A differential protection method, system, device and storage medium for new energy access

Abstract

The present invention discloses a differential protection method and system for the access of new energy sources, which collects current signals and voltage signals on the first side and the second side of the grid-connected point in the power system, as well as the sampling time of each current signal and voltage signal, obtains differential current and braking current according to the sampling time and the current signals on the first side and the second side of the grid-connected point, and judges whether the differential protection equation is satisfied based on the differential current and braking current. If satisfied, the voltage and current vector value is obtained according to the current signal and voltage signal on the first side and the second side of the grid-connected point, and judges whether to make a protection action decision according to the voltage and current vector value and the impedance angle of the grid-connected point, and executes the protection action decision if the impedance angle meets the preset range. Through the above method, it is achieved that the differential protection can work accurately in the case of the access of new energy sources, and the recognition accuracy of the differential protection for system faults is improved.

Description

Technical Field

[0001] The present invention relates to the field of relay protection technology, and in particular to a differential protection method, system, device and storage medium for new energy access. Background Art

[0002] With the increasing number of distributed power sources, especially photovoltaic, wind power and other power sources (hereinafter referred to as IIDG), in the distribution line, the access location of the distributed power source exists in the downstream, upstream position of the feeder or T-connected to the feeder. When the differential protection equipment is deployed on the two section switches of the feeder and the differential protection is formed, due to the characteristics of the differential protection, the distributed power source connected to the upstream or downstream will not cause the false operation of the differential protection. For the distributed power source T-connected to the feeder, the output current of the inverter distributed power source is determined by the control strategy of the controller, and the direction is uncertain.

[0003] The existing differential protection method is to compare the differential current and the braking current through the differential protection equation. When the distribution network fails, according to the grid connection requirements, the IIDG needs to have low voltage ridethrough (LVRT). At the same time, in order to improve the output characteristics of the IIDG when an asymmetric short circuit fault occurs in the distribution network, the IIDG adopts the elimination of negative sequence current control. The IIDG can be equivalent to a current source controlled by the positive sequence voltage of the grid connection point. Therefore, the traditional phase difference method is adopted. Under the influence of the IIDG, when an out-of-area fault occurs, it is very likely that the differential malfunction will occur. For example, patent CN117977510A uses the characteristics of the distributed power supply that only outputs positive sequence current and does not output negative sequence current when a fault occurs, and uses the negative sequence current component as the criterion for differential protection. However, the prerequisite for using the above technical solution must be two-phase short circuit and two-phase grounding short circuit faults, because when a three-phase fault occurs, the system does not output negative sequence current, only positive sequence current, so it is invalid for the fault types of three-phase interphase fault and three-phase grounding fault. Summary of the invention

[0004] In order to solve the above technical problems, the embodiments of the present invention provide a differential protection method, system, computer device and storage medium for new energy access, which enables the differential protection to work accurately when new energy is accessed, and improves the accuracy of differential protection in identifying system faults.

[0005] A first aspect of an embodiment of the present invention provides a differential protection method for new energy access, the method comprising:

[0006] Collecting current signals and voltage signals on the first side and the second side of the grid connection point in the power system, as well as sampling times of each current signal and voltage signal;

[0007] According to the sampling time and the current signals on the first side and the second side of the grid-connected point, the differential current and the braking current are obtained, and based on the differential current and the braking current, whether the differential protection equation is satisfied is judged, and if satisfied, the voltage and current vector value and the impedance angle are obtained according to the current signals and the voltage signals on the first side and the second side of the grid-connected point;

[0008] If the voltage-current vector value is greater than the unbalanced current value and the impedance angle of the grid-connected point meets the preset range, the protection action decision is executed. If the voltage-current vector value is less than the unbalanced current value, it is determined whether the impedance angle of the grid-connected point meets the preset range. If so, the protection action decision is executed.

[0009] In a possible implementation manner of the first aspect, obtaining a differential current and a braking current according to a sampling time and current signals on a first side and a second side of a grid connection point includes:

[0010] Subtracting the current signal on the first side of the grid connection point from the current signal on the second side at the same sampling time to obtain a differential current;

[0011] The current signal of the first side of the grid-connected point and the current signal of the second side at the same sampling time are added together to obtain the braking current.

[0012] In a possible implementation manner of the first aspect, obtaining a voltage and current vector value according to current signals and voltage signals at a first side and a second side of a grid-connected point includes:

[0013] According to the current signal, voltage signal and positive sequence impedance at the first side and the second side of the grid connection point, the voltage and current vector value is obtained, wherein the expression of the voltage and current vector value is:

[0014]

[0015] In the formula, is the voltage at point M, is the voltage at point N, is the current at point N, is the current at point M, is the positive sequence impedance from the N side to the grid connection point, It is the positive sequence impedance from the M side to the grid connection point.

