Characteristics Analysis of Consequent-Pole Ferrite Magnet Vernier Machine Using Novel Equivalent Magnetic Circuit

This study deals with a consequent-pole (CP) vernier motor with low-cost ferrite magnets. To investigate the magnetic behavior of the CP permanent magnet vernier machine (CP-PMVM) quantitatively, two magnetic equivalent models are newly proposed which are applied to estimate the main and the modulation flux densities in air gap, respectively. Using the proposed models, it is revealed that the CP structure substantially reduces the effective air-gap length, and thus, a CP-PMVM with half number of magnets has much higher modulation flux density than that of a regular surface PM vernier machine (SPMVM). Consequently, the CP-PMVM is expected to able to keep the vernier effect high even with thick ferrite magnets, producing higher back electromotive force (EMF) than the SPMVM does. Moreover, large variation of air-gap length due to thick magnet thickness leads to a considerable advantage of reluctance torque. For a proto-designed CP-ferrite PMVM, the electromagnetic characteristics, such as main and modulation flux densities, back EMF,
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inductances, and torque, have been investigated by using the proposed method as well as finite-element (FE) method. In addition, through the demagnetization analysis, it is proved that the proposed CP-PMVM has certainly enough antidemagnetization capability, whereas an SPMVM with ferrite magnets loses its magnetism. From the analysis results, it is confirmed that the proposed machine with less magnet volume and low-cost ferrite magnets has higher torque compared with its SPM vernier counterpart. Finally, to validate the analytical and numerical analyses, experimental results are provided.