PLL Synchronization Stability Analysis of MMC-Connected Wind Farms Under High-Impedance AC Faults
Yingbiao Li, Xiongfei Wang, Jianbo Guo, Heng Wu, Bing Zhao, Shanshan Wang, Guanglu Wu, Tiezhu Wang
Abstract
This article analyzes the transient stability of an offshore wind farm connected via modular multilevel converter (MMC)-based high-voltage direct-current transmission system. The wind farm is composed by full-scale type-4 wind turbines, whereas short-circuit faults occurring in between the MMC and wind farm are considered. The MMC tends to be switched to the current limiting mode or the overmodulation mode during the ac-side fault, which further interacts with the control systems of wind turbines, complicating the transient stability problem of the system. Hence, in this work the parametric impacts of the phase-locked loop of wind turbine converters and over-current/-modulation limiters of the MMC are revealed analytically, and further corroborated by time-domain simulations.