Space Vector Based Capacitor Voltage Balancing for a Three-Level NPC Traction Inverter Drive

A dc-link capacitor voltage balancing topology based on virtual space vector is proposed for traction drive application in the field-weakening region. Four different strategies are implemented and their duty ratios are individually derived. The system is then connected to an interior permanent magnet synchronous machine (IPMSM) generally used for traction applications. A comprehensive investigation on the capacitor voltage variation in the field-weakening region is studied and the main contributing vectors are identified. All the required duty cycles of the vectors are analytically calculated based on the three nearest available voltage vectors. All the four proposed strategies helped to minimize the neutral point potential fluctuation (NPPF) considerably in comparison to the earlier proposed schemes. The proposed scheme is then supported by the simulation and experimental verification with a 6.0-kW IPMSM.