Interaction Analysis of the Grid-Connected VSC System Based on Transient Energy Inflow

The main interface of renewable energy generation and AC grid is the voltage source converter (VSC) whose control system contains several control loops with similar bandwidth. The interaction between VSC control loops directly affects the stability of the power system under severe faults. Unfortunately, the understanding of these interaction mechanisms and their involvement in the power system transient stability have not been thoroughly analyzed. To fill the gap, an analytical model of the grid-connected VSC system based on transient power inflow is proposed in this paper, and the power interaction with the phase locked loop (PLL), outer loop, AC grid and its instability mechanism is analyzed. Then, based on the analytical model, the paper reveals the instability dominated by PLL and outer loop respectively and discusses the related instability paths. The work in this paper is helpful to understand the transient instability of the grid-connected VSC system caused by the interaction between the control loops, which provides support for the instability mechanism of the power system and the renewable energy generation off-grid under severe faults.