Disturbance observer-based nonlinear energy-saving control strategy for electro-hydraulic servo systems

Precise tracking performance and significant energy-saving effect are both important issues for electro-hydraulic servo system. Nevertheless, the electro-hydraulic servo system usually demonstrates inferior efficiency compared with other available actuation methods. To improve the efficiency of the electro-hydraulic servo system during the task of position tracking, a nonlinear energy-saving control strategy is proposed. The presented controller employs a variable supply pressure control to make the pump pressure adapt to the system demand and utilizes a nonlinear cascade controller for precise position tracking. Additionally, a disturbance observer is developed to compensate for the lumped uncertainties including parametric uncertainties and uncertain nonlinearities both in the design of variable supply pressure control and nonlinear cascade controller. Results indicate that the presented multi-input single-output system combined with the nonlinear energy-saving control strategy can save 45% energy in a harmonic trajectory tracking test and 68% energy in a multi-step trajectory tracking test, respectively, compared with its counterparts. Furthermore, the maximum tracking errors of both tests are 1.2mm.