Phase Compensation Factor-Based Low Frequency Crossing for Sensorless Induction Motor Drives With Changing Loads

This article deals with speed observation methods for sensorless induction motor drives (SIMDs). The speed observability of SIMD near zero stator frequency is a well-known concern. Using adaptive magnetizing current, existing methods are capable of crossing the zero-stator-frequency line, but still limited to constant load conditions. To solve these problems, this article presents a phase compensation factor-based low frequency crossing method with changing loads (PCF-LFCCL) to realize low frequency crossing process with decreased overcurrent and speed spikes. First, the influence of load variations is studied finely, the LFCCL method is proposed with adaptive magnetizing current. Secondly, the torque output capacity analysis is given and illustrated. On this basis, the synchronous speed limit can be adopted properly. Thirdly, a generalized current model is developed for SIMD. The model reveals the phase delay phenomenon between magnetizing current reference and actual torque current, which can lead to speed spikes and overcurrent. To address this issue, a phase compensation factor (PCF) based method is developed by reconstructing compensation values to correct the torque current. Finally, comparative experiments are presented to validate the PCF-LFCCL method, including stator resistance error test for parameter robustness.