Nonlinear Modeling of DC/DC Converters Using the Hammerstein's Approach

This paper deals with the modelling of highly nonlinear switching power electronics converters using black-box identification methods. The duty cycle and the output voltage are chosen, respectively, as the input and the output of the model. A nonlinear Hammerstein-type mathematical model, consisting of a static nonlinearity and a linear time-invariant model, is considered in order to cope with the well known limitations of the more common small signal models, i.e. the entity of the variations of the variables around a well defined steady-state operating point and the incorrect reproduction of the steady state behaviour corresponding to input step variations from the above steady state operating point. The static nonlinearity of the Hammerstein model is identified from input-output couples measured at steady-state for constant inputs. The linear model is identified from input-output data relative to a transient generated by a suitable Pseudorandom Bynary Sequence (PRBS) constructed with two input values used to identify the nonlinearity. The identification procedure is, firstly, illustrated with reference to a Boost DC/DC converter using results of simulations carried out in PSpice environment as true experimental results. Then, the procedure is experimentally applied on a prototype of the above converter. In order to show the utility of the Hammerstein models, a PI controller is tuned for a nominal model. Simulation and experimental results are displayed with the aim of showing the peculiarities of the approach followed.