Voltage Stability Limit Research Articles

Voltage stability assessment of a power system incorporating FACTS controllers using unique network equivalent

Voltage instability is considered as a main threat to stability, security, and reliability in the modern power systems. Prediction of voltage stability limit of multi-bus system through its two-bus equivalent model is a hot topic of the research in the field of power system operation and control. This paper presents a novel method to assess voltage stability status using a unique two-bus π-network equivalent derived with OPF solution of the actual system at different operating conditions. As the FACTS controllers are now an ineluctable part of power system, this paper considers an SVC and a TCSC in OPF formulation to assess voltage stable states of any interconnected power system in terms of its reduced two-bus integrated π-equivalent system. Simulation results for a practical power system establish that the proposed methodology is highly promising to assess voltage stability in a better way as compared to existing series equivalent model.

The Static Voltage Stability Limit Calculation of AC/DC Hybrid Power System Based on Improved Continuation Power Flow Algorithm

With the HVDC system interconnected to power grid, the voltage stability problem of power grid has become increasingly prominent. This paper establishes the mathematical model of AC/DC hybrid power system and proposed an improved Continuation Power Flow (CPF) algorithm to calculate the static voltage stability limit of AC/DC hybrid system, the characteristics of this algorithm are as following: PQ decoupled power flow algorithm is used; Lagrange quadric interpolation is used in the process of predictor and step control; local parameter method is used in the correction. The iterations of AC/DC calculation alternate to solve power flow equations and select the step control near the critical power limit points to ensure the convergence of power flow solution. In order to verify the correctness of the proposed algorithm, this paper compares the calculation results by the improved algorithm and Matpower on the IEEE 14 bus-system. This paper calculates the static voltage stability limit of AC/DC hybrid power system under different DC control patterns of modified IEEE 14 bus-system and analyzes the impacts of different DC control pattern to the system voltage stability.

Geometric Parameterization Technique Based Continuation Power Flow and its Applications in AC/DC Hybrid Power System

A new continuation power flow method based on local geometric parameterization technique is proposed for voltage stability analysis of AC/DC hybrid power system. By means of the alternating iteration method as the AC/DC power flow algorithm, the proposed method takes the coupling relationship between AC and DC systems into account to modify Jacobian matrix of AC system. Constraints of variables in DC system are also considered, as well as the adjustment of converter transformers tap position and the conversion of converters control modes. Based on the predictor-corrector method, this paper adopts the geometric corrector, and changes the direction of convergence effectively. According to different operation modes of AC/DC system, accurate voltage stability limit and the entire PV curve can be acquired. Simulation results of IEEE test systems are used to show the validity of the proposed algorithm.

Research on Impacts of FACTS on Static Voltage Stability Characteristics of AC/DC Power System

Based on the improved Continuation Power Flow algorithm, this paper investigates the impacts of FACTS on static voltage stability characteristics of AC/DC hybrid power system. This paper introduces the steady-state model of different FACTS devices, and the power flow mathematical model is established about AC/DC power system with FACTS devices. The impacts of FACTS devices with various capacities in different locations on static voltage stability are compared and analyzed. The calculation results of a four-machine two regions AC/DC power system show that FACTS are able to improve the voltage stability and the installation of SVC shunt compensation can possess a better effect to improve the system static voltage stability limit than TCSC series compensation.

Big Bang-Big Crunch Algorithm for Voltage Stability Limit Improvement by Coordinated Control of SVC Settings

Modern power system networks are operated under highly stressed conditions and there is a risk of voltage instability problems owing to increased load demand. A power system needs to be with sufficient voltage stability margin for secured operation. In this study, SVC parameters of location and size along with generator bus voltages, transformer tap settings are considered as control parameters for voltage stability limit improvement by minimizing loss and voltage deviation. The control parameters are varied in a coordinated manner for better results. The line based LQP voltage stability indicator is used for voltage stability assessment. The nature inspired meta heuristic Big Bang-Big Crunch (BB-BC) algorithm is exploited for optimization of the control variables and the performance is compared with that of PSO algorithm. The effectiveness of the proposed algorithm is tested on the standard IEEE 30 bus system under normal and N-1 line outage contingency conditions. The results obtained from the simulation encourage the performances of the new algorithm.

