Active power distribution network self-adaptive stage difference matching method based on positive sequence voltage space distribution

Abstract

According to the active power distribution network adaptive stage difference cooperation method based on positive sequence voltage spatial distribution, the problem of traditional protection setting failure caused by DG random access and network topology flexible adjustment is solved, and the spatial characteristics that positive sequence voltage fault components are distributed along a feeder line and are strongly related to fault positions are utilized; constructing a logarithmic inverse time limit characteristic equation based on the component; and by comparing actual measurement values and reckoning values of local and adjacent protection positive sequence voltage fault components in real time, online self-adaptive setting of equation parameters is carried out. And on the basis of parameters updated in real time, adjacent protectors calculate respective action time in parallel, and an action time level difference meeting absolute selectivity is dynamically generated, so that the remote backup protection quickness is effectively improved. According to the method, the starting criterion and the steady-state voltage action criterion for distinguishing the fault and the disturbance are combined, and finally self-adaptive step-by-step matching of multi-stage protection independent of network topology and power supply types is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system relay protection, and in particular relates to an active distribution network adaptive differential coordination method based on positive sequence voltage spatial distribution. Background Art

[0002] Inverse-time overcurrent (ITOC) protection is a type of protection where the operating time is inversely proportional to the current amplitude, offering a certain degree of adaptability. However, with the large-scale integration of distributed generation (DG) systems, the types and topologies of power sources in active distribution networks are changing dynamically, leading to variations in the magnitude, direction, and short-circuit current contribution of fault currents. This, in turn, causes setting issues and coordination difficulties for traditional ITOC protection, seriously threatening the reliability of system protection.

[0003] Existing improvement methods often optimize ITOC inverse-time parameters (such as starting current and time constant) or introduce measurement signals such as voltage and impedance for compensation. However, these methods still rely on fixed network parameters and power source types, resulting in a complex setting process and insufficient real-time performance. This makes it difficult to achieve effective adaptive response to power source characteristics and topology changes, and thus fails to meet the requirements of active distribution networks for protection adaptability and coordination. Furthermore, topology adjustments such as DG insertion and removal and switching operations further increase the dynamic nature of protection coordination, making traditional offline setting of differential coordination difficult to adapt to complex and changing operating conditions.

[0004] To solve the above problems, the present invention constructs a logarithmic inverse time characteristic equation using the positive sequence voltage fault component and proposes an adaptive differential coordination method for active distribution network based on the positive sequence voltage spatial distribution. Summary of the Invention

[0005] The purpose of the present invention is to provide an adaptive differential coordination method for active distribution networks based on the spatial distribution of positive-sequence voltage, so as to solve the problems of complex setting and coordination failure of traditional ITOC protection based on fixed topology offline setting due to changes in power supply characteristics and network topology in active distribution networks, and to ensure the adaptive differential coordination capability of the active distribution network backup protection system in complex and changing environments, thereby improving the protection selectivity and the speed of remote backup protection.

[0006] The technical solution adopted by the present invention is an adaptive differential coordination method for active distribution network based on the spatial distribution of positive sequence voltage, and the steps are as follows: S1. Determine the spatial distribution characteristics of the positive sequence voltage fault component amplitude along the line based on the number of adjacent protection devices involved in parameter setting and their coordination relationships on the distribution line; S2. Construct a logarithmic inverse time characteristic equation and derive the adaptive tuning formula for the inverse time parameter; S3. Calculate the amplitude of the positive-sequence voltage fault component of the adjacent upper or lower protection device based on the real-time positive-sequence voltage and current fault components of the current protection device; S4. Calculate the inverse time parameter value using the adaptive setting formula of S2 and update it into the logarithmic inverse time characteristic equation of S2 to obtain the operating time of the adjacent protection device under the current fault condition. S5. Combined with the preset steady-state voltage action criterion, adjacent protection devices are enabled to perform adaptive time difference coordination according to their updated action times.

