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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.

Wind-Energy systems based on permanent magnet synchronous generators (PMSG) offer attractive advantages due to the higher reliability and power density. Considering the uncertainty influence of wind speed, PMSG with the traditional control method has poor-dynamic performance. Therefore, the Maximum Wind-Energy Captured based on the Inverse-System (MWECIS) method is proposed to improve the control precision and speed tracking rapidity of PMSG. In this paper, the inverse system is illustrated according to the conventional PMSG systems, and two systems (inverse system and PMSG system) are cascaded to obtain a decoupled pseudo-linear system. The proposed MWECIS method contributes to present a linear control law for PMSG system. Compared with the tip–speed-ratio control based on proportional–integral​ (TSR-PI) method, the proposed MWECIS method shows the better dynamic performance such as quickly and stably speed tracking ability. The simulation and experimental results verify the effectiveness of the proposed method, which could achieve the maximum wind-energy capture.