HVDC transmission system architectures and control - A review

High-voltage dc (HVDC) is an attractive alternative to conventional ac transmission for offshore wind farms as well as bulk power transmission application. This paper reviews different HVDC architectures and their control methods for systems based on both conventional line commutated converters (LCC) and new voltage-source converters (VSC). The reviewed system architectures include both point-to-point and multi-terminal connections, such as parallel and series systems. The control methods are introduced in a way that highlights their development and various practical considerations each new method was intended to address. Comparison of the different methods focuses on steady-state characteristics, as dynamic characteristics and stability have been treated separately in the literature for specific systems.