Self-Circulating Testing Method for Both Rectifying and Inverting Submodules of Modular Multilevel Converter With Low DC Supply Voltage

This article proposes a testing method for multiple submodules (SMs) in a modular multilevel converter (MMC), along with its topology, control strategy, and basic design. The proposed testing method is capable of emulating the operating conditions of multiple SMs both in rectifying and inverting modes of the back-to-back MMC system. The configuration of the testing system significantly reduces the requirements for the dc supply voltage and is independent of the numbers of tested SMs. In the proposed testing approach, analytical equations are introduced in the control loop in order to emulate the dynamic mission profiles of SMs. The comparisons between the MMC system and the testing method in the simulations, as well as the scaled-down experimental setup, verify the validity and accuracy of the proposed testing approach.