Research on Triple-Port MMC-Based PET Scheme Based on High Frequency Links Interconnection of Horizontal Sub-Modules

Abstract

Development of power electronic transformers (PET) has made DC power distribution a preferred solution for future electrical network expansion. This paper focuses on the PET solution connecting medium-voltage and low-voltage networks. A triple-port PET (TP-PET) topology based on modular multilevel converter (MMC) structure is proposed. Based on the traditional MMC, the horizontal sub-modules (SMs) are interconnected by high frequency links (HFL) of isolated four full-bridges (IFFB), which also forms a low-voltage DC bus. SM voltage fluctuation is an inherent problem of conventional MMC, which usually needs to be solved by large size capacitor. In this paper, the phase difference between SM fluctuating powers is used to achieve mutual cancellation, which significantly reduces the size of capacitor. Moreover, the cancellation process is completed automatically through interconnected channels, which simplifies the control of the system. This paper analyzes the structural characteristics of the proposed topology, HFL operating characteristics, triple-port power transmission characteristics and corresponding control strategy. Finally, the simulation results verify the correctness and effectiveness of the proposed topology scheme and control strategy.