The role of HVDC in reducing carbon emissions

High-Voltage Direct Current (HVDC) is the most high-power application of power electronics. HVDC has been commercially available as a niche technology in power grids for 70 years, first using Line- Commutated Converters and, in the last 25 years, using Voltage-Sourced Converters. However, in the last five years the growth of HVDC has been spectacular, much of it associated with the large- scale integration of renewable energy sources. HVDC has been used for decades to connect remote hydro generating stations to load centres. More recently, HVDC allows offshore wind farms to be built far from shore, where the wind is stronger and steadier, beyond the maximum distance over which the power can be efficiently transmitted using AC cables. HVDC is now starting to be used for connecting large-scale solar parks to the grid. HVDC also allows long-distance interconnectors to be built between neighbouring power grids so that local fluctuations of renewable energy output can be smoothed out by aggregating power generation over a wider geographical area. With this growth comes new challenges. Two in particular will be discussed in the talk. The first concerns the transition from point-to-point HVDC links (the established practice)) to multi-terminal HVDC networks. The second concerns how the HVDC converters are controlled, especially in view of the fact that the growth of renewable energy sources means that power grids now contain far less rotating inertia in the form of synchronous machines than was the case 20 years ago. The first challenge involves new protection methods and new types of HVDC equipment, while the second involves new control algorithms for the HVDC converters. Both challenges make HVDC a fascinating and important topic for the industry.