Instantaneous speed estimation of induction motor by time-varying sinusoidal mode extraction from stator current

When an induction motor operates at variable speed, the fundamental wave and harmonics in the stator current are presented in the form of nonstationary sinusoidal components with timevarying parameters. To estimate the instantaneous speed of the motor utilizing the stator current signal, a time-varying sinusoidal mode extraction (TVSME) method is firstly proposed. In TVSME, a variational model, which compacts the frequency bandwidth of the desired timevarying sinusoidal mode (TVSM) to the narrowest bandwidth and excludes other harmonics as much as possible, is constructed to optimally extract the desired TVSM and to estimate its instantaneous frequency (IF). Then, the fundamental wave and the principal slot harmonics (PSH) are extracted by TVSME, and their IFs are used to calculate the instantaneous rotational speed of the motor. As a result, a highly accurate and smooth rotational speed curve, which is valuable for performance evaluation and fault diagnosis of induction motors, can be obtained. The proposed method is evaluated by both an artificial signal and two experimental signals collected from actual motors. Results show that the instantaneous speed of induction motor can be accurately estimated under the condition of speed variation and multi-harmonic interference.