What is flexible DC transmission?

Flexible DC transmission is a new transmission technology based on voltage source converter, self-switching device and pulse width modulation (PWM). This technology has the advantages of supplying power to passive network, no commutation fault, no communication between commutation stations and easy construction of multi-terminal DC system.

The converter stations at both ends of the flexible DC transmission system are composed of converter stations, converter transformer equipment and converter reactance equipment. Variable structure control is the core part of variable structure control, which consists of current bridge and DC capacitor. Flexible DC transmission has strong technical advantages in island power supply and capacity expansion and transformation of urban distribution network.

Extended information

Unlike HVDC based on phase-controlled converter technology, the converter in flexible HVDC is voltage source converter (VSC). Its biggest feature is the use of turn-off devices (usually IGBT) and high-frequency modulation technology.

active power and reactive power can be controlled independently by adjusting the magnitude of converter outlet voltage and the power angle difference between converter outlet voltage and system voltage. In this way, active power transmission between two AC power grids can be realized by controlling the converter stations at both ends.

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