Micro-grid protection method based on measured impedance amplitude-phase variation

Abstract

The invention relates to the technical field of power system protection, relates to a micro-grid protection method based on measured impedance amplitude-phase variation, and provides a protection method based on measured impedance amplitude-phase variation for the protection problem of a micro-grid containing an inverter distributed power supply (IIDG). According to the method, voltage and current measured values at the two ends of a protection circuit in the micro-grid are collected in real time, a criterion is started by using voltage drop and phase current abrupt change to judge a fault, and a criterion of a measured impedance module value is adjusted by combining a zero-sequence current detection result. And when a module value criterion is met, further determining a fault section by adopting a phase angle criterion. And if the communication fails or the data is lost, self-adaptive over-current backup protection or zero-sequence current measurement is started to carry out fault positioning. The method can adapt to the grid-connected operation mode and the off-grid operation mode of the micro-grid, the fault type and the fault section are accurately judged, safe and stable operation of the micro-grid is ensured, protection sensitivity and selectivity are improved, and the method has important practical application value.

Description

Technical Field

[0001] The present invention relates to the technical field of power system protection, and in particular to a microgrid protection method based on measuring impedance amplitude and phase variation. Background Art

[0002] The power grid is actively transforming to an innovative structural form and efficient operation mode. Among them, the smart microgrid with the core of absorbing new energy has become a key path for development. As a micro power system composed of distributed power sources and local loads, the microgrid not only directly serves the user's power demand, but also bears the heavy responsibility of optimizing the energy structure. However, the inverter-type distributed power source (IIDG) widely used in microgrids has unique volatility, intermittent and nonlinear characteristics, and the complex fault scenarios brought about by the dual-mode operation of microgrids on-grid and off-grid are severe challenges to the selectivity, sensitivity and speed of traditional protection schemes.

[0003] At present, microgrid protection strategies are mainly based on local information and communication, but both have limitations. Among them, the protection method based on local information focuses on using local measurement data to achieve microgrid protection by transforming or upgrading traditional protection technologies. Its advantages are simple implementation, high cost-effectiveness, and no need to rely on communication. However, the access of IIDG increases the complexity of fault characteristics and the diversity of scenarios, making it difficult to fully respond to various fault conditions of microgrids based on local information alone.

[0004] The communication-based protection method centrally processes the information of each node inside and outside the microgrid and relies on the comparative analysis of fault information to achieve accurate positioning. Although the multi-terminal information interaction strategy is effective, it is highly dependent on the perfection and stability of the communication network. As the scale of the microgrid expands, the communication burden and cost also increase. Nevertheless, with the continuous advancement of communication technology, the communication-based protection method has shown stronger adaptability and potential.

[0005] In summary, it is particularly important to conduct in-depth research on the fault characteristics of microgrids after IIDG access and to develop efficient protection methods that can adapt to the dual-mode operation of microgrids in grid-connected and off-grid modes. Summary of the invention

[0006] The present invention provides a microgrid protection method based on measuring impedance amplitude and phase changes, which can effectively improve the performance and reliability of microgrid protection through refined fault feature recognition and rapid response mechanism.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A microgrid protection method based on measuring impedance amplitude and phase change comprises the following steps:

[0009] Real-time collection of voltage and current measurements at both ends of the protection line in the microgrid;

[0010] The voltage measurement value and the current measurement value are evaluated respectively by the protection start criterion, and whether the protection line is faulty is determined;

[0011] Calculate the measured impedance at both ends of the protection line based on the voltage measurement value and the current measurement value, and perform zero-sequence current detection;

[0012] Determine the modulus criterion of the measured impedance at both ends of the protection line based on the detection result of the zero-sequence current;

[0013] If the modulus criterion is met, the impedance phase angle difference measured before and after the fault is screened and judged through the phase angle criterion to determine the fault section and isolate the fault;

[0014] If the measured values ​​at both ends of the protected line cannot be read, the overcurrent backup protection is activated.

[0015] Further, the voltage measurement value and the current measurement value are evaluated respectively by the protection start criterion, including the following steps:

[0016] The voltage measurement is evaluated by setting the voltage sag threshold, and the following voltage sag start criteria are used:

[0017] ΔU>10%U N ;

[0018] Among them, ΔU is the voltage drop value, U N is the rated voltage;

[0019] The current measurement value is evaluated by setting the phase current mutation threshold, and the following phase current mutation start criterion is used:

[0020] Δi≥K S I N ;

[0021] Wherein, Δi=||i(k)-i(kN)|-|i(kN)-i(k-2N)||, i(k) is the current sampling value of the phase current at the current moment k; N is the number of sampling points for each cycle, I N is the rated current effective value, K s is the starting coefficient;

[0022] When the voltage drop and the phase current mutation amount meet the voltage drop start criterion and the phase current mutation amount start criterion respectively, the protection line fault is determined.

