An adaptive reclosing method for active distribution network based on multi-harmonic current injection by IIDG

• A phase-to-phase FNI method was established, which utilizes the phase variation trends of multi-harmonic response voltages. • A digital frequency divider was developed to achieve decoupling between fundamental and harmonic frequency controls. • An adaptive reclosing method with active fault characterization capability was proposed. The traditional auto-reclosing (AR) method based on fixed time delay cannot avoid blind reclosing on permanent faults. Moreover, with the increasing penetration of inverter interfaced distribution generations (IIDG) in the active distribution networks (ADNs), the method encounters significant challenges in properly setting the delay. The main reason is that it cannot actively identify the differences between transient and permanent faults. To realize the actively fault nature identification (FNI), an adaptive reclosing method for ADNs based on multi-harmonic current injection by IIDG was proposed in the paper. Firstly, the differences in response voltage characteristics between transient and permanent faults after the injection of the multi-harmonic currents are analysed. Subsequently, an additional control for IIDGs is designed to enable IIDGs to actively inject multi-harmonic current. Then, a FNI criterion based on the characteristics of response voltages, which result from the injected multi-harmonic currents, is established. On the basis above an adaptive reclosing method that accelerates reclosing for transient faults while reliably locking out for permanent faults. Through additional control of existing IIDGs in the network after a fault, the proposed method uses the injected multi-harmonic currents to achieve an adaptive reclosing correctly, eliminating the need for extra signal injection equipment. Furthermore, the proposed FNI criterion relies on local voltage information from PT, thus requiring no communication. Simulation and hardware-in-loop experimental results validate that under different fault scenarios, the proposed method can substantially reduce the power outage time during transient faults, while avoiding the risk of blind reclosing, which improving the reliability of the ADNs.