On computational delay in digital and adaptive controllers

System performance deterioration due to computational delay in digital controllers is studied in this paper. The numerical example in this paper shows that if the computation delay is included in the simulation, the closed-loop system performance with an adaptive controller designed under an assumption of no computation delay is worse than that with a simple fixed parameter digital controller. A modified computation sequence in self tuning control is suggested to reduce the computational delay and it is concluded that, although the speed of digital devices has been improved dramatically in recent years, computation delay should still be taken into account in digital control system modelling, analysis and design especially when fast sampling and extensive computation is required.