Improved field-weakening control for IFO induction motor

Generally, good transient response and high conversion efficiency of a field-weakened indirect field-oriented (IFO) induction motor drive are difficult to obtain simultaneously owing to their contradicted behaviors. Moreover, its operating performance is quite sensitive to the flux level, detuned effect, and parameter variations. An improved field-weakening control approach for an IFO induction motor drive is developed here. In the proposed method, the saturated magnetizing inductance is represented by a fitted quadratic polynomial of flux current. And the normal d-axis flux current command is composed of a no-load, a load-compensating, and a transient compensating component. The first one is represented by a third-order polynomial of rotor speed, which is estimated at no-load to consider the effects of nonlinear magnetizing inductance and the limitation of motor rated voltage. As for the latter two compensating current command components, they are utilized to further weaken the field such that current tracking performances during loaded cases and transient period can be improved. And hence the torque-generating capability is also enhanced accordingly. During steady-state operation, the slip angular speed command or the flux current command is tuned using the proposed approach to let the motor quickly reach the stable operating condition with better efficiency. Experimental results show that good dynamic responses and better energy conversion efficiencies can be simultaneously obtained by the proposed field-weakening control method.