A Pulse Width Alternating Modulation Strategy for Three-Level Buck-Boost Converter

The three-level buck-boost(TLBB) converter is suitable for scenarios with a wide input voltage range and high voltage levels. However, conventional soft-switching modulation strategies face the problem of losing soft-switching when the duty cycle is large. This paper proposes a pulse-width alternating modulation strategy. By alternating the modulation of two switching sequences over two cycles, this strategy ensures the existence of the reverse current freewheeling stage across the entire input voltage range, achieving soft switching throughout the entire range. Additionally, it leverages the advantage of having more degrees of freedom to optimize the RMS value of the inductor current, resulting in a simplified calculation method for modulation parameters. Finally, a 300W prototype was built to verify the theoretical analysis.