[0007] The present invention is also characterized in that S1 is specifically: S1.1. Determine the number of adjacent protection devices involved in parameter setting on the distribution line, and measure the adjacent protection R in real time. j-1 、R j The voltage and current values ​​of each level of protection use transformers to collect the local instantaneous voltage values 、 and the instantaneous value of current 、 ; S1.2. Based on the instantaneous voltage and current values ​​collected in S1.1, use the full-cycle subtraction method of the electrical quantity after the fault minus the electrical quantity before the fault to calculate the corresponding R j-1 、R j Positive sequence voltage fault component and positive sequence current fault component ; S1.3. According to R j-1 、R j The relative positions of the positive sequence voltage fault components determine the coordination relationship between them, and the spatial distribution and ratio relationship of the positive sequence voltage fault component amplitude are calculated, specifically: When R j After a fault occurs at point f on the line, R j and superior protection R j-1 With the coordination relationship, the symmetrical component method and fault boundary conditions are used to obtain the adjacent protection R j-1 、R j The positive sequence fault component augmentation network; Let R j-1 The busbar is M , the total equivalent impedance on the back side is , then

[0008] Where, Switch k j-2 Busbar when open M Back-side system positive sequence equivalent impedance, DGj-2 Positive sequence equivalent impedance; From the impedance parallel relationship, we know that The resistance is less than ,but The impedance characteristics of The impedance characteristics are determined; Applying Ohm's law and the impedance proportional relationship, we can obtain:

[0009] Where, For line L j-1 Positive sequence equivalent impedance; , then according to the attenuation characteristics along the line, Amplitude Less than Amplitude ; The above formula is transformed into the ratio expression of the positive sequence voltage fault component amplitude of adjacent protection:

[0010] The ratio of the positive sequence voltage fault component of the adjacent protection depends on the upper protection R j-1 Busbar M The back side equivalent impedance and its corresponding line length; Setting the voltage threshold ,when < When R j Return to step S1.2 to continue calculating the positive sequence voltage fault component and the positive sequence current fault component; when ≥ , proceed to step S2.

[0011] The construction process of the logarithmic inverse time characteristic equation is: For the jth protection device R j , which takes the maximum limit value in the positive sequence voltage fault component The action time is the minimum action time limit of the backup protection t min , that is, the logarithmic inverse time characteristic equation to be solved passes through the constant point , its mathematical expression is:

[0012] Where, Represents R j The action time, x is the inverse time parameter to be determined.

[0013] The formula for deriving the adaptive tuning of the inverse time parameter is as follows: Adjacent protection R j-1 、R j Action time difference for:

[0014] Adjacent protection voltage ratio Determine, and when the ratio is determined, the same x Under the value equal, Greater than or equal to the protection coordination time interval requirement, so R j-1 、R j Corresponding to x The adaptive tuning formula is:

[0015] Where CTI is the protection coordination time interval, which is generally 0.2~0.5s; R j-1 The calculated positive sequence voltage fault component amplitude of the adjacent lower protection and R j The calculated amplitude of the positive sequence voltage fault component of the adjacent upper protection.

[0016] S3 specifically: According to the real-time positive sequence voltage fault component and positive sequence current fault component of the protection device at this level, the amplitude of the positive sequence voltage fault component of the upper protection inferred adjacent lower level and the amplitude of the positive sequence voltage fault component of the lower protection inferred adjacent upper level are calculated. The formula is:

[0017] Where, To be protected by this level R j The relationship between node current and branch current eliminates DG j Positive sequence current fault component after impact.

[0018] S4 is specifically: S4.1. Substitute the positive-sequence voltage fault component amplitude and positive-sequence current fault component calculated in step S3 into the inverse time parameter adaptive setting formula of S2, and adaptively calculate the inverse time parameter values ​​of adjacent protections; S4.2. Substitute the inverse time parameter value calculated in step S4.1 and the positive sequence voltage fault component amplitude measured by the corresponding protection into the logarithmic inverse time characteristic equation in S2, update the logarithmic inverse time characteristic equation, and calculate the action time t j-1 、 t j .

[0019] S5 is specifically: S5.1. All protection devices update their operating times synchronously. The operating time closest to the fault point is the smallest. The operating time of the adjacent upper protection is one step delay CTI longer than the operating time of its immediate lower protection.

[0020] S5.2. When the protection at this level operates correctly and isolates the fault, its upper-level protection starts the return logic. When the protection at this level fails to operate, the upper-level protection performs the tripping operation after the steady-state action criteria are met and the action time is reached, completing the adaptive coordination of the protection action sequence and action logic.

