Active Neutral-Point Balancing of Three-Level Neutral-Point-Clamped Traction Inverters

Recently, electric vehicles have become an integral part of the global mobility system. As the battery voltage of the electric vehicles is a much-discussed topic, the high voltage technology shows several benefits, such as accomplishing the increasing on-board power demand and facilitating the wiring and connectors. For high voltage batteries, multi-level inverters can improve the output performance by reducing the harmonics. However, the asymmetric current stress of the dc-link capacitors can lead to new challenges. In this study, a three-level neutral-point-clamped inverter with a dc-link voltage of 800 V is investigated with regards to the neutral-point balancing. The self-balanced oscillation of the neutral-point voltage is analytically derived. An active balancing method is optimized to stabilize the neutral point.