A new unified control strategy for inverter-based micro-grid using hybrid droop scheme

Abstract

Micro-grid (MG) operation using voltage control methods (VCMs) has been widely recommended for parallel operation of three phase voltage source inverters, especially during islanded mode to maintain the voltage level in the MG. In contrast, this paper presents a new unified control strategy for MG parallel operation using a current control method (CCM). A hybrid control scheme which combines a universal robust droop controller (URDC) and quasi-proportional resonant (QPR) regulator is introduced. It ensures equal power sharing among parallel operated inverters during all MG's operating modes. Moreover, an improved adaptive estimator for the reference current magnitude is integrated to meet dynamic load variations. Furthermore, the scheme is enhanced with a self-synchronized capability using a simple synchronous reference frame phase locked loop (SRF-PLL). This obviates the necessity of communication links and external synchronous clocks required for synchronization process. In addition, a decentralized control action is locally managed to restore the inverter's frequency upon any reactive load change. Modeling and simulation results using MATLAB/SIMULINK software are presented to show the effectiveness of the proposed strategy.