[0021] The beneficial effects of the present invention are: The adaptive differential coordination method for active distribution networks based on the spatial distribution of positive-sequence voltage of the present invention constructs a logarithmic inverse time characteristic equation based on the spatial distribution law of positive-sequence voltage, and utilizes the spatial characteristics of the positive-sequence voltage fault component distributed along the feeder and strongly correlated with the fault location to achieve adaptive online setting of the inverse time parameter. This method eliminates the need for complex setting calculations and offline optimization, and fundamentally avoids the problem of protection setting failure caused by power supply characteristics or topology changes. The adaptive differential coordination mechanism utilizes the voltage distribution characteristics to dynamically generate protection action time, ensuring absolute selectivity and speed of action under different working conditions, and effectively solving the problem of coordination failure caused by power supply characteristics and network topology changes. It only requires the use of local electrical quantity information, without the need for communication or pre-knowledge of the topology structure, and has a small amount of calculation. It is suitable for active distribution network scenarios with a high proportion of DG access, and has important engineering application value and promotion significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the active power distribution network topology in the present invention; Figure 2 Augmenting the network for the positive sequence fault component under any fault type in the present invention; Figure 3 is the spatial distribution curve of the positive sequence voltage fault component in the present invention; Figure 4 Different in the present invention x The changing trend diagram of logarithmic inverse time characteristic curve under the value; Figure 5 R in the present invention j When the adjacent protection R is correctly operated j-1 、R j The action time limit is coordinated with the logic timing diagram; Figure 6 R in the present invention j Adjacent protection R when not in action j-1 、R j Adaptive differential protection action time limit coordination logic timing diagram; Figure 7This is a flow chart of the adaptive level difference matching in the present invention; Figure 8 This is the coordination of adjacent protection levels during a three-phase short circuit (LLL) fault in Example 7 of the present invention.

[0023] Figure 9 This is the coordination of adjacent protection levels during a two-phase short circuit (LL) fault in Example 7 of the present invention.

[0024] Figure 10 This is the coordination of adjacent protection levels when a two-phase short-circuit to ground (LLG) fault occurs in Example 7 of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1 The adaptive differential coordination method of active distribution network based on positive sequence voltage spatial distribution of the present invention aims to solve the problem of difficulty in setting ITOC protection and coordination failure in active distribution network. Figure 1 As shown, it contains two feeders, which are connected by a tie switch S1, which is disconnected during normal operation. S is a traditional synchronous machine power supply; distributed power sources DG1, DG2, and DG3 are connected by switches k 1. k 1. k The state of 3 realizes random switching; R1-R6 are protection devices; L1-L6 are corresponding line lengths; Ld1-Ld7 are constant power loads; f represents the fault point. The overall process is as follows Figure 6 As shown, please follow the steps below: S1. Determine the protection hierarchy and relationships: Determine the number of adjacent protection devices involved in parameter setting on the distribution line and their coordination relationship. Based on the number of adjacent protection devices and their relative positions, determine the spatial distribution characteristics of the positive sequence voltage fault component amplitude along the line and the ratio relationship between the positive sequence voltage fault component amplitudes of adjacent protection devices. S2. Construct a logarithmic inverse time equation: Based on the spatial distribution characteristics of the positive sequence voltage fault component amplitude and the amplitude ratio relationship of adjacent protection determined in S1, construct a logarithmic inverse time characteristic equation and derive the adaptive setting formula of the inverse time parameter of the adjacent protection. S3. Voltage Estimation and Fault Direction Identification: Based on the positive-sequence voltage and current fault components measured in real time by the current protection device, the positive-sequence voltage fault component amplitude of the adjacent upper-level or lower-level protection device is estimated to achieve adaptive fault direction identification. S4. Online parameter calculation and operation time update: Use the adaptive setting formula described in S2 to calculate the inverse time parameter values ​​required by the current protection device or adjacent protection devices online. Update the calculated parameter values ​​to the logarithmic inverse time characteristic equation described in S2 to calculate the operation time of the adjacent protection device under the current fault condition. S5. Adaptive time differential coordination execution: Based on the action time of the adjacent protection devices calculated in S4 and combined with the preset steady-state voltage action criterion, the adjacent protection devices are adaptively coordinated according to their updated action time.

