Design and voltage supply of high-speed induction machines
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Doctoral thesis (monograph)
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Date
2002-11-29
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Language
en
Pages
140
Series
Acta polytechnica Scandinavica. El, Electrical engineering series, 108
Abstract
The motivation for this work is to find good designs for high-speed induction machines. Special attention is paid to rotors suitable for these machines. Another goal is to find supply voltage waveforms appropriate for a high-speed induction machine with a solid rotor. In order to design good high-speed machines, modeling is modified and verified. A laminated rotor made for high speeds was tested on a 65 kW 30600 1/min compressor drive. Two squirrel cage solid steel rotors were tested on a 60 kW 60000 1/min high-speed machine. In both cases, the rotors were compared against a commercially used copper coated solid steel rotor. The results showed that the laminated construction with a cage should be used whenever possible. At higher speeds, a well-designed squirrel cage solid steel rotor would be better than a copper coated solid steel rotor. The copper coated rotor is preferred at very high speeds. Pulse amplitude modulation and pulse width modulation are techniques used to adjust the supply voltage of electric machines. The feasibility of these modulation types for supplying high-speed induction machines was tested. The results show that pulse amplitude modulation is the best choice for a high-speed induction motor drive. For the high-speed machines considered, the 3D effects made the 2D modeling of the electromagnetic properties difficult. Two modifications to the current modeling software were made. In the first modification, the end ring inductance was calculated with a separate 2D FEM model. In the other modification, the flux fringing in the air gap region was also modeled with a separate 2D FEM model. A discrepancy between electromagnetic loss calculated and electromagnetic loss measured was noticed. The measurements show circulatory currents flowing in the parallel paths of a stator winding of a high-speed machine. These currents produce extra power loss not modeled in the calculations. It is shown that taking circulatory currents into account, the model provides results close to the measured ones. Thus, the model can be used for the designing and optimization of high-speed machines. Genetic optimization software was used to derive the optimal parameters for a squirrel cage solid steel rotor. General topology suitable for a high-speed induction machine was also studied by using optimization. The results show that both the positioning and the volume of conductors in the rotor are important. Considering the electromagnetic performance, the choice between a laminated and a solid rotor core material is less significant for a high-speed induction machine.Description
Keywords
high-speed induction machine, rotor design, voltage modulation, PAM, PWM, circulatory currents, optimization