Fast Diagnostic Method of Open Circuit Fault for Modular Multilevel DC/DC Converter Applied in Energy Storage System

This letter presents a fast open circuit diagnostic method for modular multilevel DC/DC converter (MMDDC), which is applied in super capacitor energy storage system. The proposed method is derived based on the analysis of submodule output characteristics under both normal and fault conditions. For MMDDC, different types of open circuit fault are reflected by the output voltage of submodule in certain operating modes, thus a simple and effective diagnostic method by the aid of a hardware circuit and a fast fault location algorithm is proposed. The hardware circuit is responsible for detecting submodule output voltage and its output result is transmitted to a processor to accomplish the final fault diagnosis along with drive signals. The proposed approach avoids complex mathematical operations and minimizes fault diagnostic time; moreover, it can achieve fault diagnosis under a wide super capacitor operating voltage range. Finally, the proposed diagnostic method is verified experimentally based on a laboratory-scale MMDDC energy storage prototype.