1.State Key Laboratory of Advanced Power Transmission Technology (State Grid Smart Grid Research Institute),Beijing 102209, China;2.State Grid Corporation of China, Beijing 100031, China;3.China Electric Power Research Institute, Beijing 100192, China

The flexible low-frequency AC transmission based on voltage source converters (VSCs) has the technical advantages of both AC and DC transmission, which is a new transmission technology worthy of in-depth study. Technical characteristics of VSC-based flexible low-frequency AC transmission are analyzed, and the typical topologies of the system are listed. For the offshore wind power transmission scenario, the power transmission capacity curves of typical cross-section submarine cables at different frequencies are calculated. Taking a project of China as an example, the economic comparison is carried out. The results show that the flexible low-frequency AC transmission technology has obvious advantages in the application of medium- and long-distance offshore wind power transmission. In addition, the application scenarios such as island interconnected power supply and onshore large-scale renewable energy power collection and transmission are also analyzed. The influence of frequency changes on the key performances of main transmission equipment such as high-voltage large-capacity AC-AC converters, transformers, circuit breakers and cables is analyzed. The further research work that needs to be carried out in the engineering application of flexible low-frequency AC transmission is systematically pointed out.