Enhancing Grid Resilience Under Voltage Unbalance Using Phase-Wise Controlled Four-Leg Inverter with MCCF-PR Control

Kurzfassung

The increasing penetration of photovoltaic (PV) systems in low voltage distribution networks introduces challenges such as voltage unbalance and overvoltage tripping under asymmetrical grid conditions. Conventional grid-tied inverters assume balanced operation, limiting their ability to maintain stability and maximize power injection during uneven phase voltages. This paper proposes a four-leg grid-connected inverter control strategy to mitigate overvoltage tripping and enable continuous operation under unbalanced conditions. A Multiple Complex Coefficient Filter (MCCF) is used to extract positive and negative-sequence components for voltage estimation, sag/swell detection, and synchronization under unbalanced conditions. A damped proportional-resonant (PR) controller in the alpha-beta frame ensures precise sinusoidal current tracking in the stationary reference frame. Additionally, a phase-wise dynamic power redistribution strategy enables independent regulation of phase currents, reducing power in overvoltage phases while maximizing utilization of healthy phases. The system is modeled in MATLAB/Simulink, and results demonstrate stable operation under balanced and unbalanced conditions, with effective sequence separation, accurate voltage detection, and reduced inverter tripping.