Interlinking converters in application of bipolar dc microgrids

This paper investigates two converter topologies, including neutral-point diode-clamped (NPC) and Vienna converters, to be employed as an interlinking converter in bipolar dc microgrid. Since bipolar dc microgrids are subjected to severe voltage unbalance, the interlinking converters should be able to perform voltage-balancing function at their dc-link capacitors. In addition, they should exchange power between upper and lower terminals of bipolar dc microgrid. It is shown that the voltage-balancing function can not be integrated into the control system of the NPC converter, so the parallel connection of a voltage balancer is suggested and the pertinent voltage control system is designed. Moreover, a Vienna converter with modified topology and switching algorithm is proposed to perform voltage-balancing function. The viability of NPC and Vienna converters is evaluated using MATLAB software.