A new energy voltage stability analysis method based on an extra-high voltage AC-DC power grid

Abstract

The application discloses a new energy voltage stability analysis method based on an extra-high voltage AC-DC power grid and belongs to the technical field of voltage stability analysis. The method comprises the following steps: establishing an AC-DC large power grid voltage index system, the index system at least comprising a static voltage stability index layer and a transient voltage stability index layer, creating corresponding evaluation indexes for the corresponding index layers, and giving corresponding evaluation values; establishing a triangular fuzzy function, processing the evaluation values to obtain numerical indexes, establishing a standard database of the numerical indexes, obtaining node voltages, making a suitable evaluation value based on the index system for the obtained node voltages, and performing numerical processing on the evaluation value to obtain corresponding evaluation indexes; and comparing the evaluation indexes with the numerical indexes, judging the voltage stability state of the current AC-DC large power grid system according to the comparison result.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of voltage stability analysis, and particularly relates to a new energy voltage stability analysis method based on an extra-high voltage AC-DC power grid. BACKGROUND

[0002] With the rapid development of economy and society in China, the interconnection degree of power systems is continuously enhanced, the power grid structure is increasingly complex, and especially after the large-scale access of new energy such as wind power, the safety and stability problem of power systems is increasingly prominent. How to measure the safety state of an AC-DC large power grid and compare the voltage stability level of power grids in different regions is crucial to the overall development of the power grid. Through the evaluation of the voltage stability level of the power system, the safety and stability margin of the system can be obtained, and a theoretical basis can be provided for power dispatching, decision-making and the development of a scheme for preventing voltage instability and collapse.

[0003] The traditional voltage stability analysis method of the power system includes modal analysis, sensitivity analysis, time domain simulation method, analytical method and the like. In the process of voltage stability evaluation, only a single attribute is usually analyzed and evaluated. However, for a huge and complex power system, the evaluation of only a part of the power system stability is not enough to reflect the overall safety and stability state of the power system. Therefore, a comprehensive evaluation method of a multi-angle and multi-level index system is needed to macroscopically evaluate the voltage safety operation state of the power grid. SUMMARY

[0004] The application aims to provide a new energy voltage stability analysis method based on an extra-high voltage AC-DC power grid, which solves the above problems in the prior art.

[0005] Technical scheme: A new energy voltage stability analysis method based on an extra-high voltage AC-DC power grid, comprising the following steps:

[0006] A voltage index system of an AC-DC large power grid is established, and the index system at least includes a static voltage stability index layer and a transient voltage stability index layer; static voltage stability evaluation indexes and transient voltage stability evaluation indexes are respectively created in the static voltage stability index layer and the transient voltage stability index layer, and corresponding evaluation values are given;

[0007] A triangular fuzzy function is established, the evaluation values are fuzzily and non-dimensionalized to obtain numerical indexes, a standard database of the numerical indexes is established, node voltages are obtained, an evaluation value is made based on the index system and the obtained node voltages, the evaluation value is numerically processed to obtain corresponding evaluation indexes, the evaluation indexes are compared with the numerical indexes in the standard database, and the voltage stability state of the current AC-DC large power grid system is judged according to the comparison result;

[0008] The weight concept is introduced to each evaluation value, and the weight corresponding to the evaluation value is summed up, and the result of the weighted sum is used as the basis for the operation and dispatch of the AC / DC large power grid system.

[0009] Preferably, the static voltage stability evaluation index is obtained by the following process:

[0010] The voltage margin index, the active power margin index, the reactive power margin index, the active voltage sensitivity index, the reactive voltage sensitivity index and the bus participation factor are obtained respectively, and the static voltage stability evaluation index is obtained by using the matching curve analysis method, the sensitivity analysis method and the modal analysis method.

[0011] Preferably, the transient voltage stability evaluation index is obtained by the following process:

[0012] When the fault occurs, the fault limit switching time, the amplitude of the bus line voltage drop after the fault, the duration of the voltage drop amplitude after the fault and the time domain simulation method of the tie line power cooperation are obtained, and the transient voltage stability evaluation index is obtained.

[0013] Preferably, the voltage margin index is established by the following process: obtaining the node voltage value U under the power flow stable state, defining the node voltage U0 obtained by solving the power flow when all the loads are set to zero under the same state as the node voltage value U, and the voltage margin index is represented as U / U0.

[0014] Preferably, the active power margin index is established by the following process: obtaining the load node P0 on the PV curve, obtaining the load power limit P max of a region, and the active power margin index is represented as K P =(P max -P0) / P0.

