A microgrid protection method and device adapted to high proportion of IIDER access.

Abstract

This invention discloses a microgrid protection method and device adapted to high-proportion IIDER access. The method determines the fault direction by the phase angle difference between the positive-sequence voltage at the bus before the fault and the positive-sequence current at the protection point after the fault. It also provides criteria for the activation of undervoltage protection under forward fault conditions, inverse-time protection under grid-connected operation, and inverse-time protection under off-grid operation. This method can locally isolate faults in both grid-connected and off-grid modes of the microgrid, does not rely on communication, and is economical.

Description

Technical Field

[0001] This invention relates to the field of distribution network relay protection technology, specifically to a microgrid protection method and device adapted to a high proportion of IIDER access. Background Technology

[0002] Renewable energy sources, represented by grid-connected inverter-type distributed power sources, are increasingly being integrated into microgrids that can operate independently and have diverse modes. This has led to traditional relay protection schemes being unable to meet the requirements for protection selectivity and speed in microgrids with high distributed power source penetration.

[0003] Microgrid protection systems must ensure safe operation in both grid-connected and off-grid modes and respond to faults on both the distribution network side and within the microgrid. However, the significant difference in fault current between grid-connected and off-grid modes presents a challenge for microgrid protection. In grid-connected mode, the fault current in the microgrid is relatively large due to the contribution of the main grid. In this case, traditional overcurrent protection can detect the fault and trip. However, in off-grid mode, the fault current is very small. The output current of inverter-interfaced distributed energy resources (IIDERs) is determined by the short-time current-carrying capacity of the semiconductor switches, typically limited to 1.2-2 times the rated current. In this situation, traditional overcurrent protection may fail to operate because it cannot reach the starting current value; furthermore, due to the bidirectional current direction in the microgrid, it may falsely trip, expanding the scope of the power outage.

[0004] Existing research on local microgrid protection is incomplete. For example, the literature [Zeng Dehui. Research on New Principles of Fault Analysis and Protection of Distribution Networks and Microgrids Including Distributed Power Sources [D]. South China University of Technology, 2016] proposes to realize the protection of microgrids in two operating modes through directional element relays of programmable microprocessors. The overall scheme depends on the improved relay settings for different scenarios and installation locations. This method is complex to configure and has a long protection action time, and can only be used as backup protection. The literature [Zhang Erjia. Research on the Principle and Scheme of Multi-layer Cooperative Adaptive Protection of Microgrids [D]. Shanghai Jiaotong University, 2020] proposes a protection scheme of directional overcurrent relays. However, it does not describe the mechanism of starting the overcurrent relay with a small fault current. The literature [Huang Wentao, Tai Nengling, Tang Yuezhong. Analysis of Grid-connected Protection of AC Microgrid Systems [J]. [Automation of Electric Power Systems, 2013, 37(6): 114-120] proposes a microgrid protection method that uses the phase difference between the pre-fault current and the fault current component to determine the fault direction and uses the change in electrical energy during the fault to determine the fault. However, it does not provide an overall effective configuration scheme and lacks a complete microgrid protection scheme. On the other hand, the protection scheme that relies on communication is proposed in the literature [ZAMANI MA, SIDHU TS, YAZDANI A. A Protection Strategy and Microprocessor-Based Relay for Low-Voltage Microgrids[J]. IEEE Transactions on PowerDelivery, 2011, 26(3): 1873-1883]. It proposes a fault direction discrimination method based on the positive sequence current phase comparison of three sets of adjacent protection devices. When judging the fault, it is necessary to compare the information obtained by the three adjacent unit protection modules and then use the voltage drop on the bus to judge the fault. It is difficult to follow the changes in the microgrid topology. Summary of the Invention

[0005] The purpose of this invention is to provide a microgrid protection method and device adapted to high-proportion IIDER access. This method identifies fault segments based on the phase angle difference between the pre-fault voltage and the fault current, and uses the time coordination of improved inverse-time overcurrent protection and undervoltage protection to clear faults, forming a complete microgrid protection method. This method can clear faults locally in both grid-connected and off-grid modes, does not rely on communication, and is economical.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] In a first aspect, the present invention provides a microgrid protection method adapted to a high proportion of IIDER access, comprising:

[0008] Calculate the phase angle difference between the positive sequence voltage at the bus before the fault and the positive sequence current at the protection of the feeder outlet circuit breaker after the fault, and determine whether it is a forward fault or a reverse fault based on the phase angle difference.

[0009] Under a positive fault, determine whether to activate the undervoltage protection. If activated, the protection will trip the circuit breaker according to the undervoltage protection action time and the circuit breaker's inherent action time.

[0010] Under a positive fault, if the grid is in operation, the inverse-time overcurrent setting value under grid operation is calculated. If the fault current value is higher than the inverse-time overcurrent setting value under grid operation, the microgrid inverse-time protection is activated. Based on the action time of the inverse-time overcurrent protection under grid operation and the inherent action time of the circuit breaker, the protection is activated to trip the circuit breaker.

