Improved Testing Capability of the Model-Assisted Testing Scheme for a Modular Multilevel Converter

Modular multilevel converters (MMCs) for high-power applications may contain over a thousand submodules. In work such as submodule design or innovation to build a full system with as many levels to test the submodule is time consuming and costly. To solve the problem, testing schemes are being developed to allow an individual submodule to be tested without a complete MMC. This paper presents a new submodule testing scheme that builds on a recent development to improve the testing capability. The improved structure is introduced along with design and control techniques. A design example of a test platform to test SMs with 2000-V rated voltage is introduced, which only requires a 545-V dc supply. The voltage testing capability is increased by more than five times when compared with the original scheme. In addition, simulation results show that the proposed method can offer better current tracking accuracy than the original with the same parameter settings. A prototype test platform, designed to test submodules with 400-V rated voltage and 14-A current, has been built and tested experimentally in order to verify the design.