The doubly-fed induction generator(DFIG) unit can obtain active power reserve by overspeed load shedding to participate in frequency modulation, but due to the minimum speed limit of DFIG, it may cause serious secondary frequency drop when speed is recovered. To solve this problem, a frequency modulation strategy is proposed based on bidirectional DC/DC converter and supercapacitor energy storage. Firstly, based on the traditional overspeed load shedding and frequency modulation principle of DFIG, the causes and consequences of secondary frequency drop are analyzed. Then, combined with the operation characteristics of the supercapacitor and the DFIG grid-side converter, the supercapacitor is connected in parallel to the DC bus of the DFIG back-to-back converter through the DC/DC converter interface, and the DFIG grid-side converter collaborates with the energy storage characteristics of the supercapacitor to participate in frequency modulation, effectively avoiding the secondary frequency drop and achieving good frequency modulation effect. Finally, the effectiveness and superiority of the proposed method are verified by simulation.