[0011] Under a positive fault, if the system is in an off-grid operating state, the inverse-time overcurrent setting value in the off-grid state is calculated. If the fault current value is higher than the inverse-time overcurrent setting value in the off-grid state, the microgrid inverse-time protection is activated. Based on the operating time of the inverse-time overcurrent protection in the off-grid state and the inherent operating time of the circuit breaker, the protection operates to trip the circuit breaker.

[0012] Preferably, the calculation of the phase angle difference between the positive sequence voltage at the busbar before the fault and the positive sequence current of the protection at the feeder outlet circuit breaker after the fault includes:

[0013] ;

[0014] in, The phase angle difference is the positive sequence voltage at bus i before the fault and the positive sequence current protected at the circuit breaker at feeder ij after the fault. The voltage at bus i before the fault. This refers to the post-fault current flowing through the protection at the circuit breaker outlet of feeder ij.

[0015] Preferably, determining whether a fault is forward or reverse based on the phase angle difference includes:

[0016] if If it is a positive fault, then it is a positive fault; if If so, it is a reverse fault.

[0017] Preferably, determining whether to activate undervoltage protection includes:

[0018] Determine whether the voltage after the fault is lower than the operating voltage. If it is lower than the operating voltage, then activate the undervoltage protection. The operating voltage range is 0.6~0.85pu.

[0019] Preferably, the low voltage protection action time is determined as follows:

[0020] The settings are configured in a stepped, hierarchical manner, starting with the operating time of the last protection. The operating time of the last undervoltage protection is set higher than that of the inverse-time overcurrent protection, and the operating time of each subsequent undervoltage protection is increased by one step. ,in, This is the set value.

[0021] Preferably, the calculation of the inverse-time overcurrent setting value under grid-connected conditions includes:

[0022] If it is the protection for the load feeder, the inverse time overcurrent setting value is:

[0023] ,

[0024] in, This is the inverse-time overcurrent setting value for feeder ij under grid-connected conditions. Represents the reliability coefficient. Indicates the self-starting coefficient. Indicates the circuit breaker return coefficient. This represents the maximum load current of feeder ij during normal operation;

[0025] If it is for the protection of a distributed power source feeder, the inverse time overcurrent setting value should be selected as 0;

[0026] If it is for the protection of the connecting feeder, then,

[0027] The inverse time overcurrent setting values ​​at each protection installation point near the main power grid are:

[0028] ;

[0029] The inverse time overcurrent setting values ​​for each protection installation location far from the main power grid side are:

[0030] ,

[0031] in, This is the ratio of the installed capacity of distributed power sources connected to the end of the interconnecting feeder to the maximum load capacity. This is the maximum load current flowing through the protection of the circuit breaker at the feeder ij outlet during normal operation.

[0032] Preferably, the operating time of the inverse-time overcurrent protection under grid-connected conditions is calculated as follows:

[0033] ;

[0034] Where t is the operating time of the inverse-time overcurrent protection. The fault acceleration factor within the region is represented by the sum of the phase angle difference and the measured impedance. , This refers to the time tuning coefficient of feeder ij under grid-connected conditions. To protect against fault current at the installation location, To protect the measurement impedance at the installation location, To protect the line impedance from the installation point to the end of this feeder.

[0035] Preferably, the calculation of the inverse-time overcurrent setting value under off-grid conditions includes:

[0036] If it is the protection for the load feeder, the inverse time overcurrent setting value is:

[0037] ;

[0038] in, This is the inverse-time overcurrent setting value for feeder ij in off-grid mode. Represents the reliability coefficient. Indicates the self-starting coefficient. Indicates the circuit breaker return coefficient. This represents the maximum load current of feeder ij during normal operation;

[0039] If it is for the protection of a distributed power source feeder, the inverse time overcurrent setting value should be selected as 0;

[0040] If it is protection for a tie feeder, it shall be calculated as follows:

[0041] ,

[0042] in, This is the ratio of the installed capacity of distributed power sources connected to the end of the interconnecting feeder to the maximum load capacity. This is the maximum load current flowing through the protection of the circuit breaker at the feeder ij outlet during normal operation.

[0043] Preferably, the operating time of the inverse-time overcurrent protection in the off-grid state is calculated as follows:

[0044] ;

[0045] Where t is the operating time of the inverse-time overcurrent protection. The fault acceleration factor within the region is represented by the sum of the phase angle difference and the measured impedance. , This is the time tuning coefficient for feeder ij in off-grid mode. To protect against fault current at the installation location, To protect the measurement impedance at the installation location, To protect the line impedance from the installation point to the end of this feeder.

[0046] Secondly, the present invention provides a microgrid protection device adapted to a high proportion of IIDER access, for implementing the above-mentioned microgrid protection method adapted to a high proportion of IIDER access, the device comprising:

[0047] The judgment module is used to calculate the phase angle difference between the positive sequence voltage at the bus before the fault and the positive sequence current at the protection of the feeder outlet circuit breaker after the fault, and to determine whether it is a forward fault or a reverse fault based on the phase angle difference.

