Active power distribution network adaptive step matching method based on positive sequence voltage space distribution

Abstract

The application discloses a self-adaptive step cooperation method of an active power distribution network based on positive sequence voltage space distribution, solves the problem of traditional protection setting failure caused by random access of DG and flexible adjustment of network topology, utilizes the spatial characteristics of positive sequence voltage fault components along the distribution of a feeder and strong correlation with a fault position, constructs a logarithmic inverse time limit characteristic equation based on the components, compares the measured values and calculated values of the positive sequence voltage fault components of local and adjacent protection in real time, and sets the equation parameters online and adaptively. Based on the real-time updated parameters, adjacent protection calculates each automatic action time in parallel, dynamically generates an action time step meeting absolute selectivity, and effectively improves the speed of remote backup protection. The method of the application combines a starting criterion and a steady-state voltage action criterion distinguishing between faults and disturbances, and finally realizes self-adaptive step-by-step cooperation of multi-level protection independent of network topology and power supply types.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power system relay protection, and particularly relates to an adaptive differential coordination method for active distribution networks based on spatial distribution of positive sequence voltage. BACKGROUND

[0002] Inverse-Time Overcurrent (ITOC) is a protection mode with inverse relationship between action time and current amplitude, and has certain adaptability. However, with large-scale access of Distributed Generation (DG), the type and topology structure of power sources in active distribution networks change dynamically, resulting in changes in the amplitude and direction of fault current and short-circuit current contribution, and further causing setting problems and coordination difficulties of traditional ITOC protection, which seriously threatens the reliability of system protection.

[0003] Existing improved methods mostly optimize ITOC inverse-time parameters (such as starting current and time constant) or introduce voltage and impedance measurement signals for compensation, but still rely on fixed network parameters and power source types, and the setting process is complex and lacks real-time performance, which makes it difficult to achieve effective adaptive response to changes in power source characteristics and topology, and cannot meet the needs of active distribution networks for protection adaptability and coordination. At the same time, topology adjustment such as DG access and exit and switch operation further increases the dynamics of protection coordination, making it difficult for traditional offline-set differential coordination to adapt to complex and variable operating conditions.

[0004] To solve the above problems, the application uses the positive sequence voltage fault component to construct a logarithmic inverse-time characteristic equation, and proposes an adaptive differential coordination method for active distribution networks based on spatial distribution of positive sequence voltage. SUMMARY

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

[0006] The technical solution adopted by the application is an adaptive differential coordination method for active distribution networks based on spatial distribution of positive sequence voltage, and the steps are as follows:

[0007] S1. Determine the spatial distribution characteristics of the amplitude of positive sequence voltage fault component along the line according to the number of adjacent protection devices on the distribution line participating in parameter setting and their coordination relationship;

[0008] S2. Construct the logarithmic inverse-time characteristic equation and derive the adaptive tuning formula for the inverse-time parameter;

[0009] S3. Calculate the amplitude of the positive sequence voltage fault component of the adjacent upstream or downstream protection device based on the real-time positive sequence voltage and current fault components of the protection device at this level.

[0010] S4. Calculate the inverse time parameter value using the adaptive setting formula of S2, and update it to the logarithmic inverse time characteristic equation of S2 to obtain the operating time of the adjacent protection device under the current fault state.

[0011] S5. Combining the preset steady-state voltage action criteria, adjacent protection devices are made to adaptively coordinate based on their updated action times.

[0012] The invention is further characterized in that,

[0013] S1 specifically refers to:

[0014] S1.1. Determine the number of adjacent protection devices involved in parameter setting on the distribution line, and measure the R value of adjacent protection devices in real time. j-1 R j The voltage and current values, that is, the instantaneous voltage values ​​collected locally by the current transformers at each level of protection. , and instantaneous current value , ;

[0015] S1.2. Based on the instantaneous voltage and current values ​​collected in S1.1, the corresponding R is calculated using the full-cycle subtraction method of subtracting the electrical quantities before and after the fault from the electrical quantities after the fault. j-1 R j Positive sequence voltage fault component and positive sequence current fault component ;

[0016] S1.3. According to R j-1 R j The relative positions determine their coordination relationship, and the spatial distribution and ratio relationship of the positive sequence voltage fault component amplitude are calculated, specifically:

