Research On EMI Active Suppression Technology For Power Converter

Due to the advantages of small size,light weight,high efficiency and stable performance,the power converter has been widely used and developed rapidly in power supply.However,the Electromagnetic interference(EMI)problem caused by its high frequency on/off working characteristics can't be ignored.Especially with the development of some technologies like automotive electronics,unmanned technology,EMI not only affects the performance of the equipment,but also the personal safety.Filtering technology is one of the most effective means of EMI suppression,while in traditional passive filter,the capacitance is limited by the safety regulation,so the volume and weight of the inductor is relatively large.The power converter is developing toward the direction of high frequency and high power density,the volume and weight of the traditional passive filter limit its development.Due to the using of active components,the active filter can improve the filtering performance without increasing the inductance or capacitance,the volume and weight have more advantages.Compare with traditional passive filter,it is more in line with the development direction of the current power converter.This paper researches on active EMI filter(AEF),the study includes the design process and test evaluation scheme of the AEF.The influence of the relative position of active and passive filter in hybrid active EMI filter to filtering performance is also studied in this paper.Firstly,the evaluation methods,testing equipment and test standard of conducted EMI noise are introduced.Combined with the main circuit of the prototype,the working characteristics,noise generation mechanism,and the noise transmission path are mostly analyzed,which makes the noise characteristics of the circuit clarified.Secondly,this paper introduces the classification of active EMI filer,analyzes the design difficulties and the design differences between AC/DC application and DC/DC application.At the same time,the current detecting and current compensating scheme is taken as an example to analyze the working principle.Then the advantages and disadvantages of different active filter schemes are analyzed and compared.Finally,depend on these analysis,the AEF scheme of analog control and feedback type current-detecting and current-compensating is selected.Then,the circuit is divided into three parts:detection part,amplification part and current compensating part,the gain expression of each part is derived,and further the total gain of the system and the mathematical model of insertion loss for the circuit are deduced.According to the analysis of the model and the prototype,the circuit parameters are design.At the same time,the performance of the filter is quantitatively evaluated by using EMI receiver with 50? noise source impedance and 50? load impedance.The performance of filter is verified through simulation and experiment.Finally,in order to improve the high frequency characteristics of the filter,some passive components are added into the previous active common-mode EMI filter,composing hybrid EMI filter.The low-frequency equivalent circuit is analyzed and its mathematical model is deduced.In addition,the effect of the relative position of active and passive filter in hybrid active EMI filter is also studied.In the end,the performance of the hybrid EMI filter is verified by an AC/DC power converter prototype with a rated power of 3200W.Compare with the original passive filter,under the premise of ensuring the filtering effect,the volume of hybrid EMI filter is reduced by about 1/3,and the weight is reduced by about 2/3.