Efficiency improvement on two-switch buck-boost converter with coupled inductor for high-voltage applications

With two controllable switches, the efficiency of the two-switch buck-boost converters can be optimised by adopting appropriate control schemes. Among the control schemes, when only one switch works at high frequency, losses of the converter can be reduced effectively, but the complicated control logic and compensation technique are needed for step-up/down smooth transitions; when both switches operate at high frequency, the efficiency of these converters are low for high-voltage applications because of the serious switching losses. In this study, the coupled inductor is introduced to reduce the switching losses of these converters for high-voltage application and an asynchronous control scheme is proposed to reduce the losses much more. Based on the designed prototype, theoretical calculation, experiment results and loss analysis are provided to compare the traditional converter adopting single-winding inductor and the proposed circuit with the coupled inductor. And the comparisons of the converter adopting coupled-inductor with the tradition synchronous control scheme and that with the proposed asynchronous control scheme are also presented. The analysis and experimental results show that the efficiency of the converter adopting coupled inductor with the proposed asynchronous control scheme is the highest one. Moreover, the smooth transitions between step-up and step-down are also guaranteed by the proposed asynchronous control scheme.