[0017] When R j After a fault occurs at point f on the line, R j and the superior protection R j-1 Having a coordination relationship, using the symmetrical component method and fault boundary conditions, we obtain R including adjacent protection. j-1 R j Ortho-sequence fault component augmentation network;

[0018] Let R j-1 The busbar is M, the back side total equivalent impedance is , then

[0019]

[0020] In the formula, respectively, are switches k j-2 When opened, the bus M Back side system positive sequence equivalent impedance, DG j-2 The positive sequence equivalent impedance of the bus

[0021] From the impedance parallel relationship, The resistance value of the bus , then The impedance characteristics of the bus The impedance characteristics of the bus

[0022] Applying Ohm's law and impedance ratio relationship, we can get:

[0023]

[0024] In the formula, The positive sequence equivalent impedance of the line L j-1 , then from the line attenuation characteristics along the line, The amplitude of the bus The amplitude of the bus is less than The amplitude of the bus ;

[0025] The ratio expression of the positive sequence voltage fault component amplitude of adjacent protection is obtained by transforming the above formula:

[0026]

[0027] The ratio of the positive sequence voltage fault component of adjacent protection depends on the back equivalent impedance of the bus j-1 where the upper protection R M and its corresponding line length;

[0028] Set the voltage threshold When , the bus j Returns to step S1.2 to continue the calculation of the positive sequence voltage fault component and the positive sequence current fault component;

[0029] When ≥ , step S2 is performed.

[0030] The construction process of the logarithmic inverse time characteristic equation is as follows:

[0031] For the jth protection device R j ​, which acts when the positive sequence voltage fault component takes the maximum limit value , and the action time is the backup protection minimum action time limit value t min , that is, the logarithmic inverse time characteristic equation to be solved passes through the constant point , the mathematical expression of which is:

[0032]

[0033] In the formula, , the action time of R j , is to be solved. x

[0034] The specific derivation of the adaptive setting formula of the inverse time parameter is as follows:

[0035] The action time difference value of the adjacent protection R j-1 , R j is:

[0036]

[0037] is determined by the adjacent protection voltage ratio , and when the ratio is determined, the x value under the same is equal, is greater than or equal to the requirement of the protection coordination time interval, so the adaptive setting formula of R j-1 , R j corresponding to R j-1 , R j is: x

[0038]

[0039] In the formula, CTI is the protection coordination time interval, generally taken as 0.2-0.5s; are the positive sequence voltage fault component amplitudes of the adjacent lower-level protection calculated by R j-1 , and the positive sequence voltage fault component amplitudes of the adjacent upper-level protection calculated by R j .

[0040] S3 is specifically:

[0041] According to the real-time positive sequence voltage fault component and the positive sequence current fault component of the protection device of the current level, the positive sequence voltage fault component amplitudes of the adjacent lower-level and lower-level protection calculated by the upper-level protection are calculated, and the formula is:

[0042]

[0043] In the formula, is the positive sequence voltage fault component amplitude calculated by the protection Rj Eliminate the relationship between node current and branch current in DG j The positive sequence current fault component after the impact.

[0044] S4 specifically refers to:

[0045] S4.1. Substitute the magnitude of the positive sequence voltage fault component and the positive sequence current fault component obtained in step S3 into the adaptive setting formula of the inverse time parameter in S2, and adaptively calculate the inverse time parameter values ​​of adjacent protections.

[0046] S4.2. Substitute the inverse-time parameter values ​​calculated in step S4.1 and the corresponding measured positive-sequence voltage fault component amplitudes into the logarithmic inverse-time characteristic equation in S2, update the logarithmic inverse-time characteristic equation, and calculate the operating time. t j-1 , t j .

[0047] S5 specifically refers to:

[0048] S5.1. All protection devices update their operating times synchronously. The operating time of the device closest to the fault point is the shortest, and the operating time of the adjacent upstream protection is one step delay (CTI) longer than the operating time of its directly downstream protection.

[0049] S5.2. When the protection at this level operates correctly and isolates the fault, the protection at the next higher level starts the return logic; when the protection at this level fails to operate, the protection at the next higher level performs a trip operation after satisfying the steady-state operation criteria and reaching the operation time, thus completing the adaptive coordination of the protection operation timing and operation logic.

