On multi-phase machines and current harmonic injection for torque capability improvement

De Gaetano, Daniele (2022) On multi-phase machines and current harmonic injection for torque capability improvement. PhD thesis, University of Nottingham.

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The increased energy demand and the need for electrical machines capable to deliver high torque and power in small volumes is pushing the research community to identify suitable solutions for this target. Nowadays, electrical machines are deeply used also in applications where the weight containment is important such as automotive and aerospace.

Multi-phase electrical machines are a suitable candidate to help to get this goal. They present different advantages with respect to classical three-phase machines for example an increased machine torque capability and more tolerance to sustain fault conditions. The average torque is increased thanks to an improved winding factor whereas the fault tolerance improvement is due to the higher number of machine phases. In addition, the torque ripple is lower thanks to an improved magneto-motive force distribution. Moreover, the voltage on the single converter is lower, supplying the machine with the same current of a three-phase system. Another important advantage for the multi-phase arrangement is the possibility to control more harmonics of magnetic field independently thanks to the more degrees of freedom. It means new possibilities to implement various control techniques for improving the machine performance by the injection of additional harmonics higher than the fundamental.

This thesis describes the work which has been carried out in the past three years, during the Ph.D program with the results achieved by analytical model implementations, finite element analysis simulations and experimental tests. The main target is to improve the machine torque capability and/or reduce its permanent magnet content. To reach this goal, the multi-phase re-arrangement of three-phase machines and current harmonic injection techniques are proposed for different machine topologies.

An analytical model is implemented to reduce the magnet content in surface permanent magnet machines without affecting Joule losses and the average torque. The analytical model is validated via FEA.

A model-free technique to improve the torque capability by current harmonic injection is proposed and its concept is validated experimentally on a V-Shape interior permanent magnet machine. Sensitivity analyses are carried out to optimise the V-Shape rotor configuration to improve the torque under fifth current harmonic injection.

Studying the flux density in the stator core on a classical three-phase surface permanent magnet machine with a distributed winding layout, it is possible to highlight another advantage of multi-phase machines which consists in a better flux density distribution.

The proposed work gives a contribution to the research community in terms of new solutions for increasing the torque capability and/or reducing the permanent magnet content in the machine without affecting its efficiency for different rotor topologies. Moreover, the proposed stator flux density analysis can give important information about the electromagnetic behaviour in three-phase distributed winding surface permanent magnet machines.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Degano, Michele
Sala, Giacomo
Gerada, Christopher
Keywords: Electrical machines, multiphase, current harmonic injection
Subjects: T Technology > TK Electrical engineering. Electronics Nuclear engineering
Faculties/Schools: UK Campuses > Faculty of Engineering
Item ID: 68951
Depositing User: De Gaetano, Daniele
Date Deposited: 31 Jul 2022 04:41
Last Modified: 31 Jul 2022 04:41
URI: http://eprints.nottingham.ac.uk/id/eprint/68951

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