Adaptive control of time delay systems and applications to automotive control problems

Abstract

This thesis is about the adaptive control of time delay systems with applications to automotive control problems. The stabilization of systems involving time delays is a difficult problem since the existence of a delay may induce instability or poor performance for the closed loop system. A unique approach for controlling systems with known time delay was originated by Otto Smith in the 1950s by compensating for the delayed output using input values stored over a time window of [t - [tau], t] and estimating the plant output using a model of the plant. Later, this idea was extended to include unstable plants as well, using finite-time integrals of the delayed input values thereby avoiding unstable pole-zero cancellations that may occur in Smith's controller. Adaptive versions of these delay compensating controllers were also developed with rather complicated adaptive rules which might not be practical to use in real applications. In this thesis, a simpler adaptive version of delay compensating controllers is developed, which has adaptive rules that are easily implementable and thus suitable for real life implementations. The developed controller is tested in two important automotive control problems that are idle speed control (ISC) and fuel-to-air ratio (FAR) control. These two applications, ISC and FAR control, constitute the experimental part of this research. In ISC, the objective is to regulate the engine speed to a prescribed set-point in the presence of accessory load torque disturbances such as due to air conditioning and power steering. The adaptive controller, integrated with the existing proportional spark controller, is used to drive the electronic throttle actuator. Both simulation and experimental results demonstrating the performance improvement by employing the adaptive controller are presented. Modifications and improvements to the controller structure, which were developed during the course of experimentation to solve specific problems, are also presented. In addition, the potential for the reduction in calibration time and effort which can be achieved with our approach is discussed.

(cont.) The objective in FAR control is to maintain the in-cylinder FAR at a prescribed set point, determined primarily by the state of the Three-Way Catalyst (TWC), so that the pollutants in the exhaust are removed with the highest efficiency. The FAR controller must also reject disturbances due to canister vapor purge and inaccuracies in air charge estimation and wall-wetting (WW) compensation. Two adaptive controller designs are considered. The first design is based on feedforward adaptation while the second design is based on both feedback and feedforward adaptation. Both simulation and experimental results demonstrating the performance improvement by employing the APC are presented. In addition, modifications and improvements to the APC structure, which were developed during the course of the experiments, to solve specific implementation problems are presented.