Fault protection analysis in low voltage DC microgrids with PV generators

Because of the multiple power sources involved, fault protection is one of the most critical issues in micro-grids. If a micro-grid including a PV installation is connected to the grid by means of a front end converter, multiple possible cases of fault may occur. It is a typical feature of such configuration that, depending on fault resistance and location, fault currents from the AC grid may pass unlimited through the converter and contribute to the fault. Most general purpose converters are not able to interrupt fault currents in all situations. A specific protection system is then required to ensure fault clearance and maintain safety. Two possible philosophies for such a protection system are described in this paper, one based on future solid state circuit-breakers, and one based on electromechanical devices complemented by front end converter design modification. Advantages and drawbacks are discussed.