An Improved Hierarchical Control Structure for Robust Microgrid Operation and Seamless Mode Transfer under Linear and Nonlinear Loads conditions

This paper proposes the improved hierarchical- based control of Microgrid based on proportional and multi-resonance controllers to compensate for harmonic distortion of nonlinear loads. Moreover, the probable transition of MG, especially from grid-connected to unplanned islanding and unintentional MG resources outage are studied. In current and voltage controllers of three-phase VSIs which are located in the inner level, the proportional and multi-resonant controllers are implemented. To attain proper decoupled (P-Q) power-sharing, a selective harmonic type virtual impedance, and a droop-based control are implemented at the primary level. Next, to reach better restoration and subsequently, seamless transition in accidental islanding, unintentional MG-DG’s outage, and synchronization process, the advanced three-phase SRF-PLL with in-loop MAF along with a simple adaptive lookup table are implemented in the secondary level of control. The MATLAB/Simulink simulation results verified that the proposed method improved the performance of control, effectiveness, and robustness in upstream or local grid variation.