HVDC Converter Station

An HVDC converter station is the facility at each end of a high voltage direct current link that converts alternating current to direct current, or back again. It contains the converter valves, converter transformers, AC and DC switchgear, filters, cooling and the control and protection systems that set how much power flows and in which direction. Every point-to-point HVDC link has at least two stations, and multi-terminal schemes have one at each connection point.

Two converter technologies dominate. Line commutated converters use thyristor valves, need a strong AC network at both ends and consume reactive power, so their stations include large filter and capacitor banks. Voltage source converters, usually in a modular multilevel design, use IGBT valves, control active and reactive power independently and can energize a dead network. VSC stations are more compact, which matters offshore, where the converter sits on a platform.

Converter stations account for a large share of an HVDC project's cost and lead time, and manufacturing capacity for valves, transformers and offshore platforms is concentrated among a small number of suppliers. Supply chain slots, framework agreements and standardized designs have become strategic issues for transmission operators planning offshore grids and long-distance corridors. Converter lead times can stretch over several years, so project schedules are often set by the supply slot rather than by permitting.

Station availability drives the economics of the link, so owners pay close attention to redundancy, spare transformer strategy and long term service agreements with the manufacturer. Siting is also a constraint: onshore stations need large plots near strong substations, and their location shapes where new generation, storage and large loads can connect.