“During the search for the maximum acceleration phase of the Shanghai Soft X-ray Free Electron Laser (SXFEL), the RF output amplitude of the Microwave Low Level (LLRF) system will oscillate, affecting the stability of the device. Experts have developed vector modulator (VM) correction technology based on multi parameter estimation to stabilize the output amplitude of microwave power sources, reduce crosstalk between amplitude and phase loops, and provide a solution for the stability of SXFEL devices.”