Pressure and Friction Observer-Based Backstepping Control for a VGT Pneumatic Actuator

In this paper, we design, analyze, and experimentally validate an observer-based backstepping controller for electropneumatic actuators. These actuators are commonly used in diesel engines for variable geometry turbochargers (VGT) control. They are preferred over other actuation techniques due to better force/weight ratio; however, their drawbacks, such as nonlinear air mass flow, friction, and aerodynamic forces make their control as a challenging problem. The aim of this paper is to achieve precise control of the actuator by compensating friction and aerodynamic VGT forces. A Lyapunov-based output feedback controller is developed using backstepping technique. As the actuator position is the only measured state, pressure and friction states are obtained from sliding mode-based observers. The exponential convergence of the controller-observer closed-loop system is proved using Lyapunov analysis. Experimental results are presented, which demonstrate the effectiveness of the proposed controller.