Comparative study of different torque sharing functions for losses minimization in Switched Reluctance Motors used in electric vehicles propulsion

In this paper the authors present a comparison between optimised versions of three torque sharing functions, with different number of degrees of freedom, used for improving the efficiency in Switched Reluctance Motors. Starting from the basic rectangular variation, the ascending and descending flanks of the function are modeled using a cosine, exponential and a more general approach (further referred to as piecewise cubic sharing function). The degrees of freedom varying between two and an arbitrary number (for the general approach) are determined so as to minimize losses, when operating in smooth torque conditions. Based upon an optimisation procedure with both linear and nonlinear constraints, the total (copper and iron) losses are minimized considering a limited available DC bus voltage. Moreover, a smooth model is presented so as to be able to separate the two main causes for the torque ripple and it is shown that, neglecting the chopping ripple, a ripple-free torque can be obtained. Extensive studies have been conducted for determining the optimal number of degrees of freedom (DoFs) for the piecewise cubic function. The proposed methods were successfully implemented on a 8/6, 30kW peak power, SRM both numerically and experimentally-wise.