A Novel 3-Phase Series AC Cap-CSI-Buck Grid-tied PV Transformerless Inverter with Low Grid Voltage Fault Ride-Through Capacity

Photovoltaic (PV) cells operate at their maximum power point (MPPT) when their terminal voltage is 75-85% of the open-circuit voltage, creating design challenges for grid-tied PV inverters. These inverters must handle maximum voltage stresses while maintaining efficiency at lower MPPT voltages and comply with grid-fault voltage drop requirements. Current solutions require additional voltage regulators or low voltage fault ride-through (LVFRT) units, increasing cost, complexity, and power losses. This paper proposes a novel 3-phase grid-tied PV transformerless inverter topology combining series AC capacitors, current source inverter (CSI), and a buck converter. This design enables large voltage regulation and voltage drop without additional units. Simulated and experimental results validate its feasibility, demonstrating improved efficiency and voltage drop performance under various grid faults and solar conditions compared to traditional CSI designs.