Development of Permanent Magnet Brushless Doubly-Fed Machines Based on Segmented Structure for Wind Power Generation

Brushless doubly-fed machines (BDFMs) have received renewed attention in the field of variable speed constant frequency (VSCF) wind power systems. Two new permanent magnet BDFMs (PM-BDFMs) with segmented structures are proposed in this paper to improve the performance of the BDFMs. Compared to conventional BDFMs, PM-BDFMs have two rotors. The internal permanent magnet rotor provides an excitation magnetic field for power and control windings. The external rotor is based on a field modulation ring that provides magnetic coupling between the control and power winding. Due to the absence of the exciting current and excitation loss, the efficiency and power density of the proposed PM-BDFMs can be increased. The segmented structure is adopted for the outer rotor to solve a series of problems caused by the introduction of the field modulation ring. Finally, the performances of the proposed PM-BDFMs are validated by comparison with six other structures of BDFMs using finite element analysis (FEA). The results show that the proposed PM-BDFMs perform better than some existing BDFMs structures.