A study on high-efficiency floating multi-terminal power flow controller for next-generation DC power networks

DC microgrid has been drawing much attention in recent years. In DC microgrid, introduction of renewable energies to demand sides possibly causes power imbalance and reverse power flows on feeders. These problems cause increase of distribution losses and voltage rises in feeders. To overcome these problems, a power flow control method among multiple DC feeders (nodes) is required. We have studied bidirectional power flow controller (BPFC) based on a bidirectional buck-boost converter. It realizes power flow control by intentionally generating voltage difference between two terminals. Furthermore, BPFC has been extended to multi-terminal power flow controller (MTPFC) that realizes power flow control among multiple DC nodes. However, output voltages of BPFC and MTPFC are excessively higher than minimally required voltages for realizing the power flow control. That leads to unnecessary increase of conversion capacity of the circuit, and therefore seriously deteriorates the efficiency. Then, we studied a novel circuit structure, floating bidirectional power flow controller (F-BPFC). F-BPFC outputs the voltage just equal to the minimally required voltage for realizing the power flow control. Therefore, it is able to be implemented with low conversion capacity, and significantly improves the efficiency. In this paper, to realize high-efficiency power flow control among multiple DC nodes, we extend F-BPFC to multi-terminal cases. We call it, floating multi-terminal power flow controller (F-MTPFC). We study the power flow control by using F-MTPFC with introduction of a novel control method. The effectiveness, feasibility, and efficiency of F-MTPFC are validated by experimental studies.