Model-Based Voltage Quality Analysis and Optimization in Post-Fault Reconfigured N-Level NPC Inverter

This article proposes a model-based voltage quality analysis and optimization method for post-fault reconfigured N-level Neutral Point Clamped (NPC) inverter. It is found that the voltage quality of post-fault reconfigured multilevel inverters (MLIs) has significant degradation which could cause issues in critical applications. To analyze and solve the voltage quality problem, existing voltage quality and mathematical analyses of MLIs were reviewed. Significant limitations of existing voltage quality analysis methods and shortages of existing mathematical analysis were found. Thus, a suitable mathematical model of N-level NPC inverter is proposed in this article to accurately describe voltage quality of a reconfigured N-level NPC inverter. The mathematical model is validated by simulation and experimental results and used for voltage quality analysis. In addition, based on the accurate mathematical model and results of voltage quality analysis, an optimization method is proposed to alleviate the voltage quality degradation of post-fault reconfigured N-level NPC inverter. A five-level NPC inverter and a reconfiguration method were used as an example to illustrate the proposed optimization method. Experimental and simulation results validate the effectiveness of the proposed optimization method.