Adaptive distributed energy and load plug-and-play direct current micro-grid ground fault protection method, system, equipment and medium

Abstract

The invention discloses a self-adaptive distributed energy and load plug-and-play direct current micro-grid ground fault protection method, system and device and a medium, and the method comprises the following steps: calculating fault area positioning information in real time, and when the area fault grounding current and the power change rate meet the protection starting criterion, starting a protection starting process; a fault area is determined according to the fault area positioning information, a tripping instruction is sent to a direct-current circuit breaker connected with the fault area, and the direct-current circuit breaker is disconnected after receiving the tripping instruction. According to the characteristics of flexible and changeable source storage load area structure, various control modes, easy extraction of fault high-frequency quantity and the like in the direct-current micro-grid, a universal protection positioning method is established by adding a constant-power load simulation actual scene in a load area; the plug-and-play performance of the fault protection positioning method under the condition that the DC micro-grid source storage load structure is changeable is realized, and accurate isolation of different fault areas when the DC micro-grid source storage load has a grounding short circuit fault is ensured.

Description

Technical Field

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

[0002] With the continuous increase in energy demand and the enhancement of environmental protection awareness, the application of distributed energy systems and DC microgrids in the energy field is becoming more and more common. Today's society is facing increasingly severe challenges in energy security and environmental protection, which has promoted the widespread application and development of renewable energy. In particular, the rapid development of distributed energy resources such as solar energy and wind energy has made the position of microgrid technology increasingly prominent in the energy system. As a small-scale power system, microgrids have the ability to operate autonomously and be isolated from the main power grid, and can provide reliable power supply to areas far away from traditional power grids. Compared with traditional large-scale power grids, microgrids are more flexible and can better adapt to local energy resources and load requirements, providing new solutions for the sustainable development of energy systems.

[0003] In the continuous development and application of microgrids, DC microgrids as an emerging form have gradually attracted attention. DC microgrids have the advantages of low energy loss, fast system response, and easy interface with DC loads and distributed energy, and are considered to be one of the important development directions of future energy systems. However, unlike AC microgrids, the protection problem of DC microgrids is particularly complex and critical due to their special working principles and components. Traditional AC protection schemes cannot be directly applied to DC systems. Therefore, it is urgent to develop an innovative and adaptable DC microgrid protection method to deal with various faults and abnormal conditions that may occur in the system and ensure the safe operation and stability of the system. Due to the complex topological structure and dynamic operation characteristics of DC microgrids, their protection problems 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 for DC microgrid protection to apply the protection methods of DC distribution networks. 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 and other protections can generally only identify ground faults with smaller transition resistances. Distance protection cannot adapt to DC microgrids with shorter lines, and cannot adapt to the location of ground faults with different transition resistances. Therefore, a plug-and-play DC microgrid ground fault location protection method that is suitable for a variety of occasions is designed to provide new theoretical and technical support for the protection of DC microgrids, which is of great significance for promoting the development of DC microgrids. Summary of the invention

[0005] In view of the constant power load disturbance faced by the protection of the DC microgrid source-storage-load system in the prior art, and the small voltage and current changes of the ground short-circuit fault that is difficult to distinguish in 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, so as to realize 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 load, 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 according to the fault area location information, and a tripping command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker is disconnected after receiving the tripping command.

[0009] To optimize the above technical solutions, the 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 open and closed status:

[0013]

[0014] In the formula, V1 is the state quantity of the protection start criterion, and its value is 1 or 0. To protect the start criteria, represents the power change rate, Indicates the rate of change of regional fault ground current, Δp set Indicates the setting value of the power change rate, Δi set Indicates the setting 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 state quantity 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 harmonic high frequency value after n acquisition points from the start of the fault, and E(m) is the harmonic high frequency value after m acquisition points from the start of the fault; V2 is the state value of the protection location information; when V2=1, it means that the harmonic content meets the protection criterion |ΔE|3ΔE set , V2 = -1 indicates that the harmonic content does not meet the protection criteria, ΔE set is the setting value of harmonic variation;

