Detuning Induced by Stray Load and Iron Losses in Small Vector-Controlled Induction Motors

Detuning in vector-controlled induction motor (IM) drives is characterized by a misalignment between the actual and reference flux vectors (i.e., flux angle error) or by a non-unity ratio of actual to reference flux vector magnitudes (i.e., flux magnitude error). Such detuning generally occurs either due to the disagreement between the actual and assumed values of IM parameters or due to phenomena not accounted for in the control algorithm. This paper presents a comprehensive analysis of the detuning induced by the stray load and iron losses in voltage-fed vector-controlled IM drives. The analysis encompasses load torques up to the rated value and rotor flux values down to 50% of the rated value. For this purpose, an IM model is utilized in which the stray load and iron losses are modeled as variable with respect to the operating frequency, flux, and torque. The simulation model of the considered IM drive is built in the MATLAB-Simulink environment. Three small IMs (1.5 kW) of different efficiency and rotor material have been considered.