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A novel sensor-less position detection scheme for surface-mounted permanent magnet synchronous motor (SPMSM) at standstill and low speed is investigated in this paper. For synchronous motor's sensor-less drive, there is phase error between the synchronous reference frame and the estimated synchronous reference frame. High frequency voltage signal is injected into the estimated d-axis voltage, and the position can be demodulated from estimated q-axis current due to the small salient-ratio caused by saturation. High frequency model of the motor is analyzed with projective geometry between the estimated synchronous reference frame and the synchronous reference frame. The complex mutual inductance and stator voltage need not to be introduced. Feasibility of the proposed scheme is verified with experiments with a sample motor.