[0027] Example 2 Based on Example 1, S1 is specifically: S1.1. Determine the number of adjacent protection devices involved in parameter setting on the distribution line, and measure the adjacent protection R in real time. j-1 、R j The voltage and current values ​​of each level of protection use transformers to collect the local instantaneous voltage values 、 and the instantaneous value of current 、 ; S1.2. Based on the instantaneous voltage and current values ​​collected in S1.1, use the full-cycle subtraction method of the electrical quantity after the fault minus the electrical quantity before the fault, that is, subtract the measured voltage and current values ​​after the fault from the stored values ​​of voltage and current during normal operation to calculate the corresponding R j-1 、R j Positive sequence voltage fault component and positive sequence current fault component ; S1.3. According to R j-1 、R j The relative positions of the positive sequence voltage fault components determine the coordination relationship between them, and the spatial distribution and ratio relationship of the positive sequence voltage fault component amplitude are calculated, specifically: Taking the coordination relationship between R3 and R2 after the fault at point f on feeder 1 as an example, the symmetrical component method and fault boundary conditions are used to obtain the following: Figure 2 Augmented network with positive sequence fault component for any fault type shown.

[0028] Let the total equivalent impedance of the back side of R2 be , then (1) Where, They are k 1 is open, which is the positive-sequence equivalent impedance of the system on the back side of bus B and the positive-sequence equivalent impedance of DG1.

[0029] According to the impedance parallel relationship, when two impedances are connected in parallel, the magnitude and phase of the total equivalent impedance are dominated by the impedance with smaller resistance. The impedance characteristics are mainly determined by the system backside impedance and line impedance, and are generally resistive-inductive; and the distribution network lines are generally short, and their resistance values ​​are also small. The impedance characteristics depend on the control strategy and voltage drop depth, and may be capacitive in some scenarios. The resistance is much smaller than , then regardless of k 1How does the switch state change? The impedance characteristics are mainly manifested as characteristics.

[0030] Applying Ohm's law and the impedance proportional relationship, we get Figure 2 The voltage division relationship of the series impedance shown is: (2) Where, Represent the positive sequence voltage fault components of R3 and R2 respectively; is the positive sequence equivalent impedance of line L2.

[0031] In formula (2), If it is less than 1, then according to the attenuation characteristics along the line, Amplitude satisfy The relationship between the fault point and the amplitude is shown as follows: Figure 3 As shown in Figure 2, the amplitude of the positive sequence voltage fault component collected by the upper protection is greater than that of the adjacent lower protection.

[0032] The positive sequence voltage fault component ratio of adjacent protections is obtained by transforming formula (2), which reflects the voltage spatial relationship between adjacent protections. The expression is: (3) Where, Indicates amplitude.

[0033] Formula (3) shows that the ratio of the positive sequence voltage fault components of R3 and R2 depends only on the back side equivalent impedance of the bus where R2 is located and the length of the line where it is located, and has nothing to do with the back side equivalent impedance of R3 and the line length.

[0034] Setting the voltage threshold ,when < When R j Return to step S1.2 to continue calculating the positive sequence voltage fault component and the positive sequence current fault component; when ≥ , proceed to step S2.

[0035] Example 3 Based on Example 2, S2 is specifically: For the same input range, the logarithmic function effectively suppresses the large-scale fluctuation of the output by virtue of its inherent smooth change characteristics. Therefore, based on the spatial distribution characteristics and ratio relationship of the positive sequence voltage fault component, a logarithmic inverse time characteristic equation is constructed using only the same electrical quantities flowing through the upper and lower protection levels. For any protection device R j For example, j Indicates the protection number, which takes the maximum limit value in the positive sequence voltage fault component The action time is the minimum action time limit of the backup protection t min , that is, the logarithmic inverse time characteristic equation to be solved passes through the constant point Therefore, the mathematical expression of the logarithmic inverse time characteristic equation is: (4) Where, Respectively represent R j The operating time and positive sequence voltage fault component; x is the inverse time parameter to be determined.

[0036] when Greater than or equal to the voltage threshold When , the action time is calculated by formula (4) ;when Less than , the protection returns.

[0037] Adjacent protection R j-1 、R j Action time difference for: (5) The differential structure of the logarithmic function in formula (5) makes Only by the adjacent protection voltage ratio Decision. After confirmation, the same x Under the value Basically equal, mathematically guaranteeing the reliability of the adjacent protection coordination sequence. In order to meet the selectivity requirements, It should be greater than or equal to the protection coordination time interval (CTI) requirement, from which R can be obtained j-1 、R j Corresponding to x The adaptive tuning formula is: (6) Where CTI is the protection coordination time interval, which is generally 0.2~0.5s; R j-1 The calculated positive sequence voltage fault component amplitude of the adjacent lower protection and R j The calculated amplitude of the positive sequence voltage fault component of the adjacent upper protection.

