Reduction of magnetic saturation by using additional permanent magnets in synchronous machines

In this study, we investigate the characteristics and the advantages of field-winding synchronous machines assisted by small amount of permanent magnets. In the proposed machine, the permanent magnets are not used for the field excitation. They are mainly used for the reduction of magnetic saturation at the rotor-pole bodies. First, the mechanism of reducing magnetic saturation is investigated by using both the simple nonlinear magnetic circuit and the finite element method. The calculated characteristics are verified by the measurements of prototype machines. Next, the application of the proposed machine to large wind generators is investigated. The characteristics of the proposed machines are compared with those of conventional field-winding and permanent magnet machines. The advantages of the proposed machine over the conventional machines are clarified.