In the sensorless control of aero engine starting power generation system, it is difficult for the algorithm based on the voltage fundamental model to identify the rotor position at zero low speed, so the starting system usually adopts the strategy of combining position open-loop starting and sensorless method. In this paper, the research content of motor starting control includes current-to-frequency ratio (I_F) control and switching closed-loop algorithm. In this paper, taking the traditional V_F method as a breakthrough, the I_F method is further studied, and a high-efficiency and high-stability I_F starting method is proposed, and the instantaneous power feedback adjustment algorithm is introduced on the basis of open-loop I_F control, and the current vector is adjusted through the instantaneous power feedback of the motor. The direct switching from open-loop to closed-loop introduces current and speed disturbances that affect the start-up process. Based on the PMSM mathematical model, the mathematical formula of satisfying the voltage continuity is deduced by using the current state feedback decoupling, and it is proved that maintaining the stator voltage continuity of the motor can effectively suppress the speed disturbance in the switching process. Experimental results verify the good performance of the start-up and switching control algorithms.