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In this paper, a novel robust field-weakening control strategy is proposed for surface-mounted permanent-magnet motor drives to achieve fast dynamic response and minimum copper loss over four-quadrant operation regions. First, a closed-form solution of the maximum available torque-producing current is proposed for calculating the corresponding bounds in real time to achieve both fast response and automatic field-weakening control. Second, the partial field-weakening concept and the classification of ten operation regions for four-quadrant operations are proposed. It is seen that consideration of the stator resistance is crucial to achieve the fastest response. Third, a robust tuner based on the proposed virtual maximum phase voltage amplitude together with a minimum copper-loss controller based on the partial field-weakening concept is proposed to achieve minimum copper loss over the entire operating range. Fourth, a dc-link voltage sensorless control version is also proposed which is very useful in electrical vehicle applications. Finally, a digital-signal-processor-based prototype driver is also constructed to verify the validity of the proposed control strategy.