Online tuning of PID controllers using delayed state variable filters

Delayed state variable filters are implemented for the estimation of monotone open-loop processes which can be approximated by a dominant time delay coupled with a first order lag. Based on the delayed filtered step output response, the first and second order derivatives, the corresponding static process gain, the apparent dead time and the apparent time constant are evaluated. A new PID tuning formula is formed, which is based on the placement of the open loop zeros related to the apparent time constant and time delay. Coupling with the root locus design procedure, the algorithm provides a range of PID settings for different damping factors. Simulations are included to illustrate the concepts.<>