Prediction of field currents in flux-modulating synchronous machines under loaded conditions

In this paper, a method is presented for calculating the on-load field currents of flux-modulating synchronous machines (SMs) (FMSMs) from no-load test data. The FMSM is a new type of multipole SM in which the magnetomotive force (MMF) due to the stator field winding is modulated by the reluctance rotor to produce the rotating magnetic field. Owing to an inherent magnetic-gearing effect, the rotating magnetic field rotates at a faster speed than the rotor. Using open-and short-circuit characteristics obtained by finite element analysis (FEA), field currents in a 300-kVA machine feeding resistive loads are calculated. Experimental results conducted on a prototype 4-kVA machine are also provided to justify the calculation method.