[0023] Furthermore, the voltage and current measurements at both ends of the protection line in the microgrid are collected in real time, including the voltage at the bus A end. Current flowing through terminal A Bus B terminal voltage Current flowing through terminal B

[0024] Further, determining the modulus criterion of the impedance measured at both ends of the protection line based on the detection result of the zero-sequence current includes the following steps:

[0025] If the zero-sequence current is not detected, the modulus criterion for measuring impedance is as follows:

[0026] |Z m |>Z set ;

[0027] If zero-sequence current is detected, the modulus criterion of the measured impedance is as follows:

[0028] K m |Z m |>Z set ;

[0029] Among them, |Z m | is the impedance modulus change before and after the fault, Z set is the impedance threshold, K m is the compensation coefficient.

[0030] Further, the compensation coefficient K of the measured impedance is calculated m , including the impedance modulus compensation coefficient K at the busbar A end Am and the impedance modulus compensation coefficient K at the busbar B end Bm , where the calculation is based on the busbar A end as an example, and includes the following steps:

[0031] Obtain the measured voltages at the bus A and bus B terminals when there is a transition resistance and a fault occurs at the protection line f1. The method for obtaining the measured voltages at both ends of the bus is the same. Taking the bus A terminal as an example, the following formula is used:

[0032]

[0033] Among them, Z Af1 is the line impedance from bus A to fault point f1;

[0034] Get the measured impedance Z at the A end of the bus Am , the specific formula is as follows:

[0035]

[0036] in, To measure current The zero-sequence component of the line impedance from bus A to the fault point f1 is Z1, Z2, and Z0 respectively, and Z1 = Z2. K is the zero-sequence current compensation coefficient, K = (Z0-Z1) / 3Z1.

[0037] Get the impedance modulus compensation coefficient K at the A end of the bus Am , the specific formula is as follows:

[0038]

[0039] Among them, θ m is the phase angle of the measured impedance when a fault occurs at f1 without considering the transition resistance, θ Am To measure the impedance Z Am The phase angle of α is the additional impedance angle.

[0040] Furthermore, the phase angle criterion of the busbar impedance measurement at both ends of the protection line is as shown in the following formula:

[0041] or

[0042] The difference of impedance angle measured at the busbars at both ends of the fault section is 0 and 180° respectively. is the phase angle deviation during the measurement process.

[0043] Further, when the measured values ​​at both ends of the protection line cannot be read, the overcurrent backup protection is started, including the following steps:

[0044] The adaptive overcurrent protection strategy is used for short-circuit faults, and the specific action current calculation formula is as follows:

[0045]

[0046] in, To protect the operating current, K Z is the reliability coefficient, ranging from 1.1 to 1.2. is the positive sequence voltage at bus terminal A, Z 11 is the equivalent impedance from the fault point f1 to the busbar A end, and Z4 is the equivalent impedance of the line downstream of the fault point;

[0047] For single-phase grounding faults, zero-sequence current measurement based on zero-sequence current amplitude and phase information is used to locate the fault. The zero-sequence current measurement is calculated using the following formula:

[0048] T i =I0sign(sinδ);

[0049] Among them, T i is the zero-sequence current measurement, I0 is the zero-sequence current modulus of the line, δ is the angle of the zero-sequence current relative to the neutral point voltage, when the T of a certain line i <0 and the zero-sequence current modulus I0 is the largest, indicating that the line is faulty.

[0050] A microgrid protection device based on measuring impedance amplitude and phase change, comprising:

[0051] A data acquisition module is used to collect voltage and current measurements at both ends of the protection line in the microgrid in real time;

[0052] A protection start judgment module is used to evaluate the voltage measurement value and the current measurement value respectively according to the protection start judgment criterion, and determine whether the protection line is faulty;

[0053] An impedance and zero-sequence current calculation module, used to calculate the measured impedance at both ends of the protection line based on the voltage measurement value and the current measurement value, and perform zero-sequence current detection;

[0054] A module for determining a modulus value criterion, used for determining a modulus value criterion for measuring impedance at both ends of a protection line based on a detection result of a zero-sequence current;

[0055] The fault judgment and isolation module is used to screen and judge the impedance phase angle difference measured before and after the fault through the phase angle judgment when the module value judgment is met, determine the fault section and isolate the fault;

[0056] The backup protection module is used to start the overcurrent backup protection when the measured values ​​at both ends of the protection line cannot be read.

