Improved Amplitude Differential Protection Scheme Based on the Frequency Spectrum Index for Distribution Networks With DFIG-Based Wind DGs

With the ever-increasing integration of wind power into the distribution network (DN) in the form of distributed generations (DGs), the optimal application environment for the conventional three-stage overcurrent protection no longer exists. Meanwhile, a majority of advanced protection schemes cannot be implemented due to the lack of voltage information and weak communication conditions in DN. As the most typical wind-based DG used in the DN, the doubly fed induction generator (DFIG)-based DG is focused in this paper. First, the frequency and amplitude characteristics of the fault current supplied by a DFIG-based DG are studied. Then, the amplitude differential protection (ADP) scheme is described using the weak-infeed characteristics of the DFIG-based DG. Furthermore, the frequency spectrum index, which is constructed based on the different frequency characteristics of DFIG-based DGs from synchronous generators, is introduced as a regulator factor to further improve the sensitivity of the ADP. Since only the current amplitude information is needed and the strict synchronization of the sampling data at the two ends of the line is not required, the proposed scheme is easy to implement under the limited hardware conditions in present DN. The simulation results show that the proposed scheme has a high sensitivity to the internal faults and has absolute selectivity for external faults, especially under the existing DG permeability rules.