Variable-Slope-Based Ripple Reduction Method for Speed-Sensorless Induction Motor During Zero Frequency Crossing With Optimized Boundaries

For speed-sensorless induction motor (IM) drives (SSIMD), the adaptive magnetizing current control has already been presented to enhance the speed observability at low synchronous speeds. However, the rapid variations of magnetizing current reference would introduce inherent ripples during zero frequency crossing (ZFC). To solve this problem, this article proposes a variable-slope-based ripple reduction method (VSRRM) for SSIMD to relieve the ripples of speeds and currents during ZFC. First, the qualitative analyses are carried out to elaborate the origin of the ripples during ZFC. On this basis, the slope angle of VSRRM is derived to rearrange the operating point trajectory, reducing the ripples with rapid magnetizing current changes. Considering the introduced slope angle, the boundary points of ZFC are optimized by average current to reduce the ripples. Furthermore, the IM operating trajectory and output torque capability are analyzed with respect to magnetizing current limit. Finally, the effectiveness of the proposed method is verified on a 2.2 kW IM experimental setup.