The independent microgrid has weak inertia and strong power fluctuation. In case of encountering large power disturbance

insufficient frequency modulation capacity of main power supply source is likely to cause instability of system frequency. In order to improve the transient frequency stability of the independent micro grid

a kind of fast frequency modulation strategy considering secondary frequency modulation is proposed. Firstly

the frequency operating interval of the independent microgrid under the primary/secondary frequency modulation of the main power supply is analyzed and the control behavior and frequency characteristics of the main power supply under large disturbance are further studied through simulation. On this basis and consideration of the influence of secondary frequency modulation

the frequency modulation operation threshold value is dynamically calculated

the constant power control power supply output power is adjusted quickly and emergency frequency modulation for the auxiliary power supply is performed on the basis of micro grid coordinated controller so to improve stability of transient frequency. Finally

the effectiveness and feasibility of the strategy are verified by RTDS hardware in the loop test.