An equivalent power test scheme for modular multilevel converters (MMCs)

For modular multilevel converters (MMCs), it is important to investigate the electromagnetic and electrothermal performance of sub-modules for design validation and optimization. This paper presents an equivalent test scheme for sub-modules, which has the clear advantages of system simplicity and reduced facility requirements. Firstly, the detailed analysis on the output features of sub-modules demonstrates that submodules working in a real MMC system can be equivalent to a controlled voltage source, which consists of two independent components, the dc and ac components, respectively. Furthermore, the test circuit composed of two identical sub-modules is introduced and the corresponding control strategy is further designed to ensure the equivalence of the test scheme presented. Finally, the simulation and experiment results reveal that the sub-module behaviors under different operating conditions of MMC can be closely emulated with the proposed test scheme, which provides a convenient way to evaluate the reliability of sub-modules.