[0016] In a possible implementation manner of the first aspect, obtaining an impedance angle of the grid-connected point according to current signals and voltage signals at a first side and a second side of the grid-connected point includes:

[0017] Obtaining a voltage of the grid-connected point according to current signals, voltage signals and impedances at a first side and a second side of the grid-connected point;

[0018] The current of the grid-connected point is obtained according to the current signals of the first side and the second side of the grid-connected point, and the impedance angle is obtained based on the current and voltage of the grid-connected point.

[0019] In a possible implementation manner of the first aspect, after obtaining the voltage of the grid-connected point according to the current signal, the voltage signal, and the impedance at the first side and the second side of the grid-connected point, the method further includes:

[0020] If the voltage at the grid connection point meets the first preset condition, the fault of the power system is an out-of-area fault, wherein the first preset condition is:

[0021]

[0022] In the formula, It is expressed as the voltage value at point M. It is expressed as the positive sequence impedance from the M side to the grid-connected PV point, It is expressed as the current value at point M, It is expressed as the voltage value at point N. Expressed as the current value at point N, It is expressed as the positive sequence impedance from the N side to the grid-connected PV point;

[0023] If the voltage at the grid connection point meets the second preset condition, the fault of the power system is an intra-area fault, wherein the second preset condition is:

[0024]

[0025] A second aspect of an embodiment of the present invention provides a differential protection system for accessing new energy sources, the system comprising a collection module, a judgment module and an execution module.

[0026] The acquisition module is used to collect current signals and voltage signals on the first side and the second side of the grid connection point in the power system, as well as the sampling time of each current signal and voltage signal;

[0027] The judgment module is used to obtain the differential current and the braking current according to the sampling time and the current signals on the first side and the second side of the grid-connected point, and judge whether the differential protection equation is satisfied based on the differential current and the braking current. If satisfied, the voltage and current vector value and the impedance angle are obtained according to the current signals and the voltage signals on the first side and the second side of the grid-connected point;

[0028] The execution module is used to execute the protection action decision if the voltage and current vector value is greater than the unbalanced current value and the impedance angle of the grid-connected point meets the preset range. If the voltage and current vector value is less than the unbalanced current value, it is used to determine whether the impedance angle of the grid-connected point meets the preset range. If so, the protection action decision is executed.

[0029] In a possible implementation manner of the second aspect, the determination module includes a first calculation unit and a second calculation unit.

[0030] The first calculation unit is used to subtract the current signal on the first side of the grid connection point from the current signal on the second side at the same sampling time to obtain a differential current;

[0031] The second calculation unit is used for adding the current signal of the first side of the grid connection point and the current signal of the second side at the same sampling time to obtain the braking current.

[0032] The judgment module also includes a voltage and current vector value unit,

[0033] The voltage and current vector value unit is used to obtain the voltage and current vector value according to the current signal, voltage signal and positive sequence impedance at the first side and the second side of the grid connection point, wherein the expression of the voltage and current vector value is:

[0034]

[0035] In the formula, is the voltage at point M, is the voltage at point N, is the current at point N, is the current at point M, is the positive sequence impedance from the N side to the grid connection point, It is the positive sequence impedance from the M side to the grid connection point.

[0036] A third aspect of an embodiment of the present invention provides a computer device, including:

[0037] Memory for storing computer programs;

[0038] A processor is used to implement the differential protection method for new energy access as described in the first aspect when executing the computer program.

[0039] A fourth aspect of an embodiment of the present invention provides a storage medium having a computer program stored thereon. When the computer program is executed by a processor, the steps of the differential protection method for new energy access according to the first aspect are implemented.

[0040] The differential protection method for renewable energy access provided by the embodiment of the present invention collects the current signal and voltage signal on the first side and the second side of the grid connection point in the power system, as well as the sampling time of each current signal and voltage signal, obtains the differential current and the braking current according to the sampling time and the current signal on the first side and the second side of the grid connection point, and judges whether the differential protection equation is satisfied based on the differential current and the braking current. If satisfied, the voltage and current vector value and the impedance angle are obtained according to the current signal and the voltage signal on the first side and the second side of the grid connection point. If the voltage and current vector value is greater than the unbalanced current value, and the impedance angle of the grid connection point satisfies the preset range, the protection action decision is executed. If the voltage and current vector value is less than the unbalanced current value, it is judged whether the impedance angle of the grid connection point satisfies the preset range. If satisfied, the protection action decision is executed. Through the above method, it is achieved that the differential protection can work accurately in the case of renewable energy access, and the accuracy of differential protection in identifying system faults is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 : A schematic diagram of a differential protection method flow chart of an embodiment of a differential protection method for new energy access provided by the present invention;

