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Fuzzy based load shedding approach against voltage instability
AY Abdelaziz, ATM Taha, MA Mostafa, AM Hassan
International Journal of Engineering, Science and Technology , 2012,
Abstract: The phenomenon of voltage collapse eclipses a potential hazard for the transmission and distribution systems. The load shedding for avoiding the existence of voltage instability in power systems is taken as a remedial action during emergency states. The load shedding strategy for power systems with location and quantity of load to be shed is presented in this paper. Two methods are used for this purpose. The first method is based on a mathematical calculation of an indicator of risk of voltage instability. The second method is based on a fuzzy load shedding based algorithm that uses a voltage stability indicator for averting voltage collapse. Applications to the standard IEEE 30-bus system are presented to validate the applicability of the two proposed methods.
Estimation of Static Pull-In Instability Voltage of Geometrically Nonlinear Euler-Bernoulli Microbeam Based on Modified Couple Stress Theory by Artificial Neural Network Model  [PDF]
Mohammad Heidari,Yaghoub Tadi Beni,Hadi Homaei
Advances in Artificial Neural Systems , 2013, DOI: 10.1155/2013/741896
Abstract: In this study, the static pull-in instability of beam-type micro-electromechanical system (MEMS) is theoretically investigated. Considering the mid-plane stretching as the source of the nonlinearity in the beam behavior, a nonlinear size dependent Euler-Bernoulli beam model is used based on a modified couple stress theory, capable of capturing the size effect. Two supervised neural networks, namely, back propagation (BP) and radial basis function (RBF), have been used for modeling the static pull-in instability of microcantilever beam. These networks have four inputs of length, width, gap, and the ratio of height to scale parameter of beam as the independent process variables, and the output is static pull-in voltage of microbeam. Numerical data employed for training the networks and capabilities of the models in predicting the pull-in instability behavior has been verified. Based on verification errors, it is shown that the radial basis function of neural network is superior in this particular case and has the average errors of 4.55% in predicting pull-in voltage of cantilever microbeam. Further analysis of pull-in instability of beam under different input conditions has been investigated and comparison results of modeling with numerical considerations show a good agreement, which also proves the feasibility and effectiveness of the adopted approach. 1. Introduction Micro-electromechanical systems (MEMS) are widely being used in today’s technology. So investigating the problems referring to MEMS owns a great importance. One of the significant fields of study is the stability analysis of the parametrically excited systems. Parametrically excited micro-electromechanical devices are ever being increasingly used in radio, computer, and laser engineering [1]. Parametric excitation occurs in a wide range of mechanics, due to time-dependent excitations, especially periodic ones; some examples are columns made of nonlinear elastic material, beams with a harmonically variable length, parametrically excited pendulums, and so forth. Investigating stability analysis on parametrically excited MEM systems is of great importance. In 1995 Gasparini et al. [2] examined the transition between the stability and instability of a cantilevered beam exposed to a partially follower load. Applying voltage difference between an electrode and ground causes the electrode to deflect towards the ground. At a critical voltage, which is known as pull-in voltage, the electrode becomes unstable and pulls in onto the substrate [3]. The static pull-in behavior of MEMS actuators has been
Reliability Evaluation of Power System Considering Voltage Stability and Continuation Power Flow  [PDF]
R. K. Saket,R. C. Bansal,Col. Gurmit Singh
Journal of Electrical Systems , 2007,
Abstract: This article describes the methodology for evaluation of the reliability of an composite electrical power system considering voltage stability and continuation power flow, which takes into account the peak load and steady state stability limit. The voltage stability is obtained for the probable outage of transmission lines and removal of generators along with the combined state probabilities. The loss of load probabilities (LOLP) index is evaluated by merging the capacity probability with load model. State space is truncated by assuming the limits on total numbers of outages of generators and transmission lines. A prediction correction technique has been used along with one dimensional search method to get optimized stability limit for each outage states. The algorithm has been implemented on a six-bus test system.
