VOLTAGE CONTROL OF MODIFIED SERIES-CONNECTED HVDC BRIDGES

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.