Two-layer distributed control of hybrid AC/DC microgrids supplying nonlinear, unbalanced and constant-power loads

Abstract

Nonlinear, imbalanced, and constant power loads pose significant technical and power quality challenges in both AC and DC microgrids. Hybrid AC/DC microgrids further compound these complexities. In response, this paper presents a novel hierarchical control scheme comprising primary and secondary layers for such microgrids. The proposed scheme introduces innovative cooperative voltage and frequency secondary control methods, complementing conventional droop-based primary controllers. This hierarchical structure aims to provide acceptable voltage and frequency regulations, as well as power sharing in both AC and DC sub-grids, mitigating issues arising from various loads. Specifically, the DC sub-grid maintains its stability in the presence of constant power loads, while the AC bus output voltages maintain sinusoidal waveforms. Finally, we conduct digital time-domain simulation studies on a test microgrid system using the MATLAB/Simulink environment to assess the performance of the proposed control strategy. We compare the results with previously reported methods. The results demonstrate that the proposed methods effectively share power with reduced overshoot and faster convergence toward desired values compared to conventional controllers. Simulation analyses validate the superiority and efficacy of the proposed control scheme.