Towards autonomous PI control satisfying classical robustness specifications

PID or three-term controller tuning in industry often uses the relay experiment to find the system ultimate data followed by the use of PID coefficient calculation rules. The paper first reports a new, flexible and more accurate method of finding system frequency response data including the system ultimate data. It is then demonstrated how this new identification module can be used in closed loop to automate PI controller tuning and achieve classical robustness specifications. A new algorithm is given along with a report of a Matlab/Simulink(TM) implementation. A different non-parametric method, developed by the authors, is the phaselocked loop (PLL) approach. It is shown how the PLL module can be used to drive an automated PI controller-tuning algorithm to achieve classical performance specifications. The new algorithm yields a PI controller achieving specified phase margin and gain margin values. The algorithm is one of a family of constructive routines able to automate PI design for a combination of classical robustness specifications. Experience gained with a Matlab/Simulink(TM) implementation is described.