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Power Electronics Electromagnetic Compatibility

The electromagnetic compatibility issues in power electronic systems are essentially the high levels of conducted electromagnetic interference (EM I) noise because of the fast switching actions of the power semiconductor devices. The advent of high-frequency, high-power switching devices res ulted in the widespread application of power electronic converters for hu man productions and livings. The high-power rating and the high-switchi ng frequency of the actions might result in severe conducted EMI. Particu larly, with the international and national EMC regulations have become m ore strictly, modeling and prediction of EMI issues has been an important research topic.

By evaluating different methodologies of conducted EMI modeling and p rediction for power converter systems includes the following two primary limitations: 1) Due to different applications, some of the existing EMI m odeling methods are only valid for specific applications, which results in i nadequate generality. 2) Since most EMI studies are based on the qualitati ve and simplified quantitative models, modeling accuracy of both magnit ude and frequency cannot meet the requirement of the full-span EMI qua ntification studies, which results in worse accuracy. Supported by Nationa l Natural Science Foundation of China under Grant 50421703, this dissert

ation aims to achieve an accurate prediction and a general methodology. S everal works including the EMI mechanisms and the EMI quantification c omputations are developed for power electronic systems. The main conte nts and originalities in this research can be summarized as follows.

I. Investigations on General Circuit Models and EMI Coupling Modes In order to efficiently analyze and design EMI filter, the conducted EMI n oise is traditional decoupled to common-mode (CM) and differential-mod e (DM) components. This decoupling is based on the assumption that EM I propagation paths have perfectly balanced and time-invariant circuit stru ctures. In a practical case, power converters usually present inevitable uns ymmetrical or time-variant characteristics due to the existence of semicon ductor switches. So DM and CM components can not be totally decouple d and they can transform to each other. Therefore, the mode transformatio n led to another new mode of EMI: mixed-mode EMI. In order to underst and fundamental mechanisms by which the mixed-mode EMI noise is exc ited and coupled, this dissertation proposes the general concept of lumped circuit model for representing the EMI noise mechanism for power electr onic converters. The effects of unbalanced noise source impedances on E MI mode transformation are analyzed. The mode transformations betwee n CM and DM components are modeled. The fundamental mechanism of the on-intrinsic EMI is first investigated for a switched mode power suppl y converter. In discontinuous

conduction mode, the DM noise is highly dependent on CM noise becaus e of the unbalanced diode-bridge conduction. It is shown that with the sui table and justified model, many practical filters pertinent to mixed-mode EMI are investigated, and the noise attenuation can also be derived theore tically. These investigations can provide a guideline for full understandin g of the EMI mechanism and accuracy modeling in power electronic conv erters. (Publications: A new technique for modeling and analysis of mixed -mode conducted EMI noise, IEEE Transactions on Power Electronics, 20 04; Study of differential-mode EMI of switching power supplies with rec tifier front-end, Transactions of China Electrotechnical Society, 2006) II. Identification of Essential Coupling Path Models for Conducted EMI P rediction

Conducted EMI prediction problem is essentially the problem of EMI noi se source modeling and EMI noise propagation path modeling. These mo deling methods can be classified into two approaches, mathematics-based method and measurement-based method. The mathematics method is ver y time-consuming because the circuit models are very complicated. The measurement method is only valid for specific circuit that is conveniently to be measured, and is lack of generality and impracticability. This disser tation proposes a novel modeling concept, called essential coupling path models, derived from a circuit theoretical viewpoint, means that the simpl

est models contain the dominant noise sources and the dominant noise co upling paths, which can provide a full feature of the EMI generations. Ap plying the new idea, this work investigates the conducted EMI coupling i n an AC/DC half-bridge converter. Three modes of conducted EMI noise are identified by time domain measurements. The lumped circuit models are derived to describe the essential coupling paths based on the identifica tion of the EMI coupling modes. Meanwhile, this study illustrates the extr action of the parameters in the afore-described models by measurements, and demonstrates the significance of each coupling path in producing con ducted EMI. It is shown that the proposed method is very effective and ac curate in identifying and capturing EMI features. The equivalent models of EMI noise are sorted out by just a few simple measurements. Under th ese approaches, EMI performance can be predicted together with the filte ring strategies. (Publications: Identification of essential coupling path mo dels for conducted EMI prediction in switching power converters, IEEE T ransactions on Power Electronics, 2006; Noise source lumped circuit mo deling and identification for power converters, IEEE Transactions on Indu strial Electronics, 2006)

