A grid-tie inverter includes a power circuit and a control circuit coupled to the power circuit. The power circuit has an input terminal for coupling to a DC power source and an output terminal for coupling to an AC power grid. The control circuit is configured to perturb an AC output current of the power circuit a first time and detect a first change in an AC output voltage of the power circuit without shutting down the power circuit, perturb the AC output current of the power circuit a second time and detect a second change in the AC output voltage of the power circuit, and shut down the power circuit in response to detecting at least the first change in the AC output voltage and the second change in the AC output voltage. Example embodiments and related methods of controlling grid-tied inverters are also disclosed.