The permanent magnet synchronous motor is A technique that monitors the third harmonic voltage to increasingly playing an important role in advanced motor obtain the rotor angle has been developed in [2]. This drives. An encoder or resolver attached to the shaft of the technique is applicable to the brushless dc machine with motor typically supplies the feedbacks required for motor trapezoidal back emf waveform, but is of little relevance to speed control. Many advanced motor drives can not tolerate the PMSM, which normally has a sinusoidal air-gap flux the use of these feedback devices because of reliability concerns . . . ' in a harsh environment, price, space and weight limitations. In distri to Tethrsin [3] implem a obsed this paper model reference adaptive system-based adaptive observer to determine the rotor angle. This observer, strategy has been used for speed estimation. In compare to however, was found to be sensitive to mechanical parameters previously developed methods in the literature such as: EKF, such as load torque, viscous and damping friction and neural networks and sliding mode control this method inertia-parameters that are often changing dynamically or are consumes less computational time and it is easy to implement in unknown. In [4], the dependency on the mechanical microcontrollers and DSP. In this proposed method the parameters is removed in an observer-based approach, but Popov's criterion is used for adaptive speed estimation. The the need for an electrical model of the machine remains. For validity of the proposed adaptive strategy has been verified by a salient rotor PMSM application, the position-dependent simulation and experiments, inductance variation can be monitored to derive the rotor angle. This method, however, is unusable for the many machines that are constructed with surface-mounted