This paper proposes a novel technique for representing system security in the operations of decentralized electricity markets, with special emphasis on voltage stability. An interior point method is used to solve the optimal power flow problem with a multiobjective function for maximizing both social benefit and the distance to maximum loading conditions. A six-bus system with both supply and demand-side bidding is used to illustrate the proposed technique for both elastic and inelastic demand, and a 129-bus test system that models the Italian HV transmission network is used for testing the practical applicability of the proposed method. The results obtained show that the proposed technique is able to improve system security while yielding better market conditions through increased transaction levels and improved locational marginal prices throughout the system.

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The paper presents an advanced control scheme for a PhotoVoltaic unit (PV) to suitably drive the injection of both active and reactive power into a MV radial distribution grid. Such algorithm allows a decoupled control of active and reactive power by properly adjusting the modulating signals of the PWM interface converter with the grid. A closed loop regulation scheme has been derived and guidelines for the design of the regulators are provided. The control algorithm has been applied to a real MV grid-connected PV power plant and several simulations have been performed in order to analyze the behavior of the system and to verify the effectiveness of the adopted regulation. The positive effect of reactive power support has been highlighted showing benefits on grid current and voltage profiles with respect to the typical case of the sole active power production. ©2008 IEEE