[0057] A computer device includes a memory and a processor. The memory stores a computer program. When the processor executes the computer program, the steps of the microgrid protection method based on measuring impedance amplitude and phase changes are implemented.

[0058] A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the above-mentioned microgrid protection method based on measuring impedance amplitude and phase changes.

[0059] The beneficial effects of the present invention are:

[0060] 1. The method proposed in the present invention can adapt to both on-grid and off-grid operation modes of the microgrid, and at the same time considers the influence of transition resistance on the module value criterion and corrects the module value criterion.

[0061] 2. The method proposed in the present invention takes into account the situation where a serious fault causes a sharp drop in voltage amplitude, and adds a starting criterion to ensure reliable starting of protection.

[0062] 3. The present invention takes into account the case of communication failure and configures additional adaptive positive sequence current protection and zero sequence overcurrent protection as backup protection to ensure reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0064] Figure 1 It is a flow chart of a microgrid protection method based on measuring impedance amplitude and phase variation in the present invention;

[0065] Figure 2 It is a structural schematic diagram of the microgrid in the present invention;

[0066] Figure 3 A schematic diagram of the impedance vector relationship measured when the protection line fails in the present invention;

[0067] Figure 4 Schematic diagram of a typical 10kV microgrid simulation model constructed in the present invention;

[0068] Figure 5 It is a schematic diagram of the relationship between the phase current mutation waveform and the threshold value in the present invention. DETAILED DESCRIPTION

[0069] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0070] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

[0071] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0072] The present invention considers that the volatility, intermittency and nonlinear characteristics of the inverter-type distributed power source (IIDG) increase the complexity and diversity of microgrid faults, making it difficult for traditional protection schemes to fully cope with them; the microgrid structure containing multiple IIDGs leads to a variety of fault scenarios, requiring protection methods to adapt to its two modes of operation: grid-connected and off-grid. However, the existing overcurrent protection cannot adapt to the two modes of operation of the microgrid, and the fault current of the IIDG is limited to 2 times the rated current, which will cause the protection to refuse to operate; the existing differential protection has high requirements for synchronization error, and when the communication fails, the protection will refuse to operate; the existing distance protection method is more difficult to set the protection when considering the transition resistance.

[0073] In view of the problem that microgrid protection needs to consider both on-grid and off-grid operation modes and communication failure, the present invention proposes a microgrid main protection method based on measuring impedance amplitude and phase change, which cooperates with adaptive overcurrent backup protection to correctly distinguish faults inside and outside the protection area in both on-grid and off-grid operation modes. The microgrid protection method based on measuring impedance amplitude and phase change includes the following steps:

[0074] Collect the voltage and current measurements at both ends of the protection line in the microgrid in real time; evaluate the voltage and current measurements respectively through the protection start criterion, and determine whether the protection line is faulty; calculate the measured impedance at both ends of the protection line based on the voltage and current measurements, and perform zero-sequence current detection; determine the modulus criterion of the measured impedance at both ends of the protection line based on the zero-sequence current detection result; if the modulus criterion is met, screen and judge the phase angle difference of the measured impedance before and after the fault through the phase angle criterion, determine the fault section and isolate the fault; if the measured values ​​at both ends of the protection line cannot be read, start the overcurrent backup protection

[0075] See Figure 1 As shown, firstly, the voltage and current measurement values ​​at both ends of the line are collected, and the measurement impedance is calculated according to the measured voltage and the measured current. When the voltage drops and the phase current mutation meets the corresponding criterion, the protection is started; if the measured values ​​at both ends are read, the zero-sequence current detection is performed; otherwise, the overcurrent backup protection is started, and the protection device is activated after the criterion is met. If the zero-sequence current is detected, the compensated modulus criterion is used to screen and judge the size of the measured impedance modulus; otherwise, the original modulus criterion is used for screening and judgment. If the modulus criterion is met, the phase angle criterion is used to screen and judge the phase angle difference of the measured impedance before and after the fault. If the phase angle criterion is met, the fault section is determined and the protection device is activated.

