The load randomness of offshore oil platform leads to the increase of power grid frequency deviation, which puts forward higher requirements for power grid frequency modulation capability. With the development of energy storage technology, the application of large-scale energy storage device in the field of auxiliary frequency modulation of power grid has been developed, and the frequency modulation capability of power grid has been improved. In this paper, the component model of bidirectional converter and inverter is established, and the precise control of input and output power of the energy storage system is realized by using dual loop control strategy and PQ control strategy. The frequency variation in primary and secondary frequency modulation is simulated to verify the effectiveness of the control strategy.