Unified Direct-Flux Vector Control for AC Motor Drives

This paper introduces a unified direct-flux vector control scheme that is suitable for sinusoidal ac motor drives. The ac drives considered here are induction motor, synchronous reluctance, and synchronous permanent-magnet (PM) motor drives, including interior and surface-mounted PM types. The proposed controller operates in stator flux coordinates: The stator flux amplitude is directly controlled by the direct voltage component, while the torque is controlled by regulating the quadrature current component. The unified direct-flux control is particularly convenient when flux weakening is required since it easily guarantees maximum torque production under current and voltage limitations. The hardware for control is standard, and the control firmware is the same for all the motors under test with the only exception of the magnetic model used for flux estimation at low speed. Experimental results on four different drives are provided, showing the validity of the proposed unified control approach.