Abstract:

Capacitor commutated converter （CCC） can compensate reactive power absorbed by converter through the transformation of the main circuit structure in traditional DC transmission system with appropriate capacitor, which can make the amplitude and phase of actual commutation voltage change, reduce the reactive power absorption by converter and the probability of commutation failure of the inverter-side, so as to improve the stability of DC system. However, with the above advantages, CCC DC system also has inherent defects. This paper firstly studied the mechanism and steady-state characteristics of HVDC transmission system whose rectifier side and inverter side were based CCC. The model was built with using PSCAD, and verified by simulation, whose results were compared with traditional DC transmission system. Secondly, this paper specially analyzed the characteristics of avoiding commutation failure, the recovery characteristics after a short single-phase fault, and the follow-up fault mechanism, for CCC DC transmission system, as well as studied the impact of series capacitor size on recovery process. The research results can play a great role for improving the dynamic characteristics of CCC HVDC transmission system and its further development.

Key words: capacitor commutated converter（CCC）, line commutated converter（LCC）, HVDC transmission, commutation failure, dynamic characteristics