Research On Topologies And Reliability Analysis Of Modular Multilevel Converter With DC Fault Clearance Capability

Modular Multilevel Converter based High Voltage Direct Current (MMC-HVDC), which has received attention by engineering and academia, has a broad prospects for development due to its unique technical advantages. Starting from structure of MMC, DC fault blocking capability index (DFBCI) is proposed to evaluate DC fault ride-through capability based on the analysis of different sub-modules. A method to search sub-modules is proposed, and clamp single sub-module (CSSM) is proposed by this method. Operating principle of CSSM is analyzed, and simulation verification is performed. Configuration of sub-modules in hybrid MMC is proposed by taking both reliability and economy into account.First, working principles of half bridge sub-module (HBSM), full bridge sub-module (FBSM) and clamp double sub-module (CDSM) are analyzed. DFBCI is proposed to evaluate DC fault ride-through capability of MMC quantitatively.Second, on the basis of difference of HBSM, FBSM and CSSM, a searching approach of sub-modules is proposed. Clamp Single Sub-module (CSSM) can be get by using this approach.Next, the DC fault current champing mechanism of CSSM is studied. Comparing with FBSM, CSSM has the same DC fault clamping capability with less devices. Simulation results in PSCAD/EMTDC verify the effectiveness of CSSM.Finally, configuration of different sub-modules in hybrid MMC is analyzed on the condition of steady state. Giving consideration to reliability and economy, the optimal redundancy configuration of sub-modules is proposed. Calculation results verify the feasibility of the proposed approach.