In modern high-voltage direct current (HVDC) power transmission systems, electrical energy is transmitted at extremely high voltages, typically above 100 kV, to reduce current flow in transmission cables. Lower current levels help minimize energy losses and reduce the amount of copper required in conductors, which significantly lowers both system cost and weight.
Since individual power semiconductor devices cannot withstand such high voltage levels on their own, multiple devices are connected in series to achieve the required voltage rating. For higher power handling, devices are also connected in parallel. Together, these series and parallel arrangements form an HVDC valve, which is a key building block in HVDC converter stations.
In modern HVDC transmission systems, two main converter topologies are used: line-commutated current-source converters (CSC), which are based on thyristor valves, and self-commutated voltage-source converters (VSC), which are based on IGBT valves. Each valve consists of a large number of series-connected devices designed to handle the required DC voltage levels safely and efficiently.
Current-source converters using thyristor technology typically operate using a Graetz bridge configuration, enabling six switching operations per cycle. However, voltage-source converters based on IGBT technology have become increasingly preferred due to their superior control capabilities and flexibility in power system operation.
IGBT-based VSC systems allow independent and rapid control of both active and reactive power, improving overall grid stability and power quality. They also enable reactive power support at both ends of the transmission line, which provides greater flexibility in modern power network design and operation.
Another key advantage of IGBT-based HVDC systems is the reduction of passive components. Unlike older technologies such as GTOs, IGBT converters do not require snubber circuits, as the switching behavior can be controlled directly through gate drive voltage waveforms. This allows precise control of current rise rates and improves overall system efficiency.
In addition, IGBT-based systems help manage reverse recovery behavior of anti-parallel diodes without requiring additional snubber networks. The reduction of auxiliary components leads to lower system complexity, reduced cost, and improved reliability.
Overall, IGBT technology plays a crucial role in modern HVDC transmission systems by enabling efficient, flexible, and highly controllable power conversion, making it a key enabler of advanced electrical grid infrastructure.