Comparative Study of Brushless Doubly Fed Machine with Different Rotor Structures Used in Wind Power Generation System

The brushless doubly fed machines (BDFM) have been widely researched. The BDFM system has lots of advantages such as brushless, simplicity, robustness and reliability, and a much smaller power electronic converter compared to a conventional AC induction machine. The BDFM as a new type of AC machine and is attractive for converter-fed variable speed drive applications and variable-speed constant-frequency (VSCF) wind power generation systems. This paper presents a BDFM respectively with radial laminated reluctance and nested-loop cage rotors of the same size, and the BDFM with radial laminated reluctance rotor hasn´t been studied before. The voltage of power windings and air-gap flux harmonic order of both motors are analyzed on no-load operation; the BDFM torque capabilities are investigated with 5-pole rotor machines, and the voltage harmonic order of the power winding which used as generators at negative maximum torque are researched. All these results are based on finite element method and provide insights into the control of BDFM used in wind power generation system.