Doubly-fed induction generator wind turbine modelling for detailed electromagnetic system studies

Wind turbine (WT) technology is currently driven by offshore development, which requires more reliable, multi-megawatt turbines. Models with different levels of detail have been continuously explored but tend to focus either on the electrical system or the mechanical system. This study presents a 4.5 MW doubly-fed induction generator (DFIG) WT model with pitch control. The model is developed in a simulation package, which has two control levels, the WT control and the DFIG control. Both a detailed and a simplified converter model are presented. Mathematical system block diagrams of the closed-loop control systems are derived and verified against the simulation model. This includes a detailed model of the DC-link voltage control - a component which is usually only presented in abstract form. Simulation results show that the output responses from the two models have good agreement. The grid-side converter control with several disturbance inputs has been evaluated for three cases and its dynamic stiffness affected by operating points are presented. In addition, the relation of pitch controller bandwidth and torsional oscillation mode has been investigated using a two-mass shaft model. This model can be employed to evaluate the control scheme, mechanical and electrical dynamics and the fault ride-through capability for the turbine.