Optimal Current Control Of Externally Excited Synchronous Machines In Automotive Traction Drive Applications

Abstract

The excellent suitability of the externally excited synchronous<br> machine (EESM) in automotive traction drive applications<br> is justified by its high efficiency over the whole operation range and<br> the high availability of materials. Usually, maximum efficiency is<br> obtained by modelling each single loss and minimizing the sum of all<br> losses. As a result, the quality of the optimization highly depends on<br> the precision of the model. Moreover, it requires accurate knowledge<br> of the saturation dependent machine inductances. Therefore, the<br> present contribution proposes a method to minimize the overall losses<br> of a salient pole EESM and its inverter in steady state operation based<br> on measurement data only. Since this method does not require any<br> manufacturer data, it is well suited for an automated measurement<br> data evaluation and inverter parametrization. The field oriented control<br> (FOC) of an EESM provides three current components resp. three<br> degrees of freedom (DOF). An analytic minimization of the copper<br> losses in the stator and the rotor (assuming constant inductances) is<br> performed and serves as a first approximation of how to choose the<br> optimal current reference values. After a numeric offline minimization<br> of the overall losses based on measurement data the results are<br> compared to a control strategy that satisfies cos (ϕ) = 1.