Adaptive Fault Detection for Grid-Forming Inverters

This work introduces a residual-based adaptive threshold for detecting faults in grid-forming inverters in AC microgrids islanded from the main grid. The inverters are modeled as a nonlinear system with one-sided Lipschitz nonlinearities and modeling uncertainties. The adaptive threshold response is evaluated using unwanted events such as busbar and sensor faults. An inequality for the upper bound on the l(2) norm of the residual is derived and used for designing the adaptive threshold. The upper bound is obtained via semidefinite programming with two linear matrix inequality constraints. In the numerical tests, we consider an islanded-mode AC microgrid with two grid-forming inverters, one grid-following inverter, and one synchronous machine with the governor and excitation control. Primary and secondary control layers regulate the operation of the inverters in the microgrid. The performance of our proposed adaptive threshold clearly edges over a fixed threshold method.