[0042] Figure 2 : A schematic diagram of an equivalent circuit of a PV point connected to the grid in an inverter-type distributed power source under normal operation of a power system according to an embodiment of a differential protection method for accessing new energy provided by the present invention;

[0043] Figure 3 : A schematic diagram of the structure of a differential protection system of an embodiment of a differential protection method for access to new energy provided by the present invention;

[0044] Figure 4 : A flow chart of a differential protection method for renewable energy access according to an embodiment of the differential protection method for renewable energy access provided by the present invention;

[0045] Figure 5 : A schematic diagram of an equivalent circuit when the grid-connected PV point and the fault point F are at the same position in a system failure situation of an embodiment of a differential protection method for renewable energy access provided by the present invention;

[0046] Figure 6 : A schematic diagram of an equivalent circuit of a PV point connected to the grid in an inverter-type distributed power source under an out-of-zone fault condition in accordance with an embodiment of a differential protection method for new energy access provided by the present invention;

[0047] Figure 7 : A schematic diagram of an equivalent circuit of a PV point connected to the grid in an inverter-type distributed power source under an intra-area fault condition in accordance with an embodiment of a differential protection method for new energy access provided by the present invention;

[0048] Figure 8 : A schematic diagram of the distribution of fault points in a photovoltaic branch line according to an embodiment of a differential protection method for access to new energy provided by the present invention;

[0049] Fig. 9 : A system block diagram of an embodiment of a differential protection method for new energy access provided by the present invention. DETAILED DESCRIPTION

[0050] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0051] At present, the existing differential protection methods are mainly based on the comparison of differential currents. In power systems, differential protection is a protection mechanism used to detect and locate faults, especially in transmission lines and distribution networks. Its basic principle is: the differential protection device passes the current difference (differential current) at both ends of the protection area. Under normal operating conditions, the current entering and leaving the protection area should be equal, so the differential current is theoretically zero; braking current calculation: in order to consider the unbalanced current in actual operation (such as load imbalance), the differential protection will set a braking current value, which is usually compared with the differential current to determine whether a fault has occurred; differential action logic judgment: when the differential current exceeds the preset braking current value, the differential protection device considers that an internal fault has occurred and triggers a protection action, such as disconnecting the circuit breaker in the fault area; fast response execution: the differential protection design requires a fast response so that the fault area can be quickly isolated when a fault occurs to reduce the impact on the system.

[0052] However, with the access of distributed power sources, such as photovoltaic and wind power, the current distribution of the system will change, resulting in deviations in the calculation of differential current, especially when the distributed power source is connected to the system through an inverter. Due to the control strategy of the inverter, the direction and magnitude of its output current are uncertain, which directly affects the correct operation of the differential protection. Therefore, an improved differential protection method is needed to adapt to these changes and ensure that the differential protection can still reliably detect and locate faults when new energy is connected, while avoiding false operation. At the same time, the existing photovoltaic current cannot be collected in the branch line. When an asymmetric fault occurs between phases, the photovoltaic power source of the branch line provides a positive sequence current, which will cause a large differential current in the non-fault phase. Since the braking current of the non-fault phase is small, differential false operation will occur.

[0053] Therefore, a flow chart of an embodiment of a differential protection method for accessing new energy provided by an embodiment of the present invention is as follows: Figure 1 , including steps S101 to S103, each step is as follows:

[0054] S101 , collecting current signals and voltage signals at a first side and a second side of a grid-connected point in a power system, as well as sampling times of respective current signals and voltage signals.

[0055] In this embodiment, a normal operation equivalent circuit of the system connected to the grid and connected to the PV point is constructed, such as Figure 2 , simulates the current from the system power supply To the grid-connected PV point, and then from the grid-connected PV point to the system power supply The equivalent circuit of the PV at the grid connection point is analyzed to limit the flow path of the current from the system power supply. The first calculation path is the path from the grid-connected PV point to the system power supply. The second calculation path is recorded as the path N side. A threshold value for quantizing the imbalance of the system line current sampling is determined to handle the sampling error and ignore the capacitive current. This threshold value is used as an auxiliary criterion for differential protection to adapt to the access of distributed power sources.

