Multi-fields Analyse Of High Speed Permanent Magnet Brushless Motors And Sensorless Control Strategy

Due to the merits of high efficiency, high power density and simple system construction, high-speed motors have found extensive applications in many industry areas, such as high-speed machining center, flywheels, electric-assisted turbo chargers, compressors, centrifuges and so on. The high-speed permanent magnet brushless motor has attracted extensive attentions, for example, on the aspects of electromagnetic power losses and relevant reduction methods, excessive temperature rise and countermeasures, and sessorless control methods.This dissertation mainly focuses on the surface mounted permanent magnet brushless motor, and analyses the influencing factors on the machine electromagnetic performance, such as the stator split ratio, the stator and rotor structures, the magnet configurations, and so on. Multi-fields analyse will be adopted to calculate the rotor power losses and temperature rise, and to investigate the methods to reduce the power losses and the temperature rise. And, a new sensorless control strategy will also be presented.Firstly, a multi-fields analysis-based design method for the high speed motor is presented in this dissertation. Variation of the electromagnetic performance of the high speed motor with different stator split ratios, and stator and rotor structures is studied. Moreover, influences of the permanent magnet configurations and phase-advancing control on the machine performance and the rotor dynamics are also analyzed in this paper.Secondly, the finite element method is used to analyze the influence of rotor sleeve circumferential grooves on the rotor eddy-current loss, air friction loss and temperature rise. Also, the retaining sleeve stress before and after grooving is comparatively analyzed. All studies verifies that the circumferential grooves on the retaining sleeve can effectively reduce the rotor power loss and temperature rise, but hardly deteriorates the retaining sleeve strength.Then, a sensorless control method by which high-resolution rotor position information is estimated and used for phase-advancing operation of a high-speed surface mounted permanent magnet brushless dc motor is proposed. The proposed sensorless control approach uses hardware to observe the rotor flux vector which is excited by the permanent magnets. It can provide the rotor position which is the same as the phase angle of the observed flux vector, and the method is suitable for phase-advancing control under the high-speed condition. Whilst, for interior permanent magnet (IPM) motors, the sensorless control strategy is improved by modifying the rotor flux observer, which considers the rotor saliency.Subsequently, an experimental system of the sensorless high-speed surface-mounted permanent magnet brushless dc motor, which is associated with an electrical-assisted turbocharger, is set up. Both no-load and on-load experiments are taken, proving that the multi-fields based motor design and the proposed sensorless control strategy are workable and reliable.