Thank you! The problem has been solved. I'm building a simulink simulation diagram and a two-stage photovoltaic grid-connected power generation system. Because of the existence of power grid, there is second harmonic. After that, the harmonic is filtered by adjusting the PID parameters of BOOST stage. The cutoff frequency of the outer loop voltage loop needs to be set very low, and the last group of 5Hz can filter the harmonic, and the simulation effect is good. There is a ready-made notch filter in simulink, but I don't know how to set it. If it is programming, I will call the M file, but I can't. Not with elip. Thank you very much. I didn't land today. I'll give you extra points next time.