Micro-grid protection method and device suitable for high-proportion IIDER access

Abstract

The invention discloses a micro-grid protection method and device suitable for high-proportion IIDER access, and the method comprises the steps: judging a fault direction according to a phase angle difference between a positive-sequence voltage at a bus before a fault and a positive-sequence current at a protection position after the fault, and giving a positive-direction fault. Criterion of low-voltage protection starting, inverse time-lag protection starting in a grid-connected operation state and inverse time-lag protection starting in an off-grid operation state. According to the method, the fault can be removed in situ in the micro-grid on / off-grid mode, the method does not depend on communication, and the economical efficiency is good.

Description

Technical Field

[0001] The present invention relates to the technical field of relay protection for distribution networks, and in particular to a microgrid protection method and device adapted to high-proportion IIDER access. Background Art

[0002] Renewable energy represented by grid-connected inverter-type distributed power sources are increasingly connected to microgrids that can operate independently and in various modes. As a result, traditional relay protection solutions cannot meet the requirements of protection selectivity and speed in microgrids with high distributed power generation penetration.

[0003] Microgrid protection systems must ensure safe operation in both grid-connected and off-grid modes and respond to faults on the distribution network side and within the microgrid. The huge difference in fault current between grid-connected and off-grid modes poses a challenge to microgrid protection. In grid-connected operation mode, the fault current of the microgrid is large due to the contribution of the main grid to the fault current. In this case, traditional overcurrent protection can sense 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-term current carrying capacity of the semiconductor switch and is usually limited to 1.2-2 times the rated current. In this case, traditional overcurrent protection may refuse to operate due to the failure to reach the starting current value; at the same time, due to the bidirectional current direction in the microgrid, it may malfunction and expand the scope of the fault power outage.

[0004] The existing research on local microgrid protection is still incomplete. For example, the literature [Zeng Dehui. Research on new principles of fault analysis and protection of distribution networks and microgrids containing distributed power sources [D]. South China University of Technology, 2016] proposed to use directional element relays of programmable microprocessors to realize the protection of microgrids in two operating modes. The overall solution relies on the improved relay settings in different scenarios and installation positions. This method is complex to configure and the protection action time is long. It can only be used as backup protection; the literature [Zhang Erjia. Research on principles and schemes of multi-layer collaborative adaptive protection of microgrids [D]. Shanghai Jiaotong University, 2020. ] proposed a protection scheme of directional overcurrent relays, however, it did 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 system [J]. Automation of Electric Power Systems, 2013, 37(6): 114-120] proposed 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 electric energy during the fault to determine the fault. However, no overall effective configuration scheme is given, and a complete microgrid protection scheme is lacking. As for the protection scheme that relies on communication implementation, the literature [ZAMANI MA, SIDHU TS, YAZDANI A. A Protection Strategy and Microprocessor-Based Relay for Low-Voltage Microgrids[J]. IEEE Transactions on Power Delivery, 2011, 26(3): 1873-1883] proposed a fault direction determination method based on the comparison of the positive sequence current phase of three groups of adjacent protection devices. When determining the fault, it is necessary to compare the information obtained by the three adjacent groups of unit protection modules, and then use the voltage drop on the bus to determine the fault. It is difficult to follow the changes in the microgrid topology. Summary of the invention

[0005] The purpose of the present invention is to provide a microgrid protection method and device that is suitable for high-proportion IIDER access. The method identifies the fault section based on the phase angle difference between the pre-fault voltage and the fault current, and uses the time coordination of the improved inverse time overcurrent protection and the low voltage protection to perform fault removal, forming a complete set of microgrid protection methods. The method can remove the fault on-site in both on-grid and off-grid modes, is independent of communication, and has good economy.

[0006] To achieve the above object, the present invention is implemented by adopting the following technical solutions:

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

[0008] Calculate the phase angle difference between the positive sequence voltage at the busbar before the fault and the positive sequence current protected at 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 forward fault, determine whether to start low voltage protection. If started, the protection will trip the circuit breaker according to the low voltage protection action time and the inherent action time of the circuit breaker.

[0010] Under a forward fault, if it is in a grid-connected operation state, the inverse time overcurrent setting value in the grid-connected state is calculated. If the fault current value is higher than the inverse time overcurrent setting value in the grid-connected state, the microgrid inverse time protection is started. Based on the action time of the inverse time overcurrent protection in the grid-connected state and the inherent action time of the circuit breaker, the protection action is the circuit breaker tripping;

[0011] Under a forward fault, if it 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 started. Based on the action time of the inverse time overcurrent protection in the off-grid state and the inherent action time of the circuit breaker, the protection action occurs when the circuit breaker trips.

