HVDC Flexible is a new HVDC transmission technology, based on a voltage source converter (VSC). It makes use of insulated gate bipolar transistors (IGBTs) instead of thyristors for power conversion between AC and DC.

By switching the IGBTs of a voltage source converter in a defined manner, HVDC Flexible generates a controlled output voltage, the magnitude and phase angle of which can be changed rapidly and flexibly. As a result, HVDC Flexible allows for independent and fast control of active and reactive power.

In comparison to classic HVDC, the most outstanding features of HVDC Flexible are high controllability and flexibility, which lead to a number of potential advantages and applications.

HVDC Flexible provides an effective solution for wind farm integration, inparticular for offshore wind farms with a transmission distance over 50-100km where an AC cable technology is not feasible.

The reactive power controllability of HVDC Flexible can also be used to adjust the AC network voltage and therefore contribute to an improved power quality.

Other benefits associated with HVDC Flexible include black start capability, firewall against disturbance, inherent STATCOM functionality, low environmental impact, etc. Due to its superior technical features, HVDC Flexible has a wide range of applications:

• Renewable energy integration
• Supply of offshore loads
• In-feeds to city centres
• Multi-terminal systems
• Feeding into passive networks
• Grid interconnection and power