Design of a Digitally Controlled Four-Switch Buck-Boost Converter with Smooth Mode Transition

A digitally controlled four-switch buck-boost converter (4SBB) with a wide input voltage range, high power density, and high efficiency is designed and implemented with a new smooth mode transition methodology. Firstly, the problems occurring during mode transitions under varying input voltage have been investigated and identified through detailed simulation studies and the measurement obtained from an experimental prototype converter. The issues such as the instabilities in the control signal, the appearance of input voltage at the output without any regulation during the intervals called the dead zones, the fluctuations and harmonics at the output voltage, and the pulse skipping of switches have been identified as the major problems encountered during mode transitions. These problems have been seen to affect efficiency, regulation, and controller stability negatively. This study proposes a new smooth transition method with many advantages over the well-known techniques. With the proposed method, bringing these problems adverse effects to a practical minimum is possible. In addition to these achievements, an innovative solution has been developed for the issue of the inability to keep the top-side synchronous switch always turned on with 100% duty, which is faced in some gate driver chips using bootstrap technology. In conclusion, the superiority of the developed technology and transition method is demonstrated by comparing the results with the state-of-the-art techniques.