Control of Fourth-order Buck-Boost Converter

This work proposes a fourth-order buck-boost converter which can suitably be used for applications pertaining to point of load converters. It provides the buck-boost conversion features along with improved profile of the source current and hence lower source current ripple content. Establishment of the elaborate time-domain analysis is also done for understanding the performance traits exhibited by the proposed converter along with converter component design equations. The proposed converter control scheme yields two different circuits for which the corresponding state-space models are derived, and small-signal analysis is performed to obtain the relevant transfer functions. Using these transfer functions obtained, a digital voltage-mode controller has been designed. To demonstrate the buck-boost conversion along with low source current ripple profile, a 36 Watt, 50 kHz laboratory prototype converter is designed to test the proposed converter's power supplying capacity at constant load voltage. A 24 V battery input voltage, 15/36 V as load voltage is considered in the experimentation. The effectiveness of the performance of the proposed converter in terms of reduced source ripple content, voltage buck-boosting feature is performed on simulation and also validated experimentally.