III. High Frequency Conducted EMI Source Modeling

The conventional method of EMI prediction is to model the current or vol tage source as a periodic trapezoidal pulse train. However, the single slop e approximation for rise and fall transitions can not characterize the real s

witching transitions involved in high frequency resonances. In most com mon noise source models simple trapezoidal waveforms are used where t he high frequency information of the EMI spectrum is lost. Those models made several important assumptions which greatly impair accuracy in th e high frequency range of conducted noise. To achieve reasonable accurac y for EMI modeling at higher frequencies, the relationship between the s witching transitions modeling and the EMI spectrum is studied. An impor tant criterion is deduced to give the reasonable modeling frequency range for the traditional simple approximation method. For the first time, an im proved and simplified EMI source modeling method based on multiple sl ope approximation of device switching transitions is presented. To confir m the proposed method, a buck circuit prototype using an IGBT module i s implemented. Compared with the superimposed envelops of the measur ed spectra, it can be seen that the effective modeling frequency is extende d to more than 10 MHz, which verifies that the proposed multiple slopes s witching waveform approximation method can be applied for full-span E MI noise quantification studies. (Publications: Multiple slope switching w aveform approximation to improve conducted EMI spectral analysis of po wer converters, IEEE Transactions on Electromagnetic Compatibility, 20 06; Power converter EMI analysis including IGBT nonlinear switching tr ansient model, IEEE Transactions on Industrial Electronics, 2006)

IV. Loop Coupling EMI Modeling in Power Electronic Systems Practical examples of power electronic systems that have various electric al, electromechanical and electronics apparatus emit electromagnetic ener gy in the course of their normal operations. In order to predict the EMI no ise in a system level, it is significant to model the EMI propagation chara cteristics through electromagnetic coupling between two apparatus circuit within a power electronic system. The PEEC modeling technique which was first introduced in 1970s has recently becomes a popular choice in rel ation to the electromagnetic analysis and EMI coupling. In previous studi es, the integral equation based method was mostly applied in the electrica l modeling and analysis of the interconnect structure in very large scale in tegration systems, only at the electronic chip and package level. By introd ucing the partial inductance theory of PEEC modeling technique, this wor k investigates the EMI loop coupling issues in power electronic circuits. The work models the magnetic flux coupling due to EMI current on one c onductor and another by mutual inductance. To model the EMI coupling between the grounding circuits, this study divides the ground impedance i nto two parts: one is the internal impedance and the other is the external i nductance. The external inductance due to the fields external to the rectan gular grounding loop and flat conductor is modeled. To verify the mathe matical models, the steel plane grounding test configurations are construc

ted and the DM and CM EMI coupling generation and modeling techniqu e are experimentally studied. The comparison between the measured and calculated EMI noise voltage validates the proposed analysis and models. These investigations and results can provide a powerful engineering appl ication of analyzing and solving the coupling EMI issues in power electro nic circuits and systems. (This part of work is one of the main contributio ns of the awarded project of Military Science and Technology Award in 2 006, where the author is No. 4 position. Publication: Loop coupled EMI a nalysis based on partial inductance models, Proceedings of the Chinese S ociety of Electrical Engineering, 2007)

V. Conducted EMI Prediction for PWM Conversion Units

PWM-based power conversion units are the main EMI noise sources in p ower systems. Due to the various PWM strategies and the large number o f switches, a common analytical approach for the PWM-based switched c onverter systems has not been dated. Determination of the frequency spec trum of a PWM converter is quite complex and is often done by using an FFT analysis of a simulated time-varying switched waveform. This appro ach requires considerable computing capacity and always leaves the unce rtainty as to whether a subtle simulation round-off or error may have sligh tly tarnished the results obtained. By introducing the principle of the doub le Fourier integral, this work presents a general method for modeling the conduced EMI sources of PWM conversion units by identifying double in

tegral Fourier form to suit each PWM modulation. Appling the proposed method, three PWM strategies have been discussed. The effects of differe nt modulation schemes on EMI spectrum are evaluated. The EMI modeli ng and prediction efforts from an industrial application system are studied comprehensively. Comparison between the measured and the predicted s pectrum confirms the validity of the EMI modeling and prediction metho d. This method breaks through the limitations of time-consuming and con siderable accumulated error by traditional time-domain simulations. A sta ndard without relying on simulation but a common analytical approach ha s been obtained. Clearly, it can be regarded as a common analytical appro ach that would be useful to be able to model and predict the exact EMI pe rformance of the PWM-based power electronic systems. (Publications: D M and CM EMI Sources Modeling for Inverters Considering the PWM St rategies, Transactions of China Electrotechnical Society, 2007. High Freq uency Model of Conducted EMI for PWM Variable-speed Drive Systems, Proceedings of the Chinese Society of Electrical Engineering, 2008)