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In this paper, a rotor position estimator for the sensorless permanent magnet synchronous motor (PMSM) is developed. The proposed approach exploits the time-scale separation between the electrical and mechanical time constant of the PMSM to formulate a linear observer. The observer produces accurate rotor angle estimates in steady-state and transient, and is attractive for electric propulsion applications due to its independence from mechanical parameters such as load torque, inertia, and friction. The sensorless strategy is well-suited to the nonsaturating slotless PMSM, but the demonstrated robustness of the observer to modeling uncertainties allows for application to slotted construction as well. Experiments are conducted to confirm the effectiveness of the proposed approach.