In this article, the problem of distributed fault detection and isolation for single fault is considered for multi-agent systems affected by disturbances and communication delays. A bank of unknown input observers based on local information are constructed for distributed fault detection and isolation, and the sufficient conditions are presented to guarantee that the fault-detection residuals generated by unknown input observers satisfy [Formula: see text]. The logic of distributed fault detection is as follows: a agent can be declared as faulty when it's fault residuals exceed the threshold, and the fault residuals of its adjacent nodes are less than the threshold, declaring the existence of the fault.

This study addresses the output impedance model of the LCL-type grid-connected converter considering the dead-time effects and the digital control delay. The model shows that the digital control delay will affect the accuracy of the output impedance of the grid-connected converter, and the dead-time effects are only equivalent to superimposing a disturbance voltage on the original output impedance model. The derived output impedance model is verified by comparing it with the switching model in the PSIM simulation environment. The harmonic interaction between converter cluster and utility grid is modeled and analyzed based on the output impedance model. A combined harmonic suppression strategy is incorporated into every converter control scheme to suppress the harmonic interaction. Simulation results are presented to demonstrate the correctness of harmonic interaction analysis and the effectiveness of the proposed suppression strategy.

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