DC converter. The photovoltaic areas, energy storage areas and load areas are all equipped with DC circuit breakers.

[0053] Furthermore, the real-time calculation of the fault area location information is specifically as follows:

[0054] At each DC circuit breaker, the following calculations are performed based on the collected voltage and current information and the DC circuit breaker's open and closed status:

[0055]

[0056] Where V1 is the state variable of the protection start criterion, and its value is 1 or 0. To protect the startup criteria, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi set Indicates the set value of the current change rate;

[0057] Analyze the harmonic changes before and after the fault and compare them with the setting value of the harmonic change to obtain the status of the protection positioning information:

[0058]

[0059] Where ΔE is the harmonic change before and after the fault; E(n) is the high-frequency harmonic value after n acquisition points from the start of the fault, and E(m) is the high-frequency harmonic value after m acquisition points from the start of the fault; V2 is the state quantity of the protection location information; when V2 = 1, it means that the harmonic content meets the protection criterion |ΔE|3ΔE set When V2=-1, it means that the harmonic content does not meet the protection criteria, ΔE set is the setting value of harmonic variation;

[0060] Calculate fault judgment information for each of the photovoltaic area, energy storage area, and load area:

[0061] V b =V1*V2*S v (4)

[0062] Where S v V is the information indicating whether the DC circuit breaker is in the open or closed state. Its value is 1 or 0, 0 indicates the open state and 1 indicates the closed state. b It is the regional fault judgment information, and its value is 1, 0 or -1, indicating that a DC circuit breaker performs real-time calculation based on the collected information to determine whether a fault has occurred, and then decides whether to start the protection tripping circuit breaker based on the starting criteria. b =0 or -1 indicates that no fault has occurred in the area, V b =1 indicates that a fault has occurred in the area;

[0063] For a total of X photovoltaic areas, the calculation method for determining the ground fault status of the area is:

[0064]

[0065] Where V f1 is the ground fault state of the photovoltaic area, 1 indicates a fault occurs within the photovoltaic area, -1 indicates a fault occurs outside the photovoltaic area, where V bx 1 Indicates the fault judgment information of the xth photovoltaic area after the ground fault occurs; V bx 1 The calculation method of is formula (4);

[0066] For a total of Y energy storage areas, the calculation method for determining the ground fault state of the area is:

[0067]

[0068] Where V f2 is the ground fault state variable of the energy storage area, 1 indicates a fault occurs within the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Indicates the fault judgment information of the yth energy storage area after the ground fault occurs; Vby 2 The calculation method of is formula (4);

[0069] For a total of Z load areas, the calculation method for determining the ground fault state of the area is:

[0070]

[0071] Where V f3 is the load area ground fault state quantity, 1 indicates a fault occurs within the load area, -1 indicates a fault occurs outside the area, where V bz 3 Indicates the fault judgment information of the zth load area after the ground fault occurs;

[0072] The directed edge structure matrix of the DC microgrid source-storage-load area is A, where the i-row vector represents the number of DC microgrid source-storage-load areas, and the j-column vector represents the number of DC circuit breakers. After a ground fault occurs, the fault information vectors of the photovoltaic area, energy storage area, and load area are subjected to matrix operations with the structure matrix A to obtain the positioning information. The formula is as follows:

[0073] W=A[v pv v bat v load ] (8)

[0074] Where W represents the fault area location information, and its value is the representative value of the DC microgrid source-storage fault area, v pv 、v bat 、v load Represents the photovoltaic area V b1～X , energy storage area V b1～Y , load area V b1～Z Fault information vector.

[0075] Furthermore, the fault information vector calculation method of the photovoltaic area, energy storage area, and load area is:

[0076]

[0077] Where V a1～X 、V b1～Y 、V c1～Z It is the comprehensive judgment information value of whether a fault occurs in the area, and its value is 1 or -1; 1 means a fault occurs within the area, and -1 means a fault occurs outside the area.

[0078] Furthermore, the calculation method of the harmonic high frequency amount is:

[0079]

[0080] Where P(m) represents the power variation collected at the DC circuit breaker, E(n) represents the high-frequency harmonics generated by the ground fault, and H(nm) represents the rectangular window function with a window length of l.

