A Pilot Protection Method for Active Distribution Networks Based on Improved Fréchet Distance

The integration of inverter-interfaced distributed generations (IIDGs) has modified the fault characteristics of active distribution networks (ADNs), substantially affecting the range, sensitivity, and reliability of conventional single-ended protection. Conventional current differential protection (CDP) and existing wave form similarity-based protection methods suffer from poor tolerance to transition resistance and rely on simulations or field experiences for setting threshold values. To address these problems, this paper proposes a pilot protection method based on improved Fréchet distance by analyzing the differences in amplitude-phase characteristics of short-circuit currents during internal and external faults in ADNs with IIDGs. This method fully considers the physical significance of applying Fréchet distance to power-frequency current waveforms, offering a short operating time, high tolerance to transition resistance, and strong resistance to synchronization errors. Furthermore, a compensation criterion based on the positive-sequence current amplitude of the virtual T-connected branch is established to handle the impact of multiple unmeasurable T-connected branches. PSCAD simulations verify the effectiveness of the proposed method under different fault conditions and demonstrate its improvement over existing methods. Finally, a RTDS-based hardware test platform is used to further verify the developed differential relay prototypes based on the proposed method.