Optimum Load Shedding in Power System Strategies with Voltage Stability Indicators  [PDF]
Engineering (ENG) , 2010, DOI: 10.4236/eng.2010.21002
Abstract: An optimal load shedding strategy for power systems with optimum location and quantity of load to be shed is presented in this paper. The problem of load shedding for avoiding the existence of voltage instability in power systems is taken as a remedial action during emergency state in transmission and distribution sector.Optimum location of loads to be shed is found together with their optimum required quantity. L-Indicator index is in used for this purpose with a modified new technique. Applications to be standard 6 bus Ward-Hale test system and IEEE – 14 bus system are presented to validate the applicability of the proposed technique to any system of any size.
Voltage Instability in Electrical Network: A Case Study of the Nigerian 330 kV Transmission Grid
O.S. Onohaebi,S.T. Apeh
Research Journal of Applied Sciences , 2012,
Abstract: In this study, various aspects of voltage instability in electrical power network using the Nigeria 330 kV transmission network as a case study were analysed. The study considered various causes of voltage instability such as loss of generators or lines, 3 phase faults, load increases which were simulated on the network using the Power World Simulator. The study revealed that the present 330 kV trasmission grid is highly unstable and require remedial measures to improve the voltage stability. Thus, shunt compensation, load shedding and strengthening of the network by incoporating additional lines into the grid showed greater improvment on the network. The study therefore, proposed a modified network that will improve the voltage stability in the network.
Indirect Output Voltage Control in Negative Output Elementary Super Lift Luo Converter Using PIC plus FLC in Discontinuous Conduction Mode  [PDF]
S. Muthukaruppasamy, A. Abudhahir
Circuits and Systems (CS) , 2016, DOI: 10.4236/cs.2016.711310
Abstract: In this paper, the design of a proportional integral controller (PIC) plus fuzzy logic controller (FLC) for the negative output elementary super lift Luo converter (NOESLLC) operated in discontinuous conduction mode (DCM) is presented. In spite of the many benefits viz. the high voltage transfer gain, the high efficiency, and the reduced inductor current and the capacitor voltage ripples, it natured with non-minimum phase. This characteristic makes the control of NOESLLC cumbersome. Any attempt of direct controlling the output voltage may erupt to instability. To overcome this problem, indirect regulation of the output voltage based on the two-loop controller is devised. The savvy in the inductor current control improves the dynamic response of the output voltage. The FLC is designed for the outer (voltage) loop while the inner (current) loop is controlled by the PIC. For the developed ?19.6 V NOESLLC, the dynamic performances for different perturbations (line, load and component variations) are obtained for PIC plus FLC and compared with PIC plus PIC. The study of two cases is performed at various operating regions by developing the MATLAB/Simulink model.
Adaptive Load Shedding Scheme to Ensure Frequency and Voltage Stability
Sriram Kotipalli1 ,RambabuCh 2
International Journal of Engineering Trends and Technology , 2012,
Abstract: Synchrophasor technology based wide-area monitoring, protection, and control (WAMPAC) can be effectively utilized for system wide monitoring, coordinated real time protection and control functions required to counteract the propagation of any major disturbances in the power system. Phasor Measurement Unit (PMU) is one of the most vital elements of the WAMPAC system. PMU reports time tagged voltage and current phasors required for the dynamic monitoring functions at much faster rate as compared to the conventional Supervisory Control and Data Acquisition/Energy Management System (SCADA/EMS). Utilizing these dynamic measurements, WAMPAC system address the automated energy control functions for various instabilities like, transient, frequency and voltage instabilities. Conventionally, frequency instabilities have been controlled through load shedding in the system based on predesigned frequency and load shedding amount. Of late, adaptive schemes have been proposed in the literature by quantifying the magnitude of the disturbance through the real time measurements. And for deriving the control actions we will focus on frequency stability. However, as the frequency instability arises in a system due to critical contingencies, it may also pose a threat to the voltage stability of the system. The literature survey reveals that the existing schemes do not assess the voltage stability along with frequency stability for adaptive load shedding which is imperative for selfhealing of the power system.
