三相四线系统三电平变流器谐波发射机理及抑制策略——中点电位波动和开关死区问题分析

The neutral-point clamped (NPC) three-level converter is extensively used in low-voltage distribution networks with distributed energy resources. In a three-phase-four-wire system, the DC bus neutral-point (NP) of a three-phase converter is commonly connected to the N-wire, creating a zero-sequence current path in the system. This configuration leads to output voltage distortions caused by DC NP voltage fluctuations and switching dead-time, and further causes harmonic emission from the converter itself. First, the coupling relationship between NP voltage fluctuations and output current is analyzed, laying a foundation for establishing a quantitative model of NP voltage fluctuations. Based on this model, an active filtering circuit control system for DC bus is designed to suppress both the NP voltage fluctuations and the induced harmonics. Then, the influence of switching dead-time under various operating conditions of the three-phase converter is investigated. A quantitative relationship between the switching dead-time and output voltage distortions is derived, guiding the design of a modulation wave compensation strategy for mitigating the harmonic emission caused by switching dead-time. Finally, simulation models and an experimental platform were developed to reproduce the harmonic emission issues of the three-phase converter, and results validated the effectiveness of the proposed scheme.