[0015] Preferably, the reactive power margin index is established by the following process: obtaining the minimum value Q0 of the PV curve, judging the positional relationship between Q0 and the U axis, obtaining the load reactive power limit Q max , and the reactive power margin index is represented as K Q =(Q max -Q0) / Q0.

[0016] Preferably, the reactive voltage sensitivity index is established by the following process: obtaining the transmission limit of the reactive power and the limit operation of the voltage stability , and the reactive voltage sensitivity index is represented as

[0017] Preferably, the active voltage sensitivity index is established by the following process: obtaining the transmission limit of the active power and the limit operation of the voltage stability Then, the active voltage sensitivity index is expressed as

[0018] Preferably, the bus participation factor is established as follows: eigenvalues are obtained by solving the Jacobian matrix of the power flow equation, and the bus participation factor is expressed as P i = ξ i η i .

[0019] Preferably, when the fault occurs, the voltage stability state of the current AC-DC large power grid system is judged by obtaining the fault limit switching time, the amplitude of the bus line voltage drop, the duration of the amplitude of the voltage drop, and the tie-line power:

[0020] The fault limit switching time represents the transient disturbance time when the fault occurs. The longer the transient disturbance time, the greater the transient stability margin, and vice versa, the smaller the transient stability margin;

[0021] The amplitude of the bus line voltage drop during the fault represents the maximum value of the amplitude of the voltage drop after the fault. If the amplitude is within a predetermined range, it indicates that the transient voltage stability is high, and vice versa, it indicates that the transient voltage stability is low;

[0022] The duration of the amplitude of the voltage drop after the fault represents that the amplitude of the voltage drop after the fault is within a predetermined range and the duration is long, which indicates that the transient voltage stability is high, and vice versa, which indicates that the transient voltage stability is low;

[0023] The tie-line power represents the change rule of the active power and the reactive power of the tie-line after the fault. The lower the tie-line power, the lower the voltage stability, and vice versa, which indicates that the voltage stability is high.

[0024] Preferably, the steps of introducing the weight concept for each evaluation value are as follows:

[0025] First, a triangular fuzzy function is determined, which is expressed as:

[0026]

[0027] In the formula, s represents the lower limit of l; u represents the upper limit of l, s << l << u, s and u both represent the fuzzy degree of the evaluation value, the greater u-s, the higher the fuzzy degree, and vice versa,

[0028] The corresponding triangular fuzzy evaluation matrix A is obtained through the calculation formula of the triangular fuzzy function, A = [a ij ], wherein a ijAssign values ​​to sub-objective i relative to sub-objective j, and assign values ​​based on these values, using r. ij This indicates the corresponding assigned value;

[0029] Secondly, the process of assigning fuzzy, quantity-free tempered values ​​to the evaluation values ​​to obtain numerical indicators is as follows:

[0030] The various parameters of the node voltage are dimensionless and formed into a matrix. Using formula The various parameters of the node voltage are dimensionless, with formula a used for dimensionless determination of large parameters and formula b used for dimensionless determination of small parameters, resulting in the fuzzy evaluation matrix R. i R i =[r ij ] n×m r ij This represents the i-th factor in the evaluation factor set and the j-th grade V in the rating scale set V. j The degree of membership, wherein the evaluation factor set includes at least the fault limit clearing time after the fault occurs, the magnitude of the bus line voltage drop during the fault, the duration of the voltage drop magnitude after the fault, and the tie line power, and the evaluation level set V = {V L V M V H}, where V L This indicates poor transient voltage stability, V M This indicates that the transient voltage stability is moderate, V H This indicates good transient voltage stability, assuming x ij ≥0, and

[0031] Finally, the largest eigenvalue λmax of A is calculated. The normalized eigenvector of λmax represents the weight of the obtained index, calculated using the formula AP. (subjective)j =λ max P (subjective)j .

[0032] Preferred, through The formula uses the CR (Conformance Ratio) result to judge the consistency of A. If CR < 0.1, it indicates acceptable consistency; otherwise, the sub-objectives are judged again until A passes the consistency test. In the formula, n represents the order of A, γ... n This represents the correction value corresponding to the order of A.

