A New Motor Speed Measurement Algorithm Based on Accurate Slot Harmonic Spectral Analysis

In this paper a new induction motor speed method based on Chirp-Z Transform and zero padding of the supply current is presented. The algorithm has been implemented on a microprocessor. A virtual instrument has been built to control and to monitor on line motor speed. The motor speed method has been tested on a 7.5 kW induction motor driven by a pulse width modulation voltage source inverter for different load and supply frequency conditions. The proposed method has been compared to a FFT based one implemented on the same microprocessor. Thanks to a shorter sampling time window errors related to not stationary current signal are reduced. Then the achieved goal is an increased accuracy due to shorter sampling time window and better spectral resolution. Moreover the processing time has been reduced increasing algorithm speed response.