Improved Approach for Measuring Mains Interference

This paper presents a method for measuring the frequency and amplitude of the 1st and 3rd harmonics of mains disturbances. The first harmonic of the mains interference is removed from the signal using a basic band-pass filter. Simultaneously with the subtraction, the deviation of the mains frequency from its rated value is determined and the current correction of the band-pass filter is performed. The third harmonic is removed from the signal by means of an additional band-stop filter, the transfer coefficient of which is also continuously adjusted, together with the transfer coefficient of the main filter. After subtracting the harmonics from the signal, the ratio between the amplitudes of the third and the first harmonic is calculated. Results of research in the MATLAB environment are presented.