[0081] Furthermore, the high-frequency harmonic quantity is filtered by a Chebyshev filter based on the voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-storage system, and the double frequency, triple frequency and higher frequency harmonic frequency values ​​are set, and then calculated by the protection comprehensive judgment device.

[0082] Furthermore, the protection start criterion is:

[0083]

[0084] Where, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi set Indicates the set value of the current change rate.

[0085] Furthermore, the protection initiation criterion is as follows: by comparing the fault status of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas with the local stable operating status, the power change rate and the regional fault grounding current change rate are detected to determine whether the transient change exceeds the set value and thus determine whether the protection is activated.

[0086] Furthermore, the setting value of the power change rate ranges from 1.2 to 1.5 times the rated value.

[0087] Furthermore, the setting value of the current change rate ranges from 1.2 to 1.5 times the rated value.

[0088] Furthermore, the harmonic variation setting value ranges from 1.5 to 1.6 times the rated value.

[0089] The present invention also proposes an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the DC microgrid grounding fault protection method as described above is implemented.

[0090] The present invention also provides a computer-readable storage medium storing a computer program, wherein the computer program enables a computer to execute the DC microgrid grounding fault protection method as described above.

[0091] The beneficial effects of the present invention are:

[0092] The present invention solves the problem of insufficient reliability of existing protection methods in preventing malfunction of protection when a large number of constant power loads are connected to a DC microgrid source-storage load by introducing a fault criterion of power change rate. By comparing the changes in harmonic energy generated by a grounding fault in a DC microgrid system extracted by a DC circuit breaker, the problem of being unable to identify the voltage and current of a DC high-resistance grounding fault is solved, and plug-and-play of DC microgrid source-storage loads with different transition resistances is achieved, thereby realizing accurate positioning of the grounding fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 This is a flow chart of the DC microgrid ground fault protection method for adaptive distributed energy and load plug-and-play according to the present invention;

[0094] Figure 2 This is a typical structure of DC microgrid source storage load in the embodiment of the present invention;

[0095] Figure 3 This is the component structure of the DC microgrid grounding fault protection system in an embodiment of the present invention;

[0096] Figure 4 It is the information calculation logic of the protection comprehensive judgment device in the embodiment of the present invention.

[0097] Figure 5 This is the current information when the constant power load is disturbed in the embodiment of the present invention.

[0098] Figure 6 It is the malfunction information value of the DC circuit breaker when the constant power load is disturbed in the embodiment of the present invention.

[0099] Figure 7 This is the power change rate information of each area under different bus voltage drop disturbance conditions in the embodiment of the present invention.

[0100] Figure 8 This is the effective information of regional fault harmonic energy extracted by comparing overcurrent protection in the embodiment of the present invention. DETAILED DESCRIPTION

[0101] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0102] Example 1

[0103] The present invention proposes a DC microgrid ground fault protection method, which is implemented in a DC microgrid connected to photovoltaic, energy storage and load. The process of the method is as follows: Figure 1 As shown, the following steps are included:

[0104] The fault area location information is calculated in real time. When the regional fault grounding current and power change rate meet the protection start-up criteria, the fault area is determined based on the fault area location information, and a trip command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker disconnects after receiving the trip command.

[0105] The structure of the DC microgrid is as follows Figure 2 As shown in the figure, there are X photovoltaic areas, Y energy storage areas and Z constant power loads (CPLs). The photovoltaic areas, energy storage areas and constant power loads are all connected to the DC bus through DC-DC converters to form a DC microgrid source-storage-load system. The DC microgrid source-storage-load system is connected to the grid through AC-DC converters. The photovoltaic areas, energy storage areas and load areas are all equipped with DC circuit breakers.

[0106] The real-time calculation of fault area location information is specifically as follows:

[0107] At each DC circuit breaker, the following calculations are performed based on the collected voltage and current information and the DC circuit breaker's open and closed status:

[0108]

[0109] Where V1 is the state variable of the protection start criterion, and its value is 1 or 0. To protect the startup criteria, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi set Indicates the setting value of the current change rate; in order to avoid the influence of constant power load on the system, Δp set and Δi set Sufficient margin should be left, and the value range is generally 1.2 to 1.5 times the rated value.

