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The correlation effect between cogging torque and torque ripple of an interior permanent magnet synchronous motor is analyzed in this paper by considering magnetic saturation in the core. Cogging torque is generated because of the reluctance variation between rotor magnets and stator teeth which are independent of any current. By contrast, torque ripple is generated because of the reaction field and by inputting currents such as cogging torque. However, the motor, having high cogging torque, does not always generate high torque ripple because of the magnetic saturation effect in the core. Therefore, extracting cogging torque component from torque ripple at rated torque generation should be conducted by considering magnetic saturation effect. The technique used to extract cogging torque from torque ripple is proposed by analyzing relative permeability in the core via finite element method.