Robust indirect adaptive control of the electrohydraulic velocity control systems

A robust version of an indirect adaptive control scheme with self-excitation capability to the problem of controlling velocity of the electrohydraulic servosystems subject to unmodelled dynamics and load disturbances is proposed. The scheme contains an effective gradient least squares estimator using a dead zone technique and a certainty equivalence based adaptive controller. A design procedure for synthesising the adaptive controller is formulated by using the pole-placement technique, where a signal is created and fed back to the control law such that it has self-excitation capability and thus the stability of the closed-loop control system can be achieved. A series of simulations are performed to demonstrate the effectiveness of the proposed scheme. The results show that the proposed scheme is fairly robust to the control systems with uncertainties as well as improved performance characteristics compared with that of the suboptimal PID control scheme with constant feedback gain and that of the adaptive model following control scheme