A new complete non-linear simulation model of a buck DC-DC converter

A complete model of a switch-mode buck DC-DC converter was developed in order to fully describe the three most important characteristics of the system: small-signal model, transient simulation and start-up. Due to the inherent nonlinear nature of the switch-mode converter, the new model created with MATLAB and SIMULINK is nonlinear. The model recreates the behaviour of the PWM modulator and the switch (the transistor plus the diode) in the converter in a switched nonlinear way. Using only one model, with the values of the output filter components and some functional data from the control block, it is possible to obtain transient simulations for load changes, a start-up transient simulation and Bode plots for three different transfer functions: input-to-output, control-to-output and reference-to-output. As an example, this last transfer function is shown.