Position estimators of surface permanent-magnet synchronous motors are often designed with local stability and thus may be unstable under a large estimation error. To overcome the risk of instability, a globally stable position estimator is proposed in this paper. The proposed estimator is derived from an alternative expression of the stator model, which has the rotor position as the only parameter inside. Stability analysis of the estimator and conditions for global stability are obtained without any approximation. Design rules for global stability, dynamic, and tracking performances are clearly given. All theoretical results are finally verified by experiment. Prachuab Iamsamang (Non-member) received a B.E. degree in electrical engineering from South-East Asia University, Bangkok, Thailand, in 1997, and an M.E. degree in electrical engineering from Chulalongkorn University, Bangkok, Thailand, in 2003, where he is currently working toward his Ph.D. in electrical engineering. He is currently an Officer in the Research and Development Department of Novem Engineering Co., Ltd. His present interests are in the areas of sensorless control of synchronous machines. 909 IEEJ Trans 13: 901-910 (2018) P. IAMSAMANG AND S. SANGWONGWANICH Somboon Sangwongwanich (Member) received a B.E., M.E., and Dr Eng.

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