[0110] When a ground fault occurs in a DC microgrid's source-storage-load system, if its transition resistance is large, the voltage of photovoltaic and energy storage systems operating in power control mode, as well as the DC microgrid's source-storage-load system controlled by a constant DC bus voltage, will not experience a significant voltage drop, and the generated fault current will be subtle. However, when a ground short circuit occurs within a DC microgrid, the power electronics in the DC microgrid's converters increase the high-frequency harmonic content in the DC bus voltage and line current, making overcurrent protection unable to detect the fault. Therefore, this characteristic is exploited for fault detection.

[0111] Analyze the harmonic changes before and after the fault and compare them with the setting value of the harmonic change to obtain the status of the protection positioning information:

[0112] ΔE=E(n)-E(m)(2)

[0113]

[0114] Where ΔE is the harmonic change before and after the fault; E(n) is the high-frequency harmonic value after n acquisition points from the start of the fault, and E(m) is the high-frequency harmonic value after m acquisition points from the start of the fault; V2 is the state quantity of the protection location information; when V2 = 1, it means that the harmonic content meets the protection criterion |ΔE|3ΔE set When V2=-1, it means that the harmonic content does not meet the protection criteria, ΔE set This is the setting value of harmonic variation, which needs to be guaranteed not to be affected by constant power load disturbance.

[0115] The calculation method of the high-frequency harmonic amount is:

[0116]

[0117] Where P(m) represents the power variation collected at the DC circuit breaker, E(n) represents the high-frequency harmonics generated by the ground fault, and H(nm) represents the rectangular window function with a window length of l.

[0118] Fourier transform analysis is performed on the voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-storage-load system. The time domain information is converted into frequency domain information. Based on the number of power electronic equipment in the DC microgrid source-storage-load system and the line inductance and resistance values, the frequency information with obvious harmonic energy changes is extracted, and then calculated through the protection comprehensive judgment device.

[0119] The calculation method of high frequency harmonics can also be:

[0120] The voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-storage system is filtered by a Chebyshev filter, and the values ​​of the double frequency, triple frequency and higher frequency harmonic frequencies are set, and then calculated through the protection comprehensive judgment device.

[0121] Calculate fault judgment information for each of the photovoltaic area, energy storage area, and load area:

[0122] V b =V1*V2*S v (4)

[0123] Where S v V is the information indicating whether the DC circuit breaker is in the open or closed state. Its value is 1 or 0, 0 indicates the open state and 1 indicates the closed state. bIt is the regional fault judgment information, and its value is 1, 0 or -1, indicating that a DC circuit breaker performs real-time calculation based on the collected information to determine whether a fault has occurred, and then decides whether to start the protection tripping circuit breaker based on the starting criteria. b =0 or -1 indicates that no fault has occurred in the area, V b =1 indicates that a fault has occurred in the area;

[0124] For a total of X photovoltaic areas, the calculation method for determining the ground fault status of the area is:

[0125]

[0126] Where V f1 is the ground fault state of the photovoltaic area, 1 indicates a fault occurs within the photovoltaic area, -1 indicates a fault occurs outside the photovoltaic area, where V bx 1 Indicates the fault judgment information of the xth photovoltaic area after the ground fault occurs; V bx 1 The calculation method of is formula (4);

[0127] For a total of Y energy storage areas, the calculation method for determining the ground fault state of the area is:

[0128]

[0129] Where V f2 is the ground fault state variable of the energy storage area, 1 indicates a fault occurs within the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Indicates the fault judgment information of the yth energy storage area after the ground fault occurs; V by 2 The calculation method of is formula (4);

[0130] For a total of Z load areas, the calculation method for determining the ground fault state of the area is:

[0131]

[0132] Where V f3 is the load area ground fault state quantity, 1 indicates a fault occurs within the load area, -1 indicates a fault occurs outside the area, where V bz 3 Indicates the fault judgment information of the zth load area after the ground fault occurs;

[0133] The directed edge structure matrix of the DC microgrid source-storage-load area is A, where the i-row vector represents the number of DC microgrid source-storage-load areas, and the j-column vector represents the number of DC circuit breakers. After a ground fault occurs, the fault information vectors of the photovoltaic area, energy storage area, and load area are subjected to matrix operations with the structure matrix A to obtain the positioning information. The formula is as follows:

[0134] W=A[v pv v bat v load ] (8)

[0135] Where W represents the fault area location information, and its value is the representative value of the DC microgrid source-storage fault area, v pv 、v bat 、v load Represents the photovoltaic area V b1～X , energy storage area V b1～Y , load area V b1～Z The positioning information is calculated locally in real time, so the protection device calculation and protection system information collection are carried out simultaneously and will not be interrupted by the start-up criteria.

