Introduction

The distribution of power generation resources and main power loads in China presents an unbalanced and reverse distribution. More than 80% of power generation resources are located in the western and northern regions, and more than 70% of power loads are concentrated in the eastern coastal, and central regions. The development of large-scale energy resources and the demand for optimal allocation of resources nationwide determine that the power grid in China must develop long-distance and large-capacity power transmission channels. Many line-commutated-converter high-voltage direct-current transmission (LCC-HVDC) projects have been constructed in China. However, the conventional DC transmission technology has some problems, such as commutation failure risk, large reactive power consumption, the need to increase the capacity of the AC filter to suppress harmonics, the need for a certain strength of the AC system on the receiving side to provide commutation support, and the lack of black start capability. In addition, the ultra-high-voltage AC transmission technology also has problems of stability and reliability that are difficult to solve. This restricts its application in long-distance and large-scale transmission scenarios.