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Due to the saliency of the IPMSM, the model-based adaptive observer used in the sensorless control is nonlinear and difficult to analyze. With the extended EMF concept, the model though becomes partly linear, the extended EMF dynamic itself is very complicated making the application of an adaptive full-order observer troublesome. This problem is eliminated with a fictitious permanent-magnet flux model newly proposed in this paper for the IPMSM, because it converts the IPMSM into an equivalent SPMSM. The new model is simple, approximately linear and allows the adaptive observer algorithm to be applied easily. Also, the EMF induced by the fictitious magnet flux is exactly the fictitious EMF of the phasor diagram of the synchronous machine's two-reaction theory found in electrical machine textbooks. The initial rotor position can also be estimated easily from this fictitious EMF which always points in the d-axis at standstill. A novel sensorless scheme based on the proposed model is constructed, and its stability conditions are derived analytically to give design guidelines. Experiment results are given to verify the theoretical results.