System-Level Power Loss Evaluation of Modular Multilevel Converters

For modular multilevel converters (MMCs), reducing the design margin while fulfilling the reliability target in the design stage is challenging. To address this challenge, a system-level power loss evaluation is essential. Although many studies have discussed the power loss calculation of the MMC, most of them focus on the power losses of semiconductor devices while ignoring the impact of capacitors, arm inductors, and ac transformers. Therefore, this paper proposes a system-level power loss evaluation for MMCs from the perspective of reliability assessment. The power loss model covers switching devices, capacitors, and inductors. All the power loss calculation is starting from the active/reactive-power set points of the converter at the point of common coupling (PCC), where the converter is connected to the AC grid. The leakage inductance of the ac transformer is also considered. In addition, in order to meet the needs of long-term reliability assessment, the proposed power loss calculation is computation-efficient and easy to update parameters. The theoretical analysis has been verified by a full-scale MMC in simulations and a down-scale platform by experiments.