Lower-order linear active disturbance rejection control for electro-hydraulic servo system based on structural invariance compensation

High observer gain is the key to ensuring the full-order active disturbance rejection control (ADRC) performance for electro-hydraulic servo (EHS) systems. However, the noise sensitivity and output time delay limit the observer gain. In this paper, a lower-order linear ADRC is proposed with lower gain and uncompromised disturbance rejection ability. First, the internal nonlinear dynamics and external unknown disturbances of the EHS system are eliminated by introducing the structural invariance compensation (SIC). Then, the original EHS model is transformed into a one-order integral chain structure. A one-order linear ADRC, solving the compensation error of SIC caused by model parameter uncertainty, could be directly developed based on the equivalent model. In addition, a practical and novel b0 tuning method and frequency-domain stability analysis technology are developed. Extensive comparative experiments are carried out to illustrate the effectiveness of the proposed method.