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Title: Investigation of magnetic gearing effect in fractional slot and vernier permanent magnet synchronous machines
Author: Liu, Yue
ISNI:       0000 0004 7964 5759
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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This thesis investigates the torque production mechanism of rotor permanent magnet synchronous machines (PMSMs), with emphasis on the contribution of magnetic gearing effect. Fractional slot concentrated winding (FSCW) and Vernier permanent magnet synchronous machines (VPMSMs) will be used as examples for investigation. Then, the torque production mechanism of all existing rotorPM machine types will be unified and new slot/pole number combinations are proposed. For both FSCW PMSMs and VPMSMs, the torque production mechanisms are analysed from the perspective of the air-gap field harmonics modulation and the magnetic gearing effect, accounting for slotting effect. It is found that for both machine types, the average torque is produced by both the principle of conventional PMSM torque production and the magnetic gearing effect. A finite element analysis (FEA)-based equivalent current sheet model (ECSM) and a harmonic restoration method are firstly applied to a 12-slot/8-pole FSCW PMSM and a 12-slot/22-pole VPMSM, respectively, to quantify the respective contributions of the conventional principle and the magnetic gearing effect. Hence, the magnetic gearing effect in both machine types are revealed and the expressions of gear ratios are derived. The influence of gear ratio on different performance metrics are analysed and it shows that it can act as an index for a quick overall performance comparison in each machine type. The influence of slot opening on the torque production of all existing Ns-slot/2pr-pole rotor-PM machine types are analysed from the perspectives of both energy conversion and magnetic gearing effect. It shows that for large torque production, all rotor-PM machines with 2pr < Ns should have small slot openings to enlarge the torque produced via the conventional principle, since the contributions from the magnetic gearing effect are weak. For those with 2pr > Ns, there exists an optimal slot opening for the best trade-off between the conventional principle and magnetic gearing effect. The higher the PM pole number is, the larger the optimal slot opening will be. VPMSM can be regarded as a kind of conventional rotor-PM machine of special slot/pole number combinations, whose slot opening plays a critical role in the torque production. For FSCW PMSMs, a machine with 2pr > Ns can also be seen as a Vernier counterpart of one with 2pr < Ns. In this way, the torque production mechanisms of all kinds of rotor-PM machines are unified. Finally, a series of high power factor VPMSMs with coil-pitch of two slot pitches are developed, expanding the selections of slot/pole number combinations of rotor-PM machines. All theoretical analyses have been validated experimentally.
Supervisor: Zhu, Zi-Qiang ; Foster, Martin Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available