Harmonic and inter-harmonic detection of grid-connected distributed generation based on modified mathematical morphology filter and Hilbert-Huang transformation

Increasing demand for premium electric power, in terms of both quality and reliability, and emerging new energy technologies have led to the development of DG. In the process of connected DG with the power grid, harmonic/inter-harmonic is very serious problem. A new method based on modified MM filter and HHT is proposed to detect harmonic/inter-harmonic caused by the power electric elements. Researched intensively the characteristics of MM transform and MM filter, MM filter is modified aimed at the drawback of selection of structure elements and statistic deflection. HHT is perfectly self-adaptive analysis method. To the signal with harmonic/inter-harmonic, white pulse and positive & negative impulse, firstly, using modified MM filter to remove the white noise, positive & negative impulse and high times harmonic because of its low-passing characteristic, that method´s key element is to choosing appropriate SE and its filter effect is better than the wavelet transform. Based on this, using EMD to get a set of IMFs for the denoised signal, the IMFs are almost the single frequency signal. At last, carrying out Hilbert transform to IMFs can get the instantaneous frequency and amplitude of every harmonic/inter-harmonic accurately.