Position tracking and flatness controller with disturbance observer in hydraulic servo systems

A position tracking and flatness controller with disturbance observer (DOB) is proposed in hydraulic servo systems (HSSs). In this paper, we assume that the disturbance is a biased sinusoidal signal with unknown frequency. DOB is designed in the form of 2nd high pass filter to estimate the disturbance. The nonlinear controller is designed to compensate the estimation error of the disturbance and to track the desired position and load pressure as a near IO linearizing inner-loop load pressure controller and a feedback plus feedforward outer-loop position controller. The desired load pressure is designed using differential flatness property of the HSS mechanical subsystem. The performance of the proposed method is validated via simulations.

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