Fault ride through strategy of inverter-interfaced microgrids embedded in distributed network considering fault current management

This paper presents a fault ride through (FRT) strategy specific for a microgrid (MG) with an inverter-based interface (IB-MG) to maintain power exchange with distribution networks during network faults or disturbances. The fault current injected by IB-MG is controlled by its back-to-back converter interface. Besides guaranteeing the power quality of local loads in MGs during faults, the proposed IB-MG FRT could realize the fault current management (FCM) ability - instead of using a fault current limiter - to maintain the short circuit current level in a dense-load network. As the traditional three-phase FRT techniques conducted on the double synchronous reference frame are no longer applicable on IB-MG FRT, especially for unbalanced faults, a newly developed reference current calculation method conducted on the stationary reference frame is adopted and modified. By changing the six control variables - amplitudes and phases of the three-phase currents - based on the information of the fault voltages and the fault currents from the host network, IB-MG FRT could achieve multiple effects: (1) controlling instantaneous energy flow between the MG and the distribution network; (2) limiting the short-circuit current increase; (3) improving the MG system power quality. The application range of the proposed FRT strategy is also discussed. A 27 kV distributed network connected with a 5 MW IB-MG system was built in the MATLAB/Simulink software environment and the proposed IB-MG FRT strategy was demonstrated under the different unbalanced fault scenarios.