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

[0013] ;

[0014] in, is the phase angle difference between the positive sequence voltage at busbar i before the fault and the positive sequence current protected at the output circuit breaker of feeder ij after the fault, is the pre-fault voltage at bus i, It is the post-fault current flowing through the protection at the feeder ij outlet circuit breaker.

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

[0016] if , it is a forward fault; if , it is a reverse fault.

[0017] Preferably, the determining whether to start low voltage protection includes:

[0018] Determine whether the voltage after the fault is lower than the action voltage. If it is lower than the action voltage, start the low voltage protection; the action voltage value range is 0.6~0.85pu.

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

[0020] Adjust according to the step-by-step coordination of the upper and lower levels, starting from the last protection action time, so that the last low voltage protection action time is higher than the inverse time overcurrent protection action time, and then add one to the previous low voltage protection action time. ,in, is the set value.

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

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

[0023] ,

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

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

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

[0027] The inverse time overcurrent setting value at each protection installation near the large power grid side is:

[0028] ;

[0029] The inverse time overcurrent setting value of each protection installation far away from the large power grid side is:

[0030] ,

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

[0032] Preferably, the action time of the inverse time overcurrent protection in the grid-connected state is calculated as follows:

[0033] ;

[0034] Among them, t is the action time of inverse time overcurrent protection, The in-zone fault acceleration factor representing the combined phase angle difference and measured impedance, , is the time setting coefficient of feeder ij in the grid-connected state, To protect the installation from fault current, To protect the measured impedance at the installation location, To protect the line impedance from the installation location to the end of the feeder.

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

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

[0037] ;

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

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

[0040] If it is the protection of the interconnecting feeder, it is calculated as follows:

[0041] ,

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

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

[0044] ;

[0045] Among them, t is the action time of inverse time overcurrent protection, The in-zone fault acceleration factor representing the combined phase angle difference and measured impedance, , is the time setting coefficient of feeder ij in off-grid state, To protect the installation from fault current, To protect the measured impedance at the installation location, To protect the line impedance from the installation location to the end of the feeder.

[0046] In a second aspect, the present invention provides a microgrid protection device adapted to high proportion of IIDER access, which is used to implement the above-mentioned microgrid protection method adapted to high proportion of IIDER access, and the device includes:

[0047] A judgment module, used to calculate the phase angle difference between the positive sequence voltage at the bus before the fault and the positive sequence current protected at the feeder outlet circuit breaker after the fault, and judge 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 start the low voltage protection under a forward fault. If it is started, the protection action 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 for forward fault. If it is in the grid-connected operation state, the inverse time overcurrent setting value in the grid-connected state is calculated. If the fault current value is higher than the inverse time overcurrent setting value in the grid-connected state, the microgrid inverse time protection is started. Based on the action time of the inverse time overcurrent protection in the grid-connected state and the inherent action time of the circuit breaker, the protection action is the circuit breaker tripping;

[0050] The off-grid operation protection action module is used for forward fault. If it is in the off-grid operation 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 started. Based on the action time of the inverse time overcurrent protection in the off-grid state and the inherent action time of the circuit breaker, the protection action is the circuit breaker tripping.

[0051] In a third aspect, the present invention provides a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which, when executed by a computing device, cause the computing device to perform any of the methods described above.

[0052] In a fourth aspect, 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, and the one or more programs include instructions for executing any of the methods described above.

[0053] The beneficial effects of the present invention are:

[0054] The present invention proposes a microgrid protection method with high-proportion IIDER access, which uses the phase angle difference between the voltage before the fault and the current after the fault to judge the fault direction, and improves the action equation of the inverse time overcurrent protection by combining the phase angle difference and the fault acceleration factor of the measured impedance, thereby reducing the protection action time and improving the quickness of the protection; in view of the problem that the improved scheme has a small fault current and the protection refuses to operate in the off-grid state, a low-voltage protection criterion is set with the phase angle difference criterion as an auxiliary, thereby obtaining a microgrid protection scheme that combines the improved inverse time overcurrent protection and low voltage protection. The method can selectively remove faults in the microgrid on-grid / off-grid mode based on local information, does not rely on communication, can adapt to changes in the topology structure, and has good economic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0056] Figure 2 It is a grid-connected microgrid model provided by Embodiment 2 of the present invention;

