Variable Stator Frequency Diode Rectifier DFIG for Lower Cost MVDC Interface

This paper proposes a novel topology for doubly fed induction generator (DFIG) connected to medium voltage direct current (MVDC) bus for offshore wind farm application. The fully rated-power voltage source converter is substituted by a 12-pulse diode rectifier, which can greatly reduce cost compared to full scale solutions. Furthermore, the stator frequency can be controlled to change according to the wind speed to achieve maximum power point tracking (MPPT) even at low wind speed, which can increase the wind capturing ability of the wind turbine and generate more electricity. The stator frequency is designed according to the constraints of power rating and voltage level of rotor side converter. Simulations based on a 2 MW DFIG system are carried out to validate the effectiveness of the proposed topology and control strategy.