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The power fluctuation of distributed generation has a negative effect on the power quality, losses and operation safety, and a good solution is to mitigate the power fluctuation near the grid-connected point of this generation. A new method for mitigating grid-side power fluctuation by the grid-connected inverter itself is proposed in this paper. A certain capacity of Li-ion supercapacitor is used as the dc-link capacitor of the grid-connected inverter first, and then a dc voltage follow-up control of the grid-connected inverter is adapted to charge/discharge the Li-ion capacitor indirectly. Finally, the power fluctuation of the renewable energy generation is well compensated by the charge/discharge power of the Li-ion capacitor, and the grid-side power has been smoothed. Taking a PV generation system as an example, the simulation results show that the dc voltage follow-up control of the grid-connected inverter can effectively mitigate its grid-side power fluctuation.