Research On Robust Control For Electro-hydraulic Servo Position System With Input Saturation

Electro-hydraulic servo system (EHSS), owing to the high power-to-weight ratio,fast response and high load capability, has been widely used in many industrial, such as,defense industry, civil industry etc. However, EHSS is a complicated nonlinear system,which has a large of model uncertainties and external disturbances. Moreover, theactuator saturation nonlinearity occurs due to the actuator’s physical limitations.Therefore, the design of advanced control strategy to ensure the EHSS has reliablecontrol performance is extremely important. In this thesis, control schemes are designedto achieve position tracking for symmetric cylinder EHSS and asymmetric cylinderEHSS with parameters uncertainties, external disturbances and input saturation. The maincontents of this thesis are as follows:Firstly, the problem of position tracking control for symmetric cylinder EHSS in thepresence of parameter uncertainties, external disturbances and input saturation isinvestigated and an adaptive fuzzy controller based on backstepping method is designed.Adaptive fuzzy logic systems are used to approximate the unknown uncertainties; robustcontrol term is incorporated in the design of the controller to treat the externaldisturbances and the approximation error; an auxiliary error system is introduced tosuppress the effect caused by input saturation. Next, command filter technology isintroduced in the backstepping approach to simplify the controller design. Based oncommand filter technology, adaptive fuzzy backstepping control scheme is developed.Theory analysis and simulation results show that good tracking performance can beachieved with simplified control law, and the closed-loop system has stronger robustnessto uncertainties.Secondly, backstepping sliding mode controller for asymmetric cylinder EHSS isdesigned with the help of the extended state observer. The extended state observer is usedto estimate the lumped disturbance, which is combined by parameter uncertainties,external disturbances and uncertainties of input saturation. And the controller can forcethe system states to achieve the position tracking. Due to the estimation of lumped uncertainty by the observer, the control law does not require any information on theuncertainty, and the chatting can be alleviated effectively. The effectiveness of theproposed algorithm is verified by simulations.Then, a disturbance-observer-based adaptive robust control method is proposed forasymmetric cylinder EHSS. Adaptive control and disturbance observer are constructedfor uncertainty and lumped disturbance. Robust control term is given to treat theinestimable disturbances and an auxiliary error system is introduced to compensate forthe effect caused by input saturation. The proposed backstepping control scheme, where asecond-order filter is adopted in order to avoid the explosion of complexity, issignificantly simplified. Finally, the stability of the closed-loop system is analyzed basedon Lyapunov theory. Simulation results illustrate the effectiveness of the proposedcontrol scheme.Finally, the effectiveness of the proposed control strategy for symmetric cylinderEHSS is verified by the test based on dSPACE, and experimental results show that goodtracking performance can be achieved.