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This paper proposes a gain scheduling method that improves the stability of grid-connected systems employing an LCL-filter. The

method adjusts the current controller gain through an estimation of the grid impedance in order to reduce the resonance that occurs

when using an LCL-filter to reduce switching harmonics. An LCL-filter typically has a frequency spectrum with a resonance peak. A

change of the grid-impedance results in a change to the resonant frequency. Therefore an LCL-filter needs a damping method that

is applicable when changing the grid impedance for stable system control. The proposed method instantaneously estimates the grid

impedance and observes the resonant frequency at the same time. Consequently, the proposed method adjusts the current controller

gain using a gain scheduling method in order to guarantee current controller stability when a change in the resonant frequency

occurs. The effectiveness of the proposed method has been verified by simulations and experimental results.