[0050] The beneficial effects of this invention are:

[0051] The adaptive differential coordination method for active distribution networks based on the spatial distribution of positive-sequence voltage of this 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 parameters. This eliminates the need for complex setting calculations and offline optimization, fundamentally avoiding protection setting failures caused by power supply characteristics or topology changes. The adaptive differential coordination mechanism dynamically generates protection action time using voltage distribution characteristics, ensuring absolute selectivity and speed of action under different operating conditions, effectively solving coordination failures caused by power supply characteristics and network topology changes. It only requires local electrical quantity information, without communication or prior knowledge of the topology, and has low computational load. It is suitable for active distribution network scenarios with a high proportion of distributed generation (DG) access, and has significant engineering application value and promotion significance. Attached Figure Description

[0052] Figure 1A topology diagram of an active power distribution network in the present application;

[0053] Figure 2 An augmented network of positive sequence fault components under any fault type in the present application;

[0054] Figure 3 A space distribution curve of positive sequence voltage fault components in the present application;

[0055] Figure 4 A change trend graph of logarithmic inverse time limit characteristic curves under different x values in the present application;

[0056] Figure 5 An R j action time limit coordination logic timing diagram of adjacent protection R j-1 , R j in the present application when correctly acting;

[0057] Figure 6 An R j action time limit coordination logic timing diagram of adaptive differential protection R j-1 , R j in the present application when not acting;

[0058] Figure 7 An adaptive differential coordination flow chart in the present application;

[0059] Figure 8 A differential coordination condition of adjacent protection in the present application when a three-phase short circuit (LLL) fault occurs in Embodiment 7.

[0060] Figure 9 A differential coordination condition of adjacent protection in the present application when a two-phase short circuit (LL) fault occurs in Embodiment 7.

[0061] Figure 10 A differential coordination condition of adjacent protection in the present application when a two-phase short circuit to ground (LLG) fault occurs in Embodiment 7. DETAILED DESCRIPTION

[0062] The present application will be described in detail below in combination with the drawings and specific embodiments.

[0063] Embodiment 1

[0064] The adaptive differential coordination method of an active power distribution network based on positive sequence voltage space distribution in the present application aims to solve the problems of ITOC protection setting difficulty and coordination failure in the active power distribution network. A typical radial structure of a power distribution network is shown in Figure 1 , which contains two feeder lines, which are connected through a tie switch S1, and the switch is disconnected in normal operation. S is a traditional synchronous generator; distributed power sources DG1, DG2 and DG3 are connected through switches k1、 k 1、 k 3 State random on-off; R1-R6 are protection devices; L1-L6 are corresponding line lengths; Ld1-Ld7 are constant power loads; f represents a fault point. The overall flow is as shown in Figure 6 , and is implemented according to the following steps:

[0065] S1. Determine the protection level and relationship: determine the number of adjacent protection devices participating in parameter setting on the distribution line and the coordination relationship thereof, 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 protections according to the number of adjacent protection devices and the relative position relationship thereof;

[0066] S2. Construct a logarithmic inverse time equation: according to the spatial distribution characteristics of the positive sequence voltage fault component amplitude and the amplitude ratio relationship of adjacent protections determined in S1, construct a logarithmic inverse time characteristic equation, and derive an adaptive setting formula of the inverse time parameters of adjacent protections;

[0067] S3. Voltage calculation and fault direction discrimination: according to the real-time measured positive sequence voltage fault component and positive sequence current fault component of the protection device at this level, calculate the positive sequence voltage fault component amplitude of the adjacent upper-level protection device or adjacent lower-level protection device, and realize adaptive discrimination of the fault direction;

[0068] S4. Online parameter calculation and action time updating: use the adaptive setting formula described in S2 to calculate the inverse time parameter value required by the protection device at this level or adjacent protection devices online, and update the calculated parameter value to the logarithmic inverse time characteristic equation described in S2 to calculate the action time of the adjacent protection device under the current fault state;

[0069] S5. Adaptive differential coordination: based on the action time of the adjacent protection device calculated in S4, combine the preset steady-state voltage action criterion, so that the adjacent protection device performs adaptive time differential coordination according to the updated action time.

