Browsing by Author "Dlala, Emad Ali"

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Analysis of Hysteresis Torque in a High-Speed Induction Motor
(2005) Dlala, Emad Ali
Helsinki University of Technology | Master's thesis
This work is carried out toward the development of high-speed motor design technology. The thrust of this research is twofold: First, to address the problem of modelling hysteresis in solid rotors whose iron made of magnetically semi-hard material. Second, to investigate the consequent hysteresis torque acting on the solid rotor of a high-speed induction motor. In hysteresis torque calculation, the accurate modelling of hysteresis loops is a priority should be superiorly handled. In the absence of a delicate straightforward method to model symmetrical minor loops with satisfactory results, a novel method for modelling symmetrical minor loops in hysteresis magnetic media is introduced. The proposed method is simple and effective. It takes on experimentally measured symmetrical minor loops combined with certain portions of the initial magnetization curve (the an hysteretic curve) to identify the Preisach distribution function. The numerical simulations and experimental results show that the presented method is much more adequate than other existing methods for predicting symmetrical minor loops in terms of both the modelling quality and the computation time. We also examine the hysteresis torque produced by a solid rotor of a high-speed induction motor. By applying an experimental method to an unloaded high-speed induction motor it has been possible to determine the change of power at small positive and negative slips. The change of power is believed to correspond to the hysteresis torque associated with the high-speed induction motor. Because of the two fundamental reasons that the rotor of the high-speed motor is solid and made of semi-hard ~ material, it is found that under certain measuring conditions the obtained hysteresis torque is relatively significant and approximately represents 2.2% of the rated torque.
Magnetodynamic vector hysteresis models for steel laminations of rotating electrical machines
(2008-04-11) Dlala, Emad Ali
Faculty of Electronics, Communications and Automation | Doctoral dissertation (article-based)
This thesis focuses on the modeling and prediction of iron losses in rotating electrical machines. The aim is to develop core loss models that are reasonably accurate and efficient for the numerical electromagnetic field analysis. The iron loss components, including hysteresis, classical eddy-current, and excess losses, are determined by modeling the dynamic hysteresis loops, whereby the incorporation of the core losses into the field solution is feasible and thus the influence of the core losses on the performance of the machine is investigated. The thesis presents a magnetodynamic vector hysteresis model that produces not only an accurate, overall prediction of the iron losses, but also explicitly models the magnetization behavior and the loop shapes. The model is found to be efficient, stable, and adequate for providing accurate predictions of the magnetization curves, and hence iron losses, under alternating and rotating flux excitations. It is demonstrated that the model satisfies the rotational loss property and reproduces the shapes of the experimental loops. In addition, a more simplified, efficient, and robust version of the magnetodynamic vector hysteresis model is introduced. The thesis also aims to analyze the convergence of the fixed-point method, examine the barriers behind the slow convergence, and show how to overcome them. The analysis has proved useful and provided sound techniques for speeding up the convergence of the fixed-point method. The magnetodynamic lamination models have been integrated into a two-dimensional finite-element analysis of rotating electrical machines. The core losses of two induction motors have been analyzed and the impact of core losses on the motor characteristics has been investigated. The simulations conducted reveal that the models are relatively efficient, accurate, and suitable for the design purposes of electrical machines.