Parallel Velocity Control of an Electro-Hydraulic Actuator With Dual Disturbance Observers

In this paper, a nonlinear parallel control algorithm is developed for an electro-hydraulic actuator to achieve high velocity tracking performance and reduce energy consumption. The parallel control system consists of a servo valve and a variable displacement pump. A separate strategy is employed for practical use. The variable displacement pump is considered as feedforward according to velocity commands and leakage; while the servo valve is used to improve the dynamics and accuracy of the closed loop system. Two disturbance observers are employed to deal with the uncertainties and disturbance in the control process. A radial basis function neural network (RBFNN)-based extended disturbance observer is proposed to compensate for the unknown parameters and disturbance in the velocity control loop. To attenuate the influence of model uncertainties and disturbance in the pressure control loop, a nonlinear disturbance observer is adopted. The stability of the whole system is proved through the Lyapunov theory. The comparative experiments are conducted to verify the effectiveness of the proposed nonlinear parallel controller. The results demonstrate that the proposed algorithm can improve the velocity tracking performance for a valve-pump parallel controlled electro-hydraulic actuator under uncertainties and disturbance.