Dynamic power control of three-phase multiport active bridge DC-DC converters for interconnection of future DC-grids

Dc grid technology is currently expanding from the high-voltage to the medium-voltage range and is expected to penetrate also low-voltage grids. For interconnection of these grids, dc-dc converters that enable a flexible and highly dynamic control of the power flow between different voltage levels are required. In the scope of this paper a highly dynamic power and current control of three-phase multiport-active bridge (3ph-MAB) converters is presented. The investigations are exemplified for a three-phase triple-active bridge (3ph-TAB) converter, i.e., a 3ph-MAB converter with three ports, which connects a medium-voltage dc grid to two separate low-voltage dc grids. Firstly, the complex relation between the power at the ports and the load angles is investigated and algorithms for on-line determination of the according load angles are derived. Secondly, the instantaneous current control (ICC), which is known from the dual-active bridge converter, is adopted for the triple-active bridge converter. Thereby, a highly dynamic current control with settling times of half a switching period is achieved. Based on these considerations, a closed-loop control structure is proposed which fully utilizes the highly dynamic behavior of the ICC. The theoretic analysis is verified by simulation for a 150 kW SiC MOSFET converter prototype with three ports and nominal port voltages of 5 kV, 380 V and 760 V.