ADAPTIVE PID DESIGN EXPLOITING PARTIAL PRIOR INFORMATION

Independent of the original design strategy, linear time-invariant controllers may be viewed as generated from plant models. PID controllers, for example, are implicitly associated with second order models. The induced modelling errors place limitations on the achievable closed loop bandwidth. We call these limitations model limitations. On the other hand, delays and saturations also dictate bandwidth limitations. We call these limitations plant limitations. This distinction has interesting implications for the design of robust PID control laws and also indicates whether higher order controllers or adaptation will be beneficial. Grey box estimation emerges as a mechanism that provides faster estimator transients at the cost of potential model bias which may well be insignificant in view of plant limitations.