Design and Evaluation of a Compact 15 kW PM Integral Motor
Abstract: This thesis deals with the integral motor of tomorrow, and particularly with a variable speed, sensorless permanent magnet synchronous motor with an integrated converter. The rated power is 15 kW at 1500 r/min. The outer dimensions are approximately the same as for the equivalent standard induction motor.Control strategies for pumps and fans, i.e. suitable loads for variable speed motors, are briefly described. The huge energy savings that can be made by reducing the speed instead of throttling/choking the flow are pointed out. Compared to installing an induction motor with a separate converter, a PM integral motor will probably pay-off in less than a year.A totally analytical expression for calculating the airgap flux density of permanent magnet motors with buried magnets is derived. The analytical expression includes axial leakage, and iron saturation of the most narrow part of the magnetic circuit of the machine.A computer program for optimization of PM motors with buried magnets has been developed. It was used to design the manufactured prototype PM integral motor, and the parameters are investigated with analytical and/or FEM calculations. The optimization program is also used to suggest nearoptimum pole numbers for desired powers (4-37 kW) and speeds (750- 3000 r/min) of inverter-fed PM motors. Results show that compact buried PM motors should have relatively large airgaps and high NdFeB-magnet masses to improve the efficiency. Ferrite magnets are unsuitable.Measurements on the manufactured PM motor, the novel concept of stator integrated filter coils, and the complete PM integral motor are presented. Special attention was given to temperature and overall efficiency measurements.The rotor cage losses were investigated by time-stepping FEM. Four short circuit fault conditions were also examined in order to evaluate the risks of demagnetization of the buried magnets.
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