Influence of manufacturing and material properties on iron losses in electric traction motors : modelling for inclusion in design tools

This thesis presents modelling and experimentation to identify the discrepancy between calculated and measured motor iron loss, including the impact of high-volume manufacturing processes. An interior permanent magnet machine designed for traction applications is taken as a case study. Comprehensive measurement of soft magnetic material properties for a wide range of induction, frequency and mechanical stress is presented for the electrical steel material used in the studied motor. The impact of BH curve extrapolation and curve fitting method of material loss density on motor performance is illustrated and shows notable impact on the calculated iron loss. The no-load iron losses of ten prototypes and two variants of the studied motor are identified following an extensive measurement campaign, proposing an innovative procedure for no-load iron loss and mechanical loss measurements of permanent magnet motors to enhance repeatability of testing. The impact on iron loss of two high-volume production manufacturing processes is investigated. Cut-edge damage from lamination punching is quantified by novel simulation techniques. The loss increase has significant speed-dependency with up to 35% on the calculated iron loss via implementation of a two-layer cut-edge model. This is accompanied by an 8% increase in torque. Shrink-fitting of the segmented stator and cooling sleeve, quantified by a novel assessment of the motor geometry, shows a similar speed-dependent iron loss increase with a maximum of 36%. Each contributing factor to the iron loss increase is assigned a two-term iron loss build factor which is then combined and compared with the identified no-load iron loss. Strong agreement (