Super-multipolar permanent magnet reluctance generator designed for small-scale wind-turbine generation

Kenji Nakamura and Osamu Ichinokura (Tohoku University)

Clean energy resources including a wind-turbine and hydroelectric power generation are expected as one of the candidates to resolve the environmental issues facing us. Following the expectation, the demand for generators which have high power and efficiency at low speed revolution, and low cost is increasing. A permanent magnet reluctance generator (PMRG) has almost the same structure as a switched reluctance generator, but has permanent magnets in the stator yoke. Therefore, neither an exciting circuit nor a position sensor is required. Although the cost of the PMRG is higher than the SR generator, the outer-rotor-type PMRG employs ferrite magnets, which cost much less and have almost the same output power as the rare-earth magnet.

This paper describes a super-multipolar PMRG for small-scale wind-turbine generation, which can be directly connected to the turbine without a gear box. The designed PMRG has two features for reducing torque ripple drastically; the first one is two-stacked structure that one rotor is shifted by 180° in electrical angle from the other rotor; the second one is that the rotor pole-tips are cut off. To find the optimum shape of the rotor pole-tip efficiently, the coupled analysis of finite element method and a modeFRONTIER has been used.