Low voltage ride through control strategy for MMC photovoltaic system based on model predictive control

•The multi-step predictive control is adopted to improve the suppression effect of interphase circulating current.•The fixed-power control on the DC side is realized through model predictive control to maintain power balance between AC and DC sides.•Analyze the stability of the model predictive control algorithm, and improve the algorithm to increase its stability margin by changing AC current control target and AC voltage estimation method. Based on the photovoltaic (PV) grid-connected system with MMC, a low voltage ride through (LVRT) control strategy is proposed to overcome the problem of the voltage asymmetry drop in the power grid. On the AC side of the grid-connected system, limit the output current peak and output three-phase symmetrical current, analyze the circulating current component under grid-side asymmetric faults, and use multi-step model predictive control to suppress the circulating current and improve the suppression effect; On the DC side of the grid-connected system, according to the requirement of the inverter output current amplitude limit, the fixed power control is realized through MPC to maintain the AC-DC power balance. Analyze the stability of MPC algorithm, and improve the algorithm to increase its stability margin. The effectiveness and feasibility of the proposed control strategy are verified by the analysis of the RT-lab experimental platform.