Analysis of Neutral Point Balancing Scheme for Back-to-Back Converter in PMSG-Based Wind Energy Conversion Systems

For the high and medium power level grid integration of permanent magnet synchronous generator (PMSG)-based wind energy conversion systems (WECS), the industry utilizes back-to-back multilevel converters. The three-level neutral point clamped (NPC) converter among them, is a popular choice due to its advantages, such as lower voltage stress, reduced switching losses, and improved power quality. However, practical NPC-based back-to-back converters often suffer from neutral point voltage imbalance, which results in significant ripple in the grid current and torque of PMSG-based WECS. This research paper focuses on the a zero sequence voltage (ZSV) injection method for carrier-based pulse width modulation of a three-level NPC back-to-back converter, aiming to mitigate above issues and discusses the different mode of operation based on ZSV injection on machine side converter and grid side converter. This paper also concludes that the phase current from the converter side with higher magnitude has a greater effectiveness in achieving neutral point balance when utilizing the zero sequence voltage (ZSV) method. If ZSV is injected into both side of back-to-back converter, it will give better result for neutral point balancing for low and high modulation indices. The efficacy of this method is presented using simulation study.