[0076] Among them, ensuring the accuracy and synchronization of data acquisition is the real-time basis of the protection method, and the protection start-up criterion is an important basis for judging whether a microgrid has a fault. By setting the voltage or current threshold, when the measured value exceeds the threshold, it is considered that a fault may occur and the protection program is started. The measured impedance is an important parameter reflecting the line state, which can be calculated by the ratio of voltage and current. Zero-sequence current detection is an effective method for judging ground faults. When zero-sequence current is detected, it indicates that a ground fault may have occurred. The phase angle criterion is an important basis for further determining the fault section. By comparing the phase angle difference of the measured impedance before and after the fault, it is judged whether the fault occurs in the protection area. Finally, when communication fails or data is lost, the overcurrent backup protection needs to be started to ensure the safe operation of the microgrid; the overcurrent backup protection can judge whether a fault occurs according to the amplitude and duration of the current, and take corresponding protection measures.

[0077] The present invention realizes the correct discrimination of faults inside and outside the protection area in both the on-grid and off-grid operation modes of the microgrid by combining the measurement of impedance amplitude and phase change and adaptive overcurrent backup protection; it can adapt to the complex fault characteristics and dual-mode operation mode of the microgrid after IIDG access; by measuring impedance amplitude and phase change and zero-sequence current detection, it can accurately judge the fault type and fault section; when communication fails or data is lost, it can start the overcurrent backup protection to ensure the safe operation of the microgrid.

[0078] In this embodiment, the voltage measurement value and the current measurement value are evaluated respectively by the protection start criterion, comprising the following steps:

[0079] The voltage measurement is evaluated by setting the voltage sag threshold, and the following voltage sag start criteria are used:

[0080] ΔU>10%U N ;

[0081] Among them, ΔU is the voltage drop value, U N is the rated voltage;

[0082] The current measurement value is evaluated by setting the phase current mutation threshold, and the following phase current mutation start criterion is used:

[0083] Δi≥K S I N ;

[0084] Wherein, Δi=||i(k)-i(kN)|-|i(kN)-i(k-2N)||, i(k) is the current sampling value of the phase current at the current moment k; N is the number of sampling points for each cycle, I N is the rated current effective value, K s is the starting coefficient, which is generally taken as 0.15;

[0085] When the voltage drop and the phase current mutation amount meet the voltage drop start criterion and the phase current mutation amount start criterion respectively, the protection line fault is determined.

[0086] It should be noted that voltage drop is a common fault phenomenon in microgrids. When the voltage drop value exceeds the set threshold, it is considered that a fault may occur and the protection program is started. By real-time monitoring of voltage measurements, calculating the voltage drop value, and comparing it with the set threshold, rapid detection of voltage faults can be achieved, providing strong support for the protection of microgrids.

[0087] Furthermore, the phase current mutation is an important indicator reflecting the current change in the line. When a line fault occurs, the current usually changes suddenly. By monitoring the phase current measurement value in real time, calculating the phase current mutation, and comparing it with the set threshold, rapid detection of current faults can be achieved. It should be noted that due to the access of IIDG in the microgrid, the current waveform may change, so the phase current mutation startup coefficient Ks needs to be adjusted according to the actual situation.

[0088] In this embodiment, if Figure 2 The schematic diagram of the microgrid line with a transition resistance grounding fault at f1 is shown. If zero-sequence current is detected, the impedance modulus change is evaluated by constructing a modulus criterion compensation coefficient. It is necessary to collect the relevant electrical quantity information of the protection line. Real-time collection of voltage and current measurement values ​​at both ends of the protection line in the microgrid, including the bus A terminal voltage Current flowing through terminal A Bus B terminal voltage Current flowing through terminal B

[0089] Determining the modulus criterion of the measured impedance at both ends of the protection line based on the detection result of the zero-sequence current includes the following steps:

[0090] The measured impedance modulus values ​​at the busbars on both sides of the fault section change significantly. When the difference between the measured impedance modulus values ​​before and after the fault is greater than the impedance threshold Z set , satisfying the modulus criterion, the general impedance threshold Z set Take 0.3 times the measured impedance in the non-fault state. This value can be adjusted according to the actual situation and protection requirements of the microgrid.

[0091] If the zero-sequence current is not detected, the modulus criterion of the measured impedance is as follows:

[0092] |Z m |>Z set ;

[0093] In microgrid protection, the detection of zero-sequence current is an important basis for judging ground faults. When zero-sequence current is detected, it means that a ground fault may have occurred. At this time, the modulus criterion of the measured impedance needs to be adjusted to more accurately judge the fault.

[0094] If zero-sequence current is detected, a compensation coefficient K is added to the original modulus criterion m , the modulus criterion for measuring impedance is as follows:

[0095] K m |Z m |>Z set ;

[0096] Among them, |Z m | is the impedance modulus change before and after the fault, Z set is the impedance threshold, K m is the compensation coefficient.

