|Iq| Added flux weakening strategy for the rotor flux oriented control of a sinusoidal PWM VSI-fed induction motor

In a conventional field oriented control of induction motor the rotor flux is assumed to be constant so that the torque is controlled by controlling the q-axis current only. In field-weakening region the rotor flux is decreased to achieve a very high rotor speed, as a consequence the available torque is reduced. In the other hand, to produce a maximum torque the rotor flux should be generated as much as possible. In this paper, a novel, simple field-weakening strategy, which provides a maximum torque capability for a sinusoidal PWM VSI-fed induction motor drive, is presented. The purpose of proposed strategy is to add the absolute q-axis current to d-axis current reference so that proper flux and torque for any given torque-producing current reference are produced automatically. The maximum torque when it is required can be obtained over the entire field-weakening region without using machine parameters or special control strategy. A saturated sinusoidal PWM is used which limits the amplitude of the inverter voltage references. As an advantage, the effective output voltage as seen by the motor is boosted. Simulation and experiment results verify the performance of the proposed method.