Conducted EMI Of Pulse Power Supply For EDM

Pulse power supply for EDM provides pulse energy for gap load to realize gap breakdown and material erosion.In the machining process,the switch inside the pulse power supply will produce conducted EMI when switching at high frequency.Due to the non-linear characteristics of the spark discharge gap,the equivalent switch on the gap side will act at another low frequency to produce interference signal,which is essentially an intermittent signal interference system with high frequency superimposed on low frequency.At the same time,the conducted EMI spectrum characteristics of pulse power supply under different discharge current waveforms and machining parameters will also be different.Based on the characteristics of EDM gap,this paper establishes the gap equivalent electrical model,and designs a more general Buck pulse power supply for EDM.According to the characteristics of large transient change rate of voltage and current caused by the highfrequency action of the switch during the operation of the pulse power supply,the drain source voltage of the buck switch and the pulsating current on the input side are used as the noise source of conducted EMI,The harmonic amplitude under time-frequency characteristics is calculated and analyzed.Secondly,the gain amplitude is obtained respectively according to the common mode(CM)and differential mode(DM)interference transmission path,and then the numerical expression and spectrum diagram of CM and DM interference are obtained.According to the spectrum diagram,the variation law and size relationship of CM and DM interference value of Buck switch are analyzed respectively.Finally,the CM and DM interference values under three different discharge current waveforms and machining parameters of rectangular wave,sawtooth wave and triangular wave are obtained.The CM and DM interference values and corresponding parameters corresponding to the worst situation of CM and DM interference under each discharge current waveform and machining parameters are obtained,which provides a parameter design basis for the design of subsequent EMI filters.Finally,the principle prototype of pulse power supply is designed,and a set of conducted EMI test platform is built.The spectrum diagram obtained by circuit simulation and experimental test verifies the correctness of the theoretical analysis.At the same time,EMI filter is designed according to the worst CM and DM interference of all discharge current waveforms and machining parameters.