Control of hybrid tripole HVDC based on LCC and F-MMC

In order to overcome some inherent defects of the conventional tripole HVDC, a hybrid tripole HVDC structure is proposed, which replaces the thyristor converters of pole 3 with the modular multilevel converters (F-MMC) based on cascaded full bridge sub-modules (FBSM). To increase the transmission capacity, a special current modulation is adopted. In order to meet the demands of the reactive power (voltage) balance, the DC current balance and the sub-module capacitor voltage balance in the transition process, the corresponding control strategies are also proposed. The performance of the proposed hybrid tripole HVDC structure is evaluated through time-domain simulation studies in PSCAD/EMTDC. The results show that a satisfactory response of the system can be achieved with the proposed control strategies.