Cost-Function-Based Microgrid Decentralized Control of Unbalance and Harmonics for Simultaneous Bus Voltage Compensation and Current Sharing

Abstract

Power quality of inverter-based microgrids is a challenging issue due to nonlinearities of inverters, multiple resonance modes of network impedance, and unbalanced and nonlinear loading condition. The ideal solution is to assure the best power quality at the common bus to which loads are connected, and share the negative and harmonic sequence currents between the inverters without any communication. However, it is difficult to achieve this objective with existing virtual-impedance-based methods when nonlinearities of inverters, e.g., dead time, are not negligible. In this paper, a novel cost-function-based method is proposed to solve this problem. The proposed cost functions are optimized using continuous-control-set model predictive control. As unknown nonlinearities of inverters can be observed by introducing disturbance models, even when they are not negligible, the presented method can compensate bus voltage unbalance and harmonics and share the compensated current between inverters autonomously, with neither communication nor upper level controller. Parameter tuning of the proposed method is the key to achieve the balance between bus voltage quality and current sharing, and between stability and fast response. Experimental results demonstrate that the proposed control scheme is effective even under conditions of large inverter nonlinearities.