Adaptive backstepping sliding mode control for direct driven hydraulics

Due to the advantages of high energy efficiency and environmental friendliness, the electronic-hydraulic actuator (EHA) plays an important role in fluid power control. One variation of EHA, double pump direct driven hydraulic (DDH), was proposed, which consists of double fixed-displacement pumps, a servo motor, an asymmetric cylinder, and auxiliary components. This paper proposed an adaptive backstepping sliding mode control strategy for DDH to eliminate the negative effect producing by parametric uncertainty, nonlinear characteristics and the uncertain external disturbance. Firstly, the DDH model and a crane dynamics model were constructed in MATLAB/Simulink and validated by experiment. Based on theoretical analysis, the nonlinear system model was built and transformed. Further, by defining the sliding manifold and selecting a proper Lyapunov function，the nesting problems (of the designed variable and adaptive law) causing by uncertainty coefficients were solved. Moreover, the adaptive backstepping control and the sliding mode control were combined to boost system robustness. At the same time, the adaptive law with uncertain parameters was selected. Simulations of the DDH with the proposed control strategy and proportional-integral-differential (PID) were performed respectively. The simulation results show that the designed control strategy can realize better position tracking, and has stronger robustness to parameter changes compared with PID．