An Adaptive Identification of Rotor Time Constant for Speed-Sensorless Induction Motor Drives: A Case Study for Six-phase Induction Machine

Accurate rotor time constant (Tr) value is necessary to ensure an acceptable performance of the indirect field oriented control (IFOC) strategy, where a detuned Tr affects rotor flux orientation, in turn, results in poor dynamic and steady-state response of torque. The problems associated with detuned Tr will be exacerbated in sensorless drives, when a model-based speed estimation algorithm is employed. This paper investigates the problem of simultaneous identification of the rotor time constant and rotor speed for sensorless IFOC of six-phase induction motor (6PIM) drives. First, an adaptive observer is proposed for online detection of the low-frequency sinusoidal signal, which is intentionally injected to the rotor flux command. Then, a novel model reference adaptive system (MRAS)-based Tr estimator is proposed using the detected signal. The Lyapunov stability theorem is used to ensure the asymptotic stability of the proposed identification system. The proposed method is based on the induction machine model in primary subspace, i.e., α −β subspace. Hence, it is usable for other multi-phase induction machine (three-phase and higher). Nevertheless, the 6PIM is adopted here as a case study. The simulation and experimental results clarify the effectiveness of the proposed parallel estimation system.

Index Terms—Adaptive observer, indirect field oriented control (IFOC), model reference adaptive system (MRAS), rotor time constant estimation, sensorless, six-phase induction motor (6PIM).