An entirely different concept compared with the classical HVDC converter.
In the PWM bridge switching very fast between two fixed voltages creates the AC-voltage. The desired fundamental frequency voltage is formed through low pass filtering of the high frequency pulse modulated voltage.
VSC three phase converter
The PWM pattern and the corresponding power frequency voltage of a VSC converter
With PWM it is possible to create any phase angle or amplitude (up to a certain limit) by changing the PWM pattern, which can be done almost instantaneous. Hereby PWM offers the possibility to control both active and reactive power independently.
This makes the Pulse Width Modulated Voltage Source Converter a close to ideal component in the transmission network. From a system point of view it acts as a motor or generator without mass that can control active and reactive power almost instantaneously. Furthermore, it does not contribute to the short circuit power as the AC current can be controlled.