A Multi-Objective Bi-Level LVRT Control Strategy for Two-Stage PV Grid-Connected System Under Asymmetrical Faults

With the increasing integration of photovoltaics (PV) into power systems, the low-voltage ride-through (LVRT) control of PV grid-connected systems is drawing significant attention. This paper presents a multi-objective bi-level LVRT control strategy for the two-stage PV grid-connected system to maximize the positive and negative sequence voltage support capability while ensuring safe operation under asymmetrical faults. The AC level controls the grid side inverter, while the DC level regulates the boost converter. The grid voltage support control strategy is implemented at the AC level to support the positive and negative sequence voltage of the point of common coupling. Considering there is an inherent contradiction between grid voltage support with the overcurrent of inverter and DC voltage oscillation, the current references are automatically adjusted to facilitate the maximum positive and negative voltage support while limiting the overcurrent and oscillation of DC-link voltage. Based on the power reference shared from the AC level, the DC level regulates the boost converter to stabilize the DC-link voltage speedily by utilizing the compensation current. Finally, simulations and experiments demonstrate the voltage support capability and fast dynamic response characteristics of DC-link voltage in different scenarios.