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Under the condition of high input voltage and high power, the switch losses are unbalanced for three-level neutral point clamped( 3L-NPC). It causes that the power of 3L-NPC is limited and many NPC topologies are derivated. In order to optimally select NPC topologies and modulation strategies, modulation strategies and switch loss distribution of four 3L-NPC topologies (Diode-clamped NPC, active NPC, stacked NPC and active-stacked NPC) are analyzed. A 5 kW unified prototype of NPC topologies is developed for efficiency tests. Theoretical analysis and experimental results indicate that there are mainly four modulation strategies for NPC topologies with different configuration of zero-level freewheeling path. Appropriate NPC topologies and modulation strategies can not only balance the switch losses, but also keep the same efficiency, which lays the foundation for improving the capacity of inverters. [ABSTRACT FROM AUTHOR]