[0136] The calculation method of the fault information vector of the photovoltaic area, energy storage area, and load area is:

[0137]

[0138] Where V a1～X 、V b1～Y 、V c1～Z It is the comprehensive judgment information value of whether a fault occurs in the area, and its value is 1 or -1; 1 means a fault occurs within the area, and -1 means a fault occurs outside the area.

[0139] The protection activation criterion is as follows: the power change rate and the regional fault grounding current change rate are detected by comparing the fault status of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas with the local stable operating status, and determining whether the transient change exceeds the set value to determine whether the protection is activated.

[0140] A specific implementation of the protection start criterion is:

[0141]

[0142] Where, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi setIndicates the setting value of the current change rate. The regional power change rate and current change rate are used as the protection start judgment criteria to avoid the protection system from malfunctioning due to interference from constant power loads.

[0143] Example 2

[0144] The present invention proposes a DC microgrid grounding fault protection system based on the method described in Example 1, such as Figure 3 As shown, it includes: a protection comprehensive judgment device, a protection communication device and a DC circuit breaker;

[0145] The DC circuit breaker corresponds to each photovoltaic area, energy storage area and load area, is used to collect high-frequency information, regional power and current, and isolate the fault area by disconnecting itself;

[0146] The protection comprehensive judgment device communicates with the DC circuit breaker via the protection communication device. When a fault occurs, the protection comprehensive judgment device collects and analyzes the results of the high-frequency harmonic changes of each DC circuit breaker, and calculates the fault area location information in real time. When the regional fault grounding current and power change rate meet the protection start-up judgment criteria, the fault area is determined based on the fault area location information, and a trip command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker disconnects after receiving the trip command.

[0147] The implementation method of the functions of each device in the system is completely consistent with the steps of the method in Example 1, so it will not be repeated here.

[0148] Example 3

[0149] The present invention provides an electronic device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the DC microgrid grounding fault protection method as described in the first embodiment is implemented.

[0150] Example 4

[0151] The present invention provides a computer-readable storage medium storing a computer program, wherein the computer program enables a computer to execute the DC microgrid grounding fault protection method as described in the first embodiment.

[0152] The protection effect was verified by building a simulation in Matlab / Simulink. Figure 2 The DC microgrid source-storage system shown in the figure is configured with a disturbance in a photovoltaic area within the system set at 1s and a high-resistance grounding fault set at 2s. Figure 5 Indicates the current generated when the bus voltage drops to 90% of the rated voltage in a constant power load area. This current far exceeds the set value, causing the ordinary overcurrent protection to malfunction. Figure 6As shown, BK1-3 represent the DC circuit breaker status quantities of 1-X photovoltaic areas, 1-Y energy storage areas and a load area respectively. The circuit breaker status of the load non-fault area is the same as the circuit breaker status of the photovoltaic energy storage area. Figure 7 It represents the power change rate of the constant power load when it receives a short-term disturbance under different bus voltage drops. It can be seen that when the bus voltage drops slightly, it means that the constant power load is subjected to a small disturbance. The power change rate generated at this time is much smaller than the power change rate when a fault occurs. Therefore, the design of the protection criterion setting value avoids the normal disturbance range caused by the bus voltage drop, and the protection does not malfunction. Figure 8 For the comparison between overcurrent protection and the method of extracting high-frequency harmonic energy of fault, after a ground fault with a large transition resistance occurs, the change in the current extracted by the overcurrent protection is too small to operate, while the extraction of high-frequency harmonic energy of the fault can be used as an effective fault judgment criterion, and protection information calculation and precise positioning can still be performed.

[0153] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in this application can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0154] The above are merely preferred embodiments of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions based on the principles of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should be considered within the scope of protection of the present invention.

