EMI Optimization Design And Modeling Analysis Of Transformer Based On De-Y Flyback Converter

Under the development trend of high frequency and high power density,it has become an inevitable design link to solve the EMI problem caused by fast switching action,but the additional cost of EMI optimization often leads to serious decline in product competitiveness.It has important research and application value to find a low-cost solution that can effectively solve EMI problems without affecting performance.Flyback converter,as a common power supply topology of consumer electronics at present,usually uses adding primary and secondary Y capacitors to form a low impedance path to reduce EMI noise,but it is followed by a large increase in leakage current.This not only leads to the failure to meet national safety standards,but also directly endangers the life safety of product users.In this paper,firstly,the mechanism of EMI conduction and radiation in different operation modes of flyback converter is described,and the EMI conduction path under the condition of y-capacitor removal is accurately modeled and analyzed.Based on the conduction model,the influence of common mode / differential mode noise conversion on the high frequency performance of EMI is explained.In order to meet the leakage current safety standard,EMI test standard and converter performance index while removing the primary and secondary y-capacitors,the optimization design is proposed from two aspects of EMI filter and transformer respectively:in EMI filter,based on the mutual inductance and mutual capacitance conversion theory,two new filter inductance design schemes are proposed,which can effectively suppress the parasitic capacitance effect and improve the high frequency Filtering performance.Combined with the precise winding structure model of the plane EMI filter,the optimal parameters of the two schemes are determined through calculation and derivation.In the aspect of transformer,a new type of transformer EMI optimization structure is proposed in view of the defects of CPES existing optimization structure,such as insufficient noise suppression effect,too many restrictions on winding layout and unclear parameter design.In the case of considering all the transformer displacement current paths,the optimization effect of the original and secondary noise current of 0is achieved theoretically.Based on the law of conservation of displacement and current,an accurate lumped capacitance model of transformer is established to determine the optimal turn ratio setting and winding arrangement of the new transformer structure.The EMI optimization scheme is simulated by ANSYS,PSPICE and MATLAB,and tested based on the prototype of 18 W flyback converter.Compared with the prototype of the current phase of CPES,the EMI test results of the prototype using the EMI optimization scheme in this paper(i.e.using the traditional plane EMI filter and the balanced winding method transformer)are about 20 d B lower at the high frequency exceeding 2MHz,and about 15 d B lower at the low frequency exceeding 200 k Hz,which effectively realizes the EMI optimization.At the same time,the electrical performance of flyback converter,including standby power consumption,average power consumption and start-up time,has not deteriorated,which meets the electrical design requirements of the prototype.