A versatile series-parallel-connected bidirectional DC power flow controller for HVDC and MVDC system

This paper proposes a transformer type dc power flow controller (DCPFC) based on stacks composed of sub-modules (SMs). The converter can perform dc power flow control independently on point-to-point as well as multi-terminal connection, which can be applied to either high voltage or medium voltage dc grids. In order to explain the operation principle, different operating states of the proposed DCPFC are analysed. With phase-shift modulation and the closed-loop current control, the proposed DCPFC can achieve bidirectional power flow regulation. Following the theoretical analysis of the proposed DCPFC, simulation results have verified the feasibility of bidirectional power flow control. A downscaled experimental prototype is also built to demonstrate the operation principle and performance of the proposed DCPFC.