[0038] Example 4 Based on Example 3, S3 is specifically: To implement parameters x The adaptive setting of R requires the dynamic acquisition of the positive sequence fault voltage component of the adjacent protection. Based on the measured positive sequence voltage fault component and the current topology constraint, any protection node can realize the adaptive calculation of the positive sequence voltage fault component of the adjacent upper and lower protection. j-1 The measured positive sequence voltage fault component and positive sequence current fault component When the adjacent lower level R j The amplitude of the positive sequence voltage fault component ; Known R j The measured positive sequence voltage fault component and positive sequence current fault component When the DG j The positive sequence current fault component provided is used to obtain the positive sequence current fault component flowing through the adjacent upper line , from which we can deduce R j-1 of Therefore, the expression for bidirectional adaptive solution of positive sequence voltage fault component is: (7) When satisfied After the starting conditions are met, the positive sequence voltage fault component is calculated according to formula (7), and the protection R j Calculate the upper protection R j-1 R j-1 Calculate the lower protection R j of.

[0039] Example 5 Based on Example 4, the parameters in formula (6) x The value of determines the action characteristics of formula (4). Figure 4 As shown, with x As the value increases, its absolute value decreases and the curve becomes flatter. This characteristic is consistent with the evolution of the fault type from LLL to asymmetric fault (LLG, LL). x The increasing trend is consistent with that of the three-phase short circuit condition, while the amplitude of the positive sequence voltage fault component under asymmetric fault is significantly lower than that under three-phase short circuit condition. xThe increase in the characteristic of directly improves the protection speed. Therefore, the parameter x The adaptive setting reflects the correlation between the ratio of the positive sequence voltage fault component and the fault type. It can automatically shorten the action time of the logarithmic inverse time equation, dynamically optimize the action characteristics of different fault types, and significantly improve the protection response speed.

[0040] Because the DG equivalent impedance is much larger than the line impedance, its connection has a relatively small impact on the amplitude of the positive-sequence voltage fault component, resulting in a subtle change in the adaptively calculated protection action time. This demonstrates that the inverse time equation based on the spatial distribution of the positive-sequence voltage can effectively suppress fluctuations in protection action time caused by changes in the DG connection state, thereby improving the stability and reliability of the action time.

[0041] Combining formula (4) and formula (6), we can get the same x Next This ensures that the upper protection action time is always greater than the action time of the adjacent lower protection, and the adaptive delay differential action time is always CTI.

[0042] For adjacent protection R j-1 、R j Their action time is dynamically adjusted according to the ratio between the measured value and the estimated value of the positive sequence voltage fault component. Figure 5 The action sequence of the Figure 5 As shown, when R j When the action is correct, R j-1 Return; when R j No action, R j-1 After reaching the calculated action time, the stable voltage is met. Less than rated voltage When the low voltage action criterion is met, the circuit breaker will trip, such as Figure 6 shown.

[0043] In order to achieve the parameters x The adaptive setting and adjacent protection automatically meet the differential coordination relationship. S4 compares the measured and estimated values ​​of the local and adjacent protection positive sequence voltage fault components in real time and adaptively adjusts the equation parameters online. Specifically: S4.1. The amplitude of the positive sequence voltage fault component calculated by equation (7) in S3 is and positive sequence current fault component Substitute into formula (6) to adaptively calculate the inverse time parameters of adjacent protections x value; S4.2. x The value and the corresponding protection measured positive sequence voltage fault component amplitude Substitute into formula (4), update the inverse time equation, and calculate the action time of adjacent protections in parallelt j 、 t j-1 .

[0044] Example 6 Based on Example 5, S5 is specifically: S5.1. With differential coordination, all protection devices synchronize their operating times, with the closest protection point having the shortest operating time. The adjacent upper-level protection device operates one additional time delay (CTI) than the lower-level protection device. This dynamically generates differential operating times that meet absolute selectivity, effectively improving the speed of remote backup protection.