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

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

[0021] In the formula, 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 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 occurs, and then decides whether to start the protection trip circuit breaker based on the start-up criterion. b =0 or -1 indicates that no fault occurs in this 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 state 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 state quantity of the ground fault in the energy storage area, 1 indicates a fault occurs in the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Represents 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 source-storage-load area of ​​the DC microgrid is A, in which the i-row vector represents the number of source-storage-load areas of the DC microgrid, and the j-column vector represents the number of DC circuit breakers. After the grounding 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 solve 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 fault area of ​​the DC microgrid source and load, v pv 、v bat 、v load Respectively represent 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 in 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 harmonic 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 as follows: 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-load storage system, the time domain information is converted into frequency domain information, and the frequency information in which the power transient change is greater than the set threshold is extracted according to the number of power electronic equipment in the DC microgrid source-load storage system and the line inductance and resistance values, and then calculated through the protection comprehensive judgment device.

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

[0042] Furthermore, the protection start criterion is:

[0043]

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

[0045] Furthermore, the protection initiation criterion is: by detecting the power change rate and the regional fault grounding current change rate through the fault state of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas and the local stable operation state, it is determined whether the transient change exceeds the set value and then 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 change amount 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, and 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 through the protection communication device; when a fault occurs, the protection comprehensive judgment device will collect and analyze the results of the high-frequency harmonic change of each DC circuit breaker, and calculate the fault area positioning information in real time. When the regional fault grounding current and power change rate meet the protection start-up criterion, the fault area is determined according to the fault area positioning information, and a tripping command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker is disconnected after receiving the tripping command.

[0051] To optimize the above technical solutions, the 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 open and closed status:

[0055]

[0056] In the formula, V1 is the state quantity of the protection start criterion, and its value is 1 or 0. To protect the start criteria, represents the power change rate, Indicates the rate of change of regional fault ground current, Δp set Indicates the setting value of the power change rate, Δi set Indicates the setting 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 state quantity of the protection positioning information:

[0058]

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

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

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

[0062] In the formula, 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 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 occurs, and then decides whether to start the protection trip circuit breaker based on the start-up criterion. b =0 or -1 indicates that no fault occurs in this 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 state 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 state quantity of the ground fault in the energy storage area, 1 indicates a fault occurs in the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Represents 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 source-storage-load area of ​​the DC microgrid is A, in which the i-row vector represents the number of source-storage-load areas of the DC microgrid, and the j-column vector represents the number of DC circuit breakers. After the grounding 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 solve 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 fault area of ​​the DC microgrid source and load, v pv 、v bat 、v load Respectively represent 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 in 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 harmonic generated by the ground fault, and H(nm) represents the rectangular window function with a window length of l.

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

[0082] Furthermore, the protection start criterion is:

[0083]

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

[0085] Furthermore, the protection initiation criterion is: by detecting the power change rate and the regional fault grounding current change rate through the fault state of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas and the local stable operation state, it is determined whether the transient change exceeds the set value and then 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, wherein 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 protection malfunction when existing protection methods cannot avoid a large number of constant power loads 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, and accurate positioning of the grounding fault is realized. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0095] Figure 3 It 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 It 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 It 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 the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0102] Embodiment 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 according to the fault area location information, and a tripping command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker is disconnected after receiving the tripping 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 (CPL). The photovoltaic area, energy storage area and constant power load 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 area, energy storage area and load area are all equipped with DC circuit breakers.

