DC grid power flow control devices

This chapter presents an overview of DC power flow control devices (DCPFCs) and the effects of DCPFCs on DC grids. There are mainly three types of DCPFCs to realize the flexible power flow control: DC transformers, variable series resistors (VSR), and series voltage sources (SVS). DC transformers are shunt connected devices, while VSR and SVS are series connected devices. The chapter describes the topologies of power flow control devices and provides generic modeling of DCPFCs for power flow calculation of DC grids and the sensitivity analysis. It presents some case studies using a five-terminal DC grid with these facilities and case tests to investigate effects of DCPFCs on a DC grid based on the CIGRE test system. The chapter also provides a comparison of DCPFCs. Comparisons of the three devices have been made in terms of the control flexibility, the power rating, and power losses.