Suitable Mother Wavelet for Harmonics and Interharmonics Measurements Using Wavelet Packet Transform

When considering harmonic distortion, the fast Fourier transform (FFT) performs well in calculating root mean square (RMS) values of some distorted waveforms. However, in the case of inter-harmonics the FFT produces large errors in estimating these RMS values. This paper introduces the use of wavelet packet transform (WPT) for RMS measurements in case of harmonics and inter-harmonics distortion. In order to minimize the spectral leakage associated with WPT the paper proposes an algorithm that is capable of choosing the most suitable wavelet family and hence mother wavelet. This reduces the error associated with wavelet analysis. The proposed algorithm is applied to two case studies considering harmonics and inter-harmonics distortion and the results are compared with the true values and the FFT based values.