Thrust ripple compensation of PMLSM based on second-order sliding mode observer with super-twisting algorithm

This paper presents a novel thrust ripple estimation method for PMLSM based on second-order sliding-mode disturbance observer. The super-twisting algorithm (STA) with no sliding-mode surface derivative term is superior in reducing chattering while both retaining strong robustness of conventional sliding-mode, thus it is utilized to design the observer. Then, the equivalent q-axes current according to observed thrust ripple are configured as feedforward compensation term to suppress the force ripple and obtain smooth velocity response within the velocity and current double-closed-loop control system. Coincident observation results with the measured one and obvious velocity ripple reduction verifies the validity and effectiveness of the proposed method on an air-bearing PMLSM test stage.