Optimal Scheduling of Distributed Energy Resources and Responsive Loads in Islanded Microgrids Considering Voltage and Frequency Security Constraints

Abstract

Low inertia of distributed energy resources (DERs), high penetration levels of renewable energy sources (RESs) and load demand variations put the islanded microgrids (MGs) security at risk of instability. This paper proposes a two-stage stochastic model for coordination of DERs and responsive loads in islanded MGs with regard to voltage and frequency security constraints. Based on the proposed model, scheduling of the controllable units in both supply and demand sides is done in a way not only to maximize the expected profit of MG operator (MGO), but also to minimize the energy payments of customers under the premise of security and stability of MG. An AC optimal power flow (AC-OPF) procedure is also used to study operating condition of the system under uncertainties and to guarantee acceptable nodal voltages and system frequency during different scenarios. The proposed stochastic optimization model is then applied to a typical autonomous MG and its effectiveness is demonstrated through different scenarios under uncertainties in load consumption and renewable energy resources (RESs) productions. Simulation results demonstrate that customers’ participation in DR programs have significant effect on the system’s performance in terms of voltage and frequency stability. Moreover, optimal coordination of DERs and responsive loads can increase the expected profit of MGO significantly. The effectiveness of the proposed scheduling approach is verified on an islanded MG test system over a 24-h period