[0070] Example 2

[0071] On the basis of Example 1, S1 is specifically:

[0072] S1.1. Determine the number of adjacent protection devices participating in parameter setting on the distribution line, and measure the voltage and current values of adjacent protections R j-1 、 j in real time, that is, each level of protection uses a mutual inductor to collect local voltage instantaneous value 、 and current instantaneous value 、 ;

[0073] S1.2. According to the voltage instantaneous value and the current instantaneous value collected in S1.1, the post-fault electrical quantity is subtracted from the pre-fault electrical quantity by the full-cycle subtraction method, that is, the post-fault voltage and current measured values are subtracted from the normal voltage and current stored values, to calculate the positive sequence voltage fault component j-1 and the positive sequence current fault component j ; ;

[0074] S1.3. According to the relative position of R j-1 and R j , the coordination relationship between them is determined, and the positive sequence voltage fault component amplitude space distribution and ratio relationship are calculated, specifically as follows:

[0075] Taking the coordination relationship between R3 and R2 after the fault at point f on feeder 1 as an example, the positive sequence fault component augmented network under any fault type is obtained by using the symmetrical component method and the fault boundary condition, as shown in Figure 2 .

[0076] Let the total equivalent impedance on the back side of R2 be , then

[0077] (1)

[0078] In the formula, Z 1 and Z k are respectively the positive sequence equivalent impedance of the bus B back side system and the positive sequence equivalent impedance of DG1 when the switch is opened.

[0079] It is known from the impedance parallel relationship that when two impedances are in parallel, the size and phase of the total equivalent impedance are dominated by the impedance with smaller resistance. In formula (1), the impedance characteristics of Z are mainly determined by the system back side impedance and the line impedance, and generally exhibit resistive and inductive characteristics; and the line of the distribution network is generally short and has small resistance. The impedance characteristics of Z depend on the control strategy and the voltage drop depth, and may exhibit capacitive distribution in some scenarios. Considering that the resistance of Z is much smaller than that of Z k , the impedance characteristics of Z mainly exhibit the characteristics of Z regardless of the switch state of Z .

[0080] According to Ohm's law and the voltage division relationship of the series impedance shown in Figure 2 , the following formula (2) can be obtained:

[0081] (2)

[0082] In the formula, Z These represent the positive sequence voltage fault components of R3 and R2, respectively. This is the positive sequence equivalent impedance of line L2.

[0083] In equation (2), If it is less than 1, then according to the attenuation characteristics along the line, amplitude satisfy The relationship shows a spatial distribution pattern where "the closer to the fault point, the greater the amplitude." For example... Figure 3 As shown, the amplitude of the positive sequence voltage fault component collected by the upper-level protection is greater than that of the adjacent lower-level protection.

[0084] The ratio of positive-sequence voltage fault components of adjacent protections is obtained by transforming equation (2), which reflects the voltage spatial relationship between adjacent protections. The expression is:

[0085] (3)

[0086] In the formula, Indicates the amplitude.

[0087] Equation (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 is independent of the back-side equivalent impedance of R3 and the length of the line.

[0088] Set voltage threshold ,when < At that time, R j Return to step S1.2 to continue calculating the positive sequence voltage fault component and the positive sequence current fault component;

[0089] when ≥ Then proceed to step S2.

[0090] Example 3

[0091] Based on Example 2, S2 specifically includes:

[0092] For the same input range, the logarithmic function, with its inherently smooth variation characteristics, effectively suppresses large-range output fluctuations. Therefore, based on the spatial distribution characteristics and ratio relationships of the positive-sequence voltage fault components, a logarithmic inverse-time characteristic equation is constructed that utilizes only the same electrical quantities flowing through the upstream and downstream protection systems. For any protection device R... j In other words, j This indicates the protection number, which takes the maximum value during positive-sequence voltage fault components. The operating time is the minimum operating time limit for backup protection. t min That is, the logarithmic inverse-time characteristic equation to be solved passes through a constant point. Therefore, the mathematical expression of the logarithmic inverse time characteristic equation is:

[0093] (4)

[0094] wherein, respectively represent the action time of R j , the positive sequence voltage fault component; x is the inverse time parameter to be solved.

[0095] When is greater than or equal to the voltage threshold , the action time is calculated by formula (4); when is less than , the protection returns.

