A Novel Hybrid-Excited Dual-PM Machine with Bidirectional Flux Modulation

This paper presents a novel hybrid-excited dual permanent magnet (PM) brushless machine with bidirectional flux-modulating effect. Two sets of windings are housed in the stator slots, in which the armature windings are used to produce the rotating magnetic field, and dc field windings are used to generate the excitation field. The air-gap flux can be regulated effectively by controlling the direction and magnitude of the dc currents, and hence the constant power operating region can be expanded efficiently. Meanwhile, both the rotor and the stator have PM excitations, and dual field modulating effect is artfully incorporated into the machine design to ensure an effective magnetic coupling among the magnetic fields excited by the armature windings, dc field windings and the two sets of PMs. The torque capability of the proposed machine can be improved. Through analytically studying the air-gap field harmonics, the working principle of the proposed machine is discussed. The electromagnetic performances are investigated using finite element method and verified by experimental results.