The work aims to suppress the effect of harmonic signal, so as to extract more accurate rotor position information and improve the performance of packaging machine power system. A sensorless control strategy based on sliding mode observer, improved generalized second-order integral frequency locked loop and phase-locked loop was proposed and the ability of this method to extract the position information of the motor rotor was verified by Simulink simulation experiment. The method could effectively reduce the DC harmonic component and the 5th and 7th harmonic components in the back EMF signal, improve the purity of the fundamental signal, reduce the speed estimation error, and enhance the speed stability and reliability of the PMSM during operation. The static and dynamic experiments in Matlab/Simulink verify that the control strategy has better suppression effect on different order harmonic noise signals and improves the speed estimation accuracy of PMSM and the performance of packaging power system.