Computational methods for the steady-state performance prediction of cage induction machines fed from nonsinusoidal supplies

Cage induction motors can be supplied from various types of solid-state adjustable frequency controllers with a wide range of operating characteristics. However, the inverter/machine combination results in the necessity to derate the motor due to harmonic effects arising from the nonsinusoidal nature of the applied voltage. The overall magnitude and distribution of the additional loss and consequent reduction in motor rating depends on the harmonic content of the applied waveform, and on certain aspects of the machine design. Calculation of this additional loss requires a detailed knowledge of the current and flux redistributions which occur at high frequencies. A comprehensive study of the performance and design of inverter-fed machines is being undertaken at ERA as part of a major collaborative research programme. The authors summarise the general approach adopted in the study and outline suitable techniques for evaluating the major sources of additional loss