Estimating of DC motor rotational speed by the spectral structure of consumed current

Abstract: A method for estimating the rotational speed of a DC motor based on analysis of the spectral structure of consumed current is presented. The used principle implements the fact that the first harmonic frequency in the spectral structure of the consumed current is proportional to the rotational speed of the motor. Compared to the known methods of measuring the motor rotational speed, a narrow-band filter with adjustable frequency and quality factor is used to highlight the sinusoidal form of the first harmonic. The evaluation algorithm is implemented on a microcontroller, which provides a closed loop to adjust the frequency and the quality factor of the filter. As an alternative to the fast Fourier transform, an original algorithm to search the first harmonic is proposed. The experimental results are presented on AtMega328 and STM32F103 microcontrollers.

Keywords: motor speed evaluation, microcontroller, spectral analysis