Because of its controlled power factor and no commutation failure

current source converter (CSC) made up of reverse-blocking IGCTs (RB-IGCTs) offers broad application prospects in the field of HVDC system. Valve voltage and power operating range as the most important operating characteristics should be paid attention to but they are always contradictory. First

the relationship between valve voltage and modulation index is obtained. In particular

valve voltage of converter under the three typical modulation methods is compared

analyzed

and verified. Second

with the help of the independent control strategy and coordinated control strategy of both ends

power operating ranges of the three modulation methods are comprehensively analyzed and compared. Third

in order to solve power coupling at a low active power

the improved coordination control strategy at both ends in this paper is proposed and the relationships among active power

reactive power

DC current and phase angle difference are given in detail. Finally

a 500 kV/3 kA simulation system was built in PSCAD/EMTDC to obtain comparison results of the key operating characteristics of CSC under different modulation methods and the converter can realize unity power operation under random active power after adopting the improved coordinated control strategy

and DC current does not decrease to zero

verifying effectiveness of the coordinated control strategy.