[0097] In the above embodiment, the compensation coefficient K of the measured impedance is calculated m , including the impedance modulus compensation coefficient K at the busbar A end Am and the impedance modulus compensation coefficient K at the busbar B end Bm , where the calculation is based on the busbar A end as an example, and includes the following steps:

[0098] Obtain the measured voltage at the bus A and bus B when there is a transition resistance and a fault occurs at the protection line f1. The method for obtaining the measured voltage at both ends of the bus is the same. Figure 2 As shown, taking the bus A end as an example, when there is a transition resistor, when a fault occurs at f1, the short-circuit current in the transition resistor is no longer the current at the protection installation. At this time, the relationship between the measured voltage and the measured current at the protection CB1 can be expressed by the following formula:

[0099]

[0100] Among them, Z Af1 is the line impedance from bus A to fault point f1;

[0101] Get the measured impedance Z at the A end of the bus Am , the specific formula is as follows:

[0102]

[0103] in, To measure current The zero-sequence component of the line impedance from bus A to the fault point f1 is Z1, Z2, and Z0 respectively, and Z1 = Z2. K is the zero-sequence current compensation coefficient, K = (Z0-Z1) / 3Z1.

[0104] When considering the transition resistance, the impedance vector relationship measured during the fault is as follows: Figure 3 As shown, where Z L is the line impedance, θ L It's Z L The phase angle, Z m is the measured impedance when a fault occurs at f1 without considering the transition resistance, θ m It's Z m The phase angle.

[0105] according to Figure 3 The impedance modulus compensation coefficient K at the A end of the busbar is obtained by using the triangle relationship. Am , the specific formula is as follows:

[0106]

[0107] Among them, θ m is the phase angle of the measured impedance when a fault occurs at f1 without considering the transition resistance, θ Am To measure the impedance Z Am The phase angle of α is the additional impedance angle.

[0108] The additional impedance angles for single-phase grounding, two-phase grounding and three-phase grounding faults are respectively expressed as follows:

[0109]

[0110] a≈0°.

[0111] In this embodiment, the phase angle criterion of the busbar measurement impedance at both ends of the protection line is as shown in the following formula:

[0112] or

[0113] Among them, the difference of impedance angle measured at the busbars at both ends of the fault section is 0 and 180° respectively. Considering that there will be errors in the actual system during the measurement process, resulting in a certain deviation in the phase angle, is the phase angle deviation angle during the measurement process. Figure 2 In the scenario, Take 35°.

[0114] In this embodiment, when the measured values ​​at both ends of the protection line cannot be read, the overcurrent backup protection is started, including the following steps:

[0115] The adaptive overcurrent protection strategy is used for short-circuit faults, and the specific action current calculation formula is as follows:

[0116]

[0117] in, To protect the operating current, K Z is the reliability coefficient, ranging from 1.1 to 1.2. is the positive sequence voltage at bus terminal A, Z 11 is the equivalent impedance from the fault point f1 to the bus A end, and Z4 is the equivalent impedance of the line downstream of the fault point. By considering the changes in system voltage and impedance, the protection action current can be adaptively adjusted to improve the sensitivity and selectivity of the protection.

[0118] For single-phase grounding faults, zero-sequence current measurement based on zero-sequence current amplitude and phase information is used to locate the fault. The zero-sequence current measurement is calculated using the following formula:

[0119] T i =I0sign(sinδ);

[0120] Among them, T i is the zero-sequence current measurement, I0 is the zero-sequence current modulus of the line, δ is the angle of the zero-sequence current relative to the neutral point voltage, when the T of a certain line i <0 and the zero-sequence current modulus I0 is the largest, indicating that the line is faulty. Combining the amplitude and phase information of the zero-sequence current can more accurately locate the single-phase grounding fault.

[0121] Through the above backup protection strategy, even in the event of communication failure, the local information can be used to quickly and accurately judge and isolate the faults in the microgrid, ensuring the safe and stable operation of the system.