Static synchronous series compensator and static var compensator interaction on voltage stability limit enhancement and active power loss minimization through differential evolution algorithm

This paper proposes an application of differential evolution (DE) algorithm based extended voltage stability margin and minimization of real power loss incorporating static synchronous series compensator (SSSC) and static var compensator (SVC) devices. A new circuit element based model of SSSC and variable susceptance model of SVC are utilized to control the line power flows and bus voltage magnitudes for voltage stability limit improvement. The line stability index is used to assess the voltage stability of a power system. Voltage profile improvement values, real power loss minimization values and the location and size of SSSC and SVC devices were optimized by differential evolution algorithm. The results are obtained from the IEEE-30 Bus test case system and were analyzed with the voltage and real power loss under normal loading, critical loading and single line outage contingency conditions. Key words: Differential evolution algorithm (DEA), voltage stability, static synchronous series compensator (SSSC), static var compensator (SVC), line stability index, FACTS devices, load flow.

To study the voltage stability limits of distributed generation using induction machine in distribution networks

There are now a lot of distributed generation (DG) using asynchronous machines are connected to power distribution grid. These machines do not usually generate reactive power, even consume reactive power, so they generally affect the voltage stability of whole power grid, and can cause instability in itself it is no longer balanced by the torque to work. In this paper, we investigate the voltage stability problem of the asynchronous machine of wind turbines used in power distribution networks. From the static model of the asynchronous machine, this paper will apply the pragmatic criteria to analysis the voltage stability of the asynchronous machine based on the results of the power flow in power distribution network.

An enhanced bacterial foraging algorithm approach for optimal power flow problem including FACTS devices considering system loadability

Obtaining optimal power flow solution is a strenuous task for any power system engineer. The inclusion of FACTS devices in the power system network adds to its complexity. The dual objective of OPF with fuel cost minimization along with FACTS device location for IEEE 30 bus is considered and solved using proposed Enhanced Bacterial Foraging algorithm (EBFA). The conventional Bacterial Foraging Algorithm (BFA) has the difficulty of optimal parameter selection. Hence, in this paper, BFA is enhanced by including Nelder–Mead (NM) algorithm for better performance. A MATLAB code for EBFA is developed and the problem of optimal power flow with inclusion of FACTS devices is solved. After several run with different initial values, it is found that the inclusion of FACTS devices such as SVC and TCSC in the network reduces the generation cost along with increased voltage stability limits. It is also observed that, the proposed algorithm requires lesser computational time compared to earlier proposed algorithms.

Functional Approximation of Power System Steady-State Voltage Stability Limits by Artificial Neural Networks

The estimation of steady-state voltage stability limits represented by the critical value of a voltage stability index (VSI) in power flow-based electric energy system models may be a very difficult task, which might render their applicability impractical. When voltage collapse is associated with a generation bus reaching one of its reactive power generation limits, critical values of VSIs based on properties of the system Jacobian are difficult to be predicted without actually solving the maximum loading problem. In this context, this paper proposes the functional approximation of power system steady-state voltage stability limits, represented by the critical values of the minimum singular value (MSV) and tangent vector norm (TVN) indices, by means of artificial neural networks (ANNs). To construct a steady-state voltage stability boundary, the maximum loading problem was solved for a normalized even distribution of generation and load increase patterns using an optimal power flow-based approach. With these collapse points, the MSV and TVN indices were calculated and then used in the training and testing processes of the ANNs. A 6-bus system was used for carrying out this study. Results show that the proposed architecture of ANNs can be readily applied to the functional approximation of these VSIs at the voltage collapse.

Voltage Stability Assessment of Large Power Systems and Identification of Weekest Buses

This paper discusses the voltage stability analysis of large power systems using a modal analysis technique. Voltage instability within a power system has a severe consequences including wide spread low voltage profile and system blackout. The development and use of accurate methods to predict incipient voltage instability is crucial in preventing such voltage collapse situations. Voltage collapse may cause the outage in the entire power system. A modal analysis technique computes using steady state system model, a specified no. of smallest Eigen values and the associated Eigen vectors of reduced Jacobian matrix. The Eigen value provides relative measure of proximity to voltage instability. The Eigen vectors each of which is associated with a mode of voltage / reactive power are used to describe the mode shape and to provide information about the network elements and generators which participate in each mode. Using the bus participation factors, the weak load buses are identified. Real time prediction of voltage stability is applied in IEEE 30 bus system, the modal analysis technique was shown to provide an accurate estimate of the system’s proximity to voltage stability limit and consistently and correctly predict the critical buses and weakest branches in the transmission system.

