Research On Prediction And Suppression Of The Far-field Radiation Of Flyback Converter

Products of SMPS entering the market must meet the relational EMC teststandards. However, with high density and high frequency of SMPS makessuppression and analysis of EMI more complex. Especially in the Far-fieldradiated interference’s prediction and suppression has been a problem. Therefore,prediction and suppression of the Far-field radiation has the important practicalsignificance and applied value. In this paper, the Flyback converter is for thestudy, analyzes its emissive mechanism and characteristics of the Far-fieldradiation, then establishes the model of the Far-field radiated emission, and forthe prediction and suppression. The main contents are as follows:Taking the Flyback converter with long cable for a specific object, analyzesthe causes of interference and the mechanism of the Far-field radiated emission,and establishes the model of the radiated emission. Analyzes the impact of theDM、CM and AM currents in long cables to the Far-field radiation. Calculates,taking the electric dipole as the basic unit, their electric field intensity of theFar-field radiation.Design a low-power Flyback converter for the Far-field radiated research’splatform. Establish the physical-level model of high frequency of simpletransformer, and verified by simulation and actual. On this basis, establish thebehavioral model of the transformer of the Flyback converter, including theforster network of the excitation impedance、the high-frequency network of theleakage impedance、 high-frequency capacitive model and ideal transformer.Under different termination method of the input impedance of the transformer,then compared the measuring with simulation to proof the correctness of themodel.Establish the high-frequency model of passive devices, use the SPICEmodels of active devices and extract parameters of the high-frequency PCBlayout, then finished the establishment of a complete high-frequency EMI modelof the Flyback converter, and by simulation and measurement of the interferedsource’s waveform are verified. Establish a long cable-type Far-field radiatedemission model，base on interfered source，to predict the Far-field radiation, and through experimental verified its validity. At the same time, analyze the impactof the different turns of three-phase inductor and CM inductor，and ground ofcable shield on the Far-field radiation, to find the appropriate suppressionmeasures.