Analytical Modeling of Iron Lossesfor a PM Traction Machine

University essay from KTH/Elektrisk energiomvandling


Permanent magnet (PM) machines offer several advantages in traction applications such as high efficiencyand high torque per volume ratio. The iron losses in these machines are estimated mostly with empiricallaws taken from other types of machines or with finite element simulations (FEM). In the first part of thisthesis the objective is to define an accurate analytical model for the stator yoke, teeth and rotor of a PMmotor which should work well enough for all operating point (different loads and frequency).This analytical model is found using an iterative process. After building a loss matrix and flux matrix basedon FEM simulations, it is possible to curve fit each of the lines or the rows of the matrix in order to achievethe best fitting for every operating point. This is a very new approach; it was shown that it gives thepossibility, even with a very limited number of FEM simulations, to achieve an accurate estimation of thelosses.The second part of this report focuses on optimizing this analytical method, comparing it with otherpossibilities, analyzing limits and advantages. Special attention is also given to the effects of the losses onthe temperatures in different parts of the machine. In the last part of the thesis, the analytical model isused to test a new control strategy. Its goal is to reduce the total losses of the motor and optimize the ratiobetween torque and total losses for a given driving cycle.

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