[0048] The low voltage protection action module is used to determine whether to activate low voltage protection under positive fault conditions. If activated, the protection will trip the circuit breaker according to the low voltage protection action time and the inherent action time of the circuit breaker.

[0049] The grid-connected operation protection action module is used to calculate the inverse time overcurrent setting value under grid-connected operation state if the fault current value is higher than the inverse time overcurrent setting value under grid-connected operation state under positive fault conditions. The microgrid inverse time protection is activated based on the action time of the inverse time overcurrent protection under grid-connected operation state and the inherent action time of the circuit breaker. The protection action is to trip the circuit breaker.

[0050] The off-grid operation protection action module is used to calculate the inverse-time overcurrent setting value under off-grid operation state in the case of a positive fault. If the fault current value is higher than the inverse-time overcurrent setting value under off-grid operation state, the microgrid inverse-time protection is activated. Based on the action time of the inverse-time overcurrent protection under off-grid operation state and the inherent action time of the circuit breaker, the protection action is to trip the circuit breaker.

[0051] Thirdly, the present invention provides a computer-readable storage medium for storing one or more programs, said one or more programs including instructions that, when executed by a computing device, cause the computing device to perform any of the methods described above.

[0052] Fourthly, the present invention provides a computing device comprising one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs comprising instructions for performing any of the methods described above.

[0053] The beneficial effects of this invention are as follows:

[0054] This invention proposes a microgrid protection method with a high proportion of IIDER (In-Time Overcurrent Protection) connections. The fault direction is determined by the phase angle difference between the pre-fault voltage and the post-fault current. An in-zone fault acceleration factor, combining the phase angle difference and measured impedance, is used to improve the operating equation of the inverse-time overcurrent protection, thereby reducing the protection's operating time and improving its speed. To address the issue of protection failure due to small fault currents in off-grid conditions, a low-voltage protection criterion, using the phase angle difference criterion as an auxiliary, is established, resulting in a microgrid protection scheme that integrates improved inverse-time overcurrent protection and low-voltage protection. This method selectively isolates faults in both on-grid and off-grid modes based on local information, is communication-independent, adaptable to topology changes, and is economically efficient. Attached Figure Description

[0055] Figure 1 This is a flowchart of a microgrid protection method adapted to a high proportion of IIDER access provided by an embodiment of the present invention;

[0056] Figure 2 This is the grid-connected microgrid model provided in Embodiment 2 of the present invention;

[0057] Figure 3 This is the inverse time overcurrent protection operation time curve under grid-connected state provided in Embodiment 2 of the present invention;

[0058] Figure 4 This is the off-grid microgrid model provided in Embodiment 3 of the present invention. Detailed Implementation

[0059] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The embodiments described below with reference to the accompanying drawings are illustrative and intended to explain the present invention, and should not be construed as limiting the present invention.

[0060] It should be noted that, as used in this invention, "an embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that can be included in at least one implementation of this invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that excludes other embodiments.

[0061] It should be emphasized here that the step markers mentioned below are not a limitation on the order of the steps, but should be understood as meaning that the steps can be executed in the order mentioned in the embodiments, or in a different order than in the embodiments, or several steps can be executed simultaneously.

[0062] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0063] Example 1

[0064] This embodiment 1 provides a microgrid protection method adapted to a high proportion of IIDER access, see [link to documentation]. Figure 1 The specific implementation process of this method is as follows:

[0065] 1. When the program starts, the local protection device continuously collects and processes the voltage and current information at the protection installation location and memorizes the amplitude and phase angle of the voltage and current before the fault.

[0066] 2. When a fault occurs, calculate the phase angle difference between the positive sequence voltage at bus i before the fault and the positive sequence current at protection point ij after the fault: ,in, The voltage at bus i before the fault. To protect the fault current flowing through ij.

[0067] 3. Based on the calculated phase angle difference, determine whether it is a forward fault or a reverse fault. The determination method is as follows (1).

[0068] (1)

[0069] if ,Right now If the value is greater than 0, it is a positive fault; proceed to step 4. ,Right now If the value is less than 0, it indicates a reverse fault, and the process returns to step 1.

[0070] 4. Determine whether the voltage after the fault is lower than the operating voltage. If it is lower than this set value, activate the undervoltage protection and proceed to step 5. If not, return to step 1.

[0071] In power distribution networks, the operating voltage range for undervoltage protection is typically 0.6~0.85 pu. In this method, the operating voltage setting for undervoltage protection is taken as 0.85 pu.

[0072] At the same time, determine whether the microgrid is in grid-connected operation. If it is in grid-connected operation, calculate the inverse-time overcurrent setting value in grid-connected operation; otherwise, calculate the inverse-time overcurrent setting value in off-grid operation and proceed to step 6.

[0073] 5. Start timing according to the low voltage protection action time. When the action time is up, the protection will activate the output circuit breaker and proceed to step 8.