[0045] S5.2, action sequence and action logic, when the lower level protection R j After the fault is isolated by correct action, its upper protection R j-1 Start return logic; when R j When refusing to move, R j-1 In the steady-state action criterion of distinguishing faults from disturbances ,achieve t j-1 The tripping operation is performed after the time has passed, thereby completing the adaptive coordination of the protection action sequence and action logic.

[0046] Based on the attenuation law of the positive sequence voltage fault component Figure 3 As shown in Figure 2, the logarithmic inverse time characteristic equation (4) is constructed to transform the physical characteristics into mathematical criteria, realize the parallel calculation of the protection action time of each level under different fault conditions, and form a natural time ladder, as shown in Figure 2. Figure 5 Parameters are dynamically generated by the ratio of measured value to estimated value. x , completely get rid of the dependence on network parameters and DG access status, and achieve adaptive coordination without relying on power type and network topology.

[0047] Example 7 Build in PSCAD Figure 1 The 10kV active distribution network model shown in the figure verifies the parameter adaptive setting and protection adaptive coordination under different fault conditions and different DG capacities. Among them, CTI is taken as 0.2s. Take it as 0.5s. According to the "DL / T 5729-2016 Technical Guidelines for Distribution Network Planning and Design", the allowable deviation of the three-phase power supply voltage of 10(20)kV and below systems is ±7% of the nominal voltage. Considering the supporting effect of DG access on voltage, take ,but .

[0048] Table 1 shows the different transition resistances when no DG is connected. R gAnd the positive sequence voltage fault component amplitude and parameters of R3 and R2 under different fault types x The calculated value and protection action time of DG1 and DG2 are 2MW. n 1 and n 2 respectively represent their access numbers, μ It represents the ratio of the distance between the fault point f and the busbar C to the total length of the line. Table 2 shows the different DG capacities and different μ The positive sequence voltage fault component amplitude and parameters of R3 and R2 x The calculated value and protection action time.

[0049] Table 1

[0050] As shown in Table 1, when the fault type changes from LLL to LL and then to LLG, △ U 13 ,△ U 12 It shows a significant decreasing trend. This change law is essentially a direct reflection of the difference in the distribution characteristics of the positive sequence voltage of the power grid under different fault types. The parameters are adaptively generated by formula (6) x After, action time t 3 and t A difference of 2 is always the CTI.

[0051] Figure 8 、 Figure 9 、 Figure 10 The distribution of the positive-sequence voltage fault component and action time of R3 and R2 under different fault conditions is clearly shown. Among the three typical faults of LLL, LL and LLG, the amplitude of the positive-sequence voltage fault component generated by the LLL fault is significantly larger than that of the LL and LLG faults, which is consistent with the physical characteristics of strong metallic faults leading to higher voltage drops. It is worth noting that although the voltage amplitudes of LL and LLG faults are lower, their calculated protection action times do not show significant differences compared with LLL faults. This phenomenon verifies the core advantage of the method of the present invention: by dynamically adjusting the inverse time parameter of the positive-sequence voltage fault component amplitude, the action time is adaptively compensated for the difference in electrical quantities caused by different fault types, thereby ensuring the stability of the protection sequence. When the fault type is determined and the transition resistance is increased to 10Ω, the amplitude of the positive-sequence voltage fault component decreases and the adaptively calculated action time increases, but the difference in adjacent protection action times is always 0.2s, which is completely consistent with the preset CTI value. This quantitative law verifies the effectiveness of the scheme: the inverse time parameter x The online setting accurately offsets the voltage amplitude change caused by the transition resistance and maintains a constant action time difference.

[0052] Table 2

[0053] Table 2 shows that in a typical scenario where the DG access capacity and location change, the protection device is U 13 ,△ U 12 Dynamic Updates x The adaptive calculation of adjacent protection operation times is implemented using Equation (1), verifying the robustness of the proposed adaptive coordination mechanism. This process is completely online and autonomous, requiring no human intervention or preset setting tables. This demonstrates that the logarithmic inverse time equation deeply matches the dynamic distribution characteristics of the positive sequence voltage fault component as the fault location changes.

