HVDC CONVERTER USING SELF-COMMUTATED DEVICES

A three-phase bridge for a high-voltage direct-current (HVDC) converte r which uses auxiliary (bypass thyristor valves connected to tapping p oints on the transformer secondary windings has been previously descri bed. The performance is enhanced by using self- or force-commutated de vices for these valves, and three different schemes are examined, Expe rimental tests on a laboratory model validate the theoretical results, Fast and continuous control of the de voltage is possible with a typi cal reduction of 20%-30% of the reactive volt-ampere (VAR) absorption compared with a conventional scheme. An additional feature of the sche me is that the transformer tap changer could have a reduced range with fewer taps or even be eliminated.