Nonlinear adaptive position tracking of an electro-hydraulic actuator

This paper deals with position tracking control of a single-rod electro-hydraulic actuator subject to external disturbances and parameter uncertainties. In previous disturbance observer design methodologies for electro-hydraulic actuators, parameter uncertainties have been commonly regarded as disturbances and lumped together with external perturbations. However, in practical electro-hydraulic systems, system parameters are unknown and varying. If considerable parameter uncertainties exist in the system or if the disturbance dynamics induced by parameter uncertainties exceed the bandwidth of the disturbance observer, estimation accuracy will degrade, which will significantly affect system performance. To solve this problem, an extended disturbance observer is proposed in this paper to estimate disturbances while dealing with parameter uncertainties. In addition, a nonlinear position tracking controller is designed for position tracking based on the proposed disturbance observer using a backstepping technique. The proof of the stability of the overall closed-loop system is based on Lyapunov theory. The performance of the proposed controller is verified through simulations and experiments using a shock absorber as a load force generator. A detailed nonlinear physical model of the load force is developed and implemented in the simulation. The results show that the proposed nonlinear position tracking controller, together with the extended disturbance observer, provide excellent tracking performance in the presence of parameter uncertainties and external disturbances.