Adaptive control can robustify uncertain control systems

A "nominal" plant is usually the object of design. The controllers then attempt to maintain some performance in spite of the uncertainty usually existant in the real world. In the presence of large, and possibly time-varying, uncertainties, fixed linear controllers may result in poor behavior or even in total divergence. Adaptive techniques have been conceived to cope with uncertainty. However, real-time identification of plant parameters may be too slow to allow for a solution in fast changing environments, such as flight control, power plants, etc. Simple adaptive control techniques have been developed for uncertain systems. These techniques utilize the stabilizability property of the plant to be controlled and automatically tune the control gains. The stability and performance are maintained in spite of the large variations in plant parameters. The adaptive gains increase only at those moments when high gains are required to maintain the performance, and may decrease immediately afterwards. The adaptive controller acts to fit the right gains at the right time as a function of the changing need. This way, during regular times the control system is almost unaffected by adaptation, but it is strongly supported during difficult times.