Adaptive DC-Link Voltage Control of Two-Stage Photovoltaic Inverter During Low Voltage Ride-Through Operation

This paper proposes an adaptive dc-link voltage control method for the two-stage photovoltaic inverter during the low voltage ride-through (LVRT) operation period. The dc-link voltage will be controlled to follow the change of grid voltage during the LVRT operation to maintain the high modulation ratio so that the high frequency harmonics injected into the grid can be attenuated significantly. Besides, when suffering the asymmetrical grid faults, the proposed control method could to some extent attenuate the double-line-frequency dc-link voltage ripple to keep the dc-link voltage in the safe operational range by shifting the double-line-frequency power ripple to the front-end dc input source, which can be achieved by intentionally fluctuating the dc input power or employing a bidirectional dc-dc converter depending on the voltage drop ratio and the input power level. The theoretical findings were verified by MATLAB simulations and the constructed experimental prototype.