Shift-Angle-Based Speed Adaptive Scheme for Stability Enhancement of Speed-Sensorless Induction Motor Drives

Speed-sensorless induction motor drive (SSIMD) systems are widely used in rail transportation. However, the instability in low-speed regenerating region is a well-known problem to be solved. To cope up with this problem, this paper proposes a shift-angle-based speed adaptive scheme to enhance the stability of SSIMD systems. Firstly, there is an unstable region within the operating area of the motor by analyzing the determinant of extended error coefficient matrix. Then, using the proposed shift-angle-based speed adaptive scheme, a shift angle ϕ is introduced to coincide the two boundaries of the unstable region, eliminating the unstable region. Finally, the proposed method is verified by bode plot analysis and experiment.