Claims

1. A DC microgrid ground fault protection method is implemented in a DC microgrid connected to photovoltaic, energy storage and load, characterized in that: The following steps are involved: The fault area location information is calculated in real time. When the regional fault grounding current and power change rate meet the protection start criterion, the fault area is determined according to the fault area location information, and a trip command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker is disconnected after receiving the trip command. The DC microgrid contains X photovoltaic areas, Y energy storage areas and Z constant power loads. The photovoltaic areas, energy storage areas and constant power loads are all connected to the DC bus through DC-DC converters to form a DC microgrid source-storage-load system. The DC microgrid source-storage-load system is connected to the grid through AC-DC converters. The photovoltaic areas, energy storage areas and load areas are all equipped with DC circuit breakers. The real-time calculation of fault area location information is specifically as follows: At each DC circuit breaker, the following calculations are performed based on the collected voltage and current information and the DC circuit breaker's open and closed status: Where V1 is the state variable of the protection start criterion, and its value is 1 or 0. To protect the startup criteria, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi set Indicates the set value of the current change rate; Analyze the harmonic changes before and after the fault and compare them with the setting value of the harmonic change to obtain the status of the protection positioning information: ΔE=E(n)-E(m) (2) Where ΔE is the harmonic change before and after the fault; E(n) is the high-frequency harmonic value after n acquisition points from the start of the fault, and E(m) is the high-frequency harmonic value after m acquisition points from the start of the fault; V2 is the state quantity of the protection location information; when V2 = 1, it means that the harmonic content meets the protection criterion |ΔE| ≥ ΔE set When V2=-1, it means that the harmonic content does not meet the protection criteria, ΔE set is the setting value of harmonic variation; Calculate fault judgment information for each of the photovoltaic area, energy storage area, and load area: Vb=V1*V2*Sv (4) Where S v V is the information indicating whether the DC circuit breaker is in the open or closed state. Its value is 1 or 0, 0 indicates the open state and 1 indicates the closed state. b It is the regional fault judgment information, and its value is 1, 0 or -1, indicating that a DC circuit breaker performs real-time calculation based on the collected information to determine whether a fault has occurred, and then decides whether to start the protection tripping circuit breaker based on the starting criteria. b =0 or -1 indicates that no fault has occurred in the area, V b =1 indicates that a fault has occurred in the area; For a total of X photovoltaic areas, the calculation method for determining the ground fault status of the area is: Where V f1 is the ground fault state of the photovoltaic area, 1 indicates a fault occurs within the photovoltaic area, -1 indicates a fault occurs outside the photovoltaic area, where V bx 1 Indicates the fault judgment information of the xth photovoltaic area after the ground fault occurs; V bx 1 The calculation method of is formula (4); For a total of Y energy storage areas, the calculation method for determining the ground fault state of the area is: Where V f2 is the ground fault state variable of the energy storage area, 1 indicates a fault occurs within the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Indicates the fault judgment information of the yth energy storage area after the ground fault occurs; V by 2 The calculation method of is formula (4); For a total of Z load areas, the calculation method for determining the ground fault state of the area is: Where V f3 is the load area ground fault state quantity, 1 indicates a fault occurs within the load area, -1 indicates a fault occurs outside the area, where V bz 3 Indicates the fault judgment information of the zth load area after the ground fault occurs; The directed edge structure matrix of the DC microgrid source-storage-load area is A, where the i-row vector represents the number of DC microgrid source-storage-load areas, and the j-column vector represents the number of DC circuit breakers. After a ground fault occurs, the fault information vectors of the photovoltaic area, energy storage area, and load area are subjected to matrix operations with the structure matrix A to obtain the positioning information. The formula is as follows: W=A[v pv v bat v load ] (8) Where W represents the fault area location information, and its value is the representative value of the DC microgrid source-storage fault area, v pv 、v bat 、v load Represent the fault information vectors of photovoltaic area, energy storage area and load area respectively. The value of the element in the fault information vector is determined by the regional fault judgment information V b get.

2. The DC microgrid ground fault protection method according to claim 1, characterized in that: The calculation method of the fault information vector of the photovoltaic area, energy storage area, and load area is: Where V a1～X 、V b1～Y 、V c1～Z It is the comprehensive judgment information value of whether a fault occurs in the area, and its value is 1 or -1; 1 means a fault occurs within the area, and -1 means a fault occurs outside the area.