[0074] In this step, the undervoltage protection operating time is determined as follows:

[0075] The settings are performed in a stepped, hierarchical manner, starting with the operating time of the last protection. The operating time of the last undervoltage protection is set higher than that of the inverse-time overcurrent protection, and the operating time of each subsequent undervoltage protection is increased by one step. .in, As a set value, it is usually taken as... =0.2~0.5s.

[0076] 6. Measure whether the current value is higher than the inverse time overcurrent setting value. If yes, proceed to step 7; otherwise, return to step 1.

[0077] 7. Activate the microgrid inverse-time protection and calculate the inverse-time overcurrent setting time. Start timing; when the setting time is up, the protection will activate the output circuit breaker, and proceed to step 8.

[0078] 8. Wait for the circuit breaker's inherent operating time. Once the time is up, proceed to step 9.

[0079] 9. The protection action results in the circuit breaker tripping, and the process ends.

[0080] In step 5 of this embodiment, the inverse-time overcurrent setting value under grid-connected conditions is calculated as follows:

[0081] (2)

[0082] in: The fault acceleration factor within the region is represented by the sum of the phase angle difference and the measured impedance. .

[0083] In the formula: t is the inverse time overcurrent setting time. This refers to the time tuning coefficient of feeder ij under grid-connected conditions; This is the inverse-time overcurrent setting value for feeder ij under grid-connected conditions; To protect against fault current at the installation location; To protect the measurement impedance at the installation location; To protect the line impedance from the installation point to the end of this feeder. Among other things, and The values ​​need to be selected according to the parameter settings of the inverse time overcurrent protection under grid-connected conditions.

[0084] by Figure 2 Taking the grid-connected microgrid model shown as an example, feeders that are connected to the bus at one end and directly connected to the load or IIDER at the other end are called branch feeders (including load feeders and distributed generation feeders), and feeders that are connected to the bus at both ends are called tie feeders.

[0085] The feeder numbering is defined as follows:

[0086] In feeder ij, i refers to the busbar number, and j refers to the line number on the busbar, for example... Figure 2 In the diagram, feeder A1 indicates the line numbered 1 connected to busbar A, and protection A1 indicates the protection at the circuit breaker at feeder A1's output. However, on tie feeders, to distinguish the protection at the output circuit breakers on both sides, the numbering differs, such as... Figure 2 A3 and B1 in the diagram.

[0087] The parameter settings for inverse time overcurrent protection under grid-connected conditions are as follows:

[0088] A. If it is protection for the load feeder

[0089] For load feeders, the direction of the normal current and fault current remains unchanged, but the magnitude of the current changes. The inverse time overcurrent setting parameter of feeder ij is set according to equation (3).

[0090] (3)

[0091] In the formula: This represents the reliability coefficient, with a value ranging from 1.25 to 1.5. This represents the self-starting coefficient, and its value should be greater than 1. This represents the circuit breaker return coefficient, and its value should be less than 1. This represents the maximum load current of feeder ij during normal operation.

[0092] When a load feeder fault occurs, the line output protection does not need to wait; the protection's operating time is the circuit breaker's factory-defined operating time. , This is the factory-defined operating time of the circuit breaker.

[0093] B. Protection for distributed power supply feeders

[0094] Under normal grid-connected operation, distributed generation (DG) feeders need to supply current. When a fault occurs on the DG feeder, the grid and other DG sources provide short-circuit current to the fault point, and the direction of the current detected at the protection installation point is opposite to that under normal conditions. To ensure that the circuit breaker at the DG feeder outlet can operate reliably and quickly during a DG feeder fault, the starting current of the DG feeder can be selected as 0.

[0095] When a fault occurs in the distributed power supply feeder, the line output protection does not need to wait and will operate at the fastest speed. The protection operation time is the circuit breaker's factory-defined operation time. , This is the factory-defined operating time of the circuit breaker.

[0096] C. If it is for the protection of the connecting feeder line

[0097] The setting current values ​​of each protection installation point near the main power grid under grid-connected status, and the starting current of protections A4, A3 and B3 can be set according to formula (3).

[0098] The setting current values ​​of each protection installation point far from the main power grid under grid-connected status, and the starting current of protections D1, B1, and C1 are set according to parameters such as source-load ratio, as shown in equation (4).

[0099] (4)

[0100] In the formula: The ratio of the installed capacity of distributed power sources at the end of the interconnection feeder to the maximum load capacity; This is the maximum load current flowing through the protection of the circuit breaker at the feeder ij outlet during normal operation.

[0101] Regarding the coordination of protection timing, the inverse time overcurrent setting value of B3 is used... According to the selective requirement, when a three-phase metallic short-circuit fault occurs at the outlet of line C2, the operating time of protection B3 is Δt longer than that of protection C2. Substituting into formula (2), the time constant of protection B3 can be obtained, as shown in formula (5):

[0102] (5)

[0103] In the formula, Let C2 be the fault current when a three-phase metallic short circuit occurs at the end of line B2. When a three-phase metallic short circuit fault occurs at the outlet of line B3, the operating time of protection A3 is Δt longer than that of protection B3, and so on. This can be used to calculate the operating time of all protections. After adjustment, the timing coordination on the feeder line is as follows: Figure 3 As shown.

