Power grid voltage sag can easily cause power angle instability and an overcurrent phenomenon on a grid-connected inverter of a renewable energy unit. This paper improves the traditional virtual synchronous generator (VSG) control strategy. A low voltage ride-through (LVRT) control strategy for a renewable energy unit with virtual impedance braking is proposed. First, the principle of equal area is used to analyze the change mechanism of a VSG power angle after voltage sag and restoration. Second, a reactive power intervention mechanism and the current limiting principle of virtual impedance are described in detail. Then, it is proposed to implement hover control on a traditional VSG power control link during grid voltage sag in order to achieve power angle stability. A clear calculation method is proposed to limit the overcurrent at different stages of voltage sag and recovery. Finally, the RT-LAB real-time simulation experiment platform is used to build a 10 kW renewable energy grid-connected unit. The low voltage ride-through control effect at different voltage sag levels is analyzed, and the feasibility and effectiveness of the proposed control strategy is verified.