Dynamic Interaction Analysis and Damping Control Strategy of Hybrid System With Grid-Forming and Grid-Following Control Modes

The dynamic behavior of converters with different synchronous control modes is significantly different. Therefore, the renewable energy grid-connected system cannot be equivalent as the same type of power electronics equipment. There are dynamic interactions among the multiple time scale controllers of each equipment, which may lead to the small signal instability of the hybrid system. In this paper, a hybrid grid-connected system with phase-locked loop (PLL) controlled doubly fed induction generator (DFIG) and virtual synchronous generator (VSG) controlled converter is studied. On the basis of the open-loop modal resonance theory, the mechanism of small signal instability of hybrid system is revealed from the perspective of mode interaction. Furthermore, a design method of additional damping controller is proposed based on normal matrix, which can achieve the minimum eigenvalue sensitivity of the hybrid system and avoid the interaction between different control loops. Finally, a hybrid system including a grid-forming VSG system and a grid-following DFIG wind farm is investigated in this paper. The correctness and effectiveness of interaction analysis and damping control strategy are confirmed by the results of modal analysis and simulation.