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

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

[0108]

[0109] In the formula, V1 is the state quantity of the protection start criterion, and its value is 1 or 0. To protect the start criteria, represents the power change rate, Indicates the rate of change of regional fault ground current, Δp set Indicates the setting value of the power change rate, Δi set Indicates the setting value of the current change rate; 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 the source-storage system of a DC microgrid, if its transition resistance is large, the voltage of the photovoltaic and energy storage in the power control operation mode and the source-storage system of the DC microgrid controlled by the constant DC bus voltage will not drop significantly, and the fault current generated is not obvious. However, when a ground short circuit fault occurs in the DC microgrid, the power electronic equipment in the converter of the DC microgrid increases the high-frequency harmonic content of the DC bus voltage and line current, making the overcurrent protection unable to detect the fault, so this feature is used to achieve 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 state quantity 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 harmonic high frequency value after n acquisition points from the start of the fault, and E(m) is the harmonic high frequency value after m acquisition points from the start of the fault; V2 is the state value of the protection location information; when V2=1, it means that the harmonic content meets the protection criterion |ΔE|3ΔE set , V2 = -1 indicates that the harmonic content does not meet the protection criteria, ΔE set It is the setting value of harmonic variation, which needs to ensure that it is not affected by constant power load disturbance.

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

[0116]

[0117] Where P(m) represents the power variation collected at the DC circuit breaker, E(n) represents the high-frequency harmonic 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 grounding fault occurs in the DC microgrid source-storage-load system, and the time domain information is converted into frequency domain information. The frequency information with obvious harmonic energy changes is extracted based on the number of power electronic equipment and the line inductance and resistance values ​​in the DC microgrid source-storage-load system, and then calculated through the protection comprehensive judgment device.

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

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

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

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

[0123] In the formula, 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. bis 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 occurs, and then decides whether to start the protection trip circuit breaker based on the start-up criterion. b =0 or -1 indicates that no fault occurs in this 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 state 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 state quantity of the ground fault in the energy storage area, 1 indicates a fault occurs in the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Represents 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 source-storage-load area of ​​the DC microgrid is A, in which the i-row vector represents the number of source-storage-load areas of the DC microgrid, and the j-column vector represents the number of DC circuit breakers. After the grounding 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 solve 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 fault area of ​​the DC microgrid source and load, v pv 、v bat 、v load Respectively represent 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 fault information vector of 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 in the area, and -1 means a fault occurs outside the area.

[0139] The protection start criterion is: through the fault state of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas and the local stable operation state, 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 then determine whether the protection is started.

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

[0141]

[0142] In the formula, represents the power change rate, Indicates the rate of change of regional fault ground current, Δp set Indicates the setting 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-up criterion to avoid the protection system from malfunctioning due to the interference of constant power load.

[0143] Embodiment 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, and 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 through the protection communication device; when a fault occurs, the protection comprehensive judgment device will collect and analyze the results of the high-frequency harmonic change of each DC circuit breaker, and calculate the fault area positioning information in real time. When the regional fault grounding current and power change rate meet the protection start-up criterion, the fault area is determined according to the fault area positioning information, and a tripping command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker is disconnected after receiving the tripping 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] Embodiment 3

[0149] The present invention 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 in Embodiment 1 is implemented.

[0150] Embodiment 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 generates a disturbance in a photovoltaic area within the system at 1s, and a high-resistance grounding fault occurs at 2s. Figure 5 It indicates the current generated in a constant power load area when the bus voltage drops to 90% of the rated voltage. This current far exceeds the setting 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 certain 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. At this time, the power change rate generated 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 the overcurrent protection and the method of extracting the high-frequency harmonic energy of the 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 the high-frequency harmonic energy of the fault can be used as an effective fault judgment criterion, and the protection information can still be calculated for precise positioning.

[0153] Those of ordinary skill 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 only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A DC microgrid ground fault protection method, 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-up criteria, the fault area is determined according to the fault area location information, and a tripping command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker is disconnected after receiving the tripping command.

2. The DC microgrid ground fault protection method according to claim 1, characterized in that: 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.

