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In order to improve the dynamic performance of the sensorless permanent magnet synchronous motor drive system, the modified pulsating high frequency voltage injection method is proposed. Firstly, the second order generalized integrator can be used to extract the high frequency voltage signal instead of band-pass filters. The specific frequency harmonic elimination unit is applied to obtain the rotor position error signal to avoid using the low-pass filter. Therefore, the system dynamic performance can be improved. In addition, the system parameter is easier to adjust than traditional methods with band-pass filters and low-pass filters. Finally, the simulation model and experimental platform are built to verify the effectiveness of the proposed method. The simulation and experimental results present that the dynamic performance of motor drive system can be improved.

In order to reduce the axial length and increase the critical speed of the small magnetic suspension drive system, a new slice hybrid magnetic bearing (SHMB) with two radial air-gaps is proposed. The structure and suspension mechanism of the SHMB is introduced, and then the mathematical models of the radial suspension force are deduced using the equivalent magnetic circuit method. The suspension mechanism is proved. The radial and axial suspension forces are then calculated by the finite element method. The experimental prototype SHMB is finally designed and constructed. The stable suspension of the rotor is realized, and the suspension forces are measured. The results of the finite element calculation and experimental measurement verify the correctness of the mathematical models.

To reduce the volume of the five degrees of freedom (DOF) magnetic suspension system and increase the critical speed, a slice hybrid magnetic bearing (SHMB) is proposed. First, the mathematical models of the radial suspension are deduced using the equivalent magnetic circuit method based on the suspension mechanism analysis. Then, the parameters of the five-DOF SHMB are designed. The magnetic circuits are analyzed, and the relationships between the radial suspension force and the suspension currents are calculated. Furthermore, the relationships between the axial force and the axial offset are also calculated. Finally, The experimental prototype five-DOF SHMB is designed and the suspension forces are tested. The research results have shown that the rotor can be levitated stably in five DOF.