Abstract: This paper uses super capacitor energy storage to assist photovoltaic units in frequency modulation,and proposes an energy storage frequency modulation control strategy suitable for the scene of frequency change caused by power fluctuation and fault disturbance. In this strategy,when the frequency is in the frequency modulation dead zone or the photovoltaic unit is in the fault stage,the photovoltaic unit will not participate in the system frequency modulation. In the recovery stage,when the frequency offset exceeds the frequency modulation dead zone or the fault is cleared,the energy storage system assists the photovoltaic unit to provide primary frequency modulation power or inertia support power to the power grid. After verification,the strategy comprehensively enhances the frequency stability of high proportion photovoltaic system.