[0057] Figure 3 is an inverse time overcurrent protection action time curve in a grid-connected state provided by Embodiment 2 of the present invention;

[0058] Figure 4 This is the off-grid microgrid model provided by Example 3 of the present invention. DETAILED DESCRIPTION

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

[0060] It should be noted that the term "one embodiment" or "embodiment" of the present invention refers to a specific feature, structure or characteristic that can be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

[0061] It should be emphasized here that the step marks mentioned below are not intended to limit the order of the steps, but it should be understood that the steps can be executed in the order mentioned in the embodiment, or in a different order from the embodiment, or several steps can be executed simultaneously.

[0062] The specific embodiments of the present invention are described in further detail below in conjunction with the accompanying drawings. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0063] Example 1

[0064] This embodiment 1 provides a microgrid protection method suitable for high-proportion IIDER access, see Figure 1 The 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 difference between the positive sequence voltage at bus i before the fault and the positive sequence current at protection ij after the fault: ,in, is the pre-fault voltage at bus i, To protect the post-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 judgment method is as follows (1):

[0068] (1)

[0069] if ,Right now If greater than 0, it is a positive fault and go to step 4; ,Right now If it is less than 0, it is a reverse fault, and then return to step 1.

[0070] 4. Determine whether the voltage after the fault is lower than the action voltage. If it is lower than this set value, start the low voltage protection and go to step 5. If not, return to step 1.

[0071] The action voltage of low voltage protection in distribution network usually ranges from 0.6 to 0.85 pu. In this method, the action value of low voltage protection is 0.85 pu.

[0072] At the same time, determine whether the microgrid is in a grid-connected operation state. If it is in a grid-connected operation state, calculate the inverse time overcurrent setting value in the grid-connected state; if not, calculate the inverse time overcurrent setting value in the off-grid state, and enter step 6.

[0073] 5. Start timing according to the low voltage protection action time. When the action time is up, the protection will act on the outlet circuit breaker and go to step 8;

[0074] In this step, the low voltage protection action time is determined as follows:

[0075] The setting is carried out in a step-by-step manner, starting from the last action time, so that the last low voltage protection action time is higher than the inverse time overcurrent protection action time, and the low voltage protection setting time is increased by one. .in, is the set value, usually =0.2~0.5s.

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

[0077] 7. Start the microgrid inverse time protection and calculate the inverse time overcurrent setting time. Start timing, and when the setting time is up, the protection will act on the outlet circuit breaker and go to step 8;

[0078] 8. Wait for the inherent action time of the circuit breaker. When the time is up, go to step 9;

[0079] 9. The protection action occurs when the circuit breaker trips and the process ends.

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

[0081] (2)

[0082] in: The in-zone fault acceleration factor representing the combined phase angle difference and measured impedance, .

[0083] Where: t is the inverse time overcurrent setting time, is the time setting coefficient of feeder ij in the grid-connected state; is the inverse time overcurrent setting value of feeder ij in the grid-connected state; To protect against fault current at the installation; To protect the measured impedance at the installation location; It is the line impedance from the protection installation to the end of the feeder. and The value needs to be determined according to the parameter setting of the inverse time overcurrent protection in the grid-connected state.

[0084] by Figure 2 Taking the grid-connected microgrid model shown in FIG1 as an example, the feeder with one end connected to the busbar and the other end directly connected to the load or IIDER is recorded as a branch feeder (including load feeders and distributed generation feeders), and the feeder with both ends connected to the busbar is recorded as a tie feeder.

[0085] The feeder numbers are defined as follows:

[0086] In feeder ij, i refers to the bus number and j refers to the line number on the bus, for example Figure 2 The feeder A1 in the figure indicates the line numbered 1 connected to the bus numbered A, and the protection A1 indicates the protection at the outlet circuit breaker of the feeder A1. On the interconnecting feeder, in order to distinguish the protection at the outlet circuit breakers on both sides, the numbers on both sides are different, such as Figure 2 A3 and B1 in the table.

[0087] The parameters of the inverse time overcurrent protection in the grid-connected state are set as follows:

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

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

[0090] (3)

[0091] Where: Represents the reliability coefficient, ranging from 1.25 to 1.5; Indicates the self-starting coefficient, the value should be greater than 1; Indicates the circuit breaker return coefficient, the value should be less than 1; Indicates the maximum load current when feeder ij operates normally.