[0033] Beneficial effects: the present application relates to a new energy voltage stability analysis method based on extra-high voltage AC / DC power grid, through static voltage stability index layer and transient voltage stability index layer, the multiple factors of voltage stability are researched and analyzed, and the research and analysis are numerized, the voltage stability state is directly judged through the numerical value, and the evaluation result of different factors is obtained through the verification of the analysis result, the weak node under different factors is obtained through the evaluation result of each factor, and the voltage stability is comprehensively evaluated. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The index system structure diagram of the present application. DETAILED DESCRIPTION

[0035] As Figure 1 shown, a new energy voltage stability analysis method based on extra-high voltage AC / DC power grid, comprising the following steps:

[0036] Establishing an AC / DC large power grid voltage index system, the index system at least includes: static voltage stability index layer and transient voltage stability index layer; static voltage stability evaluation index and transient voltage stability evaluation index are created in static voltage stability index layer and transient voltage stability index layer respectively, and corresponding evaluation value is given;

[0037] Wherein, the static voltage stability evaluation index is obtained by matching curve analysis method, sensitivity analysis method and modal analysis method through voltage margin index, active power margin index, reactive power margin index, active voltage sensitivity index, reactive voltage sensitivity index and busbar participation factor of node voltage; the transient voltage stability evaluation index is obtained by fault limit removal time after fault, amplitude of bus line voltage drop at fault, duration of voltage drop amplitude after fault and time domain simulation method of tie line power cooperation when fault occurs.

[0038] Establishing a triangular fuzzy function, the evaluation value is fuzzy and non-dimensional, and the numerical index is obtained; the obtained numerical index is established into a standard database, the node voltage is obtained, the evaluation value is obtained based on the index system, and the corresponding evaluation index is obtained through numerical processing; the evaluation index and the numerical index in the standard database are compared, and the voltage stability state of the current AC / DC large power grid system is judged according to the comparison result;

[0039] The weight concept is introduced to each evaluation value, the weight corresponding to the evaluation value is weighted and summed, and the result of weighted summation is provided as a basis for operation and dispatching of AC / DC large power grid system.

[0040] The curve analysis mode analyzes the node voltage in the compatible state by combining the voltage margin index, the active power margin index and the reactive power margin index, and assigns corresponding evaluation values to the index values obtained by the analysis, wherein the voltage margin index is obtained by dividing the node voltage value U in the power flow stable state by the node voltage U0 obtained by solving the power flow when all loads are set to zero in the same system state; the active power margin index is obtained by obtaining the load node P0 on the PV curve, obtaining the load power limit P of a region max , and calculating the active power margin index by the formula K P =(P max -P0) / P0; the reactive power margin index is obtained by obtaining the minimum value Q0 of the PV curve, judging the positional relationship between Q0 and the U axis, obtaining the load reactive power limit Q max , and calculating the reactive power margin index by the formula K Q =(Q max -Q0) / Q0.

[0041] The sensitivity analysis analyzes the node voltage in the compatible state by combining the active voltage sensitivity index and the reactive voltage sensitivity index, and assigns corresponding evaluation values to the index values obtained by the analysis, wherein the reactive voltage sensitivity index is obtained by obtaining the transmission limit of the reactive power and the limit operation of voltage stability based on the power flow equation, and the reactive voltage sensitivity index is calculated by the formula ; the active voltage sensitivity index is obtained by obtaining the transmission limit of the active power and the limit operation of voltage stability based on the power flow equation, and the active voltage sensitivity index is calculated by the formula .

[0042] The modal analysis analyzes the node voltage by combining the bus participation factor, and assigns corresponding evaluation values to the index values obtained by the analysis, wherein the bus participation factor is obtained by solving the eigenvalue of the Jacobian matrix of the power flow equation, and the bus participation factor is obtained by the formula P i =ξ i η i .

[0043] The transient voltage stability index layer is used to comprehensively evaluate and judge four factors, i.e., the fault limit removal time, the amplitude of bus line voltage drop at the time of fault, the duration of the amplitude of voltage drop after fault, and the tie-line power when the fault occurs:

[0044] The fault limit removal time represents the transient disturbance time when the fault occurs. The longer the transient disturbance time, the greater the transient stability margin, and vice versa. The transient stability margin is assigned an evaluation value

[0045] The amplitude of bus line voltage drop at the time of fault represents the maximum value of bus line voltage drop. If the amplitude is within a predetermined range, it indicates that the transient voltage stability is high, and vice versa. The high and low voltage stability is assigned an evaluation value.

[0046] The duration of the amplitude of voltage drop after fault represents that the amplitude of voltage drop after fault is within a predetermined range and the duration is long. If the transient voltage stability is high, the transient voltage stability is low, and vice versa. The high and low transient voltage stability is assigned an evaluation value.

[0047] The tie-line power represents the change rule of active power and reactive power of the tie-line after the fault. The lower the tie-line power, the lower the voltage stability, and vice versa. The high and low voltage stability is assigned an evaluation value.

