A proposed induction motor speed sensor without contact from slots harmonics. Application to rotoric time constant identification

A method to detect rotor speed electrically from the rotor slots harmonics of a three phase squirrel cage motor is proposed in this paper. Experimental results with a conventional 1.5 kW motor confirm that slots harmonics moving linearly with rotor speed and situated in the supply current spectrum have sufficient amplitudes to satisfy this aim (by a computer program using a FFT algorithm) whatever the supply type is. In AC drive systems torque control, the values of machine parameters should be known correctly. Especially the rotoric time constant is easily influenced by temperature and saturation and seriously related to the computation of torque under field oriented control. This paper shows an application of the speed detection procedure which is the feasibility of rotoric time constant identification using Fourier series expansion