[0056] exist Figure 3 In the example, the PV point is the grid-connected PV point. is the positive sequence impedance from the M side of the path to the grid-connected PV point, is the positive sequence impedance from the N side of the path to the grid-connected PV point, and It is a switch, and is in a closed state during normal operation. DG is a distributed power source. is the system power supply on the M side, and the internal resistance is Zs1. is the N-side system power supply, and the internal resistance is It should be noted that the M side of the path described above is the current from the system power supply The first calculation path is the path from the grid-connected PV point to the system power supply. It is the second calculation path; by distinguishing the M side and the N side, the system can determine on which side of the grid access point PV the fault occurs, and achieve accurate fault location. The differential protection depends on the comparison of the currents on both sides.

[0057] In the system line current flow down, the line current from the system power supply Inflow, through internal resistance ,switch and impedance After reaching the grid-connected PV point, the line current then passes through the impedance ,switch 、Internal resistance , and finally reaches the system power supply Output, where the grid-connected PV point is the distributed power source DG access point connected to the distributed power source DG; its circuit connection relationship is: ( )→ → →PV(DG)→ → → ( ), where the arrow indicates the direction of current flow, and the PV point is the grid connection point, which is also the access point of the distributed power source DG. and between.

[0058] It should be noted that the first side refers to the path M side, and the second side refers to the path N side.

[0059] In the system data acquisition stage, most of the time, several measurement points are set up on the distributed power supply line to obtain line power data information, including the phase voltage and phase current at the beginning and end of the line, as well as the voltage and output phase current of the distributed power supply grid connection point. However, this method has the constraint of fault type. Therefore, the voltage and current data on the M side and the M side of the path, the impedance data from point M to point PV, and the impedance data from point N to point PV are used for judgment. It can be understood that points M and N are differential protection devices deployed on the distribution network line and the section switch. Points M and N are selected switches for differential protection. Since the impedance data is fixed data and does not need to be sampled, it is only necessary to collect the data of points M and N to ignore any type of fault. Specific differential protection methods are as follows: Figure 4 As shown, firstly, a voltage transformer and a current transformer are used to synchronously collect the current signal and the voltage signal of the grid-connected PV point, that is, the first side and the second side of the grid-connected point, and the sampling time of each current signal and the voltage signal.

[0060] S102. According to the sampling time and the current signals on the first side and the second side of the grid-connected point, a differential current and a braking current are obtained. Based on the differential current and the braking current, it is determined whether the differential protection equation is satisfied. If so, a voltage-current vector value and an impedance angle are obtained according to the current signals and voltage signals on the first side and the second side of the grid-connected point.

[0061] In this embodiment, the collected voltage data, current data and the GPS signal at the time of collection are transmitted to the opposite device. The opposite device solves the differential current and braking current based on the GPS time stamp information of the transmitted data and the current data information in the local memory.

[0062] It should be noted that the GPS signal and GPS time stamp information refer to the sampling time of each current signal and voltage signal. The GPS time stamp information is the sampling time stamp information, that is, when each sampling value is collected, the sampling time information is also marked.

[0063] Based on the differential current and the braking current, it is determined whether the differential protection equation is satisfied. The differential protection equation is:

[0064]

[0065] In the formula, Expressed as differential current, Expressed as braking current, Represents the braking system, preferably 0.75, Expressed as differential starting setting.

[0066] However, in order to avoid unbalanced current values ​​when both sides are running, it is also necessary to identify the access of distributed power sources, that is, first calculate the voltage and current vector values ​​on both sides (M side and N side) of the PV node feeder at the grid access point. Because unbalanced current will be generated due to sampling errors on both sides, it is avoided by starting the fixed value. When the currents on both sides meet the differential protection equation, the expression of the voltage and current vector value is:

[0067]

[0068] In the formula, is the voltage at point M, is the voltage at point N, is the current at point N, is the current at point M, is the positive sequence impedance from the N side to the grid-connected PV point, It is the positive sequence impedance from the M side to the grid-connected PV point.

[0069] Then set up the conditions for entering the distributed power supply access judgment:

[0070]

[0071] In some embodiments, in step S102, "obtaining the differential current and the braking current according to the sampling time and the current signals on the first side and the second side of the grid connection point" includes but is not limited to the following steps:

[0072] Subtracting the current signal on the first side of the grid connection point from the current signal on the second side at the same sampling time to obtain a differential current;

[0073] The current signal of the first side of the grid-connected point and the current signal of the second side at the same sampling time are added together to obtain the braking current.

[0074] In this embodiment, the current signal on the first side of the grid connection point and the current signal on the second side at the same sampling time are subtracted to obtain a differential current, which is: .

[0075] The current signal on the first side of the grid-connected point and the current signal on the second side at the same sampling time are added to obtain the braking current. Expressed as braking current.

