An Adaptive Local Measurement-Based Fault Detection Method Proposed for Offgrid Small-Scaled Low-Voltage DC Microgrids

A DC microgrid (MG) has been proven to be a suitable and flexible platform to include many DC-power-generating renewable-energy resources such as photovoltaic (PV) systems, energy storage devices such as batteries, and loads in such a way that the microgrid can be properly operated at the islanded mode. To achieve the smooth operation and control, the protection system development is one major concern of DC microgrids. This paper presents an adaptive local measurement-based fault detection method proposed for off-grid low-voltage DC (LV) microgrids. This proposed method protects source and load branches in the standalone DC microgrid by using local measurements of current and voltage to detect and clear DC faults. This scheme is developed to detect pole-to-pole faults by calculating the first- and second-order derivatives of the current under transient operations and to identify the pole-to-ground faults based on over-voltage characteristics at the positive or negative line of the DC MG. The proposed fault detection scheme is validated on an off-grid PV-battery-contained MG testbed under differently staged fault tests. Experiment-based results show that the selected protection system detects P2P and P2G faults within a few microseconds of its inception and is adaptable to ungrounded or high-impedance-grounded and small-sized LVDC MGs.