Design and control of a compensated submodule testing scheme for modular multilevel converter

Modular multilevel converters (MMCs) for high power applications may contain over a thousand submodules. In situations 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 have been developed to allow individual submodules to be tested without a complete MMC system. This paper presents a new submodule testing scheme that builds on a recent development to increase testing capability. The architectural approach is introduced along with design and control techniques. A prototype test platform, designed to test submodules with 400 V rated voltage and 14 A current, has been built and tested. It is shown that the output characteristics of the tested submodule (submodule capacitor voltage, electro-thermal characteristics of power switches etc.) are very close to what it would be in a complete MMC system.