Research on super-twisting sliding mode control of continuous rotary motor electro-hydraulic servo system

To improve the ultra-low-speed performance and frequency-response range of a continuous rotary electro-hydraulic servo motor system, a transfer-function model was established, and a super-twisting sliding-mode position controller (STSMC) was designed. The STSMC principle was introduced, and a sliding surface and control law were derived from the state-space equations. A hyperbolic tangent function was then used to replace the sign function to attenuate chattering while preserving robustness. An improved particle swarm optimization PID (IPSO-PID) strategy was constructed as a strong baseline for comparison. Under 1° sinusoidal inputs over 8–16 Hz, STSMC achieved smaller amplitude and phase errors than IPSO-PID. At 15 Hz, the STSMC amplitude error was 11% of that of IPSO-PID, and the phase error was 9.88°, corresponding to an approximately 35.3% reduction in phase lag. The results indicate improved tracking accuracy and high-frequency dynamic response, providing a reference for control development in similar systems.