Unidirectional Hybrid Multilevel Rectifier Family for MV/HV Applications: Analysis and Comparative Evaluation

Medium voltage (MV) and high voltage (HV) rectifiers demonstrate lower cost and volume as well as reversal power protection compared to the bidirectional counterparts in the unidirectional ac/dc applications, such as HVdc transmission, MVdc shipboard system, subsea oil and gas production power systems, etc. Traditional modular multilevel converter (MMC) is good candidate, but suffers from large number of submodules (SMs) and capacitor size. Recently, the hybrid multilevel rectifiers (HMRs) consisting of the HV diode and MMC structure have evolved and gained significant interests. The HV diode could replace some SMs in MMC, implying improved power density and efficiency. In this article, three typical HMR topologies are selected, and each of them uses a different configuration and offers unique advantages. Therefore, this article illustrates the operation principles, and gives the comparative performance evaluation of these HMRs based on key metrics such as device number, capacitor energy storage requirement, and semiconductor losses. In this way, the favorable working conditions of these HMRs could be identified, and the most suitable applications for each configuration could be suggested. The simulation as well as the experimental results are provided to validate these HMRs. Overall, the presented analysis can provide a point of reference and a useful framework for the future developments of HMRs.