Precision Motion Control of a Servomotor-Pump Direct-Drive Electrohydraulic System With a Nonlinear Pump Flow Mapping

Pump control hydraulic systems can achieve high efficiency by the advantages of no throttling loss and high power-to-volume ratio. However, low tracking accuracy and slow frequency response are main drawbacks for the applications of pump control hydraulic systems, because of the existing high-order dynamics, uncertainties, and highly nonlinear dynamics. Recently, the advent of servomotor-pump direct-drive electrohydraulic systems shows a good prospect for this issue, and the design of the control algorithm is the key to achieve high motion accuracy. In this article, to achieve precision motion control, an adaptive robust control with a backstepping design is proposed for an electrohydraulic system, where the cylinder actuator is direct-driven by a servomotor pump. Considering the high-order dynamics and nonlinearities of hydraulic systems, the controller is processed in two steps: position tracking step and pressure step. Besides, the pump flow deviation under low speed is another important limitation for good control performance. Thus, a nonlinear pump flow rate mapping is proposed by practical fitting and used into the controller design by the proper nonlinearity compensation of the desired pump flow. Comparative experiment results show that the proposed control strategy achieves high motion control performances in spite of the nonlinearities and uncertainties.