Dynamic reactive power reserve coordination optimization method based on transient partition and predictive control

Abstract

The application particularly relates to a dynamic reactive power reserve coordination optimization method based on transient partition and predictive control, which comprises the following steps: establishing a corresponding transient voltage stability index (TVSI) according to the transient bus voltage characteristics; evaluating the fault severity based on the TVSI, and then partitioning the power grid; solving the reactive power optimization problem through the scanning of the expected fault set, the sensitivity analysis of the TVSI and the optimization of the reactive power reserve based on the result of the fault partition; optimizing the solution result of the reactive power optimization problem, replacing the reactive power output through the slow dynamic reactive power compensation device, generating a control optimization model of the dynamic reactive power reserve optimization, and realizing the coordinated control of the corresponding equipment. The dynamic reactive power reserve coordination optimization method can reduce the damage degree of the fault or disturbance at a faster speed and with a smaller control cost, and then ensure the safe and stable operation of the whole system, so that the stability of the power system operation control can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power system operation control, and particularly relates to a dynamic reactive power reserve coordination optimization method based on transient partitioning and predictive control. BACKGROUND

[0002] Accurate assessment of voltage stability of the power grid requires accurate capture of the core dynamics of the power grid and determination of the current voltage stability state of the power grid. On this basis, it is also required to reasonably and accurately predict the change of the power grid state in the future period of time, and finally calculate the margin or boundary of the safe operation of the power grid. Among them, the dynamic reactive power reserve can effectively reflect the voltage stability degree of the system, and has the advantages of intuition and simple calculation.

[0003] The existing reactive power optimization only controls the condenser group and the generator with the steady-state voltage distribution as the target, and the operation mode under fault conditions may not be reasonable. Once the commutation failure fault occurs, the dynamic reactive power reserve is insufficient, which may lead to major hidden dangers in the safe operation of the power grid. Therefore, the Chinese patent with publication number CN111030196B discloses a dynamic reactive power reserve optimization method for the receiving end of an AC-DC hybrid system based on dynamic sensitivity. First, the differential algebraic equations of the AC-DC hybrid system are established, and the first-order dynamic sensitivity of the system is calculated. Then, a dynamic reactive power reserve optimization model is established for the current situation, and solved. After the solution is completed, each dynamic reactive power control device adjusts the steady-state reactive power value according to the optimization result, such as the generator which needs to reserve the corresponding reactive power reserve after calculating the dynamic reactive power reserve result.

[0004] The dynamic reactive power reserve optimization method of the above-mentioned existing scheme enables the receiving end of the AC-DC hybrid power grid to still operate safely when the commutation failure occurs, thereby improving the reliability of the power grid operation. However, due to the instantaneous nature of the fault, short-term voltage stability assessment must give a safe assessment result within a short period of time to ensure the timeliness of the assessment result. However, blindly pursuing speed may lead to inaccurate calculation results, so a balance needs to be struck between accuracy and speed when modeling and evaluating the system. Moreover, due to the uncertainty and randomness of the system encountering large disturbances, reasonable and effective control means need to be taken to minimize the damage caused by voltage instability accidents and ensure the normal operation of the power system while ensuring economy. Therefore, how to design a method that can reduce the damage caused by faults or disturbances at a faster speed and with a smaller control cost is a technical problem that needs to be solved. SUMMARY

[0005] In view of the above prior art, the technical problem to be solved by the present application is: how to provide a dynamic reactive power reserve coordination optimization method based on transient partitioning and predictive control, which can reduce the damage degree of faults or disturbances at a faster speed and with a smaller control cost, thereby ensuring the safe and stable operation of the entire system, so as to improve the stability of power system operation control.

[0006] In order to solve the above technical problems, the present application adopts the following technical solutions:

[0007] The dynamic reactive power reserve coordination optimization method based on transient partitioning and predictive control comprises the following steps:

[0008] S1: A corresponding transient voltage stability comprehensive evaluation index, i.e. TVSI, is established according to the transient bus voltage characteristics;

[0009] S2: The fault severity is evaluated based on TVSI, and then the power grid is fault partitioned;

[0010] S3: Based on the results of fault partitioning, the reactive power optimization problem is solved through scanning of the expected fault set, sensitivity analysis of TVSI and reactive power reserve optimization;

[0011] S4: The solution of the reactive power optimization problem is optimized, the reactive power output is replaced by slow dynamic reactive power compensation devices, a control optimization model of dynamic reactive power reserve optimization is generated, and the coordinated control of the corresponding equipment is realized.