[0104] In step 5 of this embodiment, the inverse-time overcurrent setting value of the microgrid under off-grid conditions is calculated as follows:

[0105] (6)

[0106] in: The fault acceleration factor within the region is represented by the sum of the phase angle difference and the measured impedance. .

[0107] In the formula: t is the inverse time overcurrent setting time; This refers to the time tuning coefficient of feeder ij in off-grid mode; This is the inverse-time overcurrent setting value for feeder ij under off-grid conditions; To protect against fault current at the installation location; To protect the measurement impedance at the installation location; To protect the line impedance from the installation point to the end of this feeder. Among other things, and The values ​​need to be set according to the parameters of the inverse time overcurrent protection in the off-grid state.

[0108] by Figure 4 Taking the off-grid microgrid model shown as an example, feeders that are connected to the bus at one end and directly connected to the load or IIDER at the other end are called branch feeders (including load feeders and distributed generation feeders), and feeders that are connected to the bus at both ends are called tie feeders.

[0109] The parameter settings for inverse time overcurrent protection in off-grid mode are as follows:

[0110] A. If it is protection for the load feeder

[0111] For load feeders, the direction of the normal current and fault current remains unchanged, but the magnitude of the current changes. The inverse-time overcurrent setting value is set according to formula (7).

[0112] (7)

[0113] In the formula: This represents the reliability coefficient, with a value ranging from 1.25 to 1.5. This represents the self-starting coefficient, and its value should be greater than 1. This represents the circuit breaker return coefficient, and its value should be less than 1. This represents the maximum load current of feeder ij during normal operation.

[0114] When a load feeder fault occurs, the line output protection does not need to wait; the protection operating time is the circuit breaker's factory-defined operating time. .

[0115] B. Protection for distributed power supply feeders

[0116] Under normal off-grid operation, distributed generation (DG) feeders need to supply current. When a fault occurs on the DG feeder, other DG sources provide short-circuit current to the fault point, and the current direction detected at the protection installation point is opposite to that under normal conditions. To ensure that the circuit breaker at the DG feeder outlet can operate reliably and quickly during a DG feeder fault, the starting current of the DG feeder can be selected as 0.

[0117] When a fault occurs in the distributed power supply feeder, the line output protection does not need to wait and will operate at the fastest speed. The protection operation time is the circuit breaker's factory-defined operation time. , This is the factory-defined operating time of the circuit breaker.

[0118] C. If it is for the protection of the connecting feeder line

[0119] The setting current values ​​at each protection installation location in the off-grid state, and the starting currents of protections A4, A3, B3, D1, B1 and C1 are set according to parameters such as source-load ratio, as shown in equation (8).

[0120] (8)

[0121] In the formula: The ratio of the installed capacity of distributed power sources at the end of the interconnection feeder to the maximum load capacity; This is the maximum load current flowing through the protection of the circuit breaker at the feeder ij outlet during normal operation.

[0122] Regarding the coordination of protection time, the starting current of B3 is used This indicates that, according to the selective requirement, when the most severe fault occurs at the C2 line outlet, the operating time of protection B3 is Δt longer than that of protection C2. Substituting this into formula (2), the time constant of protection B3 can be obtained, as shown in formula (9).

[0123] (9)

[0124] When the most severe fault occurs at the B3 line outlet, the operating time of protection A3 is Δt longer than that of protection B3, and so on, the operating time of all protections can be calculated. After adjustment, the timing coordination on the feeder line is... Figure 3 similar.

[0125] Example 2

[0126] Based on the microgrid method of Embodiment 1 above, this Embodiment 2 uses... Figure 2 Taking the F5 fault as an example, the entire protection action process under grid-connected conditions is explained:

[0127] 1. Under normal operating conditions, protection devices A3 and B1 continuously collect and process voltage and current information at the protection installation location, and have the function of storing and memorizing voltage and current amplitude and phase angle.

[0128] 2. When a fault occurs, activate the amplitude and phase angle of the memory voltage and memory current, and calculate the phase angle difference between the positive sequence voltage at bus A and B before the fault and the positive sequence current at protection A3 and B1 after the fault. , .

[0129] 3. Calculation and ,get If the microgrid is determined to be in grid-connected operation, protection A3 will proceed to step 6. If the microgrid is determined to be in grid-connected operation, protection B1 will proceed to step 6.

[0130] 4. If the voltage at protection point A3 is lower than 0.85 pu, activate the low voltage protection and proceed to step 5; if the voltage at protection point B1 is lower than 0.85 pu, activate the low voltage protection and proceed to step 5.

[0131] 5. Start timing A3 and B1 protections at 0.4s (the set time for low voltage protection). When the set time is up, the protections will activate circuit breakers A3 and B1, and proceed to step 9.

