Optimal Location of UPFC for ATC Enhancement in Restructured Power Systems

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O CC is the UPFC capital cost
PGi and QGi are the real and reactive power generation at bus i PDi and QDi are the real and reactive load demand at bus i n is the total number of buses Gij-FACTS is the real part of the ij element of Ybus matrix including FACTS devices Bij-FACTS is the imaginary part of the ij including FACTS devices
Sij max is thermal limit of line ij NG is number of generators PGmax /PGmin are the maximum and minimum real power generation at bus i, respectively QGmax/ QGmin are the maximum and minimum reactive power generation at bus i respectively
environment, mtainties associated with risks of decision making. An important responsibility of transmission system operators (TSO) is facilitating nondiscriminatory open-access to transmission network. TSO should procure such services to ease transferring more power using the existence facilities in an economic fashion. Required reliability as well as adequate available transfer capability (ATC) is needed to ensure all economic transactions, while sufficient ATC is required to guarantee competitive electricity trading [1]. It is also desired to maintain economical and secure operation over a wide range of system conditions and constraints. Based upon the report of North American Electric Reliability Council (NERC)—ATC is defined as “a measure of the transfer capability remaining in the physical transmission network for further commercial activities over and above already committed uses”. The main part of ATC is total transfer capability (TTC), which is the largest flow increase between the selected source/sink that transfers without violation of thermal limits, voltage limits as well as dynamic stability limits. ATC enhancement is led to focus on the possible ways by which such constraints can be alleviated [2]. Various ATC boosting approaches have been proposed in 176
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element of Ybus matrix
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literature. For example, the adjustment of generators’ terminal voltages, under load taps changers (ULTCs) and rescheduling generator outputs [3]. Based on physical constraints FACTS technology with regards to the capability of flexible power flow have a major impact on the utilization of the transmission system. FACTS controllers can be effectively used to improve the utilization of the power systems in order to improve stability as well as security. FACTS devices may enhance transmission functionality in order to fully utilize existing transmission systems [4]. Static var compensator (SVC) and thyristor controlled series capacitor (TCSC) are some of the commonly used FACTS controllers. The improvements on the field of power electronics, particularly on gate turn-off (GTO) thyristor ratings have made possible a new family of versatile FACTS controllers’ namely static synchronous compensator (STATOM), static synchronous series compensator (SSSC) and the unified power flow controller (UPFC).In this paper the outlines of a novel technique identifying the optimal location for UPFC as a second generation FACTS controller, is investigated. In this paper the proposed method based upon the repeated AC power flow technique for ATC calculation using UPFC as FACTS devices is presented [5]. By employing a combination of ATC enhancement, voltage profile improvement as well as UPFC capital investment, a cost function is developed. The aim of the optimization problem is to find the best location and the optimum capacity of UPFC with regards to satisfying technical and economical constraints. A multi-objective constrained optimisation problem is solved via a hybridization of conventional as well as heuristic techniques to obtain the optimal solutions. The combinatorial optimisation methodology is examined on modified IEEE 30-bus test systems the results show significant improvements i. III. UPFC MODEL FOR LOAD FLOW STUDIES The unified power flow controller UPFC is consist of two voltage source converters (VSCs) using gate turn off (GTO) thyristor valves. These VSCs share a common capacitor on
Optimal Location of UPFC for ATC Enhancement in Restructured Power Systems 2 1 H.Farahmand , M. Rashidinejad2, A.A.Gharaveisi , G. A. Shahriary3
1
International Research Center for Science & Technology, Mahan, Iran 2 Shahid Bahonar University of Kerman, Kerman, Iran 3 Hormozgan Regional Electricity Company, Iran mrashidinejad@, mrashidi@.ac.ir