A novel stator hybrid-excited, parallel flux path, synchronous machine of doubly salient topology is proposed. It has the novel features of: (a) hybrid DC field and permanent magnet excitation in the stator, (b) magnets placed in the slots between adjacent salient stator poles, and (c) the magnetic poles of permanent magnets arranged such that the flux premagnetizes the stator but it is in a direction to oppose the DC excitation flux. The electromagnetic characteristics of the machine is analysed on open-circuit and load. Since the new machine topology is developed from the variable flux machine, a comparison of their electromagnetic torque and machine losses is conducted. The average electromagnetic torque of the hybrid-excited machine can be increased by 18% for fixed copper loss in comparison to the variable flux machine due to the reduction of magnetic saturation in the stator. It is also shown that at high temperatures some risk of permanent magnet demagnetization exists when excited with DC and armature currents due to fringing flux that exists between the stator and rotor poles. However, this affects only a very small area of the permanent magnets. The performance of the hybrid-excited machine is predicted by 2D finite element analysis and experimentally validated.Index Terms -Doubly salient, hybrid excitation, permanent magnet synchronous machines.
Purpose
– The purpose of this paper is to minimize the optimization parameter number of synchronous reluctance machine (SynRM) and permanent magnet (PM) assisted SynRM, and compare their relative merits with interior permanent magnet (IPM) machine for electric vehicle applications, in terms of electromagnetic performance and material cost.
Design/methodology/approach
– The analysis of electromagnetic performance is based on finite element analysis, by using software MAXWELL. The genetic algorithm is utilized for optimization.
Findings
– The rotor design of SynRM can be significantly simplified by imposing some reasonable conditions. The number of rotor design parameters can be reduced to three. The electromagnetic performance of SynRM is much poorer than that of IPM, although the material cost is much cheaper, approximately one-third of IPM. The ferrite-SynRM is competitive and even better than IPM especially for high electric loading, in terms of torque capability, torque-speed characteristic, power factor, threshold speed and efficiency. In addition, ferrite-assisted SynRM has great advantage over IPM in material cost, 55 percent cheaper. The performance of NdFeB-assisted SynRM is close to IPM in terms of torque capability, torque-speed characteristic, power factor, torque ripple and efficiency. The material cost of NdFeB-assisted SynRM is ∼25 percent lower than IPM.
Originality/value
– Some conditions, which can simplify the optimization of SynRM rotor, are discussed. The electromagnetic performances and material costs of SynRM, ferrite-assisted, NdFeB-assisted SynRMs and IPM are quantitatively compared and discussed.
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