ABSTRACT
In the previous chapter the design of feedback control systems was considered, where the control input was derived using the error signal as a reference. While this is perhaps the most widely applicable control system arrangement, it does have a performance limitation: with persistent excitation it is not possible to drive the error signal to zero, as then there would be no control input. The smaller the error signal is driven, the higher the control gain must be, and the less stable will be the system.
