Simultaneous identification and control

The problem of identification of a process under a feedback control system of Box and Jenkins type is discussed and various methods considered for updating the control system. Deliberate system perturbation is unnecessary since excitation is provided by the inherent disturbances. A predictor updating scheme is shown, if convergent, to result in an optimum system. However its performance is crucially dependent on the availability of a good process model. A more promising technique relies on a separation effect applicable to processes with time delays in excess of three sample intervals, based on the assumption that the disturbance is adequately described by an autoregressive model of three or fewer coefficients. The technique requires the fitting of an autoregressive model by the linear least squares method and has proved practically reliable. The more general problem is discussed using Astrom's formulation and a general technique examined. Implementation of such systems requires engineering judgement, typified by the discussion on steady-state errors.