Comparison of Different Neutral Point Balance Strategies Applied to Three-Level DFIG System

When the rotor-side converter (RSC) in the doubly-fed wind power generation system adopts the three-level structure, the neutral point voltage (NPV) is difficult to balance. In this paper, two types of average neutral point current (NPC) models in the three-level converter (TLC) are summarized. Symmetric SVPWM and virtual SVPWM based on space vector are analyzed. CBPWM with zero-sequence voltage injection and changing duty ratio CBPWM (CDR-CBPWM) based on carrier wave are investigated. CDR-CBPWM is simplified for application. The effects of symmetric SVPWM and simplified CDR-CBPWM applied to RSC are compared through simulation.