For full-speed sensorless control of surface-mounted permanent magnet synchronous motor (SPMSM), this paper proposes a hybrid sensorless control scheme that combines I/F control with a nonlinear flux observer. In the low-speed region, I/F control is utilized to ensure stable startup and reliable operation. In the medium- and high-speed regions, a nonlinear flux observer together with a phase-locked loop (PLL) is introduced for rotor position estimation. To address the common switching oscillation problem in hybrid control strategies, a current fusion switching method based on PI control is proposed. Furthermore, a linear extended state observer (LESO) is integrated with the current fusion switching method to form a composite switching method. Simulations and experiments are conducted to evaluate the switching performance of both methods. The results show that both proposed methods achieve smooth transitions between control strategies, while the composite switching method exhibits superior performance during the transition process.