The detailed magnetic field distribution of a permanent magnet electric motor is very important for the accurate prediction of performance parameters such as back electromotive force (back-EMF), rotor and stator losses, winding inductances, noise and vibration, torque profiles, etc. Although finite element analysis is a good option for accurately calculating magnetic field distribution in electrical machines, it is typically time-consuming and does not provide closed form solutions. Alternatively, analytical calculation of magnetic field distribution can be conducted in Fourier series, which is more suitable for a design tool to predict the motor performance.
This dissertation presents a novel numerical technique for calculating exact magnetic field distribution in the air gap of a surface mounted permanent magnet machine This solution can be obtained via a two-dimension analytical solution with Laplacian and quasi-Poisonian equations, assuming that the iron is infinitely permeable and the air gap is slotless. Slot effects can be added in the model by using relative air gap permeance calculated by the conformal transformation of slot geometry. This technique is constructed by multiplying the relative permeance function expressed in an infinite Fourier series with the distribution of magnetic field in the slotless air gap. This method shows a very good alignment with finite element method for a surface mounted permanent magnet machine with radial magnetization. It can also be extended to calculating magnetic field distribution of interior permanent magnet motors including consideration of magnetic saturation, cross-saturation between d-axis and q-axes, affecting both inductances and flux linkages, as well as localized effects due to rotor bridges.
Furthermore, this approach can be used to create a closed-form solution, which is the first step towards inverse modeling of electric machines. This is a complete paradigm shift in the design process for electric machines, which can reduce the time taken to design an electric machine, while reducing the active material content to make them power dense with significant reduction in cost. Furthermore, availability of analytical description of the field components will aid in the designer's ability to distinguish between the control and magnetic design aspects.
|School:||Illinois Institute of Technology|
|School Location:||United States -- Illinois|
|Source:||DAI-B 76/12(E), Dissertation Abstracts International|
|Keywords:||Field Distribution, Flux Density Distribution, Optimal Design, Permanent Magnet Machines|
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