Self-tuning control of offset: a unified approach

The CARMA model generally assumed in self-tuning control frequently leads to an offset between the measurement and the desired value when regulating a plant subjected to constant load disturbances about a nonzero set point. The normal ad hoc insertion of an integrator solves the problem but can introduce others (such as convergence difficulties). The solution explored in this paper is to use a CARIMA plant model in which the noise term is nonstationary, and it is shown that good adaptive behaviour is then possible both with generalised minimum-variance and pole-placement self-tuning controllers. The approach produces integral control terms in a natural way, and, for simplified plant models, leads directly to a general PID algorithm.