Proactive Low-Frequency Ride-Through Method for Speed-Sensorless Induction Motor Drives Against Changing Torque

It is well known that the stability of adaptive full-order observer (AFO) is of critical importance for speed-sensorless induction motors (IMs) at low speeds. The stability of AFO can be improved by feedback gains design in low-speed regenerating mode, but few pieces of literature realize the observability under zero-stator-frequency operating conditions. To address this issue, proactive low-frequency ride-through (PLFRT) method is proposed against changing torque in this paper. The magnetizing current command is adaptively changing with IM operating point to keep the synchronous speed out of the unstable region. To enhance the torque output capacity, the possible synchronous speed limit is discussed. Based on the stator current limitation analysis, the command variation of magnetizing current is derived. The effectiveness of PLFRT method is verified on a 2.2kW IM experimental setup.