Design of Twenty-One Level Modular Multilevel Converter Using a Three-level Submodule Block

In this paper, a modular multilevel converter of twenty one level is designed by using a three level submodule block. The submodule block can be half-bridge or full bridge. In a half bridge submodule block, the switching configuration is more efficient than the full bridge submodule block. But there is problem of DC fault current. Half bridge submodule block is not capable of blocking the DC fault current. In this paper, we have designed such kind of submodule block which is a combination of half bridge and flying capacitor. A capacitor which is floating with the half bridge circuit that is called flying capacitor. We have designed many modular multilevel converters of different levels using this submodule block but the twenty one level modular multilevel converter gives the best output. A simple control mechanism is implemented in this design. So, our proposed design of modular multilevel converter is simple and it shows better performance.