[0122] In the specific implementation process, the construction Figure 4 The typical 10kV microgrid simulation model shown in Figure 1. The system is connected to the distribution network through a 110 / 10kV main transformer, which is Y / Y connected; there are 4 resistive and inductive loads, with a load size of S Load1 =0.76+j0.25MVA, S Load2 =0.54+j0.26MVA, S Load3 =0.233+j0.092MVA, S Load4 =0.425+j0.263MVA. Using PI type equivalent circuit, the line unit positive sequence impedance Z1 = (0.6+j0.86)Ω / km, negative sequence impedance Z2 = Z1, zero sequence impedance Z0 = 1.5Z1. Line length L1 = 5km, L2 = 1km, L3 = 4km, L4 = 1.5km, L5 = 2.5km, L pcc=2km. When connected to the grid, DG1~DG4 adopt PQ control. When off-grid, DG4 adopts V / f control. The active power reference values ​​are P1=0.4MW, P2=0.2MW, P3=0.3MW, and P4=0.15MW. The reactive power reference value of all inverter-type distributed power sources is 0. DGs all have current limiting modules, and the maximum output current Imax is set to 2 times the rated current.

[0123] 1. Grid-connected operation mode

[0124] 1) Faults within the area

[0125] The microgrid is connected to the grid. For the protection CB1 and CB2 located at both ends of line 1, an intra-area fault occurs at f1 on line 1, which is 1 km away from bus A. The fault time is 0.5s and the duration is 0.1s. The main protection is simulated and verified. The simulation results are shown in Table 1.

[0126] Table 1. Impedance changes under different fault types during grid-connected operation

[0127]

[0128] When the microgrid is connected to the grid, when f1 has a single-phase grounding, two-phase short circuit and three-phase short circuit metallic fault, the difference in the measured impedance modulus at CB1 and CB2 is greater than the set threshold Z set ,The measured impedance phase angle difference meets the phase angle criterion, and the protection can act accurately, indicating that the main protection scheme adopted in this paper can act accurately when the microgrid is connected to the grid.

[0129] 2) Out-of-area faults

[0130] For the protection CB1 and CB2 located at both ends of line 1, an out-of-zone fault occurs at point f2 on line 2 inside the microgrid, which is 0.5 km away from bus B. At this time, the operating performance of protection CB1 and protection CB2 is shown in Table 2.

[0131] Table 2. Action of protection CB1 and CB2 during out-of-zone faults

[0132]

[0133] It can be seen from Table 2 that when the fault occurs at point f2 outside the zone, protections CB1 and CB2 do not operate, which means that the main protection scheme adopted in this paper can ensure accurate operation for faults within the zone and no false operation for faults outside the zone, thus ensuring the selectivity of the main protection.

[0134] 2. Off-grid operation mode

[0135] When the microgrid is off-grid, assuming that a fault occurs at point f1, the main protection scheme is simulated and verified. The simulation results are shown in Table 3.

[0136] Table 3. Impedance changes measured under different fault types during off-grid operation

[0137]

[0138] When the microgrid is in off-grid operation mode, when an in-area fault occurs, the module value criterion and phase angle criterion of the main protection can still be met, and the protection can operate accurately.

[0139] 3. Different transition resistance

[0140] When the microgrid is connected to the grid and a single-phase grounding fault occurs at f1 of line 1, the transition resistance Rg is set to 50Ω, 100Ω, 200Ω, 300Ω, and 500Ω respectively. The anti-transition resistance performance of the main protection is analyzed, and the simulation results are shown in Table 4.

[0141] Table 4. Protection against transition resistance performance

[0142]

[0143] Before the modulus criterion is compensated, the modulus criterion is invalid. After the modulus criterion is compensated, the changes in the measured impedance modulus values ​​on both sides A and B are much greater than the setting threshold Z. set This indicates that the compensated modulus criterion can enable the main protection to operate reliably when a non-metallic grounding fault occurs, and the main protection has a certain transition resistance tolerance capability.

[0144] 4. Backup protection action test

[0145] Assume that a short circuit fault occurs at f1 on line 1, the fault occurrence time is 0.5s, and the fault duration is 0.1s. According to the above adaptive positive sequence overcurrent protection setting, the adaptive positive sequence current setting values ​​corresponding to different fault locations are shown in Table 5.

[0146] Table 5. Adaptive positive sequence current protection setting results

[0147]

[0148] The farther the fault point is from busbar A, the smaller the fault positive sequence current flowing through protection CB5, and the larger the adaptive current protection setting value Iset. The simulation results show that when the fault location exceeds 80% of the line, the adaptive positive sequence current protection may fail and fail to protect the entire length of the line. On this basis, the adaptive II stage protection can be considered.

[0149] Assuming that a single-phase grounding fault occurs at point f1 on line 1, which is 1 km away from bus A, the backup protection criterion based on zero-sequence current amplitude and phase information is simulated and verified. The simulation results show that the zero-sequence current measurement T i=-0.1, which meets the protection criteria, and the protection at the head end of the line can operate accurately.

