Limit cycle-based exact estimation of FOPDT process parameters under input/output disturbances: a state-space approach

ABSTRACTA set of novel explicit expressions for the identification of stable, unstable and integrating first-order plus dead time process dynamics is presented. In the absence of sensor noise/static load disturbances, an autonomous relay control system with an asymmetrical relay induces a smooth limit cycle at the process output. Dynamic model parameters are estimated using the set of proposed expressions which depend on the parameters of limit cycle output and its derivatives. However, in practice, the process output is generally corrupted by the measurement noise, thereby rendering an erroneous identification of process dynamics. Furthermore, static load disturbance during an identification test also induces an asymmetrical limit cycle output resulting in inaccurate measurements. Hence, a fast Fourier transform technique and biased relay feedback methods are implemented to obviate the problem of asymmetries and chattering in the limit cycle output yielding the original limit cycle and its subsequent der...