Research Of Hybrid MMC With DC Blocking Capability And Multiterminal Hybrid Multilevel Converter

The large-scale distributed power integration, included distributed generation, energy storage device and electric vehicles, will significantly change the grid structure, and influence the security and stability of power grid operation. As the tache between grid and distributed power, multilevel converter has been widely used;especially the emergence of the high performance multilevel coverter provides opportunity for large-scale distributed power interconnection. Future power grid will be presented as smart grid with function of energy storage, in which high performance multilevel coverters are adopted as architecture, and a large number of distributed generationsare connected to grid. However, with the development of the flexible HVDC and distributed power supply technology, some problems such as dc-fault blocking of HVDC and multiterminal converter for distributed power integration are increasingly serious. In order to solve above two problems, the paper proposed two kinds of hybrid multilevel converters, included hybrid MMC with dc-fault blocking capabilityand multiterminal hybrid multilevel converter. Furthermore, the operational principle, output voltage modulation and dc capacitor voltage balancing of these converters were discussed thoroughly in the paper.Firstly, in order to obtain the dc-fault blocking capability of HVDC, three hybrid MMC topologies, included hybrid MMC with asymmetrical arms, hybrid MMC with ac side cascaded H-bridge cells and hybrid MMC with dc side cascaded H-bridge cells, were proposed, and their operational principle were described. In view of hybrid MMC with asymmetrical arms, its PSC-PWM and dc capacitor voltage balancing method were researched. In view of hybrid MMC with ac side cascaded H-bridge cells, its hybrid modulation, two energy balancing methodof cascaded H-bridge cells included amplitude modulation and phase-shift modulation, and dc capacitor voltage balancing method were researched. In view of hybrid MMC with dc side cascaded H-bridge cells, its hybrid modulation, energy balancing methodof cascaded H-bridge cells through PI feedback convtrol, and dc capacitor voltage balancing method were researched. The validity of theproposed hybrid MMC topologies and their control methods were verified by simulation, and simulation results showed that the proposed converters had good dynamic characteristic and dc-fault blocking capability.Then, in order to solve the mutliterminal conveter problem of distributed power integration, two hybrid multilevel convertertopologies, included nine-switch hybrid converter with ac side cascaded H-bridge cells and hybrid MMC with nine scitch groups, were proposed, and their operational principle were described. In view of nine-switch hybrid converter with ac side cascaded H-bridge cells, its hybrid modulation was researched. In view of hybrid MMC with nine scitch groups, its PSC-PWM was researched. The validity of the proposed hybrid multilevel converter topologies and their control methods were verified by simulation.Finally, three application architectures of hybrid MMCs applied in flexible HVDC, included monoplar system, bipolar system, and tripolar system, and the precharge of the dc capacitors and dc-fault blocking process were discussed. Then, application architectures of hybrid multilevel converters applied in integrating distributed power to dc or ac grid were introduced, and the independent operation and complement operation of distributed power supplies were disscussed. The presented application architectures had great significance for applying the proposed hybrid multilevel converters in smart grid.