Reactive power management of distribution networks with wind generation for improving voltage stability

This paper proposes static and dynamic VAR planning based on the reactive power margin for enhancing dynamic voltage stability of distribution networks with distributed wind generation. Firstly, the impact of high wind penetration on the static voltage stability of the system is analysed and then the effect of composite loads on system dynamics is presented through an accurate time-domain analysis. A new index, reactive power loadability (Q-loadability), is used to measure the vulnerability of the network to voltage collapse. Compensating devices are located using Q-loadability to increase the system voltage stability limit. Finally, a cost-effective combination of shunt capacitor bank and distribution static compensator (D-STATCOM) is determined through static and dynamic analyses to ensure voltage stability of the system after a sudden disturbance for different wind penetration levels. This study takes into account the induction motor dynamic characteristics which influence the transient voltage recovery phenomenon. The results show that the proposed approach can reduce the required sizes of compensating devices which, in turn, reduces costs. It also reduces power losses and improves the voltage regulation of the system.

A cost-effective approach for fast voltage recovery of power distribution networks with renewable energy

This paper presents a cost-effective reactive power planning for active distribution networks based on a new index called reactive power loadability (Q-loadability). The impact of high renewable energy penetration on the static voltage stability of the system is analysed. The effect of load models in distributed generation planning is also demonstrated through nonlinear simulations. In order to ensure fast voltage recovery after a sudden disturbance, compensating devices are located using Q-loadability to increase the system voltage stability limit. Both static and dynamic analyses are carried out to determine the size of distribution static synchronous compensator (D-STATCOM). The parameters of the controller are also tuned to reduce the rating of D-STATCOM. Simulation results show that the proposed approach can reduce the sizes of compensating devices required which, in turn, reduces costs. The effectiveness of the proposed algorithm is verified through several case studies.

Power Flow Control in Power System Using FACT Device Thyristor Controlled Series Capacitor (TCSC)

In modern days due to the ever increasing demand for power in expansion of transmission network, the transmission line are to be operated under loaded condition and there is a risk of power flow control and voltage instability. This paper proposes power flow control in a power system network by incorporating TCSC and SVC devices. The TCSC is a series compensated device to reduce the transmission line reactance in order to improve power flow through it, while the SVC is a shunt compensated device and they improve the voltage profile. This paper presents a systematic procedure for modeling and simulation using MATLAB/SIMULINK (Simpower System blockset). The optimal location of TCSC and SVC device are considered for power flow control and voltage stability limit. The proposed approach is carried out on two-area four-machine 11-bus test system model and the simulated result are presented to validate the proposed test case system. In this paper performance of TCSC and SVC device is analyzed and compare its simulated result for better power flow control in power system.

Identification of weak buses and elements participation in voltage instability of large multi bus power system

In heavily loaded systems, voltage stability limit is usually dominant and voltage instability is usually observed following large disturbance. This is typically the case in the deregulated environment as the transmission systems are operating under more stressed condition due to increased transaction level associated with open access. In this paper simple voltage stability analysis is carried out for a multibus power system (26 bus system) using V-Q sensitivity analysis and modal analysis. The bus participation, line participation and generator participation in critical mode of voltage stability is determined. This is useful for implementation of contingencies in power system for further study of voltage stability. A novel idea of small increment in reactive power and distributing the same in proportional to bus participation factor for calculation of generator and line participation is presented. Also the correlation between the voltage sensitivity factor and bus participation factor is established for identification of weak buses.

