Research On The Methods Of Harmonic Detection AC-DC Electric Locomotives

The quality of electric energy, which is tied to everyday lives, have directly effect on industrial manufacturing, rail transportation, aerospace and in all kind of fields. The effect of harmonics on electric energy is the most important part. The detecting for harmonic by the most expeditious means is the primary guide and ultimate goal of elimination of effectElectrified railway as electric power systems part of the special, is non-linear load in electric locomotive. Because of electric locomotive braking and running random, voltage current characteristics are asymmetric, strong volatility, and other characteristics. The characteristics of harmonics generated by the voltage current are nonlinear, randomly distributed, not smooth and vulnerable to weather. Due to the above, it’s not possible to detect harmonic fast and correctly by routine ways. So the new trend is that developed a new method.The detection method based on the instantaneous reactive power theory is widely applied in APF device. By MATLAB simulation, it can be concluded that the method based on instantaneous reactive power theory is on fit for the electrified railway supply system because of its quick response velocity and little delay.Due to the good performance of time-frequency localization of wavelet transform, more and more experts and scholars further study in the field.Our research have important theoretical and practical significanceIt has an important influence on signal detection that selection of wavelet generating functions and to determination of wavelet decomposition level. Select db10wavelet frequently used in non-stationary signals as wavelet generating functions, determine wavelet decomposition level under the principle "Fundamental frequency at the lowest sub-band center" and analyze simulation results of L1harmonic current of motorcycle type in mainstream, results reveals many advantages of wavelet analysis over other harmonics. Finally, the paper also noted that the wavelet detection applies not only to the harmonic detection, but also contact system of PQ detection.The results show that the wavelet transform can accurately separate harmonics from harmonic current. Wavelet transform can be regarded us practical and provides a powerful tool for the non-steady-state harmonic detection.