Reinforced droop for active current sharing in parallel NPC inverter for islanded AC microgrid application

Abstract

The paper investigates the current sharing in parallel 3-level Neutral point clamped inverter for islanded AC microgrid application. In Distributed generation, parallel power electronic interface based microgrid suffers from power quality issues due to inaccurate output current sharing. To address the current sharing problem, the paper proposes an improved droop technique that reinforces the droop loop by infusing the incurred voltage drop accountable for inaccurate current sharing at the inverter output. The control based on droop reference is bounded with regard to output current since the output impedance influences the output current of the inverter largely. Besides that, the parallel NPC inverter also suffers from dc link voltage imbalance due to neutral currents. To address these issues a control strategy is proposed in the research work in which the processed DC offset is incorporated into the reinforced droop loop and the generated reference is utilized with feedback control to accurately share the currents under linear and nonlinear load conditions. The effectiveness of devised reinforced droop strategy is realized in MATLAB/Simulink environment and experimental validation is carried out with the field-programmable gate array as hardware interface to the hardware laboratory prototype of parallel NPC inverter.