A nine-pulse line-commutated converter for six-wire bipolar HVDC transmission

Commitment to decarbonization and pursuit of sustainable energy goals have accelerated the utilization of renewable energy resources where the electrical grid would have to transmit massive amounts of carbon-free power via the high- voltage network along transmission corridors operating at or nearing capacity. Constructing new transmission lines is significantly challenging due to regulatory restraints and public opposition. Alternatively, expansion of existing transmission corridors can be accomplished by converting the HVAC system into HVDC system. This paper employs a 9-pulse line-commutated converter (LCC) to transform the commonly adopted double circuit HVAC into a six-wire bipolar HVDC transmission system. Compared to equivalently rated 6- and 12-pulse LCCs, the 9-pulse LCC topology reduces the size of converter station by employing fewer thyristor valves. The principle of operation and mathematical analysis of the 9-pulse LCC are explained in this paper. The implementation of 6-wire HVDC transmission system using 9-pulse LCCs is presented and validated using MATLAB simulations for 100kV, 960MW system. A quantitative comparison between 9-pulse LCC-based HVDC system and 6- and 12-pulse counterparts is also provided to highlight the pros and cons of the suggested system.