In the Distribution Generation (DG) grid-connected system, in order to realize the Low-Voltage Ride-Through (LVRT) ability, it is necessary to dynamically support the grid voltage under grid faults. In order to obtain the best support effect on the PCC voltage, the design methods of active and reactive power injections are proposed using the multi-variable protected method. First, the topologies in the DG systems and the multi-variable protected method are introduced. Then calculation principle of the positive- and negative-sequence components of converter AC side under grid codes is deduced. The formula for calculating injected power under optimal voltage support is given, and the calculation process of the AC current reference in dq axis is proposed. Finally, a simulation platform based on Matlab/Simulink is established to verify the theoretical analysis and design methods. This work is supported by National Key Research and Development Project of China (No. 2016YFB0900201).