Two control-parameter synthesis approaches: small signal discrete modelling and optimization using sensitivity functions. Application to a variable frequency DC-DC converter

In this paper, a comparison between two methods for the control-synthesis of a digital PI controller applied to a variable-frequency converter is proposed. In the first method, the small signal modelling approach including the poles locus technique is used. In the second method, Newton´s algorithm for minimizing the variance between a second order step response and the output voltage of the converter is used; the sensitivity functions of the output with respect to the control parameters are calculated. Consequently the optimal gains allow large variations of the input, not possible with the small signal method. Furthermore the small signal method could induce an unstable behaviour for low frequencies. Simulation results illustrate the comparison