[0096] The difference value j-1 of the action time of adjacent protections R j is:

[0097] (5)

[0098] The difference structure of the logarithmic function in formula (5) makes only determined by the voltage ratio of the adjacent protection. And when is determined, the x at the same value is basically equal, which mathematically guarantees the reliability of the coordination timing of the adjacent protection. In order to meet the requirement of selectivity, should be greater than or equal to the coordination time interval (CTI), from which the adaptive setting formula of j-1 , R j corresponding to x can be obtained.

[0099] (6)

[0100] In formula (6), CTI is the coordination time interval, generally taken as 0.2-0.5s; are respectively the positive sequence voltage fault component amplitude of the adjacent lower protection calculated by R j-1 and the positive sequence voltage fault component amplitude of the adjacent upper protection calculated by R j .

[0101] Embodiment 4

[0102] On the basis of embodiment 3, S3 is specifically:

[0103] In order to realize the parameter​x The adaptive setting requires dynamically acquiring the positive-sequence fault voltage components of adjacent protections. Any protection node, based on measured positive-sequence fault voltage components and current topology constraints, can adaptively calculate the positive-sequence fault voltage components of adjacent upstream and downstream protections. That is, given R... j-1 Measured positive sequence voltage fault component and positive sequence current fault component At that time, the adjacent lower-level R can be calculated. j positive sequence voltage fault component amplitude Given R j Measured positive sequence voltage fault component and positive sequence current fault component At that time, the relationship between branch current and node current is used to eliminate DG. j The provided positive-sequence current fault component is used to obtain the positive-sequence current fault component flowing through the adjacent upstream line. From this, R can be calculated. j-1 of Therefore, the expression for bidirectional adaptive solution of the positive-sequence voltage fault component is:

[0104] (7)

[0105] When satisfied After the start-up conditions are met, the positive sequence voltage fault component is calculated according to equation (7), and the R of this level of protection is used. j Calculate the upstream protection R j-1 Protected by higher authorities j-1 Calculate the lower-level protection R j of.

[0106] Example 5

[0107] Based on Example 4, the parameters in Equation (6) x The value of determines the action characteristics of equation (4). For example, Figure 4 As shown, with x As the value increases, its absolute value decreases, and the curve becomes flatter. This characteristic is related to the evolution of fault types from LLL to asymmetric faults (LLG, LL). x The increasing trend is consistent, but the amplitude of the positive sequence voltage fault component under asymmetrical fault conditions is significantly lower than that under three-phase short-circuit conditions. x The increased characteristic directly improves the protection's quick-acting capability. Therefore, the parameters x The adaptive setting reflects the correlation between the ratio of positive sequence voltage fault components and fault type, can automatically reduce the action time of logarithmic inverse time equations, dynamically optimize the action characteristics of different fault types, and significantly improve the protection response speed.

[0108] Since the equivalent impedance of DG is much larger than the line impedance, its access has relatively small influence on the amplitude change of the positive sequence voltage fault component, so the adaptive calculation of the protection action time change is also not obvious. Thus, it is shown that the inverse time equation based on the spatial distribution of the positive sequence voltage can effectively suppress the fluctuation of the protection action time caused by the state change of the DG access, thereby improving the stability and reliability of the action time.

[0109] Combining equation (4) and equation (6), the same x CTI . This ensures that the action time of the upper protection is always greater than the action time of the adjacent lower protection, and the differential action time of the adaptive delay is always CTI.

[0110] For adjacent protections R j-1 , R j , their action times are dynamically adjusted according to the ratio relationship between the measured value and the calculated value of the positive sequence voltage fault component, and the adaptive cooperation is realized according to the action time sequence of Figure 5 . As shown in Figure 5 , when R j correctly acts, R j-1 returns; when R j does not act, R j-1 reaches the calculated action time, and when the low-voltage action criterion that the stable voltage is less than the rated voltage is met, the circuit breaker is tripped, as shown in Figure 6 .