[0048] The evaluation value is obtained by the above method, and the weight concept is introduced for each evaluation value. The steps of introducing the weight concept are as follows:

[0049] First, determine the triangular fuzzy function, which is represented as:

[0050]

[0051] In the formula, s represents the lower limit of l; u represents the upper limit of l, s << l << u, s and u represent the fuzzy degree of the evaluation value, the greater u-s, the higher the fuzzy degree, and vice versa,

[0052] The evaluation value is calculated by the calculation formula of the triangular fuzzy function to obtain the corresponding triangular fuzzy evaluation matrix A, A = [a ij ], wherein a ij is the importance of sub-target i relative to sub-target j, and is assigned a value according to the importance, and r ij represents the corresponding assigned value, r ij The assignment rules are as follows:

[0053] r ij ]]> Reason for assignment 1 [a ij as important as (i+1j) as important as 3 [a ij With a (i+1j) Somewhat important 5 [a ij With a (i+1j) Significant importance 7 [a ij With a (i+1j) Strongly important 9 [a ij With a (i+1j) of utmost importance 2，4，6，8 [a ij With a (i+1j) some other cases between a

[0054] Secondly, the process of assigning fuzzy, quantity-free tempered values ​​to the evaluation values ​​to obtain numerical indicators is as follows:

[0055] The various parameters of the node voltage are dimensionless and formed into a matrix. Using formula The various parameters of the node voltage are dimensionless, with formula a used for dimensionless determination of large parameters and formula b used for dimensionless determination of small parameters, resulting in the fuzzy evaluation matrix R. i R i =[r ij ] n×m r ij This represents the i-th factor in the evaluation factor set and the j-th grade V in the rating scale set V. j The degree of membership, wherein the evaluation factor set includes at least the fault limit clearing time after the fault occurs, the magnitude of the bus line voltage drop during the fault, the duration of the voltage drop magnitude after the fault, and the tie line power, and the evaluation level set V = {V L V M V H}, where V L This indicates poor transient voltage stability, V M This indicates that the transient voltage stability is moderate, V H This indicates good transient voltage stability, assuming x ij ≥0, and

[0056] Finally, the largest eigenvalue λmax of A is calculated. The normalized eigenvector of λmax represents the weight of the obtained index, calculated using the formula AP. (subjective)j =λ max P (subjective)j ;pass The formula uses the CR (Conformance Ratio) result to judge the consistency of A. If CR < 0.1, it indicates acceptable consistency; otherwise, the sub-objectives are judged again until A passes the consistency test. In the formula, n represents the order of A, γ... n This represents the correction value corresponding to the order of A.

[0057] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids, characterized in that, Includes the following steps: A voltage index system for a large AC / DC power grid is established, the index system including at least: a static voltage stability index layer and a transient voltage stability index layer; static voltage stability evaluation index and transient voltage stability evaluation index are created in the static voltage stability index layer and the transient voltage stability index layer respectively, and corresponding evaluation values ​​are assigned; A triangular fuzzy function is established to assign fuzzy and infinitely rigid values ​​to the evaluation values ​​to obtain numerical indicators. The obtained numerical indicators are used to establish a standard database. The node voltage is obtained. Based on the indicator system, an appropriate evaluation value is made for the obtained node voltage. The evaluation value is then numerically processed to obtain the corresponding evaluation indicators. The evaluation indicators are compared with the numerical indicators in the standard database. Based on the comparison results, the voltage stability status of the current AC / DC power grid system is determined. The concept of weight is introduced for each evaluation value, and the weights corresponding to the evaluation values ​​are summed in a weighted manner. The result of the weighted sum is used to provide a basis for the operation and scheduling of the AC / DC power grid system. The steps for obtaining the transient voltage stability evaluation index are as follows: When a fault occurs, the fault limit clearing time after the fault occurs, the magnitude of the bus line voltage drop during the fault, the duration of the voltage drop magnitude after the fault, and the tie line power are obtained in combination with the time domain simulation method to obtain the transient voltage stability evaluation index. When a fault occurs, the voltage stability of the current AC / DC power grid system is determined by acquiring the fault clearance time, the magnitude of the bus voltage drop, the duration of the voltage drop, and the tie-line power. The fault clearance time represents the transient disturbance time that the fault can withstand when it occurs. The longer the transient disturbance time, the greater the transient stability margin, and vice versa. The magnitude of the voltage drop on the bus line during a fault indicates the duration of the voltage drop after the fault. The magnitude of the voltage drop on the bus line during a fault indicates the maximum value of the voltage drop. If the magnitude is within a predetermined range, it indicates high transient voltage stability; otherwise, it indicates low transient voltage stability. The duration of the voltage drop amplitude after a fault indicates that the voltage drop amplitude is within a predetermined range and the duration is long, which indicates high transient voltage stability; conversely, it indicates low transient voltage stability. The tie line power indicates the change in active and reactive power of the tie line after a fault. The lower the tie line power, the lower the voltage stability, and vice versa.

