Proposal of DC Ground Fault Detection and Interruption Method in the Ungrounded Photovoltaic Array

摘要

Here, we propose a new method for detecting and interrupting DC ground fault in an ungrounded PV (photovoltaic) system. In the conventional method that has been adapted, the fault current is monitored through the distribution resistors to detect the DC ground fault, and the circuit is interrupted by using the electrical switch. However, in this method, the power loss always occurs due to the distribution resistors. In addition, there was a possibility of fire and difficulty in switching off the DC circuit due to the arc generation by the use of the electrical switch. In contrast, the proposed method monitors the voltage difference through distribution capacitors instead of distribution resistors to determine the abnormality. In addition, when the DC circuit is interrupted, the generation of DC arc is minimized by using the power semiconductor switch instead of the electrical switch. Simulations and experiments have been carried out to verify the advantage of our proposed DC ground fault detection and interruption method. Furthermore, the most optimized capacitance of the distribution capacitors is decided through calculation with comparison of the capacitor discharge time. The most suitable power semiconductor switch is also selected by comparing the cutoff speed and the conduction loss according to the type of power semiconductor switches.