Impacts of PLL on the DFIG-based WTG's electromechanical response under transient conditions: analysis and modeling

Increased penetration of wind energy in the electric grid has necessitated studying the impact of wind integration on the transient stability of the power system, with urgency to develop appropriate electromechanical models of the wind turbine generator (WTG). The representation and control of the WTG's electric signals are typically in a rotational dq coordinate system whose reference angle is provided by a phase-locked-loop (PLL). The PLL is commonly considered as a measurement device and is often absent in existing WTG electromechanical models. This paper studies the impact of PLL on the DFIG-based WTG electromechanical response by theoretical and simulation analyses. The dynamics of the PLL are found to greatly influence the WTG electromechanical response, suggesting that PLL should be regarded as an indispensable control loop rather than a measurement device, and its impact should be modeled when establishing the WTG electromechanical model.