[0054] Simulation verification shows that no matter how the network power flow changes, the equation can accurately capture the spatial gradient variation characteristics of the positive sequence voltage fault component and achieve x Adaptive adjustment; the set value no longer relies on offline calculation and static setting, but is dynamically generated according to the real-time status of the power grid (fault type, DG status). The adaptive differential coordination mechanism is constructed by utilizing the spatial difference of the positive sequence voltage fault component, and the adaptive setting of the action time is realized by the logarithmic inverse time characteristic equation. The inverse time parameter and action time are adjusted in real time according to the changes in the fault condition and network topology, ensuring that the protection action time can be adaptively adjusted according to the severity of the fault, ensuring selectivity and speed, and effectively responding to changes in network topology, DG output and R g The diverse scenarios and fault conditions provide solutions for distribution network protection with a high proportion of DGs access.

[0055] The present invention discloses an adaptive differential coordination method for an active distribution network based on the spatial distribution of positive-sequence voltage. The working principle is as follows: utilizing the spatial distribution law of the positive-sequence voltage fault component along the feeder, which is strongly correlated with the fault location, to construct a logarithmic inverse time characteristic equation based on the positive-sequence voltage fault component; by comparing the positive-sequence voltage fault component amplitudes actually measured and inferred by local and adjacent protections, adaptive discrimination of the fault direction is achieved, and the protection determined to be a positive direction fault has its inverse time parameters adaptively adjusted online; based on real-time updated parameters, adjacent protections calculate the action time in parallel, and the action time of the protection closest to the fault point is the shortest; utilizing the inherent relationship between the voltage ratios of adjacent protections, an action time differential with absolute selectivity is dynamically generated; and combining precise protection start-up criteria and a steady-state voltage action criterion for distinguishing between faults and disturbances to ensure the reliability of the differential coordination of adjacent protections.

[0056] The key advantage of this method lies in its strong adaptability: regardless of fault type, DG output fluctuations, or network topology changes (such as DG switching or topology reconfiguration), protection settings can be adjusted online in real time, dynamically generating differential operating times that ensure absolute selectivity. This enables adaptive, step-by-step coordination of multi-level protection, eliminating the need to rely on preset network topology and power source type information, fundamentally avoiding protection setting failures caused by power source characteristics or topology changes. The adaptive differential coordination mechanism leverages voltage distribution characteristics to dynamically generate protection operating times, ensuring absolute selectivity and rapidity under different operating conditions. This effectively addresses the protection coordination challenges faced by active distribution networks with high penetration rates of new energy access and flexible and changeable topologies, significantly improving protection selectivity and rapidity. Relying solely on local electrical quantity information, it requires no communication or pre-knowledge of the topology, requires minimal computational effort, and is suitable for active distribution network scenarios with a high proportion of DG access. It holds significant engineering application value and widespread application significance.

Claims

1. An adaptive differential coordination method for active distribution network based on positive sequence voltage spatial distribution is characterized by: Here are the steps: S1. Determine the spatial distribution characteristics of the positive sequence voltage fault component amplitude along the line based on the number of adjacent protection devices involved in parameter setting and their coordination relationships on the distribution line; S2. Construct a logarithmic inverse time characteristic equation and derive the adaptive tuning formula for the inverse time parameter; S3. Calculate the amplitude of the positive-sequence voltage fault component of the adjacent upper or lower protection device based on the real-time positive-sequence voltage and current fault components of the current protection device; S4. Calculate the inverse time parameter value using the adaptive setting formula of S2 and update it into the logarithmic inverse time characteristic equation of S2 to obtain the operating time of the adjacent protection device under the current fault condition. S5. Combined with the preset steady-state voltage action criterion, adjacent protection devices are enabled to perform adaptive time difference coordination according to their updated action times.

2. The method for adaptive differential coordination of active power distribution network based on positive sequence voltage spatial distribution according to claim 1, characterized in that: The S1 is specifically: S1.

1. Determine the number of adjacent protection devices involved in parameter setting on the distribution line, and measure the adjacent protection R in real time. j-1 、R j The voltage and current values ​​of each level of protection use transformers to collect the local instantaneous voltage values 、 and the instantaneous value of current 、 ; S1.

2. Based on the instantaneous voltage and current values ​​collected in S1.1, use the full-cycle subtraction method of the electrical quantity after the fault minus the electrical quantity before the fault to calculate the corresponding R j-1 、R j Positive sequence voltage fault component and positive sequence current fault component ; S1.

3. According to R j-1 、R j The relative positions of the positive sequence voltage fault components are used to determine their coordination relationship, and the spatial distribution and ratio relationship of the positive sequence voltage fault component amplitude are calculated.

