Totally Parameter Independent Speed Estimation of Synchronous Machines Based on Online Short Time Fourier Transform Ridges

High frequency signal injection is considered a parameter independent sensorless speed and position estimation technique which operates efficiently at low and zero speed. That is due to the saliency presence in the machine, which gives information about the rotor speed and position. Therefore the high frequency signal injected into the motor is modulated by the rotor speed and position information. Conventionally, to extract the useful information from the spectrum of the resultant signal, Phase-Locked Loop structure based demodulation schemes have been used. However, the PLL dynamics can be affected by the variation of inductances, PI parameters, and filter characteristics. In addition the error between the actual and estimated angle has to be small at the beginning of the estimation process. These restrictions are essential to maintain stability and to track the rotor speed and position accurately. However, such conditions are not always satisfied and are dependent on the operating conditions of the machine. 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 algorithm is proposed to detect the rotor speed and position. Theoretical and simulation aspects of the conventional and proposed methods are discussed and the obtained results are compared.