2026/05/21 by Peng Zhang, Hao Xiao, Guoju Zhang +6
Engineering · #Multilevel Inverters and Converters #Microgrid Control and Optimization #HVDC Systems and Fault Protection
paper · doi:10.1109/tpel.2026.3695514
Achieving zero-voltage switching (ZVS) for parallel neutral-point-clamped (NPC) converters under high switching frequency and high power conditions is highly desirable for improving efficiency and power density, but remains challenging without auxiliary resonant circuits. In parallel converter systems, the circulating current between parallel legs provides an additional control degree of freedom that can be exploited to establish ZVS conditions. This paper proposes a software-based ZVS strategy based on variable phase-shift control for two-parallel T-type NPC converters. By actively regulating the circulating current between parallel legs, the inductor current is shaped into a quadrilateral waveform, enabling ZVS turn-on operation while maintaining a strictly constant switching frequency. Based on accurate prediction of the circulating current within one switching cycle, the phase-shift angle required to satisfy the ZVS condition over the line cycle is analytically derived. The proposed method effectively decouples the three phases and is applicable to both single-phase and three-phase systems. Experimental results obtained from a laboratory prototype validate the feasibility and effectiveness of the proposed strategy.