Neutral-Point Voltage Interactions on a Medium-Voltage DC-Link

The neutral-point-clamped (NPC) converter has been often used in power systems for various applications. A key difficulty with its application is the balancing of the neutral-point (NP) voltage. If this is not done correctly then harmonics can appear at the output voltage and overvoltages can cause device failure. Much research has been carried out to balance the NP voltage. However, investigations have mainly focused on single converters, without considering the interactions of the NP voltages of various connected NPC converters. Research has rarely examined the NP voltages under dynamic conditions. Herein, we present the study of the interaction of NP voltages of two converters connected via a medium-voltage DC (MVDC)-link. In addition, we examine the relationships between the NP voltages and the operation of the converters. Our results may help to improve the implementation of NPC converters to increasingly complex power systems. This will enable the connection of renewable energy sources and distributed generation, which require specific considerations of robustness and stability.