A New Mothod For Harmonic And Inter-Harmonic Detection In Power System Based On Modified MM Filter And HHT

With the development of modern Power System and application of nonlinear electric elements, for example, electric arc furnaces, converters, induction motors and so on, harmonics have changed into more complex question and the situation have endangered Power System and electric equipments, in which inter-harmonics and sub-harmonics are important factors.To reduce these harms, various methods of harmonics detection and harmonics compensation were proposed. However, these methods are only localized in frequency field or time field and the methods of harmonics compensation in inter-harmonics are not satisfied. Therefore, it is necessary to study how to analyze inter-harmonics and fundamental component extraction under inter-harmonics background furthermore.A new method based on Mathematical Morphology and HHT is proposed to detect the signal with harmonic and inter-harmonic. Firstly, MM filter is modified as to selection of structure elements via doing fine researching for MM transformation and disadvantage of selection structure element and statistic deflection. The signal is de-noised though character of low-passing in time field. Then, the signal is EMD to obtain a series of IMF, and every IMF is hilbert-transformed to get amplitude and frequency accurately. This method realized detection of harmonic and inter-harmonic on the ground of noise on the real sense.Large quantity of emulations show that modified MM filter which can restrain not only flat noise but also positive and negative impulse noise, is more effectively to restrain noise than traditional MM filter. HHT is perfectly self-adaptive analysis method. EMD can decompose smooth signal into a series of single frequency signal in order to make Hilbert transformation actual physical sense. Then this method realizes extracting of parameters of harmonic and inter-harmonic accurately.