Redundant Design of Modular DC Solid-State Transformer Based on the Long Term Reliability Evaluation

The solid-state transformer (SST) is promising to be applied in smart grid, traction systems and distributed generation systems, for its high efficiency, low costs and high controllability compared with line-frequency transformers. As the interface of future energy systems, the reliability of SST is of great importance. As a converter with modular structure, the redundancy design is one important measure to improve the reliability of SST. However, current redundancy designs are usually based on the reliability evaluation results obtained from the stable operation condition of SST, without taking the longterm mission profile of the converter into account. Besides, the aging of power semiconductor devices (PSDs) and capacitors are seldom considered while evaluating the reliability. In this paper, the reliability of the modular DC-SST for power distribution applications, including the long-term mission profile and aging of critical devices, is evaluated. An improved aging model of capacitors is also used. Moreover, the loss model of PSDs and capacitors that considers the number of modules is proposed in this paper as well. It combines the reliability evaluation result and redundancy design together, making the redundancy design of DC-SST more creditable.