Composite control of speed sensorless for bearingless permanent magnet synchronous motor

It is difficult to achieve precise estimation of rotor position for a bearingless permanent magnet synchronous motor(BPMSM) with a single position sensorless control method in different speed range. In order to solve this problem, a composite control strategy combining an improved pulsating high frequency signal injection and second order generalized integrator frequency-locked phase-locked loop(SOGI-FLL-PLL) method is proposed. Firstly, the structure and working principle of the BPMSM are introduced. Secondly, the principle of position and speed estimation by high frequency pulsating signal injection method based on SOGI is studied. Thirdly, the method of SOGI-FLL-PLL used in medium and high speed operation is analyzed. In the state of low and medium switching interval, a linear weighted control algorithm is adopted to make the two control strategies transit smoothly. Finally, the simulations and experiments are carried out. The results show that the proposed composite control method can estimate rotor position and speed accurately and the rotor can return to the balance position quickly under the conditions of load disturbance, which validate good effectiveness of composite strategy and good robustness of the whole sensorless control system.