Voltage Stability Based Formation of Voltage Control Areas Considering Impact of Contingencies  [cached]
Tarun Martolia,M.K. Verma
International Journal of Applied Power Engineering , 2012, DOI: 10.11591/ijape.v1i3.1489
Abstract: This paper presents a new approach for formation of voltage control areas (VCAs) based on sensitivity of reactive power generations with respect to reactive power demands, together with bus voltage variations under contingencies. The load buses in geographically compact region showing similar sensitivity of reactive power demand to reactive generations have been clubbed together to form voltage control areas. The voltage control areas so formed have been modified based on voltage variations under contingencies at different loadings. Case studies have been performed on IEEE 14-bus system. The VCAs formed by proposed method have been compared with VCAs formed by few existing approaches. The superiority of proposed approach of voltage control areas formation over few existing approaches has been established on the test system considered.
The Coupling of Voltage and Frequecncy Response in Splitting Island and Its Effects on Load-shedding Relays  [PDF]
Hao Yang, Baohui Zhang
Energy and Power Engineering (EPE) , 2013, DOI: 10.4236/epe.2013.54B128

The voltage and frequency dynamics interact with each other in the island after splitting. The current frequency response model without considering the voltage effect would bring remarkable errors when analyzing the frequency dynamic progress in the island with large-capacity active-power shortage. In this paper, coupling effects of voltage and frequency are studied to indicate that initial reactive-power deficit and load characteristics have strong effects on the coupling effects of the voltage and frequency. Moreover, control effects of currently used under frequency load-shedding relays (UFLS) and under voltage load-shedding relays (UVLS) which are installed and executed independently are examined to find that it would sometimes cause excessive or inadequate control without considering the coupling, suggesting that it is necessary to develop coordinate control methods for voltage and frequency problems.

Voltage Stability Control of Electrical Network Using Intelligent Load Shedding Strategy Based on Fuzzy Logic  [PDF]
Houda Jouini,Kamel Jemai,Souad Chebbi
Mathematical Problems in Engineering , 2010, DOI: 10.1155/2010/341257
Abstract: As a perspective to ensure the power system stability and to avoid the vulnerability leading to the blackouts, several preventive and curative means are adopted. In order to avoid the voltage collapse, load shedding schemes represent a suitable action to maintain the power system service quality and to control its vulnerability. In this paper, we try to propose an intelligent load shedding strategy as a new approach based on fuzzy controllers. This strategy was founded on the calculation of generated power sensitivity degree related to those injected at different network buses. During the fault phase, fuzzy controller algorithms generate monitor vectors ensuring a precalculated load shedding ratio in the purpose to reestablish the power balance and conduct the network to a new steady state. 1. Introduction Various disturbances occur in electrical networks every year which lead to blackouts. As the frequency and voltage represent two important parameters to the power system safety, it should have a continuous control of these parameters and this to ensure the best service quality. It is characterized by standard criteria related to the service continuity, the voltage profile, the purity of injected frequency, and the network static and transient robustness according to a set of possible exploitations and disturbance scenarios. The network vulnerability control is an important rivalry, since preventive and curative means can be considered in order to guarantee network service quality. In the case of vulnerable cascading events leading to blackouts, the load shedding will be the most desirable action avoiding network instability [1]. Different methods were proposed in order to decide the place and the quantity of loads to be shed. Indeed, Faranda et al. proposed a new load shedding approach called distributed interruptible load shedding [2]. Subramanian made a new model based on the sensitivity in the electric networks in conjunction with the linear programming for solutions of load shedding [3]. Tom?i? et al. started with a dynamic model of the frequency that permits to simulate the impact of the most important system on the response of the frequency following disruptions and to determine the optimal number of load shedding stages and the percentage to shed in every stage [4]. Parker et al. used the medium-term dynamic simulation to prove the impact of the load shedding action and this in order to affect the appropriate systems control. We must to indicate that it's a voltage modal analysis combined with the determination of the reactive power margin [5].
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