[0092] When a load feeder fails, the line outlet protection does not need to wait, and the protection action time is the factory inherent action time of the circuit breaker, that is, the factory inherent action time of the circuit breaker. , It is the factory-set action time of the circuit breaker.

[0093] B. If it is the protection of distributed power feeder

[0094] The distributed power feeder needs to transmit current when the system is in normal grid-connected operation; when a fault occurs on the distributed power feeder, the power grid and other distributed power sources provide short-circuit current to the fault point, and the current direction detected at the protection installation is opposite to the normal state. To ensure that the circuit breaker at the outlet of the distributed power feeder can operate reliably and quickly when the distributed power feeder fails, the starting current of the distributed power feeder can be selected as 0.

[0095] When a distributed power feeder fails, the line outlet protection does not need to wait and acts at the fastest speed. The protection action time is the factory-set action time of the circuit breaker. , It is the factory-set action time of the circuit breaker.

[0096] C. If it is the protection of the interconnection feeder

[0097] In the grid-connected state, the setting current value of each protection installation near the large grid side, the starting current of protection A4, A3 and B3 can be set according to formula (3).

[0098] In the grid-connected state, the set current value of each protection installation away from the large power grid side, protection D1, B1, C1 set the starting current according to parameters such as source-to-load ratio, as shown in formula (4),

[0099] (4)

[0100] Where: It is the ratio of the installed capacity of the distributed generation at the end of the interconnection feeder to the maximum load capacity; It is the maximum load current flowing through the protection at the feeder ij outlet circuit breaker during normal operation.

[0101] For the coordination of protection time, the inverse time overcurrent setting value of B3 is It means that according to the selectivity requirement, when a three-phase metallic short circuit fault occurs at the outlet of line C2, the action time of protection B3 is higher than that of protection C2 by △t. Substituting into formula (2), the time constant of protection B3 can be obtained, as shown in formula (5):

[0102] (5)

[0103] In the formula, is the fault current when a three-phase metallic short circuit occurs at the end of C2. When a three-phase metallic short circuit occurs at the outlet of B3 line, the action time of protection A3 is higher than that of protection B3 by △t. By analogy, the action time of all protections can be calculated. After setting, the time coordination relationship on the interconnection feeder is as follows: Figure 3 shown.

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

[0105] (6)

[0106] in: The in-zone fault acceleration factor representing the combined phase angle difference and measured impedance, .

[0107] Where: t is the inverse time overcurrent setting time; is the time setting coefficient of feeder ij in off-grid state; is the inverse time overcurrent setting value of feeder ij in the off-grid state; To protect against fault current at the installation; To protect the measured impedance at the installation location; It is the line impedance from the protection installation to the end of the feeder. and The value needs to be determined according to the parameter setting of the inverse time overcurrent protection in the off-grid state.

[0108] by Figure 4 Taking the off-grid microgrid model shown in FIG1 as an example, the feeder with one end connected to the busbar and the other end directly connected to the load or IIDER is recorded as a branch feeder (including load feeders and distributed generation feeders), and the feeder with both ends connected to the busbar is recorded as a tie feeder.

[0109] The parameters of the inverse time overcurrent protection in the off-grid state are set as follows:

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

[0111] For the load feeder, the normal current and fault current have the same direction but the current magnitude changes. The inverse time overcurrent setting value is set according to formula (7):

[0112] (7)

[0113] Where: Represents the reliability coefficient, ranging from 1.25 to 1.5; Indicates the self-starting coefficient, the value should be greater than 1; Indicates the circuit breaker return coefficient, the value should be less than 1; Indicates the maximum load current when feeder ij operates normally.

[0114] When a load feeder fails, the line outlet protection does not need to wait, and the protection action time is the factory inherent action time of the circuit breaker, that is, the factory inherent action time of the circuit breaker .

[0115] B. If it is the protection of distributed power feeder

[0116] The distributed power feeder needs to transmit current when the system is in normal off-grid operation; when a fault occurs on the distributed power feeder, other distributed power sources provide short-circuit current to the fault point, and the current direction detected at the protection installation is opposite to the normal state. To ensure that the circuit breaker at the outlet of the distributed power feeder can operate reliably and quickly when the distributed power feeder fails, the starting current of the distributed power feeder can be selected as 0.

