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Wang K.,University of Sheffield | Zhu Z.Q.,University of Sheffield | Ombach G.,Brose Fahreugteile GmbH and Co. Kommanditgesellschaft
IEEE Transactions on Energy Conversion | Year: 2014

This paper presents optimal third harmonics in both permanent magnet (PM) shaping and current waveform to improve the output torque of five-phase surface-mounted PM (SPM) machines. The optimal value of third harmonic injected into the sinusoidal PM shape and current waveform for maximum torque improvement is analytically derived and validated by both finite element (FE) analyses and experiments. It is found that the optimal third harmonic is 1/6 of the fundamental one for both PM shape and current waveform. For the five-phase SPM machines having rotors without shaping, Sine shaping, or Sine shaping with third harmonic injected, the electromagnetic performance including the back EMF waveform, cogging torque, average torque, torque ripple, copper loss, iron loss, impact on power inverter, and demagnetization withstand capability are compared. It is demonstrated that, although the copper loss and iron loss increase due to additional third harmonic in the winding current and magnet shape, the average torque with optimal third harmonics injected in PM shaping and current waveform can be improved by >30% while the torque ripple and remains similar to that of the one with Sine shaping. In addition, this will reduce the dc bus voltage while maintaining the machine torque density. Furthermore, the machine with Sine and Sine+3rd rotors presents much better demagnetization withstand capability performance than conventional rotor. © 2014 IEEE.


Wang K.,University of Sheffield | Zhu Z.Q.,University of Sheffield | Ombach G.,Brose Fahreugteile GmbH and Co. Kommanditgesellschaft | Chlebosz W.,Brose Fahreugteile GmbH and Co. Kommanditgesellschaft
Proceedings - 2012 20th International Conference on Electrical Machines, ICEM 2012 | Year: 2012

This paper presents optimal rotor shape design to increase the torque capability in IPM machines by introducing optimal 3rd harmonic to the inverse cosine shaped rotor. The impact of the optimal 3rd harmonic to the rotor shape on the electromagnetic performance is investigated by finite element method. It is demonstrated that under the same amount of permanent magnets as the inverse cosine shaped IPM machine, the average torque for the machine of inverse cosine with optimal 3rd harmonic shaped rotor can be improved by >5% while the torque ripple can be maintained almost the same. In addition, the inductance saliency ratio is also improved, which increases the average torque further. The impact of 3rd harmonic on stator and rotor iron and rotor eddy current magnet losses is also compared with the machine without 3rd harmonic in the rotor shape, which shows that the iron loss increases slightly. All results have been verified with finite element method. © 2012 IEEE.


Wang K.,University of Sheffield | Zhu Z.Q.,University of Sheffield | Ombach G.,Brose Fahreugteile GmbH and Co. Kommanditgesellschaft | Koch M.,Brose Fahreugteile GmbH and Co. Kommanditgesellschaft | And 2 more authors.
2013 8th International Conference and Exhibition on Ecological Vehicles and Renewable Energies, EVER 2013 | Year: 2013

AC synchronous reluctance machine (SynRM) or permanent magnet assisted synchronous reluctance machine presently receives a great deal of interest, since there is less or even no rare earth permanent magnet in the rotor. Most of SynRM machines employ a stator that is originally designed for a standard squirrel cage induction motor for a similar output rating and application, or the SynRM machine with 24-slot, 4-pole are often directly chosen for investigation in most of the available literature. Therefore, it is necessary to investigate the influence of stator and rotor pole number combinations together with the flux-barrier layers number on the performance of SynRM machine with emphasis on output torque capability and torque ripple. In order to investigate the impact of slot/pole number combinations on performance of SynRM machine, the same ratio of rotor insulation width to the rotor iron width has been used for all the slot and pole number combinations machines. In addition, the effect of flux-barrier layer number of this machine on average torque and torque ripple has also been investigated. © 2013 IEEE.


Wang K.,University of Sheffield | Zhu Z.Q.,University of Sheffield | Ombach G.,Brose Fahreugteile GmbH and Co. Kommanditgesellschaft | Koch M.,Brose Fahreugteile GmbH and Co. Kommanditgesellschaft | And 2 more authors.
COMPEL - The International Journal for Computation and Mathematics in Electrical and Electronic Engineering | Year: 2015

Purpose - The purpose of this paper is to reduce the torque ripple but not to decrease the average torque of synchronous reluctance machines by using one step or more than two axially laminated rotors with asymmetric flux-barrier. Design/methodology/approach - A 24-slot four-pole synchronous reluctance machine with overlapping windings and asymmetric flux-barrier in the rotor is, first, described and designed by finite element (FE) method for maximizing average torque. The dimensions of asymmetric flux-barrier including the pole span angle and flux-barrier angle will be optimized to minimize the torque ripple and its influence on the average torque is also investigated by FE analysis. The impact of current angle on the average torque and torque ripple are also analysed. The step laminations together with the asymmetric flux-barrier are employed for further torque ripple reduction which can consider the both rotation directions. Findings - The torque ripple of synchronous reluctance machine can be significantly reduced by employing asymmetric flux-barrier but the average torque is not reduced. Research limitations/implications - The purely sinusoidal currents are applied in this analysis and the effects of harmonics in the current on torque ripple are not considered in this application. The 24-slot/four-pole synchronous reluctance machine with single-layer flux-barrier has been employed in this analysis, but this work can be continued to investigate the synchronous reluctance machine with multilayer flux-barrier. This asymmetric flux-barrier can be easily applied to permanent magnet (PM)-assisted synchronous reluctance machine and the interior PM machine with flux-barrier in the rotor, since the space which is used for PM insertion is the same as the SynRM machines. Originality/value - This paper has analysed the torque ripple and average torque of synchronous reluctance machines with asymmetric flux-barrier and step laminations with asymmetric flux-barrier. The torque ripple can be reduced by this flux-barrier arrangement. The difference of this technique with the other techniques such as stator/rotor skew is that the average torque can be improved. © Emerald Group Publishing Limited.

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