Secondary frequency modulation method based on VSG in island state

The invention discloses a secondary frequency modulation method based on a VSG in an island state. The method comprises the following steps: calculating the instantaneous output power of a virtual synchronous generator (VSG) by using a PQ instantaneous power calculation unit based on a secondary frequency modulation method of the VSG in an island state; the fractional order PID unit collects the angular frequency omega of the VSG, and compares the omega with a preset angular frequency omega n to obtain delta omega; the delta omega serves as an input signal to be input into a fractional order PID unit to be corrected, and a correction value is multiplied by a parameter k to obtain a new signal omega k; inputting the omega k into an active loop unit to obtain an output signal, and performing three-phase voltage signal synthesis on the output signal and a signal output by a reactive loop unit; and finally, a pulse signal for controlling the inverter is generated through a voltage and current double-closed-loop c