Operation characteristics of LCC-HVDC split-pole connected to power grids and its influence on control and protection system

Multiple LCC-HVDCs deployed at the receiving-end load center can aggravate the local power flow of power systems and lead to potential stability issues such as voltage concern, concurrent commutation failure, etc. To solve these problems, some literatures have proposed split-pole connection mode on the inverter side of LCC-HVDC. However, the mechanism how this connection mode reduces the risk of commutation failure and its influence on control and protection system have been seldom studied before. By deducing and applying the mathematic formula of the multi-infeed short circuit ratio (MISCR) for the LCCHVDC split-pole connection mode and comparing it with that of the conventional LCC-HVDC topology, this paper demonstrates that the split-pole connection mode can improve the voltage support capability of the receiving-end AC system. Then, the influences of the two split-pole access topologies on the LCCHVDC control and protection system are studied. Finally, based on the principle of MISCR, the paper establishes the electromagnetic transient model of a typical case of LCC-HVDC split-pole connection mode in PSCAD/EMTDC, analyzing its operation characteristics and proving the validity of the above studies by simulations. The work in this paper contribute to lay a solid foundation for the engineering application of LCC-HVDC split-pole connection mode in the Yongren-Funing HVDC project in Yunnan, China.