Optimal design of controllers and harmonic compensators for three-level cascaded control in stationary reference frame for grid-supporting inverters-based AC microgrid

In this paper, new optimal procedures are introduced to design the finest controllers and harmonic compensators (HCs) of three-level cascaded control for three-phase grid-supporting inverters based-AC microgrid. The three control levels, comprising primary, secondary and synchronization control levels, are developed in stationary alpha beta-frame and based on the proportional-integral (PI) controllers and the proportional-resonant controllers along with additional HCs. The new optimal design guidelines of microgrid's controllers and HCs are aimed to fulfill the study requirements. The optimization objectives and constraints are employed to minimize both the total harmonic distortion (THD) and individual harmonics of microgrid's voltage to enhance the quality of microgrid's output power. The THD of microgrid's voltage can be reduced to 0.19% under the nonlinear loads. Moreover, the microgrid's voltage and frequency can be perfectly regulated with zero deviations. Furthermore, these new optimal procedures accelerate the speed of synchronization process between the external power grid and the microgrid to be accomplished in time less than 20 ms. Additionally, an accurate power sharing among paralleled operated inverters can be achieved to avoid overstressing on any one. Also, seamless transitions can be guaranteed between grid-tied and isolated operation mode. The optimal controllers and HCs are designed by a new optimization algorithm called H-HHOPSO, which is created by hybridizing between Harris hawks optimization and particle swarm optimization algorithms. The effectiveness and robustness of the H-HHOPSO-based controllers and HCs are compared with other meta-heuristic optimization algorithms-based controllers and HCs. A microgrid, including two grid supporting inverters based optimal controllers and optimal HCs, are modeled and carried out using MATLAB/SIMULINK to test the performance under linear and nonlinear loads, and also during the interruption of any one of two inverters. The performance is investigated according to IEC/IEEE harmonic standards, and compared with the conventional control strategy developed in synchronous dq-frame and based on only PI controllers.(c) 2021 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).