Enhancement of Voltage Stability Margin Using FACTS Controllers

Optimal allocation of Var source involves optimal location and determination of the size of the Var source. The purpose is to find the right tradeoff between the investment cost of the new Var source and the benefits in system operation derived from the presence of the additional reactive compensators. Traditionally, the locations for placing new Var sources were either simply estimated or directly assumed. This paper categorizes the literature relevant to optimal allocation of shunt dynamic Var source SVC and STATCOM, based on the voltage stability analysis tools used. Those tools include static voltage stability analysis ones such as P-V and V-Q curve analysis, continuation power flow (CPF), optimization methods (OPF), modal analysis, saddle-node bifurcation analysis, and dynamic voltage stability analysis ones such as Hopf bifurcation analysis and time-domain simulation. Static voltage stability analysis techniques are also used in dynamic Var planning. At the end of the paper, the advantages of static and dynamic voltage stability analysis tools are summarized. (7 pages)

Power systems are being operated close to their voltage security limit which makes their reliable operation more challenging. Voltage stability has been a major problem faced by utilities now a days. Many blackout have been reported around the world related to voltage instability problem. Many voltage stability analysis methods have been presented up till now. Here artificial neural network based approach for voltage stability analysis of power system is presented. Voltage stability analysis of power system has been done in terms of voltage stability margin. Voltage stability margin is calculated by estimating distance from current operating point to maximum voltage stability point according to loading parameter. Principal Component Analysis is an efficient feature selection method used here to find few input variables required to estimate voltage stability margin with sufficient accuracy and execution speed. Major drawback of previously published work is they need to train new neural network whenever change in system topology occur which is very time consuming process. Therefor in this paper single ANN has been prepared for estimating VSM for several system configuration. Feed forward neural network and radial basis function neural network have been used for voltage stability analysis of power system. The final result indicate that proposed method provide an efficient and compact ANN model for different system configuration as well as base case operating condition with lowest possible input required.

In the static voltage stability analysis, the dynamics of the components in the power system are not considered and the creditability of the results obtained is more or less affected. Based on the continuation algorithm, this paper investigates the dynamic stability using the small signal analysis method. The stability type is distinguished by the modal participation factors of the state variables. Firstly, the equilibrium manifold is traced by a locally parameterized continuation method. Then, the dynamic stability of each equilibrium point is analyzed using the small disturbance analysis method considering the components dynamics. The system state matrix is calculated numerically by applying small perturbation to each state in turn. Simulation results show remarkable differences in the stability critical points obtained by the small signal perturbation dynamic analysis and the static analysis. Also a region of dynamic voltage stability is found in the lower portion of the PV curve.

With the development of power electronic devices, the research of Flexible AC Transmission System (FACTS) in regulating line power flow and improving static voltage stability is more in-depth. This paper discusses the static voltage stability of power grid with new energy taking into account the distributed static series compensator (DSSC), and evaluates the power flow control efficiency of DSSC from the aspect of system static voltage stability. First, the equivalent circuit and working principle of DSSC are analyzed, and the power flow equations are obtained based on the equivalent power injection model of DSSC; Secondly, based on the power flow calculation equation, the efficiency evaluation index that can reflect the static voltage stability of the system is proposed, and the impact of new energy with different capacities on the static voltage stability is calculated and analyzed; Finally, the proposed method is verified by the simulation analysis of IEEE-24 bus system and actual power grid: the proposed method is fast and simple, and has certain engineering application value.

Comprehensive evaluation of voltage stability based on EW-AHP and Fuzzy-TOPSIS

The study of static voltage stability is actually based on asymptotic stability, which is affected by the operation state of the power grid. In this paper, the voltage stability margin index is deduced, and the stability margin of the existing power grid under different actual working conditions is analyzed based on the proposed index. the leading factors and the worst system conditions are determined by practical experience. The correctness of the proposed method is verified by the simulation analysis of the actual provincial power grid.

This paper discusses voltage stability analysis of power systems using two static voltage stability analyses: voltage sensitivity, modal analysis including participation factor. These methods determine how far the power system is from its break point providing relative measure of voltage instability proximately. Results show all method indices share voltage stability margins having a precise voltage collapse point when a power system is subjected to sudden load increase. The application has been demonstrated on the IEEE 14-bus System.

The power system is experiencing a higher penetration of renewable energy generations (REGs). The short circuit ratio (SCR) and the grid impedance ratio (GIR) are two indices to quantify the system strength of the power system with REGs. In this paper, the critical short circuit ratio (CSCR) is defined as the corresponding SCR when the system voltage is in the critical stable state. Through static voltage stability analysis, the mathematical expression of the CSCR considering the impact of GIR is derived. The maximum value of CSCR is adopted as the critical value to distinguish the weak power system. Based on the static equivalent circuit analysis, it is proved that the CSCR is still effective to evaluate critical system strength considering the interactive impact among REGs. Finally, we find that the GIR can be neglected and the SCR can be used individually to evaluate the system strength when SCR>2 or GIR>5. The correctness and rationality of the CSCR and its critical value are validated on ADPSS.

