Abstract
Interior permanent magnet synchronous machines (IPMSMs) with V-shaped permanent magnet (PM) rotors are widely used as traction motors in electric vehicles because of their high torque density and high efficiency. However, the V-shape IPMSMs have the disadvantages of inevitable torque ripple due to the non-sinusoidal air-gap flux density distribution and the utilisation of the reluctance torque. In this study, with the aim of improving the torque ripple characteristics, a modified V-shaped IPMSM rotor configuration with bridges extended inwards towards the pole centre is proposed to generate a more sinusoidal air-gap flux density waveform. The proposed topology, referred to as ‘Type C’ within this study, is compared with baseline rotor configuration references, namely ‘Type A’ which is a conventional V-shaped PM rotor, as well as ‘Type B’ which is a related configuration with a mechanically non-uniform air gap. The analysis results show that the rotor ‘Type C’ exhibits significant advantages in terms of reducing cogging torque, torque ripple and radial force, without incurring additional air-gap friction losses. Finally, a prototype of the IPMSM with the proposed rotor configuration is manufactured and tested, verifying the predicted benefits experimentally.
Highlights
With the increasingly stringent emissions requirements and with many countries setting dates eliminating sales of ICE-based vehicles, research and development on electric vehicles (EVs) is at an all time high
Ref. [6] performs a study on the demagnetization characteristics of permanent magnet (PM), and the results show that the PMs in the flat-shaped PM rotor are much easier to be demagnetized under the maximum torque operation with respect to the V-shaped magnets
As the windings of the Interior permanent magnet synchronous machines (IPMSMs) are excited with three-phase sinusoidal currents, it is crucial to obtain the sinusoidal back electromotive force (EMF) waveform as well as the sinusoidal air-gap flux density
Summary
With the increasingly stringent emissions requirements and with many countries setting dates eliminating sales of ICE-based vehicles, research and development on electric vehicles (EVs) is at an all time high. In [9] and [10], the skewed slot stator is adopted in order to reduce the cogging torque and the torque ripple while in [11][12][13], the step-skewed rotor is used to achieve similar effects These are infact widely adopted traditional methods, which lead to the increase of the manufacturing cost/time and the decrease of the average output torque. In order to reduce the torque ripple without detriment to the average output torque, an asymmetrical V-shape rotor configuration of an IPMSM is presented in [14]. This is proven to be an effective way to reduce the torque ripple albeit there exists a limitation to single rotation direction (i.e. unidirectional benefit). The prototype with the proposed rotor concept is built and experimentally validated in Section 5, and in Section 6 conclusions from this research are discussed
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