Adaptive Sliding Mode Control for Active Hydro-Pneumatic Suspension Based on Extended State Observer

Hydro-pneumatic suspension is widely used due to its favorable nonlinear stiffness and damping characteristics. However, with the presence of parameter uncertainties and high nonlinearities in the hydro-pneumatic suspension system, the effectiveness of the controller is often suboptimal in practical applications. To mitigate the influence of these issues on the control performance, an adaptive sliding mode control method with an expanded state observer (ESO) is proposed. Firstly, a nonlinear mathematical model of hydro-pneumatic suspension, considering seal friction, is established based on the hydraulic principle and the knowledge of fluid mechanics. Secondly, the ESO is designed to estimate the total disturbance caused by the nonlinearities and uncertainties, and it is incorporated into the sliding mode control law, allowing the control law to adapt to the operating state of the suspension system in real time, which solves the effect of uncertainties and nonlinearities on the system. Finally, the real road surface data are collected using laser displacement sensors and other devices to simulate the control effect of the proposed control method under real road surface conditions. The effectiveness of the adaptive sliding mode control method based on the ESO is verified through simulation. The results show that the RMS value of body acceleration is reduced by more than 50% and that it is robust to load variations when using the proposed method for the real road test, compared to the passive hydro-pneumatic suspension, which significantly improves the overall performance of the vehicle. This study provides some references for the design of active hydro-pneumatic suspension control methods.