[0076] In some embodiments, the step S102 of "obtaining a voltage and current vector value according to the current signal and the voltage signal on the first side and the second side of the grid connection point" includes but is not limited to the following steps:

[0077] According to the current signal, voltage signal and positive sequence impedance at the first side and the second side of the grid connection point, a voltage and current vector value is obtained, wherein the expression of the voltage and current vector value is:

[0078]

[0079] In the formula, is the voltage at point M, is the voltage at point N, is the current at point N, is the current at point M, is the positive sequence impedance from the N side to the grid connection point, It is the positive sequence impedance from the M side to the grid connection point.

[0080] In this embodiment, the expression of the voltage and current vector value is:

[0081]

[0082] In the formula, is the voltage at point M, is the voltage at point N, is the current at point N, is the current at point M, is the positive sequence impedance from the N side to the grid-connected PV point, It is the positive sequence impedance from the M side to the grid-connected PV point.

[0083] If the voltage-current vector value is greater than the unbalanced current value, that is:

[0084]

[0085] In the formula, is the voltage at point M, is the voltage at point N, is the current at point N, is the current at point M, is the positive sequence impedance from the N side to the grid-connected PV point, is the positive sequence impedance from the M side to the grid-connected PV point, Indicates the unbalanced current value.

[0086] The differential protection action decision result is the protection action decision.

[0087] If the voltage-current vector value is less than the unbalanced current value, that is:

[0088]

[0089] In the formula, is the voltage at point M, is the voltage at point N, is the current at point N, is the current at point M, is the positive sequence impedance from the N side to the grid-connected PV point, is the positive sequence impedance from the M side to the grid-connected PV point, Indicates the unbalanced current value.

[0090] At this time, it is also necessary to compare the impedance angle range of the PV of the grid-connected access point on the M side and the N side to determine whether to execute the protection device action decision.

[0091] S103. If the voltage-current vector value is greater than the unbalanced current value and the impedance angle of the grid-connected point meets the preset range, a protection action decision is executed. If the voltage-current vector value is less than the unbalanced current value, it is determined whether the impedance angle of the grid-connected point meets the preset range. If so, a protection action decision is executed.

[0092] In this embodiment, an equivalent circuit is constructed in which the grid-connected PV point and the fault point F are co-located in the case of a system operation failure, such as Figure 5 , use Kirchhoff's theorem to calculate the current flowing into the grid-connected PV point through the M side and the N side, and then determine the voltage and impedance angle of the grid-connected PV point to locate the fault point F. The current logic sequence is: from the system power supply Inflow, through internal resistance ,switch and line impedance Arriving at the grid-connected PV point, and then through the impedance ,switch 、Internal resistance Reaching system power , where the grid-connected PV point is the distributed power source DG access point, which connects the distributed power source DG and the impedance .

[0093] If the differential protection action decision result is a protection action decision, that is, At this time, the protection device action decision is executed and the M and N side switches are tripped. If the impedance angle If the range meets the preset range, the protection device action decision is executed and the M and N side switches are opened. Otherwise, the protection device non-action decision is executed.

[0094] It should be noted that the preset range is preferably or .

[0095] If the fault point is an out-of-area fault, then according to the low voltage ride-through regulations, the distributed generation DG provides not only active power but also reactive power to the system line according to the voltage drop procedure, and its impedance angle range is:

[0096]

[0097] If the fault point is at the grid connection point, the grounding resistance shows resistance characteristics or inductance characteristics, the fault point shows absorption of active power, and reactive power can be shown as absorption or provision. According to the inductive size of the grounding impedance, the impedance angle range is:

[0098]

[0099] like , then the impedance angle differential protection action decision result of the grid connection point is a non-protection action decision, but at this time it is also necessary to compare the impedance angle of the grid connection point PV on the M side and the N side Range, if the impedance angle If the range meets the preset range, the protection device action decision will continue to be executed.

[0100] In some embodiments, in step S103, "obtaining the impedance angle of the grid-connected point according to the current signal and the voltage signal on the first side and the second side of the grid-connected point" includes but is not limited to the following steps:

[0101] Obtaining a voltage of the grid-connected point according to current signals, voltage signals and impedances at a first side and a second side of the grid-connected point;

[0102] The current of the grid-connected point is obtained according to the current signals of the first side and the second side of the grid-connected point, and the impedance angle is obtained based on the current and voltage of the grid-connected point.

