A protection scheme for active distribution network based on the cooperative control of inverter-interfaced distributed generators

Due to the existence of bidirectional fault currents in active distribution networks (ADN), a key issue of its protection is how to identify the fault direction. In traditional power systems, the positive sequence fault component (PSFC) based protection schemes are widely used, since they have good performance under different types of fault. However, due to the diversity of voltage variants and the influence from low-voltage ride-through (LVRT) requirement, the PSFC impedance angle of an inverter-interfaced distributed generator (IIDG) is difficult to determine. To solve this problem, this paper proposed a solution based on the cooperative design of the IIDG fault control strategy. Within a few power cycles after the fault occurs, each IIDG is controlled to output a specific positive sequence current according to the voltage variant. In this way, the PSFC impedance angle of IIDG is fixed to a given value under any fault scenario, thereby ensuring the applicability of PSFC-based protection in ADN. On this basis, the fault direction identification method and trip logic for the protection device are proposed. The effectiveness of the proposed method is verified by Matlab simulation results. The PSFC impedance angle of IIDG stabilizes at the desired value, and the output current of IIDG is always limited within a safe range during the whole process. Based on the sampled signals in the second power cycle after the occurrence of a fault, the protection device can use the PSFC-based criterion to accurately determine the direction of the fault.