An active protection scheme for islanded microgrids

The paper proposes a relatively simple active protection strategy incorporating controllers of the inverter for islanded microgrids dominated by inverter based distributed generators (IBDGs) that can overcome well-understood shortcomings in traditional overcurrent protection schemes applied to weak islanded systems. During a fault, the scheme identifies that a fault has occurred and instructs each IBDG in the islanded microgrid to inject specific harmonic components in conjunction with fault current; relays in the network can subsequently detect the presence and location of the fault based on the injected combination of harmonic components. The coordination of relays is achieved through definite time settings, hence communication between the protective relays is not required to operate the scheme. Furthermore, the scheme categorises the protective relays into two groups to isolate the faulty section effectively to cater for bidirectional fault current flow - this is described fully in the paper. The paper presents the structure of the proposed protection scheme along with injection strategy through the control of IBDGs. Different fault scenarios are presented using a realistic microgrid model so that effectiveness of the proposed scheme can be demonstrated in terms of detecting, identifying the faulted section and isolating the fault to ensure dependability, security and selectivity of the microgrid protection scheme.