[0150] 5. Impact of synchronization error on protection

[0151] The main protection based on measuring impedance at both ends of the line needs to compare the amplitude and size of the impedance measured at both ends at the same sampling time, while data synchronization error often affects the phase information and has little effect on the amplitude information.

[0152] This paper uses voltage drop and phase current mutation as the protection start-up criteria. When an in-area fault occurs, the main protection's anti-synchronization error performance is tested with feeder AB as the protection section. The protection start-up element uses the mutation fault detection method. The sampling frequency of the protection device is set to 10kHz, and the phase current mutation start-up threshold is 0.15 times the rated current. Assume that a three-phase short circuit fault occurs at f1 on line 1, 1km away from bus A. The fault occurs at 0.5s, and the A side protection start-up delay is 1ms. The relationship between the phase current mutation waveform and the threshold is as follows: Figure 5 shown.

[0153] The sudden change of the current in phase B on the bus B side reaches the threshold first, and the protection of phase B is started first, with the start time of 0.50382s. At this time, the start time difference of the protection on both sides of the protection section is about 2.82ms, and the protection has a certain ability to resist synchronization errors. In the case of delayed start on one side, the protection on the opposite side can still be effectively started.

[0154] In this embodiment, a microgrid protection device based on measuring impedance amplitude and phase change is provided, including:

[0155] A data acquisition module is used to collect voltage and current measurements at both ends of the protection line in the microgrid in real time;

[0156] A protection start judgment module is used to evaluate the voltage measurement value and the current measurement value respectively according to the protection start judgment criterion, and determine whether the protection line is faulty;

[0157] An impedance and zero-sequence current calculation module, used to calculate the measured impedance at both ends of the protection line based on the voltage measurement value and the current measurement value, and perform zero-sequence current detection;

[0158] A module for determining a modulus value criterion, used for determining a modulus value criterion for measuring impedance at both ends of a protection line based on a detection result of a zero-sequence current;

[0159] The fault judgment and isolation module is used to screen and judge the impedance phase angle difference measured before and after the fault through the phase angle judgment when the module value judgment is met, determine the fault section and isolate the fault;

[0160] The backup protection module is used to start the overcurrent backup protection when the measured values ​​at both ends of the protection line cannot be read.

[0161] In this embodiment, a computer device is provided, including a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the method for constructing an expert database of fault characteristic information of converter stations are implemented.

[0162] In this embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the steps of the method for constructing an expert database of fault characteristic information of converter stations are implemented.

[0163] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties.

[0164] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited to this.

[0165] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0166] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A microgrid protection method based on measuring impedance amplitude and phase change, characterized in that: The following steps are involved: Real-time collection of voltage and current measurements at both ends of the protection line in the microgrid; The voltage measurement value and the current measurement value are evaluated respectively by the protection start criterion, and whether the protection line is faulty is determined; Calculate the measured impedance at both ends of the protection line based on the voltage measurement value and the current measurement value, and perform zero-sequence current detection; Determine the modulus criterion of the measured impedance at both ends of the protection line based on the detection result of the zero-sequence current; If the modulus criterion is met, the impedance phase angle difference measured before and after the fault is screened and judged through the phase angle criterion to determine the fault section and isolate the fault; If the measured values ​​at both ends of the protected line cannot be read, the overcurrent backup protection is activated.

2. The microgrid protection method based on measuring impedance amplitude and phase change according to claim 1 is characterized in that: The real-time acquisition of voltage and current measurement values ​​at both ends of the protection line in the microgrid includes the acquisition of the voltage at the bus A end. Current flowing through terminal A Bus B terminal voltage Current flowing through terminal B 3. The microgrid protection method based on measuring impedance amplitude and phase change according to claim 1 is characterized in that: The method of evaluating the voltage measurement value and the current measurement value respectively by the protection start criterion comprises the following steps: The voltage measurement is evaluated by setting the voltage sag threshold, and the following voltage sag start criteria are used: ΔU>110%U N : Among them, ΔU is the voltage drop value, U N is the rated voltage; The current measurement value is evaluated by setting the phase current mutation threshold, and the following phase current mutation start criterion is used: Δi≥K S I N ; Wherein, Δi=||i(k)-i(kN)|-|i(kN)-i(k-2N)||, i(k) is the current sampling value of the phase current at the current moment k; N is the number of sampling points for each cycle, I N is the rated current effective value, K s is the starting coefficient; When the voltage drop and the phase current mutation amount meet the voltage drop start criterion and the phase current mutation amount start criterion respectively, the protection line fault is determined.

