A Super-Twisting Sliding Mode Robust Load Observer of PMSM for Electric Cylinder Considering Magnetic Saturation Effect

The electric cylinder has become a research hotspot in the future because of its high energy efficiency and excellent dynamic performance. The electric cylinder is driven by a permanent magnet synchronous motor (PMSM). However, the existing high-performance control strategies of permanent magnet synchronous motor, such as sliding mode variable structure control (SMC), model predictive control (MPC), and load torque feedforward, often face the challenge of unknown load torque when improving dynamic performance. The traditional load observation methods of PMSM involve the dq-axis inductance, which neglects the impact of inductance variation in interior PMSM (IPMSM) caused by the cross-coupling effect, flux weakening, or magnetic saturation effect. In this paper, a super-twisting sliding mode robust load observer (ST-RLO) is proposed, which performs load torque observation without reliance on inductance parameters. The feasibility and stability of the observer are analyzed theoretically. Experiments are carried out. The results show that compared with the conventional Luenberger load observer (CLLO) involving inductance, a better observation of the load torque is achieved by the ST-RLO, which has a better robustness for inductance variations and mismatching of inductance and inertia parameters.