An Offline Rotor Resistance Estimation Method for Indirect Vector-Controlled Induction Motors Using MTPA Reference

Indirect vector control is widely used to control induction motors, and accurate identification of the rotor resistance is essential for achieving high-performance torque and flux control. Rotor resistance estimation methods are generally categorized into online approaches, which compensate for temperature-induced variations during operation, and offline approaches, which provide initial values for vector control and facilitate the construction of current reference look-up tables in the early stages of testing. Although various online techniques with improved performance have been proposed, offline approaches remain limited, most commonly relying on the locked-rotor and no-load tests as defined in IEEE Std. 112. However, the locked-rotor test is prone to significant errors, arising from rapid rotor heating caused by high current levels and several additional factors. To address this limitation, this study proposed a novel offline approach based on the principle that the maximum torque per ampere operation can only be achieved when the rotor resistance is correctly identified in an indirect vector controller. The rotor resistance was experimentally identified using the proposed method, and the results were compared with those obtained through finite element analysis and a model reference adaptive system. The results showed strong agreement across all methods, confirming the effectiveness of the proposed approach.