[0103] In this embodiment, Kirchhoff's theorem is applied to calculate the PV point voltage and impedance angle on the M side and the N side:

[0104]

[0105]

[0106] In the formula, It is expressed as the current value flowing into the photovoltaic point, is the voltage at the PV point;

[0107] Then the impedance angle of the PV point is for:

[0108]

[0109] In some embodiments, step S103 of "after obtaining the voltage of the grid-connected point according to the current signal, voltage signal and impedance at the first side and the second side of the grid-connected point" includes but is not limited to the following steps:

[0110] If the fault of the power system is an out-of-area fault, the calculation formula of the voltage of the grid connection point is the first preset formula, wherein the first preset formula is:

[0111]

[0112] In the formula, It is expressed as the voltage value at point M. It is expressed as the positive sequence impedance from the M side to the grid connection point, It is expressed as the current value at point M, It is expressed as the voltage value at point N. Expressed as the current value at point N, It is expressed as the positive sequence impedance from the N side to the grid connection point, is the voltage at the PV point;

[0113] If the fault of the power system is an intra-regional fault, the calculation formula of the voltage of the grid connection point is the second preset formula, wherein the second preset formula is:

[0114]

[0115] In this embodiment, the power system fault conditions include out-of-area faults and in-area faults. Out-of-area faults refer to faults occurring outside the feeder segment set by the system protection device. In-area faults refer to faults occurring inside the feeder segment set by the system protection device.

[0116] exist Figure 6 In the case of an out-of-zone fault, the grid-connected PV point voltage on the M and N sides needs to be calculated using the circuit theorem. The grid-connected PV point voltage is:

[0117]

[0118] In the formula, It is expressed as the voltage value at point M. It is expressed as the positive sequence impedance from the M side to the grid-connected PV point, It is expressed as the current value at point M, Expressed as the voltage value at point N, Expressed as the current value at point N, It is expressed as the positive sequence impedance from the N side to the grid-connected PV point, is the voltage at the PV point.

[0119] exist Figure 7 In the case of a fault in the zone, the PV point voltage on the M side and the N side is calculated, and the PV point voltage is:

[0120]

[0121] It can be understood that the distinction between out-of-zone and in-zone faults is based on the differential protection equation. Faults that satisfy the differential protection equation are in-zone faults, while those that do not satisfy the equation are out-of-zone faults. Due to the access of branch line photovoltaics, the differential protection equation may be misjudged, so auxiliary criteria are introduced to solve this problem.

[0122] Apply Kirchhoff's theorem to calculate the PV point voltage and impedance angle on the M and N sides:

[0123]

[0124]

[0125] In the formula, It is expressed as the current value flowing into the photovoltaic point, is the voltage at the PV point;

[0126] Then the impedance angle of the PV point is for:

[0127]

[0128] According to the low voltage ride-through regulations and grounding resistance characteristics, the impedance angle range of the fault point F when it is at the fault point outside the zone or at the PV point is determined to further enhance the accuracy of the auxiliary judgment criteria of the differential protection. The specific steps are as follows:

[0129] If the fault point F is an out-of-zone fault, then according to the low voltage ride-through regulations, the distributed generation DG provides not only active power but also reactive power to the system line according to the voltage drop procedure, and its impedance angle range is:

[0130]

[0131] If the fault point is at PV, the grounding resistance shows resistance characteristics or inductance characteristics, and the fault point F shows active power absorption. Reactive power can be absorbed or provided. According to the inductive size of the grounding impedance, the impedance angle range is:

[0132]

[0133] It can be understood that by applying Kirchhoff's theorem to accurately calculate the voltage and impedance angle of the PV point, and combining the low voltage ride-through regulations and grounding resistance characteristics to determine the location of the fault point F, high-accuracy fault location can be achieved, further enhancing the reliability of the differential protection auxiliary judgment criteria and optimizing the protection strategy for distributed power generation access to the power system.

[0134] It should be noted that when a system failure occurs, Figure 8 There are several fault points, F1, F2, F3, F4. When F1 or F2 fault occurs, for the differential protection formed by points M and N, this is an out-of-area fault. When there is no photovoltaic power supply in the branch line, the differential protection equation can identify the out-of-area fault. However, since there is a distributed photovoltaic power supply in the branch line, it may cause the differential protection to misjudge. At this time, if an out-of-area fault occurs, the voltage at the PV point must satisfy: Therefore, if the above formula is satisfied at this time, the differential protection cannot be operated to prevent false operation of out-of-zone faults.

[0135] For example Figure 8 As shown in Figure 2, when F3 fault occurs, the differential protection equation is satisfied, and at this time, since there is a fault current flowing through point F3, there must be ; Therefore, the auxiliary criterion can determine the differential protection action at this time; when F4 fails, since it is an internal fault at this time, the differential protection equation is satisfied, but it also satisfies If the differential protection is judged not to operate at this time, it is a misjudgment; therefore, it is necessary to analyze the impedance angle of the PV point in this case: .

