Research On The Adaptive Detection Method Of Weak Sinusoidal Signal

When exploring and researching on macroscopical and microcosmic world, the weak signal detection is needed. Much internal noise exists in analog detection instruments and the useful signal is covered by noise, so the useful weak signal can't be detected by using amplifier and analog filter. The subject we discussed in this paper is the extraction of stable periodic sinusoidal signal. Correlation detection method is widely used in this case since sinusoidal signals is periodic and correlative and orthogonal to each other.A new method is proposed apply in the extraction of stable periodic sinusoidal signal—adaptive sinusoidal filtering. The digital filter is constructed by modern optimization control theory, the input of the filter is standard sinusoidal signal, the filter coefficients are automatically adjusted by certain rule, the output of the filter is the useful information(amplitude and phase) of weak signal when a certain goal is satisfacted.We do the simulation of correlation method and adaptive sinusoidal filtering method by MATLAB. The result of simulation proves that the adaptive sinusoidal filtering method is effective and feasible, in the case of the source signal is composed of signals with different frequency, the adaptive sinusoidal filtering method is more flexible, and can extract weak signal in more short time.At last, the adaptive sinusoidal filtering method is applied in the extraction of harmonic signal in power system. We extract the third harmonic voltage and current signals successfully before and after stator singel-phase earth fault, so we provide technical support for the new method of stator singel-phase earth protection based on the third harmonic impedance.