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A large number of photovoltaic grid-connected operation will cause the decline of system frequency response performance, and the identification of system time-varying inertia is helpful for photovoltaic to participate in the setting of frequency regulation parameters. In view of this, an optimization strategy of photovoltaic frequency regulation control parameters was proposed by identifying the equivalent inertia and damping. Firstly, based on the equivalent model of photovoltaic grid connected system, the prediction error method (PEM) was used to identify the equivalent inertia and damping of the system. Then, the state space prediction model of frequency response of photovoltaic grid connected system was further established, and the parameters of primary frequency modulation coefficient and virtual inertia coefficient of photovoltaic frequency modulation control were optimized to ensure that the equivalent inertia and damping of the system meet the requirements of system frequency modulation. Finallly, the simulation model of three machines and nine nodes standard system was built based on Matlab / Simulink. The simulation results show that the proposed method can effectively improve the frequency characteristics of photovoltaic grid-connected system and improve the flexibility of photovoltaic frequency regulation, so that the lowest frequency and the maximum frequency change rate increase by 0.1 Hz and decrease by about 50% compared with the traditional primary frequency regulation.