Browsing by Author "Belahcen, Anouar, Prof., Aalto University, Dept. of Electrical Engineering and Automation., Finland"

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Design and Analysis of Bearingless Synchronous Reluctance Machines
(2020) Mukherjee, Victor
School of Electrical Engineering | Doctoral dissertation (article-based)
A bearingless machine is a special type of electrical machine where the mechanism to levitate the rotor is integrated into the machine design. This thesis focuses on modelling and analysing different electromechanical behaviours of bearingless synchronous reluctance machines. Three models have been developed for different computational requirements, which include one finite element model, one reduced-order model and one analytical model. The models yield reasonably accurate results which are subsequently verified by the experimental results from a prototyped machine. It is found that the levitation force generation influences the iron losses of the machine, especially the hysteresis component. The vibration characteristics of the machine are also influenced by the levitation force production. Using numerical simulations, it is shown that the vibration components can be used to track the rotor displacement from the centre of the stator. The proposed analytical model clearly explains the variations in the inductance components of the machine's windings with the rotor's displacement. A novel algorithm has been proposed for the reduced-order model since the snapshot matrix selection requires additional consideration due to the complexities raised from the levitation force production. The levitation force ripple appears to be a major concern due to the properties of the reluctance rotor. The force harmonics are modelled with a novel method and an indexing technique which improve the understanding of the forces produced by the spatial harmonics of the magnetic flux density. Different reluctance rotor designs are investigated showing that a design compromise lies between maximising average torque, levitation force and minimising their corresponding ripple.
Effect of Manufacturing Processes on Electrical Machine’s Performance
(2020) Sundaria, Ravi
School of Electrical Engineering | Doctoral dissertation (article-based)
This thesis focuses on the effects of manufacturing processes on electrical machine performance. The effects of cutting, welding, and shrink ﬁtting are considered and the effects of cutting are studied more thoroughly in this thesis. A 37 kW induction motor is used as a test machine. A cutting loss model is proposed based on Epstein frame measurements of non-oriented strips of different cutting lengths. The loss model is validated with core loss measurements of the strips and stators manufactured with wire electric discharge machining and laser cutting. The proposed cutting loss model is also evaluated with grain-oriented strips cut with punching, water jet and laser cutting. Furthermore, two different ﬁnite element approaches based on higher and mixed-order elements are proposed for computationally efﬁcient modelling of the cutting effects. The effect of welding is analysed with measurements of the ring cores of loose and welded sheets of stator laminations. In addition, stator core losses are measured with and without the frame to quantify the shrink ﬁtting effects. Different approaches are proposed to include the effects of welding and shrink ﬁtting in the ﬁnite element analysis of an electrical machine. A dummy blocked rotor test setup is designed and manufactured to measure the effect of different manufacturing processes on the stator core losses. As a result of manufacturing processes, the stator core losses of the induction machine increased by 23 % at the rated ﬂux (400 V, 50 Hz). The contributions of cutting, welding, and shrink ﬁtting are observed to be about 10 %, 7 %, and 6 % respectively. The presented loss models are found to predict the corresponding effects of manufacturing processes accurately.