3. The DC microgrid ground fault protection method according to claim 1, characterized in that: The calculation method of the high-frequency harmonic amount is: Where P(m) represents the power variation collected at the DC circuit breaker, E(n) represents the high-frequency harmonics generated by the ground fault, and H(nm) represents the rectangular window function with a window length of l.

4. The DC microgrid ground fault protection method according to claim 3, wherein the power variation is calculated by performing Fourier transform analysis on the voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-storage-load system, converting the time domain information into frequency domain information, extracting the frequency information where the power transient variation is greater than a set threshold based on the number of power electronic devices in the DC microgrid source-storage-load system and the line inductance and resistance values, and then performing calculation using a comprehensive protection judgment device.

5. The DC microgrid ground fault protection method according to claim 1, wherein: The high-frequency harmonic quantity is filtered by a Chebyshev filter based on the voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-storage system, and the double frequency, triple frequency and higher frequency harmonic frequency values ​​are set, and then calculated by the protection comprehensive judgment device.

6. The DC microgrid ground fault protection method according to claim 1, wherein: The protection start criterion is: Where, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi set Indicates the set value of the current change rate.

7. The DC microgrid ground fault protection method according to claim 1, wherein: The protection activation criterion is as follows: the power change rate and the regional fault grounding current change rate are detected by comparing the fault status of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas with the local stable operating status, and determining whether the transient change exceeds the set value to determine whether the protection is activated.

8. The DC microgrid ground fault protection method according to claim 2, wherein: The setting value of the power change rate ranges from 1.2 to 1.5 times the rated value.

9. The DC microgrid ground fault protection method according to claim 2, wherein: The setting value of the current change rate ranges from 1.2 to 1.5 times the rated value.

10. The DC microgrid ground fault protection method according to claim 1, wherein: The harmonic variation setting value ΔE set The value range is 1.5 to 1.6 times the rated value.

11. A DC microgrid ground fault protection system implemented in a DC microgrid connected to photovoltaic, energy storage and loads, characterized in that: include: Protection comprehensive judgment device, protection communication device and DC circuit breaker; the DC microgrid contains X photovoltaic areas, Y energy storage areas and Z constant power loads, the photovoltaic areas, energy storage areas and constant power loads are all connected to the DC bus through DC-DC converters to form a DC microgrid source-storage-load system, the DC microgrid source-storage-load system is grid-connected through AC-DC converters, and the photovoltaic areas, energy storage areas and load areas are all equipped with DC circuit breakers; The DC circuit breaker corresponds to each photovoltaic area, energy storage area and load area, is used to collect high-frequency information, regional power and current, and isolate the fault area by disconnecting itself; The protection comprehensive judgment device communicates with the DC circuit breaker via the protection communication device; When a fault occurs, the protection comprehensive judgment device collects and analyzes the results of the high-frequency harmonic changes of each DC circuit breaker and calculates the fault area location information in real time. When the regional fault grounding current and power change rate meet the protection trigger judgment criteria, the fault area is determined based on the fault area location information and a trip command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker opens after receiving the trip command. The real-time calculation of fault area location information is specifically as follows: At each DC circuit breaker, the following calculations are performed based on the collected voltage and current information and the DC circuit breaker's open and closed status: Where V1 is the state variable of the protection start criterion, and its value is 1 or 0. To protect the startup criteria, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi set Indicates the set value of the current change rate; Analyze the harmonic changes before and after the fault and compare them with the setting value of the harmonic change to obtain the status of the protection positioning information: ΔE=E(n)-E(m) (2) Where ΔE is the harmonic change before and after the fault; E(n) is the high-frequency harmonic value after n acquisition points from the start of the fault, and E(m) is the high-frequency harmonic value after m acquisition points from the start of the fault; V2 is the state quantity of the protection location information; when V2 = 1, it means that the harmonic content meets the protection criterion |ΔE| ≥ ΔE set When V2=-1, it means that the harmonic content does not meet the protection criteria, ΔE set is the setting value of harmonic variation; Calculate fault judgment information for each of the photovoltaic area, energy storage area, and load area: V b =V1*V2*S v (4) Where S v V is the information indicating whether the DC circuit breaker is in the open or closed state. Its value is 1 or 0, 0 indicates the open state and 1 indicates the closed state. b It is the regional fault judgment information, and its value is 1, 0 or -1, indicating that a DC circuit breaker performs real-time calculation based on the collected information to determine whether a fault has occurred, and then decides whether to start the protection tripping circuit breaker based on the starting criteria. b =0 or -1 indicates that no fault has occurred in the area, V b =1 indicates that a fault has occurred in the area; For a total of X photovoltaic areas, the calculation method for determining the ground fault status of the area is: Where V f1 is the ground fault state of the photovoltaic area, 1 indicates a fault occurs within the photovoltaic area, -1 indicates a fault occurs outside the photovoltaic area, where V bx 1 Indicates the fault judgment information of the xth photovoltaic area after the ground fault occurs; V bx 1 The calculation method of is formula (4); For a total of Y energy storage areas, the calculation method for determining the ground fault state of the area is: Where V f2 is the ground fault state variable of the energy storage area, 1 indicates a fault occurs within the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Indicates the fault judgment information of the yth energy storage area after the ground fault occurs; V by 2 The calculation method of is formula (4); For a total of Z load areas, the calculation method for determining the ground fault state of the area is: Where V f3 is the load area ground fault state quantity, 1 indicates a fault occurs within the load area, -1 indicates a fault occurs outside the area, where V bz 3 Indicates the fault judgment information of the zth load area after the ground fault occurs; The directed edge structure matrix of the DC microgrid source-storage-load area is A, where the i-row vector represents the number of DC microgrid source-storage-load areas, and the j-column vector represents the number of DC circuit breakers. After a ground fault occurs, the fault information vectors of the photovoltaic area, energy storage area, and load area are subjected to matrix operations with the structure matrix A to obtain the positioning information. The formula is as follows: W=A[v pv v bat v load ] (8) Where W represents the fault area location information, and its value is the representative value of the DC microgrid source-storage fault area, v pv 、v bat 、v load Represents the photovoltaic area V b1～X , energy storage area V b1～Y , load area V b1～Z Fault information vector.

