Abstract
The introduction of an HVDC system into the trunk power supply system requires to transmit as much DC power as possible for improving the whole AC/DC system stability. Continued operation scheme of HVDC system which makes it possible to operate even under very low commutation bus voltage is adopted to cope with such system requirement. Further stability improvement can be achieved by adding damping control which modulates converter active and/or reactive power.
To take full advantage of these control effects, it is essential that HVDC system can maintain stable operation during the AC system faults and reclosing. Particular attention should be given to a repetitive commutation failure following the unbalanced AC transmission line faults. This paper first discusses the cause of the repetitive commutation failure when supplied with unbalanced AC system voltage based on an experiment using the CRIEPI's AC-DC Power System Simulator. Then a stabilization control scheme with an on-line extinction angle estimation is proposed and the effect is verified by digital simulation.
