Control strategy of low voltage ride-through for grid-connected photovoltaic inverter

With increasing penetration of grid-connected photovoltaic (PV) power generation, the grid codes about low-voltage ride-through (LVRT) of PV plants and their interface inverters have been established. Under a grid voltage sag, the underlying reasons may cause overcurrent of the grid-connected inverter and failure in ride-through. In this paper, a positive-sequence current injection with feedforward of positive- and negative-sequence grid voltages is proposed to meet the LVRT requirement. The proposed method not only reduces the risk of overcurrent but also suppresses the negative sequence current during the LVRT operation. What´s more, a rapid detection of voltage sag is proposed to disable the DC link voltage control and the PV maximum power point tracking (MPPT) control during the grid sag, which is another way to reduce the risk of overcurrent. A test bench has been established, and testing results of a 500kVA prototype inverter are presented to validate the effectiveness of the proposed methods.