Finite element analysis and design optimisation of shaded pole induction motors

  • Dawei Zhou

    Student thesis: Doctoral Thesis


    In the area of performance analysis of the Shaded Pole Induction Motors (SPIMs),much research has been done with different equivalent circuit models, but the results are generally not satisfactory. The emergence of Finite Element (FE) methods provides an opportunity to take a fresh look at the design of SPIMs and this forms the backbone of my research.

    In the research, a more accurate two-dimensional time-stepping eddy-current FE model was developed. The multi-slice technique, justified as the more efficient way to consider the effect of a skewed rotor, has been adopted in the model. For the first time,the end-ring resistance was investigated under the condition that the end-ring current distributes itself non-sinusoidally along the circumferential direction in the end-ring area. An instantaneous non-uniform end-ring resistance model was therefore presented and coupled with the two-dimensional multi-slice FE model. Thus, compared with using the normal two-dimensional FE model, the three-dimensional nature of electric machines, e.g. the skew and end-ring, could be considered more properly by using the proposed FE Model. Meanwhile, the harmonics, the skin effect and the saturation of the permeable parts can all be taken into account with the new model.

    On the other hand, in order to reduce the computing time required, by the time-stepping technique, a variable step size method was adopted and a more reliable method of estimating the truncation error of time-stepping has been developed. Additionally, by coupling the external circuits equations directly to the field equations, the time cost was further reduced and the performance of a SPIM including current and torque might be obtained immediately after the systems equations were solved.

    With the developed two-dimensional FE model, the effects of variation of design parameters, including air gap profile, pole bridge, the skew, rotor slot number and closed-slot rotor, have been investigated. By introducing a new harmonic analysis method based directly on the time-stepping finite element method, the effect of different designs on the spatial harmonic in the air gap field and the time harmonic in the rotorbar current can be learned.

    The optimisation technique was applied to the design of SPIMs in order to obtain a proper combination of the design variables. A more efficient global-local hybrid search algorithm that combines the Genetic Algorithm with the direct search method was proposed in this study. To meet the demand of either speed or accuracy, a multi-slice fixed-mesh model of SPIMs was built up and used to calculate of the motor performance, the objective function of the optimisation. Because the optimisation program was based on FE analysis directly, an automatic re-mesh scheme depending on the optimisation variables was required and therefore developed in this research as well. A great performance improvement was achieved when applying the proposed optimisation method to maximising the starting torque.

    Finally, In order to validate the result of the two-dimensional, multi-slice FE model proposed, a PC-based experimental rig has been set up. With this test rig, two SPIMs have been tested in both the steady state and the transient state and the measuring results proved the accuracy of the analysis model developed in the study.
    Date of AwardMar 2001
    Original languageEnglish

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