High voltage direct current (HVDC) power transmission systems constitu
te an important application of power electronics technology. This arti
cle presents a new method to control the HVDC converters by modified s
eries-connected bridges to give a reduction in both harmonic generatio
n and reactive volt-ampere absorption for the rectifier and inverter m
odes of operation. Moreover, a voltage control scheme is proposed whic
h uses by-pass thyristor valves connected to tapping points on the sec
ondary windings of the transformer for one bridge with the other one o
perating as a conventional bridge. Fast and continuous control of the
DC voltage are possible using the proposed scheme without the conventi
onal on load-tap changer on the converter transformer. (C) 1997 Elsevi
er Science S.A.