A Complete Impedance Model of a PMSG-Based Wind Turbine System Considering Machine-Side Dynamics

Impedance modeling of a permanent magnet synchronous generator (PMSG)-based wind turbine system (WTS) usually ignores the machine-side dynamics, instead, the machine-side system is simplified as a constant power load, while keeping the detailed grid-side converter model. This practice is mainly based upon the intuition that the dc-bus capacitor is large enough so that the machine- and grid-side dynamics can be decoupled. However, the assumption on large dc-bus capacitor probably does not hold in practice since there is always a tendency to minimize the capacitor size to achieve a smaller package for installation. Therefore, the effect of the machine-side system should not be ignored, otherwise maybe leading to error for stability analysis. To address this issue, this paper developed a complete ac-side impedance model of the PMSG-based WTS by considering the machine-side system. The accuracy of the complete impedance model of the PMSG-based WTS was validated by the measured impedances from simulations, as well as its correctness in frequency-domain stability analysis.