Overcurrent protection for inverter-based distributed generation system

Microgrids can provide various economic and environmental benefits but their implementation poses great technical challenges in control, protection and energy management. One of the most important technical aspects in microgrids is distribution system protection. This paper proposes an overcurrent protection strategy for microgrid consisting of only inverter-based distributed generation (IBDG) in islanded operation mode. On the basis of protecting semiconductor devices from damage once a short circuit fault occurs at the distribution line, a “short circuit impedance versus fault current (Z_f-I_f)” droop mechanism is introduced in the current-limiting controller to imitate the characteristic of power system short circuit current, which benefits the adoption of conventional overcurrent protection principle. Through using the microprocessor-based relay, a two-segment current protection algorithm is applied to guarantee the selectivity, rapidity and reliability of the protection system. The proposed protection method can provide a reference for the future microgrid protection. Experiments have been carried out to verify the feasibility of the proposed scheme.