Gessese Mekuria, Y: Development of a High Speed Solid Rotor

This work deals with design, construction and testing of high speed solid rotor induction motors fed by a frequency converter system. In high speed applications, like in the compressor technology, for distributed power generators (micro gas turbines), in industry (machine power tools) and in the automotive technology (turbochargers, hybrid drives), the mechanical strength of the solid rotor induction motor (SRIM) is recognized as a significant benefit. The performance characteristics of 3-phase, 4- & 2-poles, 24000 /min, axially slitted, radially grooved solid rotor induction motors with copper end rings (GLIDCOP AL-15) at sinusoidal voltage supply are designed and optimized using 2D, non linear, finite element method (FEM) analysis. Although the calculation of the solid rotor is a complex three dimensional eddy current problem, the characteristics of the rotors are well estimated using 2D FEM tools. The rotor end currents and the three dimensionality of the rotor geometry are considered by equivalent end effect factors. A prototype drive system is developed and tested, which confirms the validity of the simulation results. The current harmonics, caused by the inverter supplied modulated voltage, are well damped by a low pass LC sine filter, which gives an almost sinusoidal current supply to the motor terminals. Furthermore, quantitative performance comparisons with alternative high speed motors (squirrelcage and permanent magnet motors), which were developed and tested in previous doctoral works, have been done, showing their superior performance in higher power density and lower steady state temperature rise at the expense of a less robust rotor system.