Optimal U/f-control of high speed permanent magnet motors

High speed motors are used nowadays more and more in many applications such as turbo blowers and compressors, microturbine gas generators, machine tools and down-hole oilpumps. Benefits of high speed motor drives are the reduced size and the increased efficiency compared to the conventional technology consisting typically of a motor and a gearbox. High speed motors used are mainly permanent magnet synchronous motors (PM-motors) and induction motors. PM-motors are more widely used due to the better power factor and efficiency although the control of PM-motors is more difficult, for example, due to the insufficient natural damping of motor dynamics. Furthermore the carbon fiber sleeve, usually used around the rotor magnets, prevents the heat conducting away from the rotor surface. This, together with a poor control, easily results in rotor overheating problems. Special control methods and pulse width modulation are usually needed to overcome this kind of problems. In this presentation, special control issues are discussed for the optimal U/f-control of high speed PM-motors