A feedback linearization controller for an electro-hydraulic servo system through using Lyapunov functions is proposed to solve the problem that position output with high-precision and high-stability is difficult to obtain from traditional control algorithms due to the time-varying parameter and strong nonlinear characteristics of the system. The controller applies a feedback linearization method to drive position outputs to a predetermined trajectory
making the system response accurate and rapid. Since the bulk modulus of oil in hydraulic system is highly uncertain and its parameters cannot be measured on-line
inaccurate estimation of the parameters will weaken control performances of the controller and may even cause instability of the control system. Hence
the Lyapunov direct method is applied to redesign the feedback linearization controller. A simple Lyapunov function is constructed through system tracking errors
and a method is given to calculate the optimal value for parameter estimation. The optimal estimation of parameters meets the requirement that the derivative of the Lyapunov function is non-positive and guarantees the asymptotic stability of the system. Simulation results show that the proposed controller has satisfactory tracking performance with high control accuracy and strong robustness to parameter variation.
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