Losses and flux penetration in non-grain-oriented low-loss steel with nonsinusoidal excitation

Abstract

The cyclic magnetisation of non-grain-oriented low-loss steel laminations with nonsinusoidal excitation is examined, and theoretical values of loss, flux density and magnetising current waveshape are computed. The algorithm uses a simulation technique, previously described, which includes the effects of both hysteresis and eddy-current action with the premise that hysteresis is independent of frequency; i.e. the anomalous loss is negligible. Results are presented for a range of nonsinusoidal voltages including square, quasi-square and pulse-width-modulated square waveshapes for a wide range of frequencies up to several kilohertz. With a near-uniform value of flux density over a lamination the loss can be simply found for any specified voltage waveshape, but at higher frequencies this method generally overestimates the loss. Suppression of the triplen harmonic components in the magnetising current of three single-phase transformers energised by a three-phase supply with isolated star point is also examined. A companion paper examines flux penetration and losses in relatively thick steel plate, and considers the generation of minor loops with cyclic nonsinusoidal magnetisation.