Adaptive cascade controller applied to a hydraulic actuator

This work proposes a cascade controller for the trajectory tracking control of a hydraulic actuator. The hydraulic actuator is modeled as a forth order nonlinear system including the valve dynamics as a first order linear system. This mathematical model is interpreted as a mechanical subsystem (load and friction) driven by a hydraulic one (actuator and valve). From this interpretation, one proposes a cascade controller by combining two different control laws with parameters adaptation for each subsystem. By adapting the inverse of the hydraulic constants and by using a suitable Lyapunov function, the adapted parameters are not used in the denominator of the control and adaptation laws. The closed loop system stability is analyzed by Lyapunov´s direct method. Simulation results illustrate the main characteristics of the proposed controller.