Abstract
Due to the special doubly-salient structure, flux-reversal permanent magnet (FRPM) machines typically suffer from relatively large torque and speed ripples, as well as acoustic noise and vibration, especially at low speeds. As one of the main sources of torque ripples, harmonics in phase back electro-motive-force (EMF) should be suppressed as much as possible in order to produce a smooth torque. In this paper, an improved configuration of FRPM machine is proposed by introducing a small space-gap between the two adjacent magnets belonging to the same stator tooth to improve the symmetry of phase back-EMF waveform. The influence of the small space-gap on phase back-EMF waveform is evaluated by employing 2D finite element analysis (FEA), and consequently, an optimal value of space-gap for a more sinusoidal back-EMF waveform is obtained.
Highlights
The flux-reversal permanent magnet (FRPM) machine, as a family member of stator-PM machines, was first introduced in 1997.3 It can be considered as a combination of switched reluctance machine and PM machine, and it inherits the merits of both machines including convenient heat dissipation, high torque density, robust rotor structure, and high fault-tolerant capability.[1,4]
There are three main sources that gives rise to undesired torque ripples: (1) The cogging torque generated by the interaction of PMs and the slotted stator and rotor cores; (2) The harmonics in phase armature currents due to pulse-widthmodulation and in phase back electro-motive- force (EMF) due to doubly-salient structure; and (3) The varying reluctance torque generated by the variations of dq-axes winding inductances versus the rotor positions.[5]
Most researches are focused on the cogging torque minimization of FRPM machines to eliminate torque ripples. 2D finite element analysis (FEA) is employed to investigate the impacts of rotor pole arc variation and teeth number per rotor pole with different teeth depths on cogging torque.[6]
Summary
A new type of permanent magnet (PM) brushless machines having magnets and armature windings in stator (the so-called stator-PM machines) has attracted a lot of interests over the last few years.[1,2] The flux-reversal permanent magnet (FRPM) machine, as a family member of stator-PM machines, was first introduced in 1997.3 It can be considered as a combination of switched reluctance machine and PM machine, and it inherits the merits of both machines including convenient heat dissipation, high torque (power) density, robust rotor structure, and high fault-tolerant capability.[1,4] this machine typically suffers from severe torque and speed ripples, as well as noise and vibration, especially at low speeds. In Ref. 9, a new configuration, i.e., consequent-pole FRPM machine is proposed, which can increase the amplitude of back-EMF and effectively suppress the cogging torque and torque ripples. Based on this new configuration, the dimension of this small space-gap are optimized by combining with 2D-FEA.
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