Robust Online Rotor Time Constant Tuning Method with High-Frequency Current Injection for Indirect Field-Oriented Induction Motor Drives

For an induction motor operating as a symmetric three-phase system, the performance of indirect field-oriented vector control relies heavily on the accuracy of the rotor time constant. Any inaccuracies result in severe torque errors and compromise dynamic performance because of the coupling between the flux and torque controls. Although conventional IFOC methods are intended to compensate for the rotor time constant error, they rely on induction machine parameters such as the mutual and leakage inductances. This paper proposes an online method for tuning the rotor time constant independent of other parameters. First, an active power model of three-phase symmetric induction motor is selected to estimate the stator resistance based on a model reference adaptive system, which requires only the rotor time constant. Additionally, high-frequency current injection and torque ripple estimation without phase delay or amplitude decay are introduced to compensate for the rotor time constant. When a high-frequency current is injected, the rotor time constant and stator resistance can be simultaneously tuned without depending on other parameters. A high-frequency current is injected only when a rotor time constant error is detected from the estimated stator resistance. This behavior is enabled by the correlation between the stator resistance and the rotor time constant. Simulation results using MATLAB/Simulink regarding the symmetric three-phase induction motor validate the proposed method.