1School of Electrical and Automation Engineering, Hefei University of Technology, Hefei 230009, China;2State Key Laboratory of High-Efficiency and High-Quality Conversion for Electric Power (Hefei University of Technology), Hefei 230009, China;3School of Internet, Anhui University, Hefei 230039, China;4Marketing Service Center, State Grid Anhui Electric Power Co., Ltd., Hefei 230088, China;5Chuzhou Power Supply Company, State Grid Anhui Electric Power Co., Ltd., Chuzhou 235099, China

Due to the limited control degrees of freedom, the low-voltage ride-through (LVRT) control strategy for two-stage grid-connected photovoltaic system has difficulties in simultaneously meeting the multi-objective control requirements such as positive sequence voltage support at the point of common coupling (PCC), negative sequence voltage suppression, inverter overcurrent limitation, and rapid stabilization of the DC bus voltage. Moreover, according to the latest grid-connected photovoltaic technical regulations, most traditional LVRT control strategies lack the dynamic negative sequence reactive current support capability, and the voltage unbalance degree at the PCC is relatively high. Therefore, this paper proposes a multi-objective LVRT control strategy for two-stage grid-connected photovoltaic system. This strategy takes into account the dynamic positive and negative sequence reactive current support capabilities required by grid-connected photovoltaic technical regulations. During asymmetric faults, the LVRT mode is selected based on the state of charge of the energy storage. Current feedforward compensation control is introduced on the super-capacitor converter to rapidly stabilize the DC bus voltage. On the grid-connected inverter, the line impedance is taken into account and the grid-connected positive sequence voltage support, negative sequence voltage suppression, and inverter overcurrent limitation are integrated to control LVRT. Finally, on the MATLAB simulation and a semi-physical simulation experiment platform, the proposed control strategy is comparatively analyzed against existing LVRT control strategies, and the effectiveness of the strategy is verified.