[0012] Preferably, in step S1, the transient voltage stability comprehensive evaluation index comprises a low voltage recovery component index, an oscillation degree component index and a recovery steady state component index, which are respectively used for quantitatively describing the severity of the fault from three aspects of the amplitude and duration of voltage drop, the amplitude and decay speed of voltage oscillation and the voltage recovery level.

[0013] Preferably, in step S1, the low voltage recovery component index is constructed by the following steps:

[0014] S101: The transient voltage waveform curve V(t) is obtained through time domain simulation, the time T TSVIr at which the voltage is first restored to the steady state voltage value after fault clearing is determined, the fault occurrence time T Fault , the steady state voltage value V s after fault and the steady state voltage value V0 before fault are determined;

[0015] S102: Based on the variables determined in step S101, the low voltage recovery component index TVSI r is constructed as follows:

[0016]

[0017]

[0018] Preferably, in step S1, the oscillation degree component indicator is constructed by the following steps:

[0019] S111: Calculate the fault clearing time T by the transient voltage waveform curve V(t) Clear and the simulation end time T end , then calculate the transient voltage waveform oscillation median line V TVSIo (t) containing the low frequency and non-periodic change component in the voltage waveform;

[0020] S112: Based on the variables determined in step S111, construct the oscillation degree component indicator TVSI0 as follows:

[0021]

[0022] Preferably, in step S1, the recovery steady state component indicator is constructed by the following steps:

[0023] S121: Determine the time T s at which the voltage reaches steady state in combination with the transient voltage waveform curve V(t) and the steady state voltage V s after the fault;

[0024] S122: Based on the variables determined in step S121, construct the recovery steady state component indicator TVSI as follows: s

[0025] TVSI s = (V0-V s ) × (T s -T Clear );

[0026] In the formula: T Clear represents the fault clearing time; V0 represents the steady state voltage value before the fault.

[0027] Preferably, in step S2, it specifically includes the following steps:

[0028] S201: Define an index STVSI capable of continuous quantification for evaluating the influence of the fault on the bus voltage, to evaluate the severity of the fault;

[0029] S202: Based on numerical simulation, analyze the transient voltage stability of the power system under each expected fault, screen out severe faults in the expected fault set, calculate the action range of each severe fault and select a representative severe fault of the bus;

[0030] ​S203: Mark the representative severe faults corresponding to each bus, define the sensitivity index of voltage trajectory to dynamic reactive power output by combining the trajectory sensitivity analysis method, and construct the bus distance matrix of dynamic response corresponding to representative severe faults and dynamic reactive power reserve.

[0031] S204: Clustering of data points is achieved by constructing a two-dimensional data point matrix using the bus distance matrix to partition power grid faults.

[0032] Preferably, in step S201, the index STVSI is represented by the following formula:

[0033]

[0034]

[0035] In the formula: STVSI is T span,max With T th The ratio of T to T is in the range [0, +∞). span,max This indicates that the voltage v(t) remains below V. th The longest time; S Tspan This indicates that the bus voltage, determined by the formula, remains below V. th The time interval; v(t) represents the voltage at time t.

[0036] Preferably, in step S203, the expression for the change in voltage trajectory is first quantified, and then the sensitivity of the dynamic reactive power reserve to the voltage trajectory is calculated based on the corresponding expression. In this way, a distance matrix that can fully describe the similarity between buses is constructed to realize the quantitative expression of the influence of dynamic reactive power reserve on the bus voltage trajectory.

[0037] The formula for the distance matrix is ​​as follows:

[0038]

[0039]

[0040] In the formula: This corresponds to the representative severe fault Fltp and dynamic reactive power VAR. q The distance matrix; This corresponds to the representative severe fault Fltp and dynamic reactive power VAR. q The distance between busbar i and busbar j; This corresponds to the representative severe fault Fltp and dynamic reactive power VAR. q The VQTSI index of the bus i.

