Power flow controlling devices: an overview of their working principles and their application range

The ongoing liberalization process causes an increase in international power flows, putting substantial strain on the transmission grid. This is especially a problem when unidentified power flows or loop flows are involved. At this moment, several congestion problems arise in the European grid. Controlling power flows is one way to extend the utilization of the current grid, without investments in new transmission lines, being problematic due to political, environmental and social considerations. In this respect, power flow controlling devices are rapidly gaining interest of utilities and transmission system operators (TSO). New devices are installed, and it is expected that their number will rise significantly in the near future. This paper provides an overview of the current available power flow controlling devices and their applications. Both electromagnetic transformer based solutions as the fairly recent power electronics developments are covered. Special attention is given to HVDC, both line commutated and voltage source converter based, as they are able to fully control the power flow. In a final part, the use of multiple controllable devices in a meshed grid is treated with special emphasis on the need for global control. As a conclusion different technologies are compared