Space Vector Modulation for Three-Level NPC Converter With Neutral Point Voltage Balance and Switching Loss Reduction

Abstract

This paper investigates the different control objectives, such as loss reduction, neutral point (NP) balance and noise reduction of the space vector modulation (SVM), for the three-level neutral point clamped (NPC) converter. A detailed loss model and simulation model is built for quantitative loss and NP voltage ripple analysis. An improved SVM method is proposed to reduce NP imbalance and switching loss/noise simultaneously. The coordinately selected small vectors consider both the NP charge and the pulse sequence so that the minimized NP ripple and switching events are guaranteed in one switching cycle. In addition, the switching events between switching cycles are also considered to reduce the total switching loss. This method ensures an evenly distributed device loss in each phase leg and also a constant system efficiency under different power factors. The control result for NP balance and loss reduction is verified by using both a simulation model and an experimental prototype on a 200-kVA three-level NPC converter hardware.