A Permanent Magnet Brushless Doubly Fed Electric Machine for Variable-Speed Constant-Frequency Wind Turbines

A permanent magnet (PM) brushless doubly fed electric machine is presented in this article. This machine is developed for variable-speed constant-frequency (VSCF) wind energy generation applications. Differing from conventional doubly fed electric machines based on induction machines, a PM rotor provides the magnetic field excitations for both the control winding and the power winding in the presented machine. The operating principle of the presented machine for the VSCF operation is revealed in detail. Compared to a counterpart machine, the presented machine exhibits significantly improved back-electromotive force, torque/power density, torque per magnet volume, efficiency, etc. Finally, a proof-of-concept prototype of the presented machine is fabricated, and the corresponding experimental results are provided to verify the fact that the presented machine is capable of achieving the VSCF function.