New model and sliding mode control of hydraulic elevator velocity tracking system

A new model of hydraulic elevator dynamics has been developed. It includes an improved dynamic friction model. This hydraulic elevator dynamics model is used in a new input–output based discrete adaptive sliding mode control algorithm comprised of an integral action, a nonlinear output feedback, and an adjustable sliding mode. The characteristic feature of the algorithm is an on-line update of the hyperplane coefficients and the integral gain to enable improved control loop behavior. Compared with the optimally tuned PID controller applied to a hydraulic elevator system, the new controller exhibits an increased robustness with regard to model uncertainties, unknown external disturbances and changes in the operation conditions, as well as much better velocity tracking characteristics.