Modeling of Type 3 Wind Turbines With df/dt Inertia Control for System Frequency Response Study

A model for Type 3 wind turbines (WTs) with typical df/dt inertia control is developed for studying frequency dynamics in power systems. A simplified small-signal Type 3 WT model with df/dt control is first constructed based on the mass-spring-damping concept, such that the physical properties and frequency response of a Type 3 WT can be clearly understood, besides the frequency-domain expressions of the available inertia and the corresponding damping coefficient can be directly derived. The manifested inertia is apparently controllable and frequency-dependent, but differs from the constant inertia featured in a conventional synchronous generator (SG). Furthermore, the frequency response model of a generic two-machine system, composed of an SG and an aggregate Type 3 WTs, is established. The model synthetically considers the effects of the WTs' different controller parameters, operating points, and the SG's governor response on system frequency characteristics. Then, time-domain simulations on the studied two-machine system are performed in MATLAB/Simulink. The simulated results verify that the proposed model is effective for analyzing system frequency dynamics, and that the test system frequency characteristics can be improved based on tuning the mass-spring- damping coefficients of Type 3 WTs.