Nonlinear Observer and Control Design for Electropneumatic Clutch Actuator
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This thesis treats position control of an electropneumatic clutch actuator operated by simple on/off solenoid valves. This clutch actuator is intended for automatic manual transmission systems or clutch-by-wire systems in heavy duty trucks. Pressurized air is already present as a part of the brake system in such vehicles, and pneumatics is therefore the natural choice for actuating the manual transmission in these clutch actuator systems. Production cost is a crucial factor in all parts of the automobile industry. For the clutch actuator system this influence the choice of number of sensors present in the production system, limiting it to only a position sensor. It also lead to that a set of on/off solenoid valve is chosen for actuation over more commonly used proportional valves, even though it complicates the control task. Production quality sensors are considered in this thesis, and these are sensors which are more influenced by noise than sensors found in test rigs made for research and development. Motor vibration and possible other mechanical influence also have to be taken into consideration when testing in a full-scale truck as done in this thesis. Motivated by the choice of on/off solenoid valves as the control valves in the clutch actuator system, switched control design is considered. Switched controllers exploit the on/off solenoid valves discrete behavior, switching the valves between fully open and fully closed in a manner such that desired supply or exhaust of air from the actuator chamber is obtained, ensuring the demanded piston position. Based on this line of action, two switched controllers are developed along with a dual-mode switched controller utilizing the best features of the individual controllers. Stability analysis based on standard Lyapunov theory are provided, and the performance of the controllers are tested in a full-scale test truck at Kongsberg Automotive ASA. Both theoretical and practical performance analyses confirm that switch controllers are well suited for actuator piston position control of the clutch actuator system. Full-state feedback availability is assumed in the design of the switched controllers. Adaptive nonlinear observers are derived to provide estimates of unmeasured states and parameters for the clutch actuator system. These adaptive observers are deterministic with linear output-injection, and have adaptation laws for estimation of clutch load characteristics and friction. A full-order adaptive observer, including filtering of position for suppression of noise, shows best performance. The adaptation of unknown parameters accounts for wear of the clutch and variations in temperature, ensuring a robust design of the clutch actuator model and improving state estimates. Theoretical analyses of convergence are derived under persistence of excitation condition, and performance of the adaptive observers are validated by experimental data. The switched controller and the adaptive nonlinear are combined into an observerbased switched controller. Simulation of this is provided, comparing the results with actual truck measurements. These analysis indicate that the pressure sensor can be exchanged with an adaptive nonlinear observer without significant loss of performance for nonlinear state feedback based control designs for the system.