3L-NPC AC-DC Power Converter Using Virtual Space Vector PWM with Optimal Switching Sequence Based on g-h Coordinate

This paper presents a simplified virtual space vector PWM (VSVPWM) by using g-h coordinate for three-level neutral-point clamped power converter applications. The VSVPWM is a very appealing modulation technique due to the fact that the neutral-point (NP) voltage will be strictly balanced during one switching cycle. Current VSVPWM needs more calculation than the traditional SVPWM due to use more switching states. It can be seen that all virtual space vectors have special position in 60-degree frame. Therefore, sector/subsector judgment and dwell time calculation of VSVPWM can significantly avoid trigonometry functions (sin/cos) in g-h coordinate. This will significantly simplify calculation workload and thus allowing for being used in higher switching frequency application areas. In addition, the optimal switching sequence is selected to reduce even-order harmonics which has a bad impact on NP balancing issues in three-level power converter system. Finally, the correctness and effectiveness of VSVPWM based on g-h coordinate are verified through simulation results.