Review on Four-level Converter

Compared with three-level and five-level converters, four-level converters have achieved a good balance on the number of components, stress, voltage balancing control, etc. Thus, the four-level converters have important research significance in medium and low voltage and high-power applications. Three types of four-level converter topologies and their voltage balancing modulation strategies are comprehensively reviewed. The concept of “four-level = two-level + three-level” is proposed to guide the improvement and innovation of four-level converter topology and voltage balance modulation strategy. At the same time, the research on four-level power module packaging has also emerged and is developing towards engineering application. The application research of four-level converter is relatively weak, mainly manifested in: the commutation loops of different four-level converters are still unclear, and the corresponding circuit layout methods need to be explored urgently; existing capacitor voltage-balancing modulation strategies mostly focus on voltage-balancing control itself, but rarely pay attention to its negative effects; there is little research on four-level power module packaging, and low parasitic parameters and low thermal resistance four-level power modules need to be explored urgently. Finally, a perspective is provided on the research directions and application prospects of four-level converters.