[0111] In order to realize the adaptive setting of the parameters x and the automatic satisfaction of the differential coordination relationship of the adjacent protections, S4 compares the measured value and the calculated value of the local and adjacent protection positive sequence voltage fault components in real time to adaptively set the equation parameters online. Specifically:

[0112] S4.1, the positive sequence voltage fault component amplitude calculated by equation (7) in S3 and the positive sequence current fault component are substituted into equation (6) to adaptively calculate the inverse time parameters x of each adjacent protection;

[0113] S4.2, the x value and the measured positive sequence voltage fault component amplitude of the corresponding protection are substituted into equation (4) to update the inverse time equation, and the adjacent protections calculate their action times t j , t j-1 .

[0114] Example 6

[0115] On the basis of embodiment 5, S5 is specifically:

[0116] S5.1, the execution of the differential coordination, all protection devices update the action time synchronously, the action time of the nearest fault point is the smallest, and the action time of the adjacent upper protection is one step delay CTI than the lower protection. The action time differential that meets the absolute selectivity is generated dynamically, and the speed of the remote backup protection is effectively improved.

[0117] S5.2, the action timing and the action logic, when the lower protection R j correctly acts to isolate the fault, its upper protection R j-1 starts the return logic; when R j refuses to act, R j-1 meets the steady-state action criterion for distinguishing faults from disturbances , reaches t j-1 the time to execute the tripping operation, so as to complete the adaptive coordination of the protection action timing and the action logic.

[0118] Based on the fault component attenuation law of the positive sequence voltage as shown in Figure 3 , the logarithmic inverse time limit characteristic equation (4) is constructed, the physical characteristics are converted into mathematical criteria, the action time of each level of protection under different fault conditions is calculated in parallel, and the natural time ladder is formed, as shown in Figure 5 . The parameters x are dynamically generated through the ratio of the measured value / calculation value, which completely gets rid of the dependence on network parameters and DG access state, and realizes the adaptive coordination without relying on power supply type and network topology.

[0119] Embodiment 7

[0120] A 10kV active power distribution network model as shown in Figure 1 is built in PSCAD to verify the parameter adaptive setting and protection adaptive coordination under different fault conditions and different DG capacities. Among them, CTI is taken as 0.2s, and CTI is taken as 0.5s. According to “DL / T 5729-2016 Power Distribution Network Planning and Design Technical Guidelines”, the allowable deviation of three-phase power supply voltage of 10(20)kV and below is ±7% of the nominal voltage. Considering the supporting effect of DG access on voltage, then .

[0121] Table 1 shows the calculation values of the positive sequence voltage fault component amplitude of R3 and R2, the parameter R g and the protection action time under different transition resistances x and different fault types without DG access. Set the reference capacity of DG1 and DG2 to 2MW, and let n 1 andn 2 respectively represent their access number, μ represents the ratio of the distance between fault point f and bus C to the total length of line, Table 2 gives the different DG capacity and different μ the positive sequence voltage fault component amplitude of R3, R2, parameters x calculated value and protection action time.

[0122] Table 1

[0123]

[0124] From Table 1, when the fault type changes from LLL to LL to LLG, △ U 13 , △ U 12 shows a significant decreasing trend, which is essentially a direct reflection of the difference in the distribution characteristics of the positive sequence voltage under different fault types. After the adaptive generation of parameters x , the difference between the action time t 3 and t 2 is always CTI.

[0125] Figure 8 , Figure 9 , Figure 10 clearly shows the distribution of R3, R2 positive sequence voltage fault component and action time under different fault conditions. In the three typical faults of LLL, LL and LLG, the amplitude of the positive sequence voltage fault component generated by LLL fault is significantly larger than that of LL and LLG faults, which is consistent with the physical characteristics that strong metallic faults cause higher voltage drop. It is worth noting that although the voltage amplitude of LL and LLG faults is low, the calculated protection action time does not show significant difference compared with LLL fault. This phenomenon verifies the core advantage of the method: through the dynamic setting of the amplitude of the positive sequence voltage fault component, the action time is adaptively compensated for the electrical quantity difference caused by different fault types, which guarantees the stability of the protection time sequence. When the fault type is determined and the transition resistance increases to 10Ω, the amplitude of the positive sequence voltage fault component decreases and the adaptively calculated action time increases, but the difference between the 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 online setting of the inverse time limit parameter x precisely offsets the voltage amplitude change caused by the transition resistance, maintaining the constant action time difference.