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In new distribution systems, the proportion of distributed renewable energy generation is gradually increasing. Existing methods for static voltage stability analysis struggle to accurately reflect the impact of distributed generation output. First, this paper introduces robustness indices to quantify the impact of active and reactive power output fluctuations from distributed generation on load buses, based on the L-index. Second, a static voltage stability indicator system is constructed. Based on the characteristics of the indicators, definitions for voltage stability weak bus, active power vulnerable bus and reactive power vulnerable bus are established. Third, an optimization model to enhance static voltage stability is developed specifically for these buses. The Pareto front of the solutions obtained by it based on the NSGA-III algorithm includes the optimal solutions under different index preferences, and then it is achieved by adjusting the power output of the power source. Last, the effectiveness of the indicator system and the enhancement methods are validated through the IEEE 118-bus system.

To address the issue of static voltage stability in distribution networks with high proportion distributed pv generation(DG) during fault, this paper establish a fault equivalent model which consider the characteristics of PV equipment during low-voltage ride-through(LVRT). The model derives the constraints on the PV current phase angle required to maintain static voltage stability. Subsequently, the impact of DG capacity at the point of common coupling and the electrical distance between the distribution network and the AC power source on the PV output current phase angle constraint is quantitatively analyzed. On this basis, a current control method is proposed: when there is a voltage stability risk in the system, the active and reactive current injection from the PV is adjusted, while under no voltage stability risk, the low-voltage ride-through control strategy remains unaffected. Finally, simulation examples based on the Matlab/Simulink testing platform verify the validity of the analysis and the proposed control strategy.

Every transmission system has voltage stability limit which may lead to voltage collapse if an undetected bulk transmission network is operated close to its operating limit. This research work uses continuation power flow method to identify voltage collapse point for Bangladesh Power System Network (BPSN). For the identification of weak buses, an analytical based technique of tangent factor has been presented. The risk of voltage collapse has been mitigated by placing SVCs at the weak buses of the system using load flow analysis. Moreover, sensitivity based approach has been introduced to determine optimal location of Static VAR Compensator (SVC) for the voltage security enhancement. A comparative analysis has been documented considering the size of reactive power to improve the loading factor of the overall network at the end of this work.

The rapid growing in electrical load, and increasing the dependency on renewable energy recourses; highly affect the Jordanian power system stability and operation. This paper presents a static voltage stability analysis for the northern part of the Jordanian grid. The main purpose of this study is finding out the domain of the system from facing voltage instability conditions. In order to analyze voltage stability of the study system, static analysis techniques such as P-V curve and Q-V curve methods are applied. The DIgSILENT PowerFactory® program is used in this study to obtain the results.

The location of SVC (static VAR compensator) and other types of shunt compensating devices for voltage support is an important practical question. This paper presents a new decoupled-quadratic load flow (DQLF) approach for adjustment of parameters of SVC. The DQLF model can calculate effectively the SVC susceptance and resulting firing angle using a simple quadratic equation derived using real and reactive power injections at the SVC bus. The resulting quadratic equation, can easily evaluate system voltage stability margin. The model makes use of conventional fast decoupled load flow (FDLF) algorithm for calculation of voltage phase angle corrections. The proposed approach eliminates the formation and modification of B" matrix in FDLF models and offers considerable saving in the execution times. It is found to be very reliable for Q-adjusted studies and ill-conditioned cases. The DQLF model offers 50% faster convergence than FDLF model, when applied to large systems, having a large number of generator buses. The validity of the proposed algorithm for SVC parameter adjustment is tested on IEEE 14 bus system. The stability margins are evaluated using the proposed quadratic equation, and compared with traditional Q-V sensitivity model. The final parameters B/sub svc/ and firing angle /spl alpha/ obtained using DQLF model are compared with those obtained using Newton Raphson (NR) and FDLF models and found to be same.

This paper primarily focuses on an investigative study on allocating Flexible AC transmission system (FACTS) devices on radial distribution systems. The FACTS device that is used in this paper is static var compensator (SVC). In this paper, SVC is placed on each bus except substation bus and study the results to find the best location for allocation. A design of SVC was done by fixed reactance method. The total power loss of network and voltage of nodes have been analyzed for each allocation and the sequences of each implementation have been compared to find the best location of SVC. The proposed algorithm has been executed on IEEE 33-bus and 69-bus standard test systems.