3. The DC microgrid ground fault protection method according to claim 2, characterized in that: The real-time calculation of fault area location information is specifically: At each DC circuit breaker, the following calculations are performed based on the collected voltage and current information and the DC circuit breaker open and closed status: In the formula, V1 is the state quantity of the protection start criterion, and its value is 1 or 0. To protect the start criteria, represents the power change rate, Indicates the rate of change of regional fault ground current, Dp set Indicates the setting value of the power change rate, Di set Indicates the setting 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 state quantity of the protection positioning information: DE=E(n)-E(m)(2) Where DE is the harmonic change before and after the fault; E(n) is the harmonic high frequency after n acquisition points from the start of the fault, and E(m) is the harmonic high frequency 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 |DE|3DE set , V2 = -1 indicates that the harmonic content does not meet the protection criteria, DE set is the setting value of harmonic variation; calculate the fault judgment information of photovoltaic area, energy storage area and load area: V b =V1*V2*S v (4) In the formula, 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 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 occurs, and then decides whether to start the protection trip circuit breaker based on the start-up criterion. b =0 or -1 indicates that no fault occurs in this area, V b =1 indicates that a fault occurs in the area; For a total of X photovoltaic areas, the calculation method for determining the ground fault state 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 is as follows: (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 state quantity of the ground fault in the energy storage area, 1 indicates a fault occurs in the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Represents the fault judgment information of the yth energy storage area after the ground fault occurs; V by 2 The calculation method is as follows: (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.

4. The DC microgrid ground fault protection method according to claim 3, characterized in that: The real-time calculation of fault area location information also includes: The directed edge structure matrix of the source-storage-load area of ​​the DC microgrid is A, in which the i-row vector represents the number of source-storage-load areas of the DC microgrid, and the j-column vector represents the number of DC circuit breakers. After the grounding 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 solve 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 fault area of ​​the DC microgrid source and load, v pv 、v bat 、v load They represent the fault information vectors of the photovoltaic area, energy storage area, and load area respectively. The values ​​of the elements in the fault information vector are determined by the regional fault judgment information V b get.

5. The DC microgrid ground fault protection method according to claim 4, 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 in the area, and -1 means a fault occurs outside the area.

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

7. The DC microgrid grounding fault protection method as described in claim 6, wherein the power change is calculated by performing Fourier transform analysis on the voltage and current information uploaded by each DC circuit breaker after a grounding fault occurs in the DC microgrid source-storage-load system, converting the time domain information into frequency domain information, extracting the frequency information in which the power transient change is greater than the set threshold according to 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.

8. The DC microgrid ground fault protection method according to claim 3, characterized in that: The harmonic high-frequency quantity is filtered by a Chebyshev filter according to the voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-load storage system, and the double frequency, triple frequency and higher frequency harmonic frequency values ​​are set, and then calculated by a protection comprehensive judgment device.

9. The DC microgrid ground fault protection method according to claim 1, characterized in that: The protection start criterion is: In the formula, represents the power change rate, Indicates the rate of change of regional fault ground current, Dp set Indicates the setting value of the power change rate, Di set Indicates the set value of the current change rate.

10. The DC microgrid ground fault protection method according to claim 1, characterized in that: The protection start criterion is: through the fault state of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas and the local stable operation state, 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 then determine whether the protection is started.

11. The DC microgrid ground fault protection method according to claim 5, characterized in that: The setting value of the power change rate ranges from 1.2 to 1.5 times the rated value.

12. The DC microgrid ground fault protection method according to claim 5, characterized in that: The setting value of the current change rate ranges from 1.2 to 1.5 times the rated value.

13. The DC microgrid ground fault protection method according to claim 3, characterized in that: The harmonic variation setting value DE set The value range is 1.5 to 1.6 times the rated value.

14. A DC microgrid ground fault protection system, implemented in a DC microgrid connected to photovoltaic, energy storage and load, characterized in that: include: Protection comprehensive judgment device, protection communication device and DC circuit breaker; The DC circuit breaker corresponds to each photovoltaic area, energy storage area and load area, and 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 will collect and analyze the results of the high-frequency harmonic changes of each DC circuit breaker, and calculate the fault area location information in real time. When the regional fault grounding current and power change rate meet the protection start-up criteria, the fault area is determined according to the fault area location information, and a tripping command is sent to the DC circuit breaker connected to the fault area. The DC circuit breaker is disconnected after receiving the tripping command.

