Design aspects of hybrid HVDC system

Hybrid high voltage direct current transmission (Hybrid HVDC) is a new type of HVDC technology developed in recent years. It combines the characteristics of large-capacity and low cost of the line commutated converters (LCC) and non-commutation failure and dynamic reactive power support of the voltage sourced converters (VSCs) in one HVDC system. It has technical advantages in the fields of unidirectional power transmission and in the application of improving the stability of multi-infeed HVDCs, giving it broad application prospects. This paper defines the basic form of hybrid HVDC first and discusses the characteristics and challenges of different hybrid HVDCs. Then, it analyzes the matching characteristics between LCC and VSC in the station-station hybrid HVDC, studies the key technologies, such as VSC topologies and control strategies for clearing the DC overhead line faults, and introduces the key technologies for analyzing and suppressing the high-frequency resonances between VSC and the power grid. In this paper, using the Wudongde UHV multi-terminal HVDC as an example, the proposed key technologies are analyzed and verified.