Advanced Control Framework for Stable Operation of Parallel Connected Microgrid Inverters

The Grid-tied and Grid-forming inverters are essential components of microgrid units; for harvesting renewable energy from non-traditional sources like solar photovoltaic (PV) and the wind. Grid-connected (GC) or Grid-tied (GT), inverter control contains a frequency-locked loop (FLL) or phase-locked loop (PLL) in αβ & dq reference frames respectively for smooth synchronization with the external grid. Prior research suggests that PLL structure induces negative resistance-based oscillatory behavior in the low-frequency range, resulting in system instability. However, isolated or forming inverters can function independently with/without PLL in its control logic. Distributed generating (DG) inverters are usually required to operate in parallel; they use droop (P-f/Q-V and P-V/Q-f droop) control for power sharing, without communication. During parallel operation of DGs, generally power mismatch leads to output voltage divergence from the reference value due to mismatched resistive and inductive line impedances. The main objective of this article is to propose a novel power-sharing method with improved droop control. Improved droop control strategy increases system stability and reliability by incorporating voltage drop due to virtual resistors and inductors in the control loop. The performance of the proposed work is analyzed and validated in MATLAB/Simulink environment as per IEEE std.1547-2020.