Design Of Direct-Drive PM AC Servo Motors

According to the developing trends of direct-drive servo motors, this dissertation studies a group of problems that are frequently met in direct-drive motor design. As well, this dissertation represents some new topics.Start with the fractional-slot winding theory, this dissertation gives an account of the basic properties of fractional-slot windings, including the analysises of winding factors and coil arrangements. New coiling methods of different numbers of turns and novel coil distributions are analyzed, which give more flexibilities to motor design. FFT analyses are performed to adjust the MMF harmonics of different coil distributions, the results show that the novel coiling methods could cut down the sub-harmonics.This dissertation summarizes different analytical models for cogging torque predictions, and gives the account of the details which should be carefully considered. As well, two examples of cogging torque minimization are given.Specifically, the impacts of welding grooves and stator teeth’s saturation on cogging torques are studied. Basing on the considerations of these factors, the correct minimization methods for cogging torques are proposed and verified effective by FEA software.In PM motors, the asymmetry of poles and teeth brings radial forces, which are studied by FEM in this dissertation. The uniqueness of this study is that the radial forces caused vibrations involve not only the amplitude periodic vibrations but also the orientation periodic vibrations. As well, the radial forces in motors with shifted poles are studied.Finally, some tests are performed on a prototype motor, showing that the motor is of good performances and characteristics. As well, separation of iron losses and mechanical losses is performed.