In order to mitigate the harmonic voltage distortions caused by nonlinear loads in islanded microgrids, this paper proposes an enhanced adaptive virtual impedance control method which can achieve reduction of the harmonic voltage distortions at the point of common coupling (PCC) without feeder impedance information. A microgrid central controller (MGCC) is used to online estimate the equivalent feeder impedance in each branch using harmonic voltage and harmonic current to adjust negative harmonic virtual impedance through a triggering signal to mitigate PCC harmonic voltage. Compared with the other communication-based harmonic mitigation methods, the proposed method can greatly enhance the robustness against the communication delay and maintain the power sharing performance of unbalanced and harmonic power. Simulation and experimental results are provided to validate the proposed method.