Series capacitor compensated AC filterless flexible LCC HVDC with enhanced power transfer under unbalanced faults

This paper introduces significant performance enhancements to the ac filterless LCC HVDC by including fixed series capacitors at the primary side of a converter transformer. In terms of technical performance, 1) the amount of active power that can be transmitted is increased by more than 60% compared with ac filterless LCC HVDC, especially under severe unbalanced fault such as single-phase fault (most common fault in power systems); 2) the required voltage level of the controllable capacitor for Commutation Failure (CF) elimination is reduced by more than 70%, which leads to considerable reductions of the associated costs and losses. In terms of economic performance, due to the reduction of the required voltage from controllable capacitors (hence, the number of power electronic devices), the cost of the proposed converter station is lower than that of the ac filterless LCC HVDC. Theoretical analysis is presented to illustrate the performance enhancements and select the size of the series capacitor. Simulation results for various kinds of faults and cost analysis are presented to validate the technical and economic performances of the proposed method. Comparisons are made with ac filterless LCC HVDC. Finally, various practical issues and possible solutions are discussed.