Investigation of a PM Flux-Modulated Motor With Mechanical Flux-Weakening Solution for Wide Speed-Range Operation in Traction Applications

Journal article, 2023

In order to achieve wide speed-range operation in traction applications, an investigation of a permanent magnet (PM) flux-modulated motor with a mechanical flux-weakening solution is presented in this article. This PM flux-modulated motor consists of two sets of windings, i.e., windings I and II, and two rotors, i.e., the outer rotor and the inner rotor. The two sets of windings are connected in series. By adjusting the inner rotor position, the phase angle between the two voltage vectors of windings I and II is accordingly changed. Hence, with the speed increasing, even though the magnitudes of the two voltage vectors of windings I and II are increased, the voltage magnitude of the total series-connected windings can be maintained (instead of increased) within the voltage limit. As a result, a mechanical flux-weakening solution for wide speed-range operation is achieved. Differing from conventional electrical flux-weakening solutions, this mechanical solution shows the advantage that the flux-weakening capability is not heavily dependent on the power rating of the motor. A comparative study is conducted between the presented PM flux-modulated motor with the mechanical solution and a conventional interior PM synchronous motor (IPMSM) as well as a surface-mounted PM synchronous motor (SPMSM) with the electrical solution. The results indicate that compared to the IPMSM and SPMSM, the presented PM flux-modulated motor exhibits the advantages of high torque/power density, high torque per PM volume, and high flux-weakening capability. Finally, a prototype of the presented PM flux-modulated motor is fabricated, and experimental validation of the mechanical flux-weakening solution is provided.