An advanced service provided by the Smart Transformer (ST) is the decoupling between the Medium Voltage (MV) and Low Voltage (LV) grids. In the LV side, the ST can modify the waveform's frequency in order to interact with the droop controllers of the local generators to control the power demand among the sources without affecting the MV grid. However, most of the existing controllers for power converters cannot guarantee good performances under variable frequency conditions. To address this issue, a frequency adaptive control scheme based on the Fractional-Order Repetitive Control (FORC) as well as Frequency Locked Loop (FLL) is proposed in this paper. This proposed scheme provides fast online parameter tuning capability in order to be highly adaptive to variable frequencies, and it can be implemented either in a ST converter or in distributed generators. In this work simulation and experimental results are provided to demonstrate the effectiveness and advantages of the proposed scheme.