Sensorless Speed Estimation of PMSM near Zero Speed Using Online Short Time Fourier Transform Ridges

There are many sensorless schemes that have been proposed to estimate the rotor speed and position. However high frequency signal injection methods are able to detect the rotor speed and position even at zero speed whereas other schemes fail. Conventionally such methods use estimators based on the phase locked loop structure, which involves some restriction to maintain stability and track accurately the rotor position. Recently the concept of instantaneous frequency has become useful in many engineering applications where it is used to describe time varying signals. In this paper an instantaneous frequency estimation scheme based on the short time Fourier transform ridges is proposed to detect the rotor speed. Theoretical and simulation aspects of the conventional and proposed method are discussed and results are compared.