OPF based reactive power planning and voltage stability limit improvement under single line outage contingency condition through evolutionary algorithms

Reactive power planning is vital for maintaining the voltage stability of power systems and evolutionary algorithms are highly useful for achieving this task. This paper compares the effectiveness of the differential evolution (DE) and evolutionary programming (EP) algorithms in optimizing the reactive power planning of power systems under line outage contingency conditions. DE is efficient in exploration through the search space of the problem, while EP is simple and easy to implement. The low cost but fast response thyristor-controlled series capacitor (TCSC) flexible alternating current transmission system (FACTS) device is incorporated to control the power flows. The optimal settings of the control variables of the generator voltages, transformer tap settings, and location and parameter settings of the TCSC are considered for reactive power planning and the resultant reactive power reserves. The effectiveness of the proposed work is tested on the IEEE-30 Bus test system under the most critical line outage condition.

Quantitative method for evaluating generation margin for power system planning

AbstractAs the power system advances, the competition among the power companies becomes heated, and they seek more efficient system planning using existing facilities. Therefore, an efficient system planning method is desirable. This paper proposes a quantitative evaluation method for the (N–1) generation margin considering overload and voltage stability constraints. Concerning the generation margin related to overload, a fast solution method without recalculation of the (N–1) Y‐matrix is proposed. With reference to voltage stability, this paper proposes an efficient method of seeking the stability limit. The IEEE30 model system, composed of six generators and 14 load nodes, is employed to validate the proposed method. According to the results, the proposed method can reduce the computational cost for obtaining the generation margin related to the overload and the voltage stability limit under the (N–1) condition, and can specify the value quantitatively. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(4): 19–28, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). doi 10.1002/eej.21234

Shuffled Frog Leaping Algorithm based Voltage Stability Limit Improvement and Loss Minimization Incorporating FACTS Devices under Stressed Conditions

day power system networks are having high risks of voltage instability problems and several network blackouts have been reported. This phenomenon tends to occur from lack of reactive power supports under heavily stressed operating conditions caused by increased load demand and the fast developing deregulation of power systems across the world. This paper proposes an application of Shuffled Frog Leaping Algorithm (SFLA) based extended voltage stability margin and minimization of loss by incorporating TCSC and SVC (variable susceptance model) devices. The line stability index (LQP) is used to assess the voltage stability of a power system. The location and size of Series connected and Shunt connected FACTS devices are optimized by shuffled frog leaping algorithm. The results are obtained from the IEEE-30 bus test case system under critical loading and single line outage contingency conditions

Dynamic voltage stability constrained congestion management framework for deregulated electricity markets

Congestion management is an important part of power system operation in today deregulated electricity markets. However, congestion management is traditionally performed based on static analysis tools, while these tools may not correctly capture dynamic voltage stability limits of a power system. In this paper, a new congestion management framework considering dynamic voltage stability boundary of power system is proposed. For this purpose, precise dynamic modeling of power system equipment, including generators and loads, is incorporated into the proposed congestion management framework. The proposed method alleviates congestion with a lower congestion management cost and more dynamic voltage stability margin, resulting in a more robust power system, compared with the previous congestion management methods. The validity of proposed congestion management framework is studied based on the New England 39-bus power system. The obtained results confirm the validity of the developed approach.

A New Method for Online Assessment of Voltage Stability

In this paper we proposed a new technique for identifying system stress due to the loading in wide area of power system based on the phasor angle difference behavior. The difference of voltage phasor angle between busses can be transferred in to a simple conversion and trigonometric wave signal during load increasing. Using Discrete Fourier Transform (DFT), the signal will be transformed into the spectral frequency. The proposed technique will analyzed current condition by visualized the level of stress and proximity to voltage stability limit in the system based on the change of spectral frequency . This method also can be used to monitor such loss of generators or transmission line outages. The result shown that the proposed technique is simple, fast and reliable, requiring minimum data measurement and be suitable for Wide Area Monitoring System.

Congestion Management in Pool Electricity Markets with Loadability Limits

In a restructured electricity market environment, when the producers and consumers of electric energy desire to produce and consume in amounts that would cause the transmission network to operate at or beyond one or more transfer limits, the system is said to be congested. The congestion in the system cannot be allowed to persist for a long time, as it can cause sudden rise in the electricity price and threaten system security and reliability. Congestion management (CM) is one of the most important challenging tasks of the Independent System Operator (ISO) in the deregulated environment. In this article, generators' rescheduling-based CM approach to manage transmission line congestion considering voltage stability limit has been presented for pool-based electricity market model. The results have also been obtained without taking loadability limit for comparison. The results have been obtained for IEEE 24 bus test system.