4. The microgrid protection method based on measuring impedance amplitude and phase change according to claim 1 is characterized in that: The method of determining the module value criterion of the measured impedance at both ends of the protection line based on the detection result of the zero-sequence current comprises the following steps: If the zero-sequence current is not detected, the modulus criterion of the measured impedance is as follows: |From m |>From set ; If zero-sequence current is detected, the modulus criterion of the measured impedance is as follows: Km|Z m |>From set ; Among them, |Z m | is the impedance modulus change before and after the fault, Z set is the impedance threshold, K m is the compensation coefficient, K m Expressed as the impedance modulus compensation coefficient K at the bus A end Am and the impedance modulus compensation coefficient K at the busbar B end Bm .

5. The microgrid protection method based on measuring impedance amplitude and phase change according to claim 4 is characterized in that: Calculate the compensation factor K of the measured impedance m , including the impedance modulus compensation coefficient K at the busbar A end Am and the impedance modulus compensation coefficient K at the busbar B end Bm , where the calculation is based on the busbar end A as an example, and includes the following steps: Obtain the measured voltages at the bus A and bus B terminals when there is a transition resistance and a fault occurs at the protection line f1. The method for obtaining the measured voltages at both ends of the bus is the same. Taking the bus A terminal as an example, the following formula is used: Among them, Z Af1 is the line impedance from bus A to fault point f1; Get the measured impedance Z at the A end of the bus Am , the specific formula is as follows: in, To measure current The zero-sequence component of the line impedance from bus A to the fault point f1 is Z1, Z2, and Z0 respectively, and Z1 = Z2. K is the zero-sequence current compensation coefficient, K = (Z0-Z1) / 3Z1. Get the impedance modulus compensation coefficient K at the A end of the bus Am , the specific formula is as follows: Among them, θ m is the phase angle of the measured impedance when a fault occurs at f1 without considering the transition resistance, θ Am To measure the impedance Z Am The phase angle of α is the additional impedance angle.

6. The microgrid protection method based on measuring impedance amplitude and phase change according to claim 4 is characterized in that: The phase angle criterion of the busbar measurement impedance at both ends of the protection line is as shown in the following formula: or Among them, Δθ represents the impedance angle at the busbars at both ends of the fault section. The difference of the impedance angle measured at the busbars at both ends of the fault section is 0 and 180° respectively. is the phase angle deviation during the measurement process.

7. The microgrid protection method based on measuring impedance amplitude and phase change according to claim 1 is characterized in that: When the measured values ​​at both ends of the protection line cannot be read, the overcurrent backup protection is started, including the following steps: The adaptive overcurrent protection strategy is used for short-circuit faults, and the specific action current calculation formula is as follows: in, To protect the operating current, K Z is the reliability coefficient, ranging from 1.1 to 1.

2. is the positive sequence voltage at bus terminal A, Z 11 is the equivalent impedance from the fault point f1 to the busbar A end, and Z4 is the equivalent impedance of the line downstream of the fault point; For single-phase grounding faults, zero-sequence current measurement based on zero-sequence current amplitude and phase information is used to locate the fault. The zero-sequence current measurement is calculated using the following formula: T i =I0sign(sinδ); Among them, T i is the zero-sequence current measurement, I0 is the zero-sequence current modulus of the line, δ is the angle of the zero-sequence current relative to the neutral point voltage, when the T of a certain line i <0 and the zero-sequence current modulus I0 is the largest, indicating that the line is faulty.

8. A microgrid protection device based on measuring impedance amplitude and phase change, characterized in that: include: A data acquisition module is used to collect voltage and current measurements at both ends of the protection line in the microgrid in real time; A protection start judgment module is used to evaluate the voltage measurement value and the current measurement value respectively according to the protection start judgment criterion, and determine whether the protection line is faulty; An impedance and zero-sequence current calculation module, used to calculate the measured impedance at both ends of the protection line based on the voltage measurement value and the current measurement value, and perform zero-sequence current detection; A module for determining a modulus value criterion, used for determining a modulus value criterion for measuring impedance at both ends of a protection line based on a detection result of a zero-sequence current; The fault judgment and isolation module is used to screen and judge the impedance phase angle difference measured before and after the fault through the phase angle judgment when the module value judgment is met, determine the fault section and isolate the fault; The backup protection module is used to start the overcurrent backup protection when the measured values ​​at both ends of the protection line cannot be read.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of the microgrid protection method based on measuring impedance amplitude and phase changes described in any one of claims 1 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the microgrid protection method based on measuring impedance amplitude and phase changes described in any one of claims 1 to 7 are implemented.

Images