High-performance control method for the MSTMP motor

Permanent magnet synchronous motor (PMSM) is the ideal drive for the magnetically suspended turbo-molecular pump (MSTMP) for its high power density, reliable operation and high energy efficiency. Rotor position information is necessary to drive the PMSM. However, because of the installation space limitation and reliability requirement, position sensorless control technology without mechanical position sensors is more attractive. In this study, a sliding mode observer is adopted to estimate the back electromotive force (EMF) that contains the position information. Since the high-order harmonics in the back EMF would lead to harmonic position errors, a fixed frequency extraction filter is proposed to filter out the harmonics. A high precision speed control is of importance to ensure the performance of the MSTMP and also contributes to achieving a better position estimation accuracy, especially under strong disturbances. Therefore, a composite speed controller combining a sliding mode speed controller and a sliding mode disturbance observer is proposed to improve the speed control performance of the MSTMP. The effectiveness of the proposed high-performance control method for the MSTMP motor is evaluated with experiments.