[0041] Compared with the prior art, the dynamic reactive power reserve coordination optimization method of the present invention has the following advantages:

[0042] The application establishes a corresponding transient voltage stability comprehensive evaluation index according to the transient bus voltage characteristics, and then effectively measures the transient voltage stability degree through the comprehensive evaluation index, which can solve the problem that the existing transient voltage evaluation index cannot effectively evaluate the short-term voltage stability level of the power grid. At the same time, based on the transient voltage stability comprehensive evaluation index and the related theory of dynamic reactive power response partition, a dynamic reactive power response partition method for the expected fault set is proposed, key information is extracted from the bus dimension, fault dimension and dynamic reactive power dimension, the original large-scale reactive power optimization problem is simplified and processed, and it is compressed into a smaller problem, so that the calculation speed can be greatly improved while ensuring the calculation accuracy. Then, considering the characteristics of mutual game of economy and safety, a reactive power reserve optimization algorithm based on piecewise linear reactive power voltage sensitivity is proposed, and the change of bus voltage before and after reactive power reserve optimization is detected. Finally, in view of the problem that decentralized autonomy leads to insufficient dynamic reactive power reserve optimization, the model predictive control theory is applied to the dynamic reactive power reserve considering coordinated secondary voltage control (DRPR-CSVC) model and dynamic reactive power reserve considering optimization control (DRPR-OC) model, and an autonomous-coordinated transient voltage safety evaluation and preventive control system is constructed. In summary, through the transient partition method and model predictive control technology, the dynamic reactive power reserve optimization model is established, which can reduce the damage degree of fault or disturbance at a faster speed and smaller control cost, and then ensure the safe and stable operation of the whole system, so as to improve the stability of power system operation control. BRIEF DESCRIPTION OF DRAWINGS

[0043] In order to make the purpose, technical scheme and advantages of the application more clear, the application will be further described in detail below with reference to the drawings, in which:

[0044] Figure 1 The logic block diagram of the dynamic reactive power reserve coordinated optimization method based on transient partition and predictive control. DETAILED DESCRIPTION

[0045] The application will be further described in detail below through specific embodiments:

[0046] Embodiment:

[0047] A dynamic reactive power reserve coordinated optimization method based on transient partition and predictive control is disclosed in this embodiment.

[0048] As shown in Figure 1 The dynamic reactive power reserve coordinated optimization method based on transient partition and predictive control includes the following steps:

[0049] S1: According to the characteristics of the transient bus voltage, the corresponding transient voltage stability comprehensive evaluation index, namely TVSI, is established; in the embodiment, the TVSI is established to solve the problems that the traditional transient voltage stability index can only qualitatively determine whether the voltage is stable after the fault, and it is difficult to specifically explain the degree of voltage drop and recovery after the fault.

[0050] S2: Based on the TVSI, the fault severity is evaluated, and the power grid is divided into fault zones; in the embodiment, the initial fault set is preliminarily simplified, the dynamic reactive power response partition method for the expected fault set is established to further simplify the large-scale and difficult-to-solve reactive power optimization problem of the whole power grid, including the screening of severe faults, the rough partition of the power grid according to the response to the fault, and the further fine partition of the power grid according to the response of the dynamic reactive power source.

[0051] S3: Based on the results of the fault partition, the reactive power optimization problem is solved through the scanning of the expected fault set, the sensitivity analysis of the TVSI, and the reactive power reserve optimization; in the embodiment, the reactive power reserve optimization algorithm considering the economy and safety and taking into account the multiple time scales is established to solve the problems that the existing methods do not consider the coordination of multiple time scales when considering the transient voltage safety problem, and do not consider the economic and safety game, and the reactive power optimization problem is solved through the scanning of the expected fault set, the sensitivity analysis of the TVSI, and the reactive power reserve optimization.

[0052] S4: The solution of the reactive power optimization problem is optimized, the slow dynamic reactive power compensation device is replaced by the reactive power output to generate a control optimization model of dynamic reactive power reserve optimization, and the coordinated control of the corresponding equipment is realized; in the embodiment, the method of replacing the reactive power output of the fast dynamic reactive power compensation device SVC and SVG with the slow dynamic reactive power compensation device generator is established to form the control optimization model of dynamic reactive power reserve optimization, and the coordinated control of the decentralized autonomous equipment is realized.