[0126] Table 2

[0127]

[0128] Table 2 shows that in the typical scenario of DG access capacity and location change, the protection device according to the online monitoring of △ U 13 , △ U 12 Dynamic update x The adaptive calculation of the adjacent protection action time is realized by formula (1), which verifies the robustness of the adaptive coordination mechanism proposed.

[0129] Simulation verification shows that no matter how the network flow changes, the equation can realize the adaptive adjustment of the action time on the basis of accurately capturing the spatial gradient change characteristics of the positive sequence voltage fault component. x The fixed value is no longer dependent on offline calculation and static setting, but is dynamically generated according to the real-time state of the power grid (fault type, DG state). The adaptive differential coordination mechanism is constructed by using 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. According to the change of fault conditions and network topology, the inverse time parameters and the action time are adjusted in real time, which ensures that the protection action time can be adaptively adjusted according to the fault severity, and ensures the selectivity and rapidity, effectively coping with the variable scenarios and fault conditions of the network topology, DG output and R g The method provides a solution for the protection of distribution networks with high proportion of DGs.

[0130] The adaptive differential coordination method of the active distribution network based on the spatial distribution of the positive sequence voltage of the application has the working principle that: the logarithmic inverse time characteristic equation based on the positive sequence voltage fault component is constructed by using the spatial distribution law of the positive sequence voltage fault component along the feeder, which is strongly related to the fault location; the adaptive discrimination of the fault direction is realized by comparing the measured and calculated positive sequence voltage fault component amplitudes of the local and adjacent protections, and the inverse time parameters are adaptively set online by the protection determining the positive direction fault; the action time of the adjacent protection is calculated based on the real-time updated parameters, and the action time of the protection closest to the fault point is the shortest; the action time differential with absolute selectivity is dynamically generated by using the inherent relationship of the voltage ratio of the adjacent protection; and the reliability of the differential coordination of the adjacent protection is ensured by combining the accurate protection starting criterion and the steady-state voltage action criterion for distinguishing faults and disturbances.

[0131] The key advantage of the method is its strong adaptability: no matter the type of fault, DG output fluctuation or network topology change (such as DG switching, topology reconfiguration, etc.), the protection setting value can be adjusted online in real time, and the action time differential that meets the absolute selectivity is dynamically generated. This realizes the adaptive step-by-step cooperation of multi-level protection, without relying on preset network topology and power supply type information, fundamentally avoiding the protection setting failure problem caused by power supply characteristics or topology changes; the adaptive differential cooperation mechanism dynamically generates protection action time using voltage distribution characteristics, ensuring the absolute selectivity and speed of action under different working conditions, effectively solving the protection cooperation problem of high penetration rate of new energy access and topology flexible active distribution network, significantly improving the selectivity and speed of protection, only using local electrical quantity information, without communication or prior knowledge of topology structure, with small calculation amount, suitable for high proportion of DG access active distribution network scene, with important engineering application value and popularization significance.

Claims

1. An adaptive differential coordination method for active distribution networks based on positive sequence voltage spatial distribution, characterized in that, 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 on the distribution line and their coordination relationship; S2. Construct the 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 upstream or downstream protection device based on the real-time positive sequence voltage and current fault components of the protection device at this level. S4. Calculate the inverse time parameter value using the adaptive setting formula of S2, and update it to the logarithmic inverse time characteristic equation of S2 to obtain the operating time of the adjacent protection device under the current fault state. S5. Combining the preset steady-state voltage action criteria, adjacent protection devices are made to adaptively coordinate based on their updated action times. Specifically, S4 is: S4.

1. Substitute the magnitude of the positive sequence voltage fault component and the positive sequence current fault component obtained in step S3 into the adaptive setting formula of the inverse time parameter in S2, and adaptively calculate the inverse time parameter values ​​of adjacent protections. S4.

2. Substitute the inverse-time parameter values ​​calculated in step S4.1 and the corresponding measured positive-sequence voltage fault component amplitudes into the logarithmic inverse-time characteristic equation in S2, update the logarithmic inverse-time characteristic equation, and calculate the operating time. t j-1 , t j ; Specifically, S5 is: S5.

1. All protection devices update their action times synchronously, with the action time closest to the fault point being the shortest, and the action time of adjacent upstream protection being one step delay (CTI) longer than the action time of its directly downstream protection. S5.

