The sensorless control strategy is a commonly used motor control strategy. To solve the problem of the traditional sliding mode observer’s oscillation during the operation of permanent magnet synchronous motors (PMSM), a piecewise elliptic function is proposed in the paper. Combined with an improved integral type non-singular terminal sliding mode observer based on the extended state model, further suppresses the oscillation phenomenon of sliding mode and the phase delay generated by filters. A normalized phase-locked loop is proposed to address the issue of bandwidth changes in traditional phase-locked loops during motor speed regulation. Experiments show that the proposed scheme has the advantages of high observation accuracy, good dynamic performance, and low chattering in the static stage.