Multi-layer fault-tolerant control of MMC for shipboard MVDC power system

Abstract

In this paper, a three-phase modular multilevel converter (MMC) with four-winding medium frequency transformer (MFT) is proposed to improve the power density and fault-tolerant capability of shipboard DC power system. First, a MMC-based MVDC on-ship sub-system with double independent LVDC buses is presented. Then the modeling and analysis of the MMC integrated with four-winding MFT under normal and fault-tolerant conditions are derived. Further, the corresponding multi-layer fault-tolerant control scheme is designed to ride-though MMC sub-module (SM) fault and leg fault. With the proposed individual-phase circulating current control, the MMC can maintain normal operation with the faulty SM bypassed. With system structure and modulation reconfiguration, the MMC is able to work with the faulty leg bypassed. Finally, the effectiveness of the proposed architecture and fault-tolerant control scheme is verified by the experimental results.