Injected Harmonic Feature Based Protection Scheme for Active Distribution Networks With High Proportion IIDGs

In distribution networks with a high proportion of inverter-interfaced distributed generators (IIDGs), the fault ride-through control strategy of the inverter affects the output current of IIDGs, causing limited amplitude and time-varying phase. This hinders the effectiveness of traditional protection schemes in safeguarding active distribution networks. To address this issue, a fault protection concept involving “active harmonic injection of IIDGs, harmonic layer establishment of the distribution network, and feature difference construction of internal and external faults” is proposed in this paper. Based on this concept, initially, the amplitude characteristics of actively injected harmonics are examined for both active lines equipped with IIDG interfaces and passive lines lacking interfaced IIDG. Following this analysis, protection criteria are established, taking into account the discrepancies between the two types of branches during fault occurrences. To boost system security and complete the protection strategy, the impedance at various frequencies is used for backup protection, making protection process more reliable. Especially, the designed main protection scheme exploits harmonic current differences between adjacent lines, enabling protection with minimal communication bandwidth, balancing efficiency and effectiveness. The proposed protection scheme is validated through MATLAB/Simulink simulations, considering various scenarios such as different fault resistances, fault locations, connection of nonlinear loads, failure of main protection and disconnection of some IIDGs. These simulation results demonstrate the effectiveness of the proposed protection scheme.