15. The DC microgrid ground fault protection system according to claim 14, characterized in that: 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.

16. The DC microgrid ground fault protection system according to claim 15, characterized in that: The real-time calculation of fault area location information is specifically: At each DC circuit breaker, the following calculations are performed based on the collected voltage and current information and the DC circuit breaker open and closed status: In the formula, V1 is the state quantity of the protection start criterion, and its value is 1 or 0. To protect the start criteria, represents the power change rate, Indicates the rate of change of regional fault ground current, Dp set Indicates the setting value of the power change rate, Di set Indicates the setting 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 state quantity of the protection positioning information: DE=E(n)-E(m)(2) Where DE is the harmonic change before and after the fault; E(n) is the harmonic high frequency after n acquisition points from the start of the fault, and E(m) is the harmonic high frequency 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 |DE|3DE set , V2 = -1 indicates that the harmonic content does not meet the protection criteria, DE set is the setting value of harmonic variation; calculate the fault judgment information of photovoltaic area, energy storage area and load area: V b =V1*V2*S v (4) In the formula, 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 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 occurs, and then decides whether to start the protection trip circuit breaker based on the start-up criterion. b =0 or -1 indicates that no fault occurs in this area, V b =1 indicates that a fault occurs in the area; For a total of X photovoltaic areas, the calculation method for determining the ground fault state 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 state quantity of the ground fault in the energy storage area, 1 indicates a fault occurs in the energy storage area, and -1 indicates a fault occurs outside the energy storage area; where V by 2 Represents 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 source-storage-load area of ​​the DC microgrid is A, in which the i-row vector represents the number of source-storage-load areas of the DC microgrid, and the j-column vector represents the number of DC circuit breakers. After the grounding 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 solve 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 fault area of ​​the DC microgrid source and load, v pv 、v bat 、v load Respectively represent the photovoltaic area V b1～X 、Energy storage area V b1～Y , Load area V b1～Z Fault information vector.

17. The DC microgrid ground fault protection system according to claim 16, 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 in the area, and -1 means a fault occurs outside the area.

18. The DC microgrid ground fault protection system according to claim 16, characterized in that: The calculation method of the harmonic high frequency quantity is: Where P(m) represents the power variation collected at the DC circuit breaker, E(n) represents the high-frequency harmonic generated by the ground fault, and H(nm) represents the rectangular window function with a window length of l.

19. The DC microgrid ground fault protection system according to claim 16, characterized in that: The harmonic high-frequency quantity is filtered by a Chebyshev filter according to the voltage and current information uploaded by each DC circuit breaker after a ground fault occurs in the DC microgrid source-load storage system, and the double frequency, triple frequency and higher frequency harmonic frequency values ​​are set, and then calculated by a protection comprehensive judgment device.

20. The DC microgrid ground fault protection system according to claim 14, characterized in that: The protection start criterion is: In the formula, represents the power change rate, Indicates the rate of change of regional fault ground current, Dp set Indicates the setting value of the power change rate, Di set Indicates the set value of the current change rate.

21. The DC microgrid ground fault protection system according to claim 14, characterized in that: The protection start criterion is: through the fault state of each circuit breaker in X photovoltaic areas, Y energy storage areas, and Z load areas and the local stable operation state, 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 then determine whether the protection is started.

22. The DC microgrid ground fault protection system according to claim 16, characterized in that: The setting value of the power change rate ranges from 1.2 to 1.5 times the rated value.

23. The DC microgrid ground fault protection system according to claim 16, characterized in that: The setting value of the current change rate ranges from 1.2 to 1.5 times the rated value.

24. The DC microgrid ground fault protection system according to claim 16, characterized in that: The harmonic variation setting value ranges from 1.5 to 1.6 times the rated value.

25. 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 13 is implemented.

26. 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 as described in any one of claims 1 to 13.

Images