[0053] The application establishes corresponding transient voltage stability comprehensive evaluation indexes according to the characteristics of the transient bus voltage, and then effectively measures the transient voltage stability degree through the comprehensive evaluation indexes, which can solve the problem that the existing transient voltage evaluation indexes cannot effectively evaluate the short-term voltage stability level of the power grid. Meanwhile, based on the transient voltage stability comprehensive evaluation indexes and the related theory of dynamic reactive power response partition, a dynamic reactive power response partition method for the expected fault set is proposed, key information is extracted from the bus dimension, fault dimension and dynamic reactive power dimension, the original large-scale reactive power optimization problem is simplified and processed, and it is compressed into a smaller problem, so that the calculation speed can be greatly improved while ensuring the calculation accuracy. Then, considering the characteristics of the mutual game of economy and safety, a reactive power reserve optimization algorithm based on piecewise linear reactive power voltage sensitivity is proposed, and the change of bus voltage before and after the reactive power reserve optimization is detected. Finally, in view of the problem that the decentralized autonomy leads to insufficient dynamic reactive power reserve optimization, the model predictive control theory is applied to the dynamic reactive power reserve considering coordinated secondary voltage control (DRPR-CSVC) model and dynamic reactive power reserve considering optimization control (DRPR-OC) model, and an autonomous-coordinated transient voltage safety evaluation and preventive control system is constructed. In summary, through the transient partition method and the model predictive control technology, the dynamic reactive power reserve optimization model is established, which can reduce the damage degree of fault or disturbance at a faster speed and with a smaller control cost, and then ensure the safe and stable operation of the whole system, so as to improve the stability of the power system operation control.

[0054] In the specific implementation process, the transient voltage stability comprehensive evaluation index includes a low voltage recovery component index, an oscillation degree component index and a recovery steady state component index, which are respectively used for quantitatively describing the severity of the fault from the aspects of the amplitude and duration of voltage drop, the amplitude and decay speed of voltage oscillation, and the voltage recovery level. In this embodiment, the index capable of quantitatively evaluating the short-term voltage stability needs to be considered, and it is necessary to ensure that the short-term voltage stability comprehensive index of the power grid can be reliably and effectively evaluated under various operating modes of the power system.

[0055] The low voltage recovery component index reflects the influence of the reactive power injection of the synchronous generator and the dynamic reactive power device and the reactive power consumption of the dynamic load and HVDC, and fully reflects the low voltage recovery capability of the bus. The smaller the value is, the better the low voltage recovery capability of the bus is.

[0056] The oscillation degree component index reflects the amplitude and decay speed of voltage oscillation, which is influenced by factors such as high-gain fast excitation device, dynamic load, weak interconnection of power grid, generator speed regulation system, and fully reflects the oscillation of voltage in the transient process. The smaller the value is, the smaller the oscillation degree of voltage in the transient process is.

[0057] The recovery steady-state component index depends on the influence of the power grid topology and operation mode before and after the fault occurs, fully reflects the ability of the voltage waveform to recover the steady state, and the smaller the value, the stronger the ability of the voltage waveform to recover the steady state.

[0058] The low-voltage recovery component index is constructed by the following steps:

[0059] S101: Obtain the transient voltage waveform curve V(t) through time domain simulation, determine the time T when the voltage first recovers to the steady-state voltage value after the fault is cleared TSVIr (If the voltage cannot reach the steady state after the fault is cleared, T TSVIr is the time when the simulation ends), determine the time T Fault when the fault occurs, the steady-state voltage value V s after the fault (if the simulation ends without entering the steady state, use the oscillation median value) and the steady-state voltage value V0 before the fault;

[0060] S102: Based on the variables determined in step S101, construct the low-voltage recovery component index TVSI r as follows:

[0061]

[0062]

[0063] The oscillation degree component index is constructed by the following steps:

[0064] S111: Calculate the time T Clear when the fault is cleared and the time T end when the simulation ends through the transient voltage waveform curve V(t), calculate the transient voltage waveform oscillation median line V TVSIo (t) containing the low-frequency and non-periodic change components in the voltage waveform to reflect the oscillation within the small disturbance stability research range, and the components containing the low-frequency and non-periodic changes.

