A Model Reference Adaptive System-Based Online Rotor Time Constant Estimation Method for Induction Motor Field-Weakening Control Utilizing Dot Product of Stator Voltage and Stator Current

As the induction motor speed increases, the coupling problem between flux current and torque current severely deteriorates the system performance in the field-weakening region. To address this problem, the accurate field-orientation is required, which is decided by the accuracy of rotor time constant. In this paper, by utilizing dot product of stator voltage and stator current, a model reference adaptive system (MRAS)-based online rotor time constant estimation method is proposed for field-weakening control. The designed adaptive mechanism makes the system immune to the variation of stator inductance, thereby breaking the coupling relation between the rotor time constant estimation and the field-weakening control. The stator frequency and the torque current are incorporated into the convergence condition. On this basis, the sign coefficient is designed to extend the effective range to the conditions of reverse speed driving and reverse load driving. Based on Lyapunov theorem, the system stability is derived, as well as the adaptive law. The equilibrium points and their stability properties are derived by small-signal analysis, which reveals the instability mechanism in such a high-nonlinearity system. The experimental results verify the effectiveness of the proposed method.