Quantitative analysis of the harmonic distribution characteristics of three-level grid-connected converters based on Alternative phase opposition Disposition (APOD) is conducted, which is to address the problems such as increased low harmonics for three-level grid-connected converters with unbalanced Neutral-Point Potential (NPP). The influence of each component of the traditional topology grid-connected current and filtering current on the NPP is derived, and the main factors influencing the self-balancing capability of the neutral-point are given. In view of the long self-balancing time of the traditional topology, an improved topology was supposed, in which the principle of taking parameters and the factors affecting the self-balancing time are analyzed in detail. Finally, the simulation results show that the improved topology can achieve fast self-balancing of the NPP under various operating conditions while ensuring the power quality of the grid-connected current, which is comparable to the speed of the traditional NPP control. The speed is comparable to that of traditional NPP control, meanwhile the NPP control algorithm and sensors can be eliminated, making it easy to implement and it has good economy and reliability.

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