Abstract: The connection of a high proportion of renewable energy to the grid leads to low inertia, weak anti-disturbance ability and strong voltage volatility of micro-grid. Serving as an important device to stabilize power fluctuations of renewable energy and support voltage and frequency stability of grid, power converter system (PCS) is being widely used in microgrid. In accordance with the development of micro-grid PCS optimal control technology, this paper focuses on the influence of PCS's own nonlinear factors on output waveform from three-level PCS topology perspective, and then summarizes the generation mechanism and optimization strategy of PCS's output waveform. On this basis, the instability mechanism of the grid-following type PCS within weak-grid is discussed in depth, and the optimal control strategy to strengthen stability of the micro-grid system is summarized. At the same time, the control objectives and control architecture of the grid-forming PCS are sorted out, and the problems of the micro-grid system stability and control optimization strategy of PCS are analyzed and summarized. Finally, the prospects in optimization direction of related technologies are put forward to provide reference for the optimization control of micro-grid three-level PCS.