Practical adaptive control for systems with flexible modes, disturbances, and time delays

Control systems are used in a variety of applications where tracking and regulation are required, although there exist numerous problems which can cause detrimental effects for standard controllers. The field of adaptive control has been researched and applied to solve some of these difficulties, usually through the use of complete adaptive control strategies. This research proposes adaptive controllers which may be added to fixed nonadaptive controllers to form a single unified scheme. This allows the traditional control designer some intuition in the development while reaping the benefits of a controller which can compensate for unknown or changing dynamics. There are three specific problems tackled in this research: flexible modes, disturbances, and time delays. Since each of these may be uncertain or may change over time, the addition of an adaptive controller may allow the system to meet performance requirements or retain stability.;This research will contribute the design and analytical proof of adaptive mode suppression schemes to deal with unknown flexible modes. These modes may be uncertain for a variety of reasons, such as variation between production units, changes in the surrounding environment, degradation over lifetime, or wear from use. The adaptive mode suppression schemes include an adaptive notch filter which is able to track and suppress a varying flexible mode. However, disturbances can also reduce the performance of a control system, specifically one where precise tracking is paramount. For this, we contribute an adaptive neural modeled disturbance rejector which can be added to a stable control system to enhance tracking performance. Lastly, many systems in the field of process controls contain dominant time delays which can change with time, thus affecting the stability and robustness of the closed loop system. To solve this problem, we propose an adaptive Smith predictor which is able to estimate and compensate for the uncertain time delay. To show the benefit of the adaptive controllers, several applications are presented, such as a hard disk drive (HDD) where unknown high frequency flexible modes inhibit the achievable bandwidth and dynamic disturbances degrade the tracking quality. Experimental results of the adaptive mode suppression scheme and disturbance rejection scheme are included. Also simulations of an integrated scheme with the adaptive mode suppression scheme and neural modeled disturbance rejector are done to show an improvement in performance. Simulations are also conducted on a nonlinear hypersonic aircraft model which experiences changing elastic modes, where an adaptive mode suppression scheme is shown to retain stability.