Design And Analysis Of Low Harmonic Permanent-Magnet Motor With Fractional Slot Concentrated Windings

Permanent-magnet (PM) machines with fractional slots concentrated winding (FSCWs) have been used more widely, owing to their short and less complex end-winding, high-power density, high efficiency, high filling factor, low cogging torque, fault tolerance, cost-effectiveness and good field-weakening capability. However, the magnetic field of these windings has significant space harmonics. For PM machines, only the specific magnetomotive force (MMF) winding harmonic for the armature field interacts with the PM field to produce continuous torque. The others are undesirable and will degrade machine performance, such as localized core saturation, eddy current loss in PMs, additional core losses in rotor and stator, and noise and vibration, which are the main disadvantages of the FSCW types. Thus, the main problem of PM machines with FSCWs is the design of low MMF winding harmonic.In this paper, the main content of this paper is the design and analysis of low harmonic PM machines with FSCWs. Firstly, The theory of the design of low harmonic is formed from the theoretical analysis of the MMF winding. Then, finite element method (FEM) model is established and compared with the theoretical calculation, verifying the effectiveness of the theoretical analysis. The fruits of the study are:1) First, the merits and shortcomings of the PM machines with FSCWs are introduced and analyzed. Besides, it is pointed out the importance of reducing the MMF winding harmonic.2) According to the theoretical analysis, the MMF mathematic expressions of a single conductor, a single coil and a single coil winding are deduced. Furthermore, the MMF mathematic expressions of the single-phase windings and the synthetic-phase windings are derived. Finally, the mathematic expression of the harmonic content of the MMF is obtained.3) With the mathematic expression of the MMF winding harmonic content, it can be theoretically analyzed how to change the structure to reduce the harmonic content and which harmonic order can be reduced.4) According to the theoretical analysis, the 12/10 machine is selected the prototype structure. Then the model is establishing in FEM. Due to the theory of the low harmonic design, several topologies of 12-10 machine can be derived. Nine topologies are analyzed and compared, including the MMF harmonic content, eddy current loss. Finally, an optimal structure is choosen. And the the MMF harmonic content can be calculated in FEM, verifying the effectiveness of the theoretical analysis.5) A prototype motor has been designed and manufactured, the experimental test results be identical well with the FEM one. And the measured waveform figure is obtained under different running states of the prototype, further, verifying the effectiveness of the theoretical analysis.