An Intelligent Protection Method for Multi-terminal DC Microgrids Using On-line Phaselet, Mathematical Morphology, and Fuzzy Inference Systems

In this paper, a new method for fault detection, location, and classification in multi-terminal DC microgrid (MTDC) is proposed. MTDC grids have expanded due to some issues such as the expansion of DC resources, loads, and aims to increase power quality. Diagnosing the types and location of faults is important to continue the service and prevent further outages. In this method, a circuit kit is connected to the grid. In fault time, the fault in the network is detected by passing the current through the connected kits and measuring the traveling waves derived from the fault current as well as applying it to a mathematical morphological filter. Determining the location of the fault is done using circuit equations and current calculations. Phaselet output and fuzzy inference systems are used to determine the type of faults. The presented method was tested in an MTDC microgrid connected to renewable and energy storages with many faults. The results show the ability of the proposed method. The error of the proposed fault location method is less than 7%. This method is resistant towards the change in sampling frequency (between 500 Hz and 50 kHz), fault resistance (up to 125 ohms), and loading (up to 120% of the nominal load); it acts very well in high impedance faults.