[0132] 6. Select the setting value for inverse time overcurrent protection under grid-connected conditions. , , , Proceed to step 7;

[0133] 7. Judgment , Proceed to step 8;

[0134] 8. Start the microgrid inverse time protection and calculate the inverse time overcurrent setting time of protection A3 and B1 under the microgrid grid-connected state according to formulas (10) and (11). , Assuming , Start timing; when the set time is up, the protection will activate circuit breakers A3 and B1, then proceed to step 9.

[0135] (10)

[0136] (11)

[0137] 9. Protection B1 first receives the instruction to act in 0.2s, waits for the inherent operating time of the B1 circuit breaker, and when the time is up, proceeds to step 10; Protection A3 first receives the instruction to act in 0.3s, waits for the inherent operating time of the A3 circuit breaker, and when the time is up, proceeds to step 10.

[0138] 10. The protection action trips circuit breakers A3 and B1, and the process ends.

[0139] by Figure 2 Taking the F5 fault as an example, a simulation was performed, and the results are as follows:

[0140] Build such in PSCAD Figure 2The simulation model of the microgrid with IIDER shown is based on a 10kV, 50Hz microgrid connected to the main grid via a 10kV / 110kV step-up transformer. Distributed generation (DG) systems employ a PQ control strategy with low-voltage ride-through capability. IIDER1-IIDER3 each have a capacity of 3MW, and the maximum fault current is 1.2 times the rated current. The interconnecting feeders are all 2km long, the load feeders are all 0.2km long, and the DG feeders are all 0.1km long. The line impedance Z... l =(0.125+j0.405)Ω / km. Each load has a capacity of 3MV·A and a power factor of 0.85. Assume ∆t = 0.2s, t b =0.04s. The F5 fault point is divided into two locations: 1800m away from protection A3 line and 1800m away from protection B1 line.

[0141] The microgrid protection under grid-connected status is set according to the inverse time overcurrent protection setting scheme. The setting parameters of protections A3 and B1 are shown in Table 1.

[0142] Table 1 Parameters of protections A3 and B1 under grid-connected conditions

[0143]

[0144] Table 2. Action status of protections A3 and B1 under grid-connected conditions.

[0145]

[0146] Three-phase and two-phase short-circuit faults were set at a distance of 1800m from protection line A3 and 1800m from protection line B1, respectively. The operation of the protection is shown in Table 2.

[0147] Example 3

[0148] Based on the microgrid method of Embodiment 1 above, this Embodiment 3 uses... Figure 4 Taking the F3 fault as an example, the entire operation process in the off-grid state is explained:

[0149] 1. Under normal operating conditions, protection D2 continuously acquires and processes real-time electrical characteristic quantities, and has the function of storing and memorizing voltage and current.

[0150] 2. When a fault occurs, activate the amplitude and phase angle of the memory voltage and memory current, and calculate the phase angle difference between the positive sequence voltage at bus D before the fault and the positive sequence current at protection D2 after the fault. .

[0151] 3. Calculation ,get If the microgrid is determined to be in an off-grid operation state, protection D2 will proceed to step 6.

[0152] 4. If the voltage at D2 is lower than 0.85pu, the low voltage protection will be activated, and the process will proceed to step 5.

[0153] 5. Start timing D2 protection at 0.2s (the time set for low voltage protection). When the set time is up, the protection will activate circuit breaker D2 and proceed to step 9.

[0154] 6. Select the setting value for inverse time overcurrent protection in off-grid mode. , Proceed to step 7.

[0155] 7. Judgment Proceed to step 8.

[0156] 8. Start the microgrid inverse-time protection and calculate the operating time of the inverse-time overcurrent protection D2 under the off-grid state of the microgrid according to formula (12). Assuming Start timing; when the set time is up, the protection activates circuit breaker D2, proceeding to step 9;

[0157] (12)

[0158] 9. Protection D2 first receives the 0s action command, waits for the inherent action time of D2 circuit breaker, and when the time is up, proceeds to step 10.

[0159] 10. The protection action trips circuit breaker D2, and the process ends.

[0160] by Figure 4 Taking the F3 fault as an example, a simulation was performed, and the results are as follows:

[0161] Build such in PSCAD Figure 4 The simulation model of the microgrid including IIDER is shown. The voltage level of the microgrid is 10kV and the frequency is 50Hz. All distributed generation sources adopt a PQ control strategy with low voltage ride-through capability. IIDER1-IIDER3 each have a capacity of 3MW, and the maximum fault current is 1.2 times the rated current. The length of the tie feeder is 2km, the length of the load feeder is 0.2km, and the length of the distributed generation feeder is 0.1km. The line impedance Z... l =(0.125+j0.405)Ω / km. Each load has a capacity of 3MV·A and a power factor of 0.85. Assume ∆t = 0.2s, t b =0.04s. The fault point of F3 is 200m away from the protection line D2.

[0162] The microgrid protection under off-grid conditions is set according to the inverse time overcurrent protection setting scheme. The setting parameters of protection D2 are shown in Table 3.

