A hybrid cascaded converter applicable for UHVDC transmission and feeding to load centre

摘要

This paper proposes a new kind of hybrid cascaded converter for the UHVDC systems connected to load centres. The cascaded converter is formed by the MMCs in seriesparallel connection. When the cascaded converter is applied to the UHVDC system as the inverter, the system will combine the merits of hierarchical connection with asynchronous interconnection so as to strengthen the receiving system and makes the power distribution of the receiving system more flexible. The structure of the cascaded converter is introduced in detail. The control strategy is proposed. The specific operating modes and the strategy to switch operating modes are studied in detail, for which a certain amount of power transmission can be guaranteed when one of the sub-converters quit operation. Finally, a hybrid UHVDC system based on cascaded converter is built in PSCAD / EMTDC. The simulation verifies the availability of the system and control strategy. The results indicate that the cascaded converter has a good availability in UHVDC system feeding in intensive receiving systems.