Tooth ripple losses in salient pole synchronous machines

Abstract

In the present paper, the application of analytical and numerical methods to an electromagnetic problem requiring an accurate representation of saturation is examined. The problem considered is that of tooth-ripple losses in salient-pole synchronous machines. To calculate these losses, two methods, one devised by Oberretl and a modified version of the considerably older one-dimensional approach of Gibbs, are compared with the results obtained from the finite-element and finite-difference methods. Using a time-stepping finite-difference calculation, the influence of moving boundaries and the imposed DC field are taken into account for the first time in this tooth-ripple calculation. A saturation factor is defined that allows the designer to calculate the tooth-ripple losses of solid salient-pole synchronous machines for a wide range of machine size, taking magnetic saturation into account. To verify the theory, the results are compared with measurements on a small model. These measurements were done using a torque meter placed between the model and a DC drive motor and were cross-checked by the Poynting vector method. Rules and limits are given for the use of the analytical methods.