Utilizing Full Degrees of Freedom of Control in Voltage Source Inverters to Support Micro-Grid with Symmetric and Asymmetric Voltage Requirements

Abstract

This article proposes a novel equivalent control method for voltage source inverters (VSI) with disturbance observers (DOB) to support the symmetric and asymmetric voltage requirements of a micro-grid (MG) while also matching the MG output power requirements. The method leverages the degrees of freedom (DOF) of the VSI under symmetric and asymmetric MG voltage conditions by utilizing the mean-point voltage of the MG, which is often overlooked in literature studies due to this being grounded. The method enables the three-phase inverter to generate voltages as needed by the MG inconsistently due to changing loads in the MG circuits or phases. The method is also insensitive to disturbances because of the DOB, being part of the controller. The proposed method is validated under both the balance and imbalance voltage demands of the MG. The mean voltage of the MG is used as a set-point to be corroborated as a mean voltage at the inverter’s output, in addition to active-reactive power references. The novel model is developed by augmenting the new, mean-point voltage as part of the system dynamics. The proposed method is simulated in MATLAB/Simulink® and is verified for its hardiness and effectiveness.