Improved direct and inverse gamma models for vector controlled induction machines

This paper analyses equivalent circuit models for vector controlled induction motor for dynamic and steady-state operation analysis, that accounts for stator saturation and core loss effects. The circuits, denoted as Γ or inverse-Γ model, are simpler than the conventional third order T-model of equivalent circuit. Their parameters are readily obtained from no-load and standstill measurements. Using the derived models, it is shown that the unwanted cross coupling introduced by saturation and core loss can be eliminated in order to obtain de-coupled flux and torque control. Compensation of stator saturation and iron loss may be realised through modified stator or rotor flux oriented controller. Although more complex than the standard ones, these controllers are easily implemented by DSP technologies. The additional required data is the saturation characteristics (air-gap flux vs. magnetisation current) for determining the nonlinear inductance that models the saturation and the value of the equivalent iron loss resistance