Auxiliary variable-based output feedback control for hydraulic servo systems with desired compensation approach

An auxiliary variable-based output feedback method is constructed in this paper. To obtain the state estimates, an auxiliary variable-based state observer is presented. Instead of calculating the estimates indirectly via the estimation dynamic, the distinguishing characteristic of the proposed observer lies in its ability to directly derive estimates by simply applying a low-pass filter to the observer. Therefore, the proposed observer is similar as a filter, which is more intuitive and concise in terms of structure and parameter tuning. Then, a backstepping-free controller is constructed based on the estimation results, and only one step is required. To facilitate the design procedure, the desired compensation approach is applied both in the observer and the controller. Utilizing the Lyapunov method, the system stability is assured, demonstrating that the presented controller excels in precise tracking tasks despite the presence of time-varying uncertainties. The feasibility of this approach is further corroborated through comparative results.