[0117] When a distributed power feeder fails, the line outlet protection does not need to wait and acts at the fastest speed. The protection action time is the factory-set action time of the circuit breaker. , It is the factory-set action time of the circuit breaker.

[0118] C. If it is the protection of the interconnection feeder

[0119] The set current value of each protection installation in the off-grid state, protection A4, A3, B3, D1, B1 and C1 set the starting current according to parameters such as source-to-load ratio, as shown in formula (8),

[0120] (8)

[0121] Where: It is the ratio of the installed capacity of the distributed generation at the end of the interconnection feeder to the maximum load capacity; It is the maximum load current flowing through the protection at the feeder ij outlet circuit breaker during normal operation.

[0122] For the coordination of protection time, the starting current of B3 is It means that according to the selectivity requirement, when the most serious fault occurs at the outlet of line C2, the action time of protection B3 is higher than that of protection C2 by △t. Substituting into formula (2), the time constant of protection B3 can be obtained, as shown in formula (9),

[0123] (9)

[0124] When the most serious fault occurs at the B3 line outlet, the action time of protection A3 is higher than that of protection B3 by △t. By analogy, the action time of all protections can be calculated. After adjustment, the time coordination relationship on the interconnection feeder is Figure 3 similar.

[0125] Example 2

[0126] Based on the microgrid method of the above embodiment 1, this embodiment 2 is based on Figure 2 Taking the F5 fault in the example, the whole protection action process in the grid-connected state is explained:

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

[0128] 2. When a fault occurs, the amplitude and phase angle of the memory voltage and memory current are enabled to 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 , it is determined that the microgrid is in grid-connected operation state, and protection A3 enters step 6; , it is determined that the microgrid is in grid-connected operation state, and protection B1 enters step 6;

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

[0131] 5. Protection A3 and B1 start timing at 0.4s (the time set for low voltage protection). When the set time is up, the protection acts on A3 and B1 circuit breakers and goes to step 9;

[0132] 6. Select the setting value of inverse time overcurrent protection in the grid-connected state , , , , go to step 7;

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

[0134] 8. Start the microgrid inverse time protection and calculate the inverse time overcurrent setting time of protection A3 and B1 in the microgrid grid-connected state according to equations (10) and (11). , , assuming , . Start timing, when the set time is up, the protection action is on the A3 and B1 circuit breakers, and go to step 9;

[0135] (10)

[0136] (11)

[0137] 9. Protection B1 receives the 0.2s action command first, and waits for the inherent action time of B1 circuit breaker. When the time is up, it goes to step 10. Protection A3 receives the 0.3s action command first, and waits for the inherent action time of A3 circuit breaker. When the time is up, it goes to step 10.

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

[0139] by Figure 2 Take the F5 fault in the simulation as an example, and the results are as follows:

[0140] Build in PSCAD Figure 2The microgrid simulation model with IIDER is shown in the figure. The voltage level of the microgrid is 10kV, the frequency is 50Hz, and it is connected to the large power grid through a 10kV / 110kV step-up transformer. The distributed power sources all adopt the PQ control strategy with low voltage ride-through capability. The capacity of IIDER1-IIDER3 is 3MW, and the maximum fault current is 1.2 times the rated current. The length of the interconnection feeder is 2km, the length of the load feeder is 0.2km, the length of the distributed power feeder is 0.1km, and the line impedance Z l =(0.125+j0.405)Ω / km. The capacity of each load is 3MV·A, and the power factor is 0.85. Assume ∆t=0.2s, t b =0.04s. The F5 fault point is divided into the distance protection A3 line 1800m and the distance protection B1 line 1800m.

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

[0142] Table 1 Parameters of protection A3 and B1 in grid-connected state

[0143]

[0144] Table 2 Action of protection A3 and B1 in grid-connected state

[0145]

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

[0147] Example 3

[0148] Based on the microgrid method of the above embodiment 1, this embodiment 3 is based on Figure 4 Taking the F3 fault in the example, the whole action flow in the off-grid state is explained:

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

[0150] 2. When a fault occurs, the amplitude and phase angle of the memory voltage and memory current are enabled to 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 , it is determined that the microgrid is in off-grid operation state, and protection D2 enters step 6.

[0152] 4. Protect the voltage at D2 to be lower than 0.85pu, start the low voltage protection and go to step 5.

[0153] 5. Protection D2 starts timing at 0.2s (the set time for low voltage protection). When the set time is up, the protection operates on D2 circuit breaker and goes to step 9.

