Research On EMI Modeling Of Switching Power Supply Based On Non-ideal Device Model And Field-circuit Synergistic Analysis

Switching model power supplies(SMPS)are widely used in applications ranging from small consumer electronics to large industrial equipment.With the continuous increase of the switching frequency,the rapid turn-on and turn-off of the switching device will cause large di/dt and dv/dt,which will cause serious high-frequency electromagnetic interference(EMI),including conducted EMI noise via cable transmission and radiated EMI noise via space coupling.In order to predict the conducted and radiated EMI noise generated by the SMPS without EMI standard detection equipment such as the 3m anechoic chamber,and only employ the circuit topology,device parameters and noise transmission characteristics,this paper establishes conducted and radiated EMI noise models,investigates the coupling paths of the above two noise models in SMPS,proposes a SMPS EMI noise prediction method,and a SMPS EMI filter design method based on the analysis of the internal impedance of noise sources.The above work provides a reference for the future EMI design and optimization of SMPS.(1)A high-frequency equivalent circuit modeling method for non-ideal devices that combines impedance measurement and differential evolutionary(DE)algorithm is proposed.The equivalent circuit model of SMPS passive devices including capacitors,inductors,diodes and transformers are established.Each model can accurately reflect the frequency characteristics of the devices in the frequency band of at least 100 MHz.The modeling method provides the basis for the prediction of radiated EMI and conducted EMI of SMPS.(2)Based on the working principle and topological structure of the SMPS,the generation mechanism and coupling path of the conducted EMI are analyzed,and a SMPS conducted EMI noise prediction method based on the high-frequency equivalent circuit model of the device is proposed.This method overcomes the problem of insufficient prediction accuracy caused by ideal device models in traditional methods.(3)Based on the high-frequency circuit model of the SMPS and the transmission characteristics of radiated EMI noise,a SMPS radiated EMI noise prediction method based on field-circuit cooperated analysis is proposed.This method not only considers the radiated EMI noise standard detection environment,the cable material and structure of SMPS and other factors in the field-circuit cooperated analysis model,optimizes the model of cable radiation impedance,but also extracts the transfer function of the circuit and electromagnetic field,and establishes the correlation between the circuit parameters of SMPS and the space electromagnetic field,realizes the prediction of radiated EMI noise,and avoids the calculation and computing power problems caused by repeated electromagnetic field simulation.(4)A source impedance modeling method based on genetic algorithm(GA)and Levenberg-Marquard algorithm(LM)is proposed,and the EMI filter of SMPS is designed according to the noise source impedance extracted by the method.Firstly,the internal impedance of the noise source is measured by the scattering parameter method,and then the circuit parameters of the internal impedance are extracted by GA algorithm and LM algorithm,to improve the EMI filter design of the SMPS,which has a good noise suppression effect.