Active Disturbance Rejection Control for Double Pump Direct Driven Hydraulics

As the energy crisis and further development of the electro-hydraulic actuator driven by servo motor, double-pump direct driven hydraulics (DDH) was brought forward, which mainly comprises of a servo motor, double fixed displacement pumps, a differential cylinder, a low-pressurized tank and auxiliary valves. To address the problems causing by uncertain parameters and unknown external disturbances of DDH, this paper proposed a control strategy adopting active disturbance rejection control (ADRC). Firstly, a system consists of a DDH unit and a micro-crane were modelled in MATLAB/Simulink and verified by measurement. Further, the state space equation model of the system was derived based on its mathematical model and a third-order ADRC was designed using the constructed system state-space equation. Additionally, tracking-differentiator (TD) was employed to process the input position signal transiently to avoid unnecessary oscillations, and the extended state observer (ESO) was used to accurately estimate the influence of the uncertain by nonlinear control law. After that, the proposed ADRC or Proportional-Integral-Differential (PID) control was combined with the system. Finally, the simulations were performed under varying loads, and the system performances, including position tracking and energy efficiency, were analyzed and compared. The results show that the ADRC can sufficiently suppress the unknown external disturbance under the condition of variable load, has the advantages of robustness and improves the position tracking precision.