[0154] 6. Select the setting value of the inverse time overcurrent protection in the off-grid state , , go to step 7.

[0155] 7. Judgment , proceed to step 8.

[0156] 8. Start the microgrid inverse time protection and calculate the action time of the inverse time overcurrent protection of protection D2 in the off-grid state according to formula (12) , assuming . Start timing, when the set time is up, the protection action is on the D2 circuit breaker, and go to step 9;

[0157] (12)

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

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

[0160] by Figure 4 Take the F3 fault in the simulation as an example, and the results are as follows:

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

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

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

[0164]

[0165] A three-phase and two-phase short-circuit fault is set at 200m away from the protection D2 line, and the protection action is shown in Table 4.

[0166] Table 4 Action of protection D2 in grid-connected state

[0167]

[0168] Example 4

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

[0170] A judgment module, used to calculate the phase angle difference between the positive sequence voltage at the bus before the fault and the positive sequence current protected at the feeder outlet circuit breaker after the fault, and judge 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 start the low voltage protection under a forward fault. If it is started, the protection action 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 for forward fault. If it is in the grid-connected operation state, the inverse time overcurrent setting value in the grid-connected state is calculated. If the fault current value is higher than the inverse time overcurrent setting value in the grid-connected state, the microgrid inverse time protection is started. Based on the action time of the inverse time overcurrent protection in the grid-connected state and the inherent action time of the circuit breaker, the protection action is the circuit breaker tripping;

[0173] The off-grid operation protection action module is used for forward fault. If it is in the off-grid operation 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 started. Based on the action time of the inverse time overcurrent protection in the off-grid state and the inherent action time of the circuit breaker, the protection action is the circuit breaker tripping.

[0174] It is worth pointing out that the device embodiment corresponds to the above-mentioned method embodiment, and the implementation methods of the above-mentioned method embodiments are all applicable to the device embodiment and can achieve the same or similar technical effects, so they will not be repeated here.

[0175] Example 5

[0176] This embodiment 5 provides a computer-readable storage medium storing one or more programs, wherein the one or more programs include instructions, which, when executed by a computing device, enable the computing device to execute the microgrid protection method adapted to a high proportion of IIDER access according to the above-mentioned embodiment 1.

[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 are configured to be executed by the one or more processors, and the one or more programs include instructions for executing the microgrid protection method that adapts to a high proportion of IIDER access according to the above-mentioned embodiment 1.

[0179] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present application may adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program codes.

[0180] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0181] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture including an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0182] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions 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 rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does 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 of IIDER access, characterized in that: include: Calculate the phase angle difference between the positive sequence voltage at the busbar before the fault and the positive sequence current protected at 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; Under forward fault, determine whether to start low voltage protection. If started, the protection will trip the circuit breaker according to the low voltage protection action time and the inherent action time of the circuit breaker. Under a forward fault, if it is in a grid-connected operation state, the inverse time overcurrent setting value in the grid-connected state is calculated. If the fault current value is higher than the inverse time overcurrent setting value in the grid-connected state, the microgrid inverse time protection is started. Based on the action time of the inverse time overcurrent protection in the grid-connected state and the inherent action time of the circuit breaker, the protection action is the circuit breaker tripping; Under a forward fault, if it 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 started. Based on the action time of the inverse time overcurrent protection in the off-grid state and the inherent action time of the circuit breaker, the protection action occurs when the circuit breaker trips.

2. A microgrid protection method adapted to high proportion of IIDER access according to claim 1, characterized in that: The calculation of the phase angle difference between the positive sequence voltage at the busbar before the fault and the positive sequence current protected at the feeder outlet circuit breaker after the fault includes: ； in, is the phase angle difference between the positive sequence voltage at busbar i before the fault and the positive sequence current protected at the output circuit breaker of feeder ij after the fault, is the pre-fault voltage at bus i, It is the post-fault current flowing through the protection at the feeder ij outlet circuit breaker.

3. A microgrid protection method adapted to high proportion of IIDER access according to claim 2, characterized in that: Judging whether it is a forward fault or a reverse fault based on the phase angle difference includes: if , it is a forward fault; if , it is a reverse fault.

4. A microgrid protection method adapted to high proportion of IIDER access according to claim 3, characterized in that: The determining whether to start low voltage protection includes: Determine whether the voltage after the fault is lower than the action voltage. If it is lower than the action voltage, start the low voltage protection; the action voltage value range is 0.6~0.85pu.

