Abstract:With the rapid growth of industrial and residential electricity consumption in rural and mountainous areas, under-voltage issues are becoming significant and particularly prominent in some periods due to seasonal load and population migration. It is extremely difficult to achieve a balance between input and benefit when considering adopting traditional transformation measures to solve the above problems. Therefore, two types of grid transformation measures, AC-DC series/parallel connection, are proposed to solve under-voltage issues owing to excessive power supply distance. Firstly, this paper introduces basic situations of two low-voltage distribution networks (LVDNs) before the two-type transformations, and analyzes the problems of the traditional transformation measures. Secondly, the two the two-type transformations of AC-DC series/parallel connection are introduced in detail from three aspects: construction scheme, converter equipment and equipment installation. Moreover, the effectiveness of the AC-DC series/parallel connection schemes is verified by analyzing the laboratory test data and applications, and the advantages and disadvantages of the two-type transformations are analyzed. Finally, the effects of the the two-type transformations and the future development direction are summarized.