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Viva Success for Dr Qi!

23 March 2023

We are pleased to announce that Ji Qi, part of the Electronic and Electrical Engineering Department within the University of Sheffield, successfully defended his PhD thesis during his Viva last month following robust questioning from examiners Professor Guang-Jin Li (University of Sheffield) and Dr Glynn Atkinson (University of Newcastle).

Ji Qi and colleagues.

This makes him the first PhD graduate of the FEMM Hub cohort! Funded by hub partner Protean Electric, the title of Ji’s PhD is “Electromagnetic performance of consequent pole permanent magnet machines, with particular reference to analysis and minimization of torque ripples”.

Consequent pole permanent magnet (CPPM) machines can save the amount of permanent magnet (PM) while produce comparable torque as conventional surface-mounted PM (SPM) machines. However, due to the unbalanced features between north and south poles (PM and iron poles), the presence of a large torque ripple can hinder their adoption in some applications. 

Unfortunately, the basic characteristics and generalized principles have not been fully established. This thesis investigates the electromagnetic performances of CPPM machines, with particular reference to the analysis and minimization of torque ripples.

In his thesis, a general analytical model is developed for the first time to analyse and reduce the cogging torque accounting for unequal north and south pole widths as well as pole shifting. Then, symmetrical and asymmetric pole shaping methods with different PM and iron pole shapes are proposed to reduce onload torque ripple for CPPM machines, where the counterreaction effect of torque ripple components is firstly proposed to reduce overall torque ripple.

Finally, the effect of slot/pole number combinations and armature reaction are analysed. All the investigations have been carried out by analytical analyses or FEM and experimental verification.

Based on this research, five SCI papers, among which four in IEEE Transactions and IET Proceedings, have been published.

Congratulations Dr Qi!