12. The DC microgrid ground fault protection system according to claim 11, characterized in that: The calculation method of the fault information vector of the photovoltaic area, energy storage area, and load area is: Where V a1～X 、V b1～Y 、V c1～Z It is the comprehensive judgment information value of whether a fault occurs in the area, and its value is 1 or -1; 1 means a fault occurs within the area, and -1 means a fault occurs outside the area.

13. The DC microgrid ground fault protection system according to claim 11, characterized in that: The calculation method of the high-frequency harmonic amount is: Where P(m) represents the power variation collected at the DC circuit breaker, E(n) represents the high-frequency harmonics generated by the ground fault, and H(nm) represents the rectangular window function with a window length of l.

14. The DC microgrid ground fault protection system according to claim 11, wherein: The high-frequency harmonic quantity is filtered by a Chebyshev filter based on the voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-storage system, and the double frequency, triple frequency and higher frequency harmonic frequency values ​​are set, and then calculated by the protection comprehensive judgment device.

15. The DC microgrid ground fault protection system according to claim 11, characterized in that: The protection start criterion is: Where, represents the rate of change of power, Indicates the rate of change of regional fault ground current, Δp set Indicates the set value of the power change rate, Δi set Indicates the set value of the current change rate.

16. The DC microgrid ground fault protection system according to claim 11, characterized in that: The protection activation criterion is as follows: the power change rate and the regional fault grounding current change rate are detected by comparing the fault status of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas with the local stable operating status, and determining whether the transient change exceeds the set value to determine whether the protection is activated.

17. The DC microgrid ground fault protection system according to claim 11, characterized in that: The setting value of the power change rate ranges from 1.2 to 1.5 times the rated value.

18. The DC microgrid ground fault protection system according to claim 11, characterized in that: The setting value of the current change rate ranges from 1.2 to 1.5 times the rated value.

19. The DC microgrid ground fault protection system according to claim 11, wherein: The harmonic variation setting value ranges from 1.5 to 1.6 times the rated value.

20. An electronic device, characterized in that: include: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, the DC microgrid grounding fault protection method according to any one of claims 1 to 10 is implemented.

21. A computer-readable storage medium storing a computer program, characterized in that: The computer program enables a computer to execute the DC microgrid ground fault protection method according to any one of claims 1 to 10.

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