DC and AC ground fault analysis in LVDC microgrids with energy storage systems

When a front-end converter is used to interface the AC utility and a LVDC microgrid, combined options for AC and for DC grounding and connection between respective neutrals provide several possibilities. Two common configurations are either the ground connection of the transformer neutral point or of the DC negative pole. According to the selected grounding scheme, transient and/or steady-state zero-sequences DC fault current may flow during a ground fault in specific parts of the circuit. This paper considers the two common configurations and it deals with the ground fault analysis both on AC and DC side of the converter. Results show that, the value and path of ground fault current may be such that the converter is not able to limit and break the current: in these cases, fault protection has to be implemented by specific and innovative devices, such as static circuit breakers, to protect the electronic components.