Iron losses in brushless permanent magnet DC machines.

A closed-loop computer-controlled single-sheet test system has been developed to characterise lamination materials and to measure, the iron loss density under any specified flux density waveform. The system has been 'used to validate predictions from a recently developed theoretical model, for the calculation of the excess loss component associated with domaiQ wall movement, under flux density waveforms typical of those encountered in the stator core of brushless permanent magnet dc motors. In addition, an improved expression for the calculation of the iron loss density component, from measured 71 and 7!vectors, due to rotatio~ in non-purely rotating flux conditions, has been derived. A simple analytical model from which the airgap flux density and spread of magnet working points can be determined and which accounts for the effects of curvature for radial-field permanent magnet machines has been developed and validated. The model has been coupled to an analytical technique for the prediction of the open-circuit flux density waveforms in different regions of the stator core, and has subsequently been employed for the prediction of the open-circuit iron loss. In order to predict the iron loss under any specified load condition, a technique which couples a brushless dc drive system simulation to a series of magnetostatic finite element analyses corresponding to discrete instants in a commutation cycle has been developed. It enables the prediction of the local flux density waveforms throughout the stator core under any operating condition, and has been employed to predict the local iron loss density distribution 'and the total iron loss and their variation with both the load and the commutation strategy, Finally, the theoretical findings have been validated against measurements on a representative low power brushless drive system

The effect of Duffing-type non-linearities and Coulomb damping on the response of an energy harvester to random excitations

Linear energy harvesters can only produce useful amounts of power when excited close to their natural frequency. Due to the uncertain nature of ambient vibrations, it has been hypothesised that such devices will perform poorly in real-world applications. To improve performance, it has been suggested that the introduction of non-linearities into such devices may extend the bandwidth over which they perform effectively. In this study, a magnetic levitation device with non-linearities similar to the Duffing oscillator is considered. The governing equations of the device are formed in which the effects of friction are considered. Analytical solutions are used to explore the effect that friction can have on the system when it is under harmonic excitations. Following this, a numerical model is formed. A differential evolution algorithm is used alongside experimental data to identify the relevant parameters of the device. The model is then validated using experimental data. Monte Carlo simulations are then used to analyse the effect of coulomb damping and Duffing-type non-linearities when the device is subjected to broadband white noise and coloured noise excitations. </jats:p