[0163] Table 3 Parameters of protection D2 in off-grid mode

[0164]

[0165] Three-phase and two-phase short-circuit faults were set 200m away from the protection line D2. The operation of the protection is shown in Table 4.

[0166] Table 4. Action of protection D2 under grid-connected conditions

[0167]

[0168] Example 4

[0169] Based on the same inventive concept, this embodiment 4 provides a microgrid protection device adapted to a high proportion of IIDER access, used to implement the microgrid protection method adapted to a high proportion of IIDER access in embodiment 1 above. The device includes:

[0170] The judgment module is used to calculate the phase angle difference between the positive sequence voltage at the bus before the fault and the positive sequence current at the protection of the feeder outlet circuit breaker after the fault, and to determine whether it is a forward fault or a reverse fault based on the phase angle difference.

[0171] The low voltage protection action module is used to determine whether to activate low voltage protection under positive fault conditions. If activated, the protection will trip the circuit breaker according to the low voltage protection action time and the inherent action time of the circuit breaker.

[0172] The grid-connected operation protection action module is used to calculate the inverse time overcurrent setting value under grid-connected operation state if the fault current value is higher than the inverse time overcurrent setting value under grid-connected operation state under positive fault conditions. The microgrid inverse time protection is activated based on the action time of the inverse time overcurrent protection under grid-connected operation state and the inherent action time of the circuit breaker. The protection action is to trip the circuit breaker.

[0173] The off-grid operation protection action module is used to calculate the inverse-time overcurrent setting value under off-grid operation state in the case of a positive fault. If the fault current value is higher than the inverse-time overcurrent setting value under off-grid operation state, the microgrid inverse-time protection is activated. Based on the action time of the inverse-time overcurrent protection under off-grid operation state and the inherent action time of the circuit breaker, the protection action is to trip the circuit breaker.

[0174] It is worth noting that this device embodiment corresponds to the above method embodiment. The implementation methods of the above method embodiments are all applicable to this device embodiment and can achieve the same or similar technical effects, so they will not be described in detail here.

[0175] Example 5

[0176] This embodiment 5 provides a computer-readable storage medium storing one or more programs, the one or more programs including instructions that, when executed by a computing device, cause the computing device to perform the microgrid protection method adapted to high-proportion IIDER access according to embodiment 1 above.

[0177] Example 6

[0178] This embodiment 6 provides a computing device, including one or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, and the one or more programs include instructions for executing the microgrid protection method adapted to high-proportion IIDER access according to the above embodiment 1.

[0179] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0180] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0181] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0182] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0183] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A microgrid protection method adapted to high-proportion IIDER access, characterized in that, include: The phase angle difference between the positive sequence voltage at the busbar before the fault and the positive sequence current at the feeder outlet circuit breaker after the fault is calculated as follows: ； in, The phase angle difference is the positive sequence voltage at bus i before the fault and the positive sequence current protected at the circuit breaker at feeder ij after the fault. The voltage at bus i before the fault. The fault current flowing through the protection at the circuit breaker outlet of feeder ij; Determining whether a fault is forward or reverse based on the phase angle difference includes: if If it is a positive fault, then it is a positive fault; if If so, it is a reverse fault; Under a positive fault, determine whether to activate the undervoltage protection. If activated, the protection will trip the circuit breaker according to the undervoltage protection action time and the circuit breaker's inherent action time. Under a positive fault, if the grid is in operation, the inverse-time overcurrent setting value under grid operation is calculated. If the fault current value is higher than the inverse-time overcurrent setting value under grid operation, the microgrid inverse-time protection is activated. Based on the action time of the inverse-time overcurrent protection under grid operation and the inherent action time of the circuit breaker, the protection is activated to trip the circuit breaker. Under a positive fault, if the operation is off-grid, the inverse-time overcurrent setting value under off-grid conditions is calculated. If the fault current value is higher than the inverse-time overcurrent setting value under off-grid conditions, the microgrid inverse-time protection is activated. Based on the action time of the inverse-time overcurrent protection under off-grid conditions and the inherent action time of the circuit breaker, the protection operates to trip the circuit breaker. The operating time of the inverse-time overcurrent protection under grid-connected conditions and the operating time of the inverse-time overcurrent protection under off-grid conditions are obtained by improving the operating equation of the inverse-time overcurrent protection through a comprehensive phase angle difference and the fault acceleration factor of the measured impedance.

2. The microgrid protection method adapted to high-proportion IIDER access according to claim 1, characterized in that, The determination of whether to activate undervoltage protection includes: Determine whether the voltage after the fault is lower than the operating voltage. If it is lower than the operating voltage, then activate the undervoltage protection. The operating voltage range is 0.6~0.85pu.

3. A microgrid protection method adapted to high-proportion IIDER access according to claim 2, characterized in that, The low voltage protection action time is determined as follows: The settings are configured in a stepped, hierarchical manner, starting with the operating time of the last protection. The operating time of the last undervoltage protection is set higher than that of the inverse-time overcurrent protection, and the operating time of each subsequent undervoltage protection is increased by one step. ,in, This is the set value.

