Transient analysis of low-voltage ride-through in three-phase grid-connected converter with LCL filter using the nonlinear modal series method

From a theoretical perspective, this paper develops a systematic approach to analyze the transient characteristics of the low-voltage ride-through (LVRT) in three-phase grid-connected converter with LCL filter by using the nonlinear modal series method. Firstly, the mathematical model and the corresponding second order modal series model of the system are described. And then, the simulation results and the theoretical analysis manifest that there are abundant modal interactions, particularly the stronger second order modal interaction, in the LVRT transient process. The revised expressions considering the nonlinear terms for the state variables are subsequently obtained. By selecting the appropriate parameters to weaken second order modal interaction, we can effectively reduce the amplitude and the duration of the oscillation to satisfy the requirements of the system tolerance during LVRT process. Additionally, the dominant oscillation modes of each state variable are also studied. Finally, the second order quasi-resonance boundaries are defined to facilitate the selection of practical parameters for maintaining normal transient