An Improved PLL Control Strategy for Frequency Support of DFIG-based Wind Turbines

With the rapid penetration of wind power energy, traditional power system has undergone enormous changes, characterizing with massive phase-locked loop (PLL) based power electronic devices integrated into power grids. As a result, the inertia of the modern power system is greatly weakened and even threatens the stability of the power system in severe frequency events. In order to ensure the frequency stability, this paper proposes an improved PLL-based control method for the doubly fed induction generations (DFIGs) to achieve the frequency response. Firstly, the essence of the frequency support is discussed from the perspective of internal voltage, and then main frequency support methods are classified. Based on the analysis results, an improved frequency support method by adjusting the PLL angular is put forward, which presents a faster response and is able to achieve inertial emulation and primary frequency regulation simultaneously. Meanwhile, the effect of inertia coefficient and damping coefficient on PLL is analyzed. Finally, simulation results verify the effeteness of the proposed method.