2. When the protection at this level operates correctly and isolates the fault, the protection at the next higher level starts the return logic; when the protection at this level fails to operate, the protection at the next higher level performs a trip operation after satisfying the steady-state operation criteria and reaching the operation time, thus completing the adaptive coordination of the protection operation timing and operation logic.

2. The adaptive differential coordination method for active distribution networks based on positive sequence voltage spatial distribution according to claim 1, characterized in that, Specifically, S1 refers to: S1.

1. Determine the number of adjacent protection devices involved in parameter setting on the distribution line, and measure the R value of adjacent protection devices in real time. j-1 R j The voltage and current values, that is, the instantaneous voltage values ​​collected locally by the current transformers at each level of protection. , and instantaneous current value , ; S1.

2. Based on the instantaneous voltage and current values ​​collected in S1.1, the corresponding R is calculated using the full-cycle subtraction method of subtracting the electrical quantities before and after the fault from the electrical quantities after the fault. 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 components determine their coordination relationship, and the spatial distribution and ratio of the positive sequence voltage fault component amplitude are calculated.

3. The adaptive differential coordination method for active distribution networks based on positive sequence voltage spatial distribution according to claim 2, characterized in that, Specifically, S1.3 is as follows: When R j After a fault occurs at point f on the line, R j and the superior protection R j-1 Having a coordination relationship, using the symmetrical component method and fault boundary conditions, we obtain R including adjacent protection. j-1 R j Ortho-sequence fault component augmentation network; Let R j-1 The busbar is M Its back-side total equivalent impedance is Then there is In the formula, Switches k j-2 When the bus is open M Positive sequence equivalent impedance of back-side system, 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 are determined by The impedance characteristics determine this; Applying Ohm's law and the impedance ratio, we can obtain: In the formula, For line L j-1 The positive-sequence equivalent impedance; Therefore, based on the attenuation characteristics along the line, amplitude Less than amplitude ; The expression for the ratio of the positive-sequence voltage fault component amplitudes of adjacent protections, derived from the above equation, is as follows: The ratio of the positive sequence voltage fault component of adjacent protection depends on the upstream protection R. j-1 Busbar M The back-side equivalent impedance and its corresponding line length; Set voltage threshold ,when < At that time, R j Return to step S1.2 to continue calculating the positive sequence voltage fault component and the positive sequence current fault component; when ≥ Then proceed to step S2.

4. The adaptive differential coordination method for active distribution networks based on positive sequence voltage spatial distribution according to claim 3, characterized in that, The process of constructing the logarithmic inverse time-limited characteristic equation is as follows: For the j-th protection device R j It takes the maximum value in the positive sequence voltage fault component. The operating time is the minimum operating time limit for backup protection. t min That is, the logarithmic inverse-time characteristic equation to be solved passes through a constant point. Its mathematical expression is: In the formula, R represents j Action time, x The parameter to be determined is the inverse time limit parameter.

5. The adaptive differential coordination method for active distribution networks based on positive sequence voltage spatial distribution according to claim 4, characterized in that, The derived adaptive tuning formula for the inverse time-limited parameter is as follows: Adjacent protection R j-1 R j Action time difference for: The ratio of adjacent protection voltages Decide, The value is greater than or equal to the protection coordination time interval requirement, therefore R is obtained. j-1 R j Corresponding to x The adaptive tuning formula is: In the formula, CTI is the protection coordination time interval, which is taken as 0.2~0.5s; R respectively j-1 The calculated positive sequence voltage fault component amplitude and R of the adjacent downstream protection j The calculated amplitude of the positive sequence voltage fault component of the adjacent upstream protection.

6. The adaptive differential coordination method for active distribution networks based on positive sequence voltage spatial distribution according to claim 5, characterized in that, Specifically, S3 refers to: Based on the real-time positive-sequence voltage fault component and positive-sequence current fault component of this level of protection device, the amplitude of the positive-sequence voltage fault component extrapolated by the upper-level protection to the adjacent lower-level protection and the amplitude extrapolated by the lower-level protection to the adjacent upper-level protection are calculated using the following formula: In the formula, For protection by this level R j Eliminate the relationship between node current and branch current in DG j The positive sequence current fault component after the impact.

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