5. A microgrid protection method adapted to high proportion of IIDER access according to claim 4, characterized in that: The low voltage protection action time is determined as follows: Adjust according to the step-by-step coordination of the upper and lower levels, starting from the last protection action time, so that the last low voltage protection action time is higher than the inverse time overcurrent protection action time, and then add one to the previous low voltage protection action time. ,in, is the set value.

6. A microgrid protection method adapted to high proportion of IIDER access according to claim 3, characterized in that: The calculation of the inverse time overcurrent setting value in the grid-connected state includes: If it is the protection of the load feeder, the inverse time overcurrent setting value is: ， in, is the inverse time overcurrent setting value of feeder ij in the grid-connected state, represents the reliability coefficient, represents the self-starting coefficient, Indicates the circuit breaker return factor, Indicates the maximum load current of feeder ij during normal operation; If it is the protection of distributed power feeder, the inverse time overcurrent setting value is selected as 0; If it is the protection of the interconnecting feeder, then, The inverse time overcurrent setting value at each protection installation near the large power grid side is: ； The inverse time overcurrent setting value of each protection installation far away from the large power grid side is: ， in, It is the ratio of the installed capacity of the distributed power source at the end of the interconnection feeder to the maximum load capacity. It is the maximum load current flowing through the protection at the feeder ij outlet circuit breaker during normal operation.

7. A microgrid protection method adapted to high proportion of IIDER access according to claim 6, characterized in that: The action time of the inverse time overcurrent protection in the grid-connected state is calculated as follows: ； Among them, t is the action time of inverse time overcurrent protection, The in-zone fault acceleration factor representing the combined phase angle difference and measured impedance, , is the time setting coefficient of feeder ij in the grid-connected state, To protect the installation from fault current, To protect the measured impedance at the installation location, To protect the line impedance from the installation location to the end of the feeder.

8. A microgrid protection method adapted to high proportion of IIDER access according to claim 3, characterized in that: The calculating of the inverse time overcurrent setting value in the off-grid state includes: If it is the protection of the load feeder, the inverse time overcurrent setting value is: ； in, is the inverse time overcurrent setting value of feeder ij in the off-grid state, represents the reliability coefficient, represents the self-starting coefficient, Indicates the circuit breaker return coefficient, Indicates the maximum load current of feeder ij during normal operation; If it is the protection of distributed power feeder, the inverse time overcurrent setting value is selected as 0; If it is the protection of the interconnecting feeder, it is calculated as follows: ， in, It is the ratio of the installed capacity of the distributed power source at the end of the interconnection feeder to the maximum load capacity. It is the maximum load current flowing through the protection at the feeder ij outlet circuit breaker during normal operation.

9. A microgrid protection method adapted to high proportion of IIDER access according to claim 8, characterized in that: The action time of the inverse time overcurrent protection in the off-grid state is calculated as follows: ； Among them, t is the action time of inverse time overcurrent protection, The in-zone fault acceleration factor representing the combined phase angle difference and measured impedance, , is the time setting coefficient of feeder ij in off-grid state, To protect the installation from fault current, To protect the measured impedance at the installation location, To protect the line impedance from the installation location to the end of the feeder.

10. A microgrid protection device adapted to high proportion of IIDER access, characterized in that: The device is used to implement the microgrid protection method adapted to high-proportion IIDER access as described in any one of claims 1 to 9, comprising: A judgment module, used to calculate the phase angle difference between the positive sequence voltage at the bus before the fault and the positive sequence current protected at the feeder outlet circuit breaker after the fault, and judge 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 start the low voltage protection under a forward fault. If it is started, the protection action 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 for forward fault. If it is in the grid-connected operation state, the inverse time overcurrent setting value in the grid-connected state is calculated. If the fault current value is higher than the inverse time overcurrent setting value in the grid-connected state, the microgrid inverse time protection is started. Based on the action time of the inverse time overcurrent protection in the grid-connected state and the inherent action time of the circuit breaker, the protection action is the circuit breaker tripping; The off-grid operation protection action module is used for forward fault. If it is in the off-grid operation 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 started. Based on the action time of the inverse time overcurrent protection in the off-grid state and the inherent action time of the circuit breaker, the protection action is the circuit breaker tripping.

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

12. 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, and the one or more programs include instructions for executing any of the methods according to claims 1 to 9.

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