A New Parallel-Hybrid-Excited Permanent-Magnet Machine With Harmonic-Differential Effect for Electric Vehicles

This paper proposes a new parallel-hybrid-excited permanent-magnet machine (PHEM) with harmonic-differential (HD) effect, termed HD-PHEM. The key is to place the DC-field windings in the DC pole sandwiched by the two adjacent permanent-magnet (PM) poles, thereby realizing the parallel flux paths of PM flux and DC-field flux. Moreover, the HD effect is created so that the DC-field harmonics can differentiate the effective and ineffective harmonics in the air gap to weaken the resultant effective magnetic field. Consequently, attractive flux-weakening ability and extended speed-operating range can be achieved for electric vehicle propulsion. The machine configuration, operation principle, torque-sizing equation and drive system are introduced first. Then, the harmonic analysis is conducted to elaborate on the HD effect, followed by the finite-element verification. Besides, both the electromagnetic and structural performances of the proposed machine are comprehensively evaluated by finite element analysis. Further, a comparative study is performed between the proposed design and other existing topologies in terms of electromagnetic performances. Finally, an experimental prototype is constructed and tested for verification.