An Extended State Observer Based Super-Twisting Sliding Mode Controller for Electrostatic Actuators

This paper presents a super twisting sliding mode control (STSMC) system to stabilize a parallel-plate electrostatic actuator (ESA) and extend its operating range beyond the pull-in point. A voltage-controlled ESA is stable only within one-third of the full gap due to susceptibility to pull-in, nonlinearity, and sensitivity to electronic noise and disturbances. To address these challenges, an STSMC is developed to overcome the nonlinearity and instability, while an extended state observer (ESO) estimates the ESA's displacement. Implemented on a real ESA model in MATLAB/Simulink, the ESO-based STSMC increases the ESA's travel range to 99.9% of its full gap despite noise, disturbance, and parametric uncertainty. The system's stability is proved using a Lyapunov approach.