Modelling and Controller Design of Isolated Buck(Fly-buck) converter

Abstract

An isolated buck (fly-buck) converter is one of the best suitable options for multi output isolated low power applications like industrial automation,intelligent electric meters,and communication power supplies.In this project work,different modes of operation of fly-buck converter have been discussed. After that,a comparative study on time domain analysis of fly-buck converter with and without considering the effect of parasitics in continuous conduction mode has been performed.Time domain analysis is performed to study the transient and steady state behavior of a converter in a faster and more accurate manner. It constitutes the derivation of mathematical expressions for the parameters inductor currents, capacitor voltages and output voltages in each mode by various methods such as the expansion of state transition matrix as a power series, Modal decomposition method,etc. The inductor current waveforms obtained by plotting the derived mathematical expressions from time domain analysis in MATLAB are compared with the waveforms obtained from PSPICE simulation,and percentage errors are calculated for each mode.
For regulating the converter outputs,voltage mode control of fly-buck converter using typeIII controller has been designed and simulated in PSPICE. A hardware model of voltage mode control of a 5W fly-buck converter operating with a switching frequency of 100KHz has also been developed. After voltage mode control,the constant on time control of fly-buck converter with and without ripple injection techniques has been simulated in PSPICE. Then,a comparative study on different control strategies of fly-buck converter such as voltage mode control, constant on time control with and without ripple injection techniques has been performed in terms of settling time, ripple content in output voltage etc.