Research On Modeling And Suppression Of Conducted Eletromagnetic Interference In Three-phase Two-level Power Converter

With the fast development of the power electronics,pulse-width modulation(PWM)based power converters have been widely used in the energy conversion areas.However,the fast and high-frequency switching of the power devices causes severe conducted electromagnetic interference(EMI)problems,which increases the time consumption of the product design and may do harm to the safety of the energy conversion system.Currently,there are mainly two kinds of technique which can effectively solve the EMI problem,one is the EMI prediction method,the other is the EMI suppression method.Although EMI problems have been widely studied in the past few years,there still exist plenty of challenges.For EMI prediction methods,the uncapability of fast and precisely predicting the multiple-frequency ringing effect much limits the performance of the EMI prediction methods.For EMI suppression methods,the conducted EMI in the high-frequency domain is hard to be effectively suppressed,which makes it hard to meet the electromagnetic compability(EMC)standard in the whole frequency domain for power converters.In this context,a comprehensive research on the EMI issues is conducted in the dissertation based on a three-phase two-level power converter,the generation and propagation of the common-mode(CM)and differential-mode(DM)EMI are analyzed,and several methods are proposed to deal with the existing challenges.The dissertation mainly contains four parts:1.Firstly,based on a typical three-phase two-level power converter,the physical structure of each active/passive component is analyzed,and the high-frequency model of each component is constructed.Then,the generation and propagation of the CM and DM EMI are studied.Finally,the system EMI model is deduced,which is the fundamental of the EMI prediction and EMI suppression researches.2.A time-frequency-domain EMI prediction method(TDEPM),which can fast and precisely predict the multiple-frequency ringing effect,is proposed to improve the performance of the EMI prediction methods.Firstly,the dynamic switching process of the power devices,as well as the formation of the multi-frequency ringing effect are studied.Based on that,the mathematical models of the common-mode and differential-mode EMI source are deduced.Then,based on the mathematical models of the EMI sources,TDEPM is proposed,with consideration of the multi-slope trapezoidal waveform and multi-frequency ringing effect,it fast and precisely predicts the EMI source through a novel EMI source synthesis circuit,and further accelerates the EMI prediction by means of frequency-domain prediction method.Finally,experiments verify that TDEPM can fast and accurately predict the conducted EMI with good converage and high flexibility.3.An improved H8-topology-based EMI reduction modulation method is proposed to eliminate the influence of the dead time.At first,the common-mode voltage(CMV)of the H8 converter under zero state is analyzed by considering the parasitic capacitance of the power devices.Based on that,an improved H8 topology is proposed with optimized topology and modulation strategy.Finally,simulations and experiments verify that the proposed method can effectively eliminate the influence of the dead time without complex design.Also,results show that the proposed method realizes zero CMV variation when entering and leaving zero state,and effectively suppresses the CM EMI which is caused by the CMV variation.4.In order to solve the intractable CM EMI above mega-herds,a separate-floating-heatsink based frequency-division EMI suppression strategy(SFHBFDESS)is proposed in this paper.At first,SFHBFDESS contains a separate-floating-heatsink based EMI suppression method(SFHBESM)to solve the high-frequency EMI,through reasonable parameter design,SFHBESM realizes non-ringing EMI source without introducing additional power loss.At the same time,it can effectively block the propagation path of the CM EMI.Then,based on the proposed SFHBESM,passive EMI filter is designed to suppress low-frequency EMI.Experiments verify that through low design cost,SFHBFDESS can effectively suppress the conducted EMI in the whole frequency domain,and ensure the power converter meet the EMC standard.In a word,a deep investigation on the EMI problem of a three-phase two-level power converter is conducted in the dissertation,several methods have been proposed to solve the existing challenges in the EMI prediction techniques and EMI suppression techniques.Experiments are done to verify the effectiveness of the proposed methods.Studies in the dissertation would help dealing with the EMI problems in industry.