Continuous-time indirect adaptive control of the electrohydraulic servo systems

A continuous-time robust indirect adaptive control (IAC) algorithm with a self-excitation capability is proposed for position control of an electrohydraulic servo system subject to parametric uncertainties and load disturbances. In this algorithm, a gradient least squares dead zone estimation is used to identify the plant parameters and then a linear pole-placement controller is designed using the estimate. By a coprimeness verification procedure, the proposed algorithm facilitates the establishment of the adaptive pole-placement control of the closed-loop system by using an additional nonlinear feedback signal implemented for supplying the system with sufficiently rich signals. An analysis shows this algorithm can guarantee parameter estimation convergence and system stability based on the certainty equivalence principle. The performance of the proposed algorithm is evaluated through both the simulation results and the experimental studies. Simulations and experiments are conducted to see how well the proposed algorithm compares with two existing control schemes in controlling the same process. The results show that the IAC scheme confirms the analysis and has considerable robustness subject to parametric uncertainties and load disturbances and has better performance than the other two controllers.