Core losses estimation in design of high speed electric machines

Abstract

High speed machines have been used in many applications because of high power density without pricey drivetrain in recent years. In the design process, engineers have to face challenges including higher per unit losses, bearing stiffness and lifetime, rotor dynamics, and winding cooling layouts. Nevertheless, accurate estimation of core losses is the fundamental challenge since the high operational frequency and non-sinusoidal magnetic motive force excitation. In IEC test method based on Epstein Frame, non-uniform distribution of flux density close to the four corners of the electrical steel frame made of overlapped laminates become severe along with increase in excitation frequency. The induced extra losses would dramatically influence the measurement accuracy of the test samples. Hence, when the excitation frequency is high, the corner effects in the Epstein Frame Method would deteriorate the accuracy of the IEC method. This paper proposes a revised-method based on the Epstein Frame Method with rationale steps for deduction of core losses. To separate the unnecessary extra losses from the measured data, a sample shape for the Epstein Frame Method is designed and analyzed. Then, it is evident that uniform flux density distribution in the sample must be maintained for accurate measurement of sample core losses.