Reactive power management in a deregulated power system with considering voltage stability: particle swarm optimisation approach

Abstract

During past two decades electric utilities have faced the upheaval of moving toward deregulation. It has always been its ambition of creating a clear structure in which rivals are allowed to do free enterprise in trading of electricity. Accordingly, in this new era economical rules and electricity market legislations have a big effect on secure operation of power systems. This means that, presense of a market independent entity is vital while it should only be in charge of security and stability of power system operation. This entity, called ISO, which is acronym for Independent System Operator [1]. Major task of ISO corresponds to prospect ancillary services requirments which are necessary for reliability enhancement of the system. ISO is also responsible for ancillary services procurement [2,3]. Reactive power is one kind of ancillary service that have significant effectcs on active power trading indirectly. Reactive power is utilized for different purposes e.g voltage profiles amelioration, power loss reduction and lessening occupied capacity of the transmission network. In general, a good reactive power management system increase the performance of transmission lines as unique paths for physical operation of electric power transactions. From Economical points of view, ancillary services had better be provided in a market structure than obligatory as it is operated in vertically integrated system. In recent years many researches are carried out concerning reactive power management and pricing in restructured power systems. In [4,5] applicale methods for determination of reactive power costs are discussed. In [6] a security constraint optimal power flow (SCOPF) is presented for reactive power management of NGC power system. In proposed method reactiv epower cost is modeled as a quadratic function of generators' reactive power outpus and linear programming is used to solve model and determination the reactive power shared among participatns along with prices. Considering social welfare objective for active power market in [7] it tries to dispatch reactive power in such a way power market get better performance as much as possible. It also assumes that active power consumptions are propotional to the price and obey an exponential function. Based on this strategy one can easily distinguish that reactive power price is determined indirectly and it depends on active power activities. Lagrangeian multiplyers are used for settlements of active / reactive power commodity. Reference [8] exploits an OPF based structure to show that reactive power pricing extremely depends on chosen objective for its dispatching purposes. Data analysis of [8] declares that it had better reactive power price be determined in a separate structure and independent of active power market objectives. Investigation of methods presented in above articles reveals that in all cases, reactive power is optimised around current operating point of power system after clearing active power market or simultaneous with it. In other words there is less attention to reactive power reserve necessary for perventing of voltage collapse occurance following perturbation in loads or other events. This paper presents a method in which providing of efficient reactive power reserve is also considered in price determination. Therefore, conventional OPF formulation is modified in somehow, voltage stability criterion can be modeled within reactive power market equations. In proposed structure, reactive power costs is to be minimized independently of active power activites. Particle Swarm Optimization Algorithm is used for solving OPF based market structure implemented on WSCC 9 bus test system to show capabilites of the procedure into a market based power system managenet.