Estimation of PM Machine Efficiency Maps from Limited Data

This article investigates the accuracy of the estimation of efficiency maps for permanent magnet (PM) machines using the stator resistance, d- and q-axis flux-linkages versus the corresponding axis current and the iron loss versus the speed characteristic. The ultimate goal is to apply this approach to the experimental measurements, but this article performs initial investigation using only the finite-element (FE) data. Detailed FE data for 50-kW surface PM (SPM) and interior PM (IPM) machines are used to determine the 'actual' or exact efficiency map and, hence, the accuracy of using approximations. This article examines the effect on the torque-speed capability curve when ignoring cross-saturation effects. It also examines the modeling of the variation of iron losses as a function of load in the constant torque and power regions. A novel approach based on scaling the no-load (NL) losses as a function of load is proposed and shown to give promising results. FE results from two other machines are also provided, which show good correspondence.