[0136] If the fault point is outside the area, according to the low-voltage regulation, the distributed power supply provides not only active power but also reactive power to the system according to the voltage drop procedure, so the impedance angle range is ;

[0137] If the fault point is at the PV, the grounding resistance is resistive or inductive. The fault point generally absorbs active power. Reactive power can be absorbed or provided. According to the inductive size of the grounding impedance, the impedance angle Range is .

[0138] This differential protection method takes into account the low voltage ride-through capability and negative sequence current control characteristics of distributed power sources during asymmetric short circuit faults, enhances the stability and safety of the system, and through precise data analysis and fault point location, not only improves the reliability of differential protection, but also ensures the stable operation of the power system, and is suitable for modern distribution networks with increasing number of renewable energy power sources.

[0139] It should be understood that although Figure 1The steps in the flowchart are shown in sequence as indicated by the arrows, but these steps are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, Figure 1 At least part of the steps may include multiple steps or multiple stages. These steps or stages are not necessarily performed at the same time, but can be performed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed in turn or alternately with other steps or at least part of the steps or stages in other steps.

[0140] In some embodiments, Fig. 9 As shown, it shows a block diagram of a differential protection system 900 for new energy access provided in an embodiment of the present application, including: a collection module 901, a judgment module 902 and an execution module 903, wherein:

[0141] The acquisition module 901 is used to collect current signals and voltage signals on the first side and the second side of the grid connection point in the power system, as well as the sampling time of each current signal and voltage signal;

[0142] The judgment module 902 is used to obtain the differential current and the braking current according to the sampling time and the current signals on the first side and the second side of the grid-connected point, and judge whether the differential protection equation is satisfied based on the differential current and the braking current. If satisfied, the voltage and current vector value and the impedance angle are obtained according to the current signals and the voltage signals on the first side and the second side of the grid-connected point;

[0143] The execution module 903 is used to execute the protection action decision if the voltage-current vector value is greater than the unbalanced current value and the impedance angle of the grid-connected point meets the preset range. If the voltage-current vector value is less than the unbalanced current value, it is used to determine whether the impedance angle of the grid-connected point meets the preset range. If so, the protection action decision is executed.

[0144] In some embodiments, the determination module includes a first calculation unit and a second calculation unit.

[0145] The first calculation unit is used to subtract the current signal on the first side of the grid connection point from the current signal on the second side at the same sampling time to obtain a differential current;

[0146] The second calculation unit is used for adding the current signal of the first side of the grid connection point and the current signal of the second side at the same sampling time to obtain the braking current.

[0147] In some embodiments, the determination module further includes a voltage and current vector value unit,

[0148] The voltage and current vector value unit is used to obtain the voltage and current vector value according to the current signal, voltage signal and positive sequence impedance at the first side and the second side of the grid connection point, wherein the expression of the voltage and current vector value is:

[0149]

[0150] In the formula, is the voltage at point M, is the voltage at point N, is the current at point N, is the current at point M, is the positive sequence impedance from the N side to the grid connection point, It is the positive sequence impedance from the M side to the grid connection point.

[0151] The specific implementation of the differential protection system for renewable energy access is basically the same as the specific implementation of the differential protection method for renewable energy access described above, and will not be described in detail here.

[0152] In one embodiment of the present application, a computer device is provided, which includes a memory and a processor, wherein a computer program is stored in the memory, and the above steps are implemented when the processor executes the computer program; the computer device provided in this embodiment has an implementation principle and technical effects similar to those of the above method embodiments, and will not be repeated here.

[0153] In one embodiment of the present application, a computer-readable storage medium is provided, on which a computer program is stored, and the above steps are implemented when the computer program is executed by a processor; the computer-readable storage medium provided in this embodiment has an implementation principle and technical effects similar to those of the above method embodiment, and will not be repeated here.

[0154] 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 memory, storage, database or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory can include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory can include random access memory (RAM) or external cache memory. As an illustration and not limitation, RAM is available in many forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link (Synchlink) DRAM (SLDRAM), memory bus (Rambus) direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM).

[0155] 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.

