Analytical formulation of the direct control of induction motor drives

The direct control of inverter-fed induction motor drives imposes the desired stator flux amplitude and electromagnetic torque into the motor in a closed-loop way without the intermediary of current loops and the employment of a shaft sensor. In this paper a theoretical formulation of the direct control is provided by expressing in an analytical manner the action exerted by the inverter space vectors on the stator flux amplitude and the electromagnetic torque of an induction motor. From the equations describing this action the influence of the operating conditions on the control action are evaluated. Graphical plots concerning a commercial drive help to discuss the results. A review of the induction motor and voltage inverter equations written in terms of space vectors and of the direct control concept open the paper