4. A microgrid protection method adapted to high-proportion IIDER access according to claim 1, characterized in that, The calculation of the inverse-time overcurrent setting value under grid-connected conditions includes: If it is the protection for the load feeder, the inverse time overcurrent setting value is: ， in, This is the inverse-time overcurrent setting value for feeder ij under grid-connected conditions. Represents the reliability coefficient. Indicates the self-starting coefficient. Indicates the circuit breaker return coefficient. This represents the maximum load current of feeder ij during normal operation; If it is for the protection of a distributed power source feeder, the inverse time overcurrent setting value should be selected as 0; If it is for the protection of the connecting feeder, then, The inverse time overcurrent setting values ​​at each protection installation point near the main power grid are: ； The inverse time overcurrent setting values ​​for each protection installation location far from the main power grid side are: ， in, This is the ratio of the installed capacity of distributed power sources connected to the end of the interconnecting feeder to the maximum load capacity. This is the maximum load current flowing through the protection of the circuit breaker at the feeder ij outlet during normal operation.

5. A microgrid protection method adapted to high-proportion IIDER access according to claim 4, characterized in that, The operating time of the inverse-time overcurrent protection under grid-connected conditions is calculated as follows: ； Where t is the operating time of the inverse-time overcurrent protection. The fault acceleration factor within the region is represented by the sum of the phase angle difference and the measured impedance. , This refers to the time tuning coefficient of feeder ij under grid-connected conditions. To protect against fault current at the installation location, To protect the measurement impedance at the installation location, To protect the line impedance from the installation point to the end of this feeder.

6. A microgrid protection method adapted to high-proportion IIDER access according to claim 1, characterized in that, The calculation of the inverse-time overcurrent setting value under off-grid conditions includes: If it is the protection for the load feeder, the inverse time overcurrent setting value is: ； in, This is the inverse-time overcurrent setting value for feeder ij in off-grid mode. Represents the reliability coefficient. Indicates the self-starting coefficient. Indicates the circuit breaker return coefficient. This represents the maximum load current of feeder ij during normal operation; If it is for the protection of a distributed power source feeder, the inverse time overcurrent setting value should be selected as 0; If it is protection for a tie feeder, it shall be calculated as follows: ， in, This is the ratio of the installed capacity of distributed power sources connected to the end of the interconnecting feeder to the maximum load capacity. This is the maximum load current flowing through the protection of the circuit breaker at the feeder ij outlet during normal operation.

7. A microgrid protection method adapted to high-proportion IIDER access according to claim 6, characterized in that, The operating time of the inverse-time overcurrent protection in the off-grid state is calculated as follows: ； Where t is the operating time of the inverse-time overcurrent protection. The fault acceleration factor within the region is represented by the sum of the phase angle difference and the measured impedance. , This is the time tuning coefficient for feeder ij in off-grid mode. To protect against fault current at the installation location, To protect the measurement impedance at the installation location, To protect the line impedance from the installation point to the end of this feeder.

8. A microgrid protection device adapted to high-proportion IIDER access, characterized in that, For implementing the microgrid protection method adapted to high-proportion IIDER access as described in any one of claims 1 to 7, the apparatus comprises: The judgment module is used to calculate the phase angle difference between the positive sequence voltage at the bus before the fault and the positive sequence current at the protection of the feeder outlet circuit breaker after the fault, and to determine whether it is a forward fault or a reverse fault based on the phase angle difference. The low voltage protection action module is used to determine whether to activate low voltage protection under positive fault conditions. If activated, the protection will trip the circuit breaker according to the low voltage protection action time and the inherent action time of the circuit breaker. The grid-connected operation protection action module is used to calculate the inverse time overcurrent setting value under grid-connected operation state if the fault current value is higher than the inverse time overcurrent setting value under grid-connected operation state under positive fault conditions. The microgrid inverse time protection is activated based on the action time of the inverse time overcurrent protection under grid-connected operation state and the inherent action time of the circuit breaker. The protection action is to trip the circuit breaker. The off-grid operation protection action module is used to calculate the inverse-time overcurrent setting value under off-grid operation state in the case of a positive fault. If the fault current value is higher than the inverse-time overcurrent setting value under off-grid operation state, the microgrid inverse-time protection is activated. Based on the action time of the inverse-time overcurrent protection under off-grid operation state and the inherent action time of the circuit breaker, the protection action is to trip the circuit breaker.

9. A computer-readable storage medium for storing one or more programs, characterized in that, The one or more programs include instructions that, when executed by a computing device, cause the computing device to perform any of the methods according to claims 1 to 7.

10. A computing device, characterized in that, include, One or more processors, a memory, and one or more programs, wherein the one or more programs are stored in the memory and configured to be executed by the one or more processors, the one or more programs including instructions for performing any of the methods according to claims 1 to 7.

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