Multiport Converter With Independent Control of AC and DC Power Flows for Bipolar DC Distribution
Chatumal Perera, John Salmon, Gregory J. Kish
Abstract
A multiport ac-dc converter topology is proposed that offers bidirectional power transfer capability between the two dc ports and the ac port. The decoupling of power flows can be exploited as a pole voltage balancing mechanism to accommodate unbalanced dc side loads in bipolar dc distribution systems. The proposed topology gains bipolar operation by using two three-phase two-level voltage-sourced converters connected in a differential fashion with a center-tapped transformer. The analysis shows that no penalties are incurred in terms of increased power ratings for either the grid interface transformer or the semiconductors; only access to the center point of the converter side winding is required. A control scheme for the topology is proposed with the ability to independently control power flows between the different ports. Both the topology and control scheme are validated by extensive simulations and experiments.