[0156] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A differential protection method for new energy access, characterized in that: include: Collecting current signals and voltage signals on a first side and a second side of a grid-connected point in a power system, as well as sampling times of the current signals and the voltage signals, wherein the first side is a path for the current to reach the grid-connected point from a first power source in the power system, and the second side is a path for the current to reach the second power source in the power system from the grid-connected point; According to the sampling time and the current signals on the first side and the second side of the grid-connected point, a differential current and a braking current are obtained, and based on the differential current and the braking current, whether a differential protection equation is satisfied is determined, and if satisfied, a voltage-current vector value and an impedance angle are obtained according to the current signals and the voltage signals on the first side and the second side of the grid-connected point; If the voltage-current vector value is greater than the unbalanced current value, and the impedance angle of the grid-connected point satisfies the preset range, a protection action decision is executed; if the voltage-current vector value is less than the unbalanced current value, it is determined whether the impedance angle of the grid-connected point satisfies the preset range, and if so, a protection action decision is executed; The step of obtaining the differential current and the braking current according to the sampling time and the current signals on the first side and the second side of the grid connection point comprises: Subtracting the current signal on the first side of the grid-connected point from the current signal on the second side at the same sampling time to obtain a differential current; Adding the current signal on the first side and the current signal on the second side of the grid-connected point at the same sampling time to obtain a braking current; The step of obtaining a voltage and current vector value according to the current signal and the voltage signal at the first side and the second side of the grid connection point comprises: According to the current signal, voltage signal and positive sequence impedance at the first side and the second side of the grid connection point, a voltage and current vector value is obtained, wherein the expression of the voltage and current vector value is: In the formula, is the voltage on the M side, is the voltage on the N side, is the current on the N side, is the current on the M side, is the positive sequence impedance from the N side to the grid connection point, is the positive sequence impedance from the M side to the grid connection point, the M side is the first side in the power system, and the N side is the second side in the power system.

2. The differential protection method for new energy access according to claim 1, characterized in that: The step of obtaining the impedance angle of the grid-connected point according to the current signal and the voltage signal on the first side and the second side of the grid-connected point comprises: Obtaining the voltage of the grid-connected point according to the current signal, voltage signal and impedance at the first side and the second side of the grid-connected point; The current of the grid-connected point is obtained according to the current signals at the first side and the second side of the grid-connected point, and the impedance angle is obtained based on the current and voltage of the grid-connected point.

3. The differential protection method for new energy access according to claim 2, characterized in that: The step of obtaining the voltage of the grid-connected point according to the current signal, the voltage signal and the impedance at the first side and the second side of the grid-connected point comprises: If the fault of the power system is an out-of-region fault, the voltage of the grid connection point meets a first preset condition, wherein the first preset condition is: In the formula, Expressed as the voltage value on the M side, It is expressed as the positive sequence impedance from the M side to the grid connection point, It is expressed as the current value at point M, Expressed as the voltage value on the N side, Expressed as the current value on the N side, It is expressed as the positive sequence impedance from the N side to the grid connection point, is the voltage at the PV point; If the fault of the power system is an intra-regional fault, the voltage of the grid connection point meets a second preset condition, wherein the second preset condition is: .

4. A differential protection system for new energy access, characterized in that: It includes acquisition module, judgment module and execution module. The acquisition module is used to collect current signals and voltage signals on the first side and the second side of the grid-connected point in the power system, as well as the sampling time of each of the current signals and the voltage signals, wherein the first side is the path of the current from the first power source in the power system to the grid-connected point, and the second side is the path of the current from the grid-connected point to the second power source in the power system; The judgment module is used to obtain a differential current and a braking current according to the sampling time and the current signals on the first side and the second side of the grid-connected point, and judge whether the differential protection equation is satisfied based on the differential current and the braking current. If satisfied, the voltage-current vector value and the impedance angle are obtained according to the current signals and the voltage signals on the first side and the second side of the grid-connected point; The execution module is used to execute a protection action decision if the voltage-current vector value is greater than the unbalanced current value and the impedance angle of the grid-connected point meets a preset range; if the voltage-current vector value is less than the unbalanced current value, determine whether the impedance angle of the grid-connected point meets the preset range, and if so, execute a protection action decision; The judgment module includes a first calculation unit and a second calculation unit. Wherein, the first calculation unit is used to subtract the current signal on the first side of the grid-connected point from the current signal on the second side at the same sampling time to obtain a differential current; The second calculation unit is used for adding the current signal of the first side and the current signal of the second side of the grid connection point at the same sampling time to obtain the braking current; The judgment module also includes a voltage and current vector value unit, The voltage and current vector value unit is used to obtain a voltage and current vector value according to the current signal, voltage signal and positive sequence impedance at the first side and the second side of the grid connection point, wherein the expression of the voltage and current vector value is: In the formula, is the voltage on the M side, is the voltage on the N side, is the current on the N side, is the current on the M side, is the positive sequence impedance from the N side to the grid connection point, is the positive sequence impedance from the M side to the grid connection point, the M side is the first side in the power system, and the N side is the second side in the power system.

5. A computer device, characterized in that: include: Memory for storing computer programs; A processor, configured to implement the differential protection method for new energy access as described in any one of claims 1 to 3 when executing the computer program.

6. A storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by the processor, the steps of the differential protection method for new energy access as described in any one of claims 1 to 3 are implemented.

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