A Novel Fault-Tolerant Topology for MVDC Grids Interface of Photovoltaic Generation Systems

Input-independent and output-series dc-dc converters are able to collect photovoltaic (PV) energy into a medium voltage dc (MVDC) grid without the aid of a low voltage dc (LVDC) bus, thus reducing primary power losses and hardware costs. However, in this series structure, a short-circuit fault at some of the LV ports can cause the whole system to fail, and a short-circuit fault at the MV port can easily damage the equipment. In this article, we propose a new fault-tolerant structure that can effectively solve the above problems. During an LV fault, the LC branch connected between adjacent submodules (SMs) can transfer energy and support the capacitive voltage of the faulty module to ensure that the system continues to operate stably. In the case of an MV fault, the fault-tolerant structure is blocked and the SM capacitors is reversed into the fault circuit, thus reducing the fault current quickly. The proposed structure and operating principle are verified through experiments.