Model‐free linear active disturbance rejection output feedback control for electro‐hydraulic proportional system with unknown dead‐zone

Here, a model‐free linear active disturbance rejection controller (LADRC) integrating dead‐zone inverse compensation for an electro‐hydraulic proportional (EHP) system with an unknown dead‐zone is proposed. Unlike the existing LADRC design idea, the presented method uses a new hydraulic system block diagram to select the order of LADRC instead of the highest degree of the system. Furthermore, the rationality of order selection is illustrated by the frequency domain analysis theory. To solve the dead‐zone of the proportional valve, a novel structural transformation is proposed by constructing a new dead‐zone, which has a definite physical meaning and can be obtained by the experimental measurement. Then, the dead‐zone disturbance is reduced, and the burden of the observer is relieved. At the same time, the controller parameters are decreased from three to two equivalent PI controller. Besides, the stability of the closed‐loop system is analysed by the describing function method. The performance of the proposed control solution has been investigated through extensive comparative experiments under different working conditions. The experimental results successfully demonstrate the effectiveness and practicality of the presented method.