Protection of Smart DC Microgrid With Ring Configuration Using Parameter Estimation Approach

In a smart dc microgrid, power electronic devices limit the current during fault and therefore, an overcurrent-based relaying scheme cannot provide required sensitivity and selectivity for such a system. For a dc microgrid with ring configuration having bidirectional power flow, the protection design is further complicated. For reliable supply to customers and to avoid unwanted disconnection of renewable resources, selectivity of a protection scheme is important. In this paper, using local voltage and current data, a least square-based technique estimates the parameter of the fault path, from which the direction of the fault is inferred. Using the direction of fault information of both ends of a line segment in a ring system, internal and external faults are discriminated for network protection. Using PSCAD/EMTDC simulations for a ring system, proposed method is tested for various fault situations including high resistance fault, close-in fault, signals with noise, and considering different modes of distributed generation operations. The proposed algorithm is also validated on a scaled-down hardware setup in the laboratory. The method is found to be more accurate compared to available technique.