Identification of Nonlinear Systems in Closed Loop

On the basis of the possibilities of identification of linear dynamic systems in closed loop a favourable way for nonlinear system identification in closed loop is proposed using an additional test signal. The methods od least squares, generalized least squares and maximum likelihood are used for nonlinear difference equation models of Hammerstein structure. Essential results for some steady and unsteady nonlinearities are demonstrated by means of quality values. The influence of the polynomical form of nonlinearity, the approximation of unsteady characteristics, the noise influence and the influence of the regulator structure are discussed. Based on these results the identification procedure is applied to model the dynamic behaviour of the blood pressure control system in man. The relations between an orthostatic load, the heart rate and the arterial blood pressure are described by linear and nonlinear dynamic models.