Multimode Smooth Transition Technique for Three-Level Cascaded Noninverting Buck–Boost DC–DC Converter

In this article, a new three-level cascaded noninverting buck–boost converter (TL-CNIBB) is proposed, which has a superior adaptation for a wide-range voltage input of renewable energy access. Firstly, the operation principle is analyzed for TL-CNIBB and it is mainly divided into four modes, namely buck mode with the voltage ratio below or above 0.5, boost mode with the voltage ratio below or above 2. Due to multilevel and multimode features, several fundamental issues are required to be settled, such as a dead zone between buck mode and boost mode, capacitor voltage unbalance on both sides, and subharmonics at the edge of modes. For dead zone and capacitor voltage balance problems, a systematic control strategy is proposed, and four kinds of smooth transition technologies are proposed to deal with different cases. Furthermore, to avoid the chattering and subharmonics at the edge of modes, a modified hysteretic transition method is proposed. Finally, a prototype of TL-CNIBB system is constructed, and the experiments are carried out to verify the performance of the proposed system with high viability and flexibility.