2. The method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids according to claim 1, characterized in that, The process for obtaining the static voltage stability evaluation index is as follows: The voltage margin index, active power margin index, reactive power margin index, active voltage sensitivity index, reactive voltage sensitivity index, and bus participation factor of the node voltage are obtained respectively. The static voltage stability evaluation index is obtained by matching curve analysis, sensitivity analysis and modal analysis.

3. The method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids according to claim 2, characterized in that, The process for establishing the voltage margin index is as follows: obtain the node voltage value U under the stable power flow state, define the node voltage U0 obtained by solving the power flow when all loads are set to zero but in the same state as the node voltage value U, then the voltage margin index is expressed as U / U0.

4. The method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids according to claim 2, characterized in that, The process for establishing the active power margin index is as follows: obtain the load node P0 on the PV curve, and obtain the load power limit P of the predetermined area. max Then, the active power margin index is expressed as K. P =(P max -P0) / P0.

5. The method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids according to claim 2, characterized in that, The process for establishing the reactive power margin index is as follows: obtain the minimum value Q0 of the PV curve, determine the positional relationship between Q0 and the U-axis, and obtain the load reactive power limit Q. max Then, the reactive power margin index is expressed as K. Q =(Q max -Q0) / Q0.

6. The method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids according to claim 2, characterized in that, The process for establishing the reactive power voltage sensitivity index is as follows: Obtain the transmission limit of reactive power. and voltage stability under extreme operating conditions Therefore, the reactive voltage sensitivity index is expressed as: .

7. The method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids according to claim 2, characterized in that, The process for establishing the active voltage sensitivity index is as follows: Obtain the transmission limit of active power. and voltage-stable extreme motion Therefore, the active voltage sensitivity index is expressed as: .

8. The method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids according to claim 2, characterized in that, The establishment process of the bus participation factor is as follows: eigenvalues are obtained by solving the Jacobian matrix of the power flow equation, and the bus participation factor is obtained. The expression for solving the power flow equation is P = ξη.

9. The method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids according to claim 1, characterized in that, The steps for introducing the weight concept for each evaluation value are as follows: First, determine the triangular fuzzy function, which is expressed as: ； In the formula: s represents the lower limit of l; u represents the upper limit of l, s << l << u, and both s and u represent the fuzzy degree of the evaluation value. The larger u - s is, the higher the fuzzy degree, and vice versa. The corresponding triangular fuzzy evaluation matrix A is obtained through the calculation formula of the triangular fuzzy function, A=[a ij ], where a ij Assign values ​​to sub-objective i relative to sub-objective j, and assign values ​​based on these values, using r. ij This indicates the corresponding assigned value; Secondly, the process for performing fuzzy and dimensionless assignment on the evaluation value to obtain a numerical index is as follows: The various evaluation indicators of node voltage are dimensionless and formed into a matrix. Using formula The dimensionless representation of various indicators of node voltage is achieved using the vector normalization method, where formula a is used for dimensionless representation of large indicators and formula b is used for dimensionless representation of small indicators, resulting in the fuzzy evaluation matrix R. i R i =[r ij ] n×m r ij This represents the i-th factor in the evaluation factor set and the j-th grade V in the rating scale set V. j The degree of membership, wherein the evaluation factor set includes at least the fault limit clearing time after the fault occurs, the magnitude of the bus line voltage drop during the fault, the duration of the voltage drop magnitude after the fault, and the tie line power, and the evaluation level set V = {V L V M V H }, where V L This indicates poor transient voltage stability, V M This indicates that the transient voltage stability is moderate, V H This indicates good transient voltage stability, assuming x ij ≥0, and ; Finally, the largest eigenvalue λmax of A is calculated. The normalized eigenvector of λmax represents the weight of the obtained index, calculated using the formula AP. （subjective）j =λ max P （subjective）j .

10. The method for analyzing the voltage stability of new energy sources based on ultra-high voltage AC / DC power grids according to claim 1, characterized in that, By CR= The formula uses the CR (Conformance Ratio) result to determine the consistency of A. If CR < 0.1, it indicates acceptable consistency; otherwise, the sub-objectives are evaluated again until A passes the consistency test. In the formula, n represents the order of A. This represents the correction value corresponding to the order of A.

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