Stability Enhancement through Offline Optimization of Decentralized Incremental-Cost-Based Droop Controller in Islanded Microgrids

Through the use of incremental cost (IC) based droops, power can be optimally dispatched; however, these droops can adversely affect microgrid (MG) stability. As the load increases, IC-based droops tend to shift the most dominant eigenvalues toward the right half-plane. Prior research permitted a degradation in cost-minimization capability and sacrificed optimality to maintain MG stability. This paper introduces an offline optimization framework to adjust derivative controllers associated with IC-based droops, which, in addition to optimally minimizing operating costs, improve MG stability and power-sharing dynamic performance. The proposed offline optimization iterates over all operating points and assesses MG stability through eigenvalue analysis. It tunes droop parameters, including derivative controllers for active and reactive power, to ensure enhanced stability at every optimal economic dispatch operating point without requiring communication to update these gains. The active power derivative controller gain is optimally scheduled to vary adaptively with the active power output of the distributed generator (DG). The effectiveness of the proposed droop control is confirmed through case studies in the MATLAB/Simulink environment. The case studies encompass load changes on both a 6-bus and a 38-bus test networks, variations in cost characteristics, and instances of DG tripping.