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This paper presents a method of estimating the initial rotor position of a surface permanent-magnet synchronous motor without a position sensor. The estimation is performed by using the nonlinear magnetization characteristics of the stator core caused by the magnet of the rotor. This method is based on the principle that the d-axis current value for the voltage vector applied to the motor under some conditions increases as the voltage vector generated from the inverter approaches the N pole of the rotor. During the estimation process, the rotor is practically at standstill. The experimental results show that the average of the estimation error is ±3.8 electrical degrees.