3. The method for adaptive differential coordination of active power distribution network based on positive sequence voltage spatial distribution according to claim 2, characterized in that: The S1.3 is specifically: When R j After a fault occurs at point f on the line, R j and superior protection R j-1 With the coordination relationship, the symmetrical component method and fault boundary conditions are used to obtain the adjacent protection R j-1 、R j The positive sequence fault component augmentation network; Let R j-1 The busbar is M , the total equivalent impedance on the back side is , then Where, Switch k j-2 Busbar when open M Back-side system positive sequence equivalent impedance, DG j-2 The positive sequence equivalent impedance; From the impedance parallel relationship, we know that The resistance is less than ,but The impedance characteristics of The impedance characteristics are determined; Applying Ohm's law and the impedance proportional relationship, we can get: Where, For line L j-1 Positive sequence equivalent impedance; , then according to the attenuation characteristics along the line, Amplitude Less than Amplitude ; The above formula is transformed into the ratio expression of the positive sequence voltage fault component amplitude of adjacent protection: The ratio of the positive sequence voltage fault component of the adjacent protection depends on the upper protection R j-1 Busbar M The back side equivalent impedance and its corresponding line length; Setting the voltage threshold ,when < When R j Return to step S1.2 to continue calculating the positive sequence voltage fault component and the positive sequence current fault component; when ≥ , proceed to step S2.

4. The method for adaptive differential coordination of active power distribution network based on positive sequence voltage spatial distribution according to claim 3 is characterized in that: The construction process of the logarithmic inverse time characteristic equation is: For the jth protection device R j , which takes the maximum limit value in the positive sequence voltage fault component The action time is the minimum action time limit of the backup protection t min , that is, the logarithmic inverse time characteristic equation to be solved passes through the constant point , its mathematical expression is: Where, Represents R j The action time, x is the inverse time parameter to be determined.

5. The method for adaptive differential coordination of active power distribution network based on positive sequence voltage spatial distribution according to claim 4, characterized in that: The derived inverse time parameter adaptive setting formula is specifically: Adjacent protection R j-1 、R j Action time difference for: Adjacent protection voltage ratio Decide, Greater than or equal to the protection coordination time interval requirement, so R j-1 、R j Corresponding to x The adaptive tuning formula is: Where CTI is the protection coordination time interval, which is generally 0.2~0.5s; R j-1 The calculated positive sequence voltage fault component amplitude of the adjacent lower protection and R j The calculated amplitude of the positive sequence voltage fault component of the adjacent upper protection.

6. The method for adaptive differential coordination of active power distribution network based on positive sequence voltage spatial distribution according to claim 1, characterized in that: The S3 is specifically: According to the real-time positive sequence voltage fault component and positive sequence current fault component of the protection device at this level, the amplitude of the positive sequence voltage fault component of the upper protection inferred adjacent lower level and the amplitude of the positive sequence voltage fault component of the lower protection inferred adjacent upper level are calculated. The formula is: Where, To be protected by this level R j The relationship between node current and branch current eliminates DG j Positive sequence current fault component after impact.

7. The method for adaptive differential coordination of active power distribution network based on positive sequence voltage spatial distribution according to claim 1, characterized in that: The S4 is specifically: S4.

1. Substitute the positive-sequence voltage fault component amplitude and positive-sequence current fault component calculated in step S3 into the inverse time parameter adaptive setting formula of S2, and adaptively calculate the inverse time parameter values ​​of each adjacent protection; S4.

2. Substitute the inverse time parameter value calculated in step S4.1 and the positive sequence voltage fault component amplitude measured by the corresponding protection into the logarithmic inverse time characteristic equation in S2, update the logarithmic inverse time characteristic equation, and calculate the action time t j-1 、 t j .

8. The method for adaptive differential coordination of active power distribution network based on positive sequence voltage spatial distribution according to claim 1, characterized in that: The S5 is specifically: S5.

1. All protection devices update their operating times synchronously. The operating time closest to the fault point is the smallest. The operating time of the adjacent upper protection level is one step delay (CTI) longer than the operating time of its immediate lower protection level. S5.

2. When the protection at this level operates correctly and isolates the fault, its upper-level protection starts the return logic. When the protection at this level fails to operate, the upper-level protection performs the tripping operation after the steady-state action criteria are met and the action time is reached, completing the adaptive coordination of the protection action sequence and action logic.

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