A new current limiting strategy and fault model to improve fault ride-through capability of inverter interfaced DERs in autonomous microgrids

In this paper, new current limiting strategy is proposed to improve fault ride-through capability and moreover, a generalized fault model is presented for droop-controlled and directly voltage controlled inverter-interfaced distributed energy resources to be used in the protection studies. The previously reported fault models almost did not consider the effect of control system in depth. An improved hierarchical droop-based control scheme is presented which includes a complementary stabilizing control loop. Also, a brief review for reported directly voltage-controlled schemes is provided. Moreover, a current limiting strategy is proposed that can be implemented in different reference frames. As a special case, fault contributions of wind and solar units are investigated and special recommendations are provided. Finally, the presented fault model is analytically tested for three-wire and four wire inverter topologies and various types of faults and then verified by offline time-domain simulations in MATLAB/SIMULINK environment and thereafter, validated by the investigation through real-time digital simulations using OPAL-RT simulator.