[0065] S112: Based on the variables determined in step S111, construct the oscillation degree component index TVSI0 as follows:

[0066]

[0067] The recovery steady-state component index is constructed by the following steps:

[0068] S121: Determine the time T s when the voltage reaches the steady state in combination with the transient voltage waveform curve V(t) (if the simulation ends without entering the steady state, set it as the time when the simulation ends) and the steady-state voltage V s after the fault.

[0069] S122: based on the variable determined in step S121, construct a recovery steady component index TVSI as follows s :

[0070] TVSI s = (V0-V s ) x (T s -T Clear );

[0071] In the formula, T Clear represents the moment when the fault is cleared, and V0 represents the steady voltage value before the fault.

[0072] The present application proposes a short-term voltage stability comprehensive index fully considering the relative stability degree of voltage in order to solve the problem that the existing transient voltage evaluation index cannot effectively evaluate the short-term voltage stability level of power grid, and three evaluation indexes, i.e., a low voltage recovery component index, an oscillation degree component index and a recovery steady component index, are respectively established according to the response characteristics of bus voltage in the transient process, the transient voltage stability degree is effectively measured through comprehensive evaluation index, so that the damage degree of fault or disturbance can be reduced at a faster speed and with a smaller control cost.

[0073] In step S2, the following steps are specifically included:

[0074] S201: define an index STVSI capable of continuous quantification for evaluating the influence of fault on bus voltage, so as to evaluate the severity of fault;

[0075] S202: based on numerical simulation, analyze the transient voltage stability of power system under each expected fault, screen out severe faults in the expected fault set, calculate the action range of each severe fault and select a representative severe fault of the bus;

[0076] S203: mark each bus corresponding to the representative severe fault, define a sensitivity index for measuring the sensitivity of voltage trajectory to the output of dynamic reactive power equipment in combination with the trajectory sensitivity analysis method, and construct a bus distance matrix corresponding to the dynamic response of the representative severe fault and dynamic reactive power reserve;

[0077] S204: construct two-dimensional data points by the bus distance matrix to cluster the data points, so as to realize the partition of power grid fault.

[0078] The index STVSI is represented by the following formula:

[0079]

[0080]

[0081] In the formula, STVSI is the T span,max and T thThe ratio of T to T is in the range [0, +∞). span,max This indicates that the voltage v(t) remains below V. th The longer the fault lasts, the larger the STVSI value, indicating a more severe fault. If STVSI equals 1, it means the power system is critically stable after the fault. Tspan This indicates that the bus voltage, determined by the formula, remains below V. th The time interval; v(t) represents the voltage at time t.

[0082] In step S203, the expression for the change in voltage trajectory is first quantified, and then the sensitivity of the dynamic reactive power reserve to the voltage trajectory is calculated based on the corresponding expression. In this way, a distance matrix that can fully describe the similarity between buses is constructed to realize the quantitative expression of the influence of dynamic reactive power reserve on the bus voltage trajectory.

[0083] The formula for the distance matrix is ​​as follows:

[0084]

[0085]

[0086] In the formula: This corresponds to the representative severe fault Fltp and dynamic reactive power VAR. q The distance matrix; This corresponds to the representative severe fault Fltp and dynamic reactive power VAR. q The distance between busbar i and busbar j; This corresponds to the representative severe fault Fltp and dynamic reactive power VAR. q The VQTSI index of the bus i.

