To settle the voltage-loop PI controller of flux weakening (FW) control causes large oscillations at deeper FW regions, A deep FW control method for the voltage loop of the feedback super-twisting sliding mode controller (FSTSMC) compensated by the fast sliding mode disturbance observer (FSMDO) is proposed. Firstly, a hyperlocal model of the voltage ring in the complex environment is constructed. On this basis, FSTSMC based on the feedback super-helix algorithm is designed, which can effectively suppress the jitter of the system in the FW control region. Then, the FSMDO is designed to observe the disturbances in the voltage loop and feed the results to the FSTSMC. It improves the stability of the system in FW regions. Finally, the method is compared with PI and STSMC, which proves the method has better steady-state performance and anti-interference ability in the deep FW region.