Abstract
The 6-slot/2-pole (6s/2p) permanent magnet motors with a diametrically magnetized PM rotor are popular for high speed application. Meanwhile, toroidal winding can not only reduce end-winding length but also eliminate unbalanced magnetic force for short axial length motors. Therefore, the electromagnetic performance of a 6s/2p high speed PM (HSPM) motor with toroidal windings is firstly analyzed, including air-gap flux density, flux linkage, back-EMF, cogging torque and electromagnetic torque. Then, considering modular design for auto-manufacturing, the influence of stator gap and misalignment on the electromagnetic performance is investigated. It shows that the stator gap results in unbalanced three phase back-EMFs, not only amplitudes, but also phase angles. The stator gap increases the equivalent air-gap length and PM flux leakage, which leads to lower air-gap flux density, back-EMF, and average torque. Moreover, the stator gap results in asymmetric air-gap length, which results in large cogging torque. Further, it shows that the misalignment of two stator parts mainly affects the uneven equivalent air-gap length and symmetry of winding configuration, which leads to unbalanced three phase back-EMFs, especially phase angles, and self- and mutual-inductances, as well as rotor PM loss. Experimental results of a prototype motor with/without stator gap and/or misalignment are given to validate the finite element predicted analyses.
Highlights
High speed permanent magnet (PM) motors have been widely used for various applications and become more and more popular in recent years
High speed application, 6-slot/2-pole (6s/2p) high speed permanent magnet (HSPM) motors with concentrated tooth coil windings are employed widely due to short end-winding length and no unbalanced magnetic force [1]
The results show that the motor without stator gap has almost no cogging torque, but has relatively large torque ripple, which results from the product of square brushless direct current (BLDC) currents and almost sinusoidal back-EMF waveforms
Summary
High speed permanent magnet (PM) motors have been widely used for various applications and become more and more popular in recent years. Besides the tooth coil with short end-winding length, the toroidal winding becomes a popular design alternative for high speed application which demands a short motor axial length [1], [3]–[5]. They are widely adopted in low-power application whilst the operating speed normally exceeds 100krpm. Compared with conventional distributed windings, toroidal windings are widely adopted to shorten end-winding and motor total axial length for high-power high-speed application [6]–[9] Another merit of such toroidal windings is higher thermal dissipation capability due to the presence of extra air-duct.
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