[0087] This invention proposes a dynamic reactive power response partitioning method for anticipated fault sets through the above steps, which enables the extraction of key information from three dimensions: bus dimension, fault dimension, and dynamic reactive power dimension. This simplifies the original large-scale reactive power optimization problem and compresses it into a smaller problem, thereby greatly improving the solution speed while ensuring computational accuracy.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A dynamic reactive power reserve coordination optimization method based on transient partitioning and predictive control, characterized in that, Includes the following steps: S1: Establish a corresponding comprehensive evaluation index for transient voltage stability, namely TVSI, based on the characteristics of transient bus voltage; S2: Based on TVSI, assess the severity of the fault and then divide the power grid into fault zones; Step S2 specifically includes the following steps: S201: Define the STVSI index, which can continuously quantify the impact of faults on bus voltage, to assess the severity of the fault. In step S201, the index STVSI is represented by the following formula: In the formula: STVSI is T span,max With T th The ratio of T to T is in the range [0, +∞). span,max This indicates that the voltage v(t) remains below V. th The longest time; S Tspan This indicates that the bus voltage, determined by the formula, remains below V. th The time interval; v(t) represents the voltage at time t; S202: Based on numerical simulation analysis of the transient voltage stability of the power system under various anticipated faults, the severe faults in the anticipated fault set are screened out, the scope of each severe fault is calculated, and representative severe faults of the bus are selected. S203: Mark the representative severe faults corresponding to each bus, define the sensitivity index of voltage trajectory to dynamic reactive power output by combining the trajectory sensitivity analysis method, and construct the bus distance matrix of dynamic response corresponding to representative severe faults and dynamic reactive power reserve. S204: Clustering data points by constructing a two-dimensional data point matrix through bus distance matrix to achieve grid fault partitioning; S3: Based on the results of fault partitioning, the reactive power optimization problem is solved by scanning the expected fault set, analyzing the sensitivity of TVSI, and optimizing the reactive power reserve. S4: Optimize the solution results of the reactive power optimization problem. Replace the reactive power output by using a slow dynamic reactive power compensation device to generate a dynamic reactive power reserve optimization control optimization model, and realize the coordinated control of the corresponding equipment.

2. The dynamic reactive power reserve coordination optimization method based on transient partitioning and predictive control as described in claim 1, characterized in that: In step S1, the comprehensive evaluation index for transient voltage stability includes the low voltage recovery component index, the oscillation degree component index, and the recovery steady-state component index, which are used to quantitatively describe the severity of the fault from three aspects: the amplitude and duration of the voltage drop, the amplitude and decay rate of the voltage oscillation, and the voltage recovery level.

3. The dynamic reactive power reserve coordination and optimization method based on transient partitioning and predictive control as described in claim 2, characterized in that: In step S1, the low-voltage recovery component index is constructed through the following steps: S101: Obtain the transient voltage waveform curve V(t) through time-domain simulation, and determine the moment T when the voltage first recovers to the stable voltage value after the fault is cleared. TSVIr Determine the time T when the fault occurs. Fault The steady-state voltage value V after the fault s and the steady-state voltage value V0 before the fault; S102: Based on the variables determined in step S101, construct the following low-voltage recovery component index, TVSI. r :

4. The dynamic reactive power reserve coordination and optimization method based on transient partitioning and predictive control as described in claim 2, characterized in that: In step S1, the oscillation degree component index is constructed through the following steps: S111: Calculate the fault clearing time T from the transient voltage waveform curve V(t). Clear and simulation end time T end Then, the median line V of the transient voltage waveform oscillation, which includes the low-frequency and aperiodic variation components in the voltage waveform, is calculated. TVSIo (t); S112: Based on the variables determined in step S111, construct the following oscillation intensity component index TVSI0:

5. The dynamic reactive power reserve coordination optimization method based on transient partitioning and predictive control as described in claim 2, characterized in that: In step S1, the index for restoring steady-state components is constructed through the following steps: S121: Determine the time T when the voltage reaches steady state by combining the transient voltage waveform curve V(t). s and the steady-state voltage V after the fault s ; S122: Based on the variables determined in step S121, construct the following recovery steady-state component index TVSI. s : TVSI s =(V0-V s )×(T s -T Clear ); In the formula: T Clear V0 indicates the time when the fault is cleared; V0 represents the steady-state voltage value before the fault.

6. The dynamic reactive power reserve coordination optimization method based on transient partitioning and predictive control as described in claim 1, characterized in that: In step S203, the expression for the change in voltage trajectory is first quantified, and then the sensitivity of the dynamic reactive power reserve to the voltage trajectory is calculated based on the corresponding expression. In this way, a distance matrix that can fully describe the similarity between buses is constructed to realize the quantitative expression of the influence of dynamic reactive power reserve on the bus voltage trajectory. The formula for the distance matrix is ​​as follows: In the formula: This corresponds to the representative severe fault Fltp and dynamic reactive power VAR. q The distance matrix; This corresponds to the representative severe fault Fltp and dynamic reactive power VAR. q The distance between busbar i and busbar j; This corresponds to the representative severe fault Fltp and dynamic reactive power VAR. q The VQTSI index of the bus i.

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