Beschreibung
This thesis deals with modeling and reduction of conducted electromagnetic interference (EMI) in power electronic systems, with focus on three-phase applications. Different modeling methods based on physical modeling and behavioral modeling are studied and developed, in order to achieve accurate and fast prediction of level of conducted EMI. The accuracy of prediction is validated by comparison with result from measurement which carried out in standard-defined environment. Once the problem of conducted EMI is identified, solutions should be found to get rid of it. Different methods for reduction of conducted EMI are studied, especially the use of passive EMI filter as suppression along propagation path and the use of modulation methods as suppression at the source. With simulation models and experimental implementation, the influential factors and the applications of reduction methods are analyzed and evaluated. The first part of the thesis is devoted to modeling of conducted EMI. By analyzing available data in different stages of product development, either physical modeling or behavioral modeling can be applied. During the study, physical phenomena which occur within components in power electronic system are analyzed. Analytical, numerical and empirical methods are applied to obtain parameters of the physical models which provide required accuracy in frequency range concerned. Different systematic simulation methods are compared and a new method based on linear-time-varying system is proposed in order to achieve accurate, fast and stable simulation. Behavioral modeling, which does not rely on detailed knowledge of used components, is also studied by analyzing the network representation of power electronic system. The extraction of parameters in behavioral model is accomplished by simulation and experiment. Requirements, devices and procedure of parameter extraction are analyzed and detailed described. The second part of the thesis focuses on methods for reduction of conducted EMI. Firstly, passive EMI filter as widely used countermeasure for EMI problem is chosen to be analyzed and studied. The high frequency characteristics of filter components as well as filter as a whole are predicted. Thanks to the proposed model based on symmetrical component theory, the behavior of three-phase EMI filter can be better understood and characterized. A virtual design procedure of EMI filter based on behavioral modeling of power electronic system and circuitry model of EMI filter is demonstrated, with result confirmed by measurement. Influence of the structure of EMI filter, symmetrical or unsymmetrical, is also investigated. The potential of benefit brought by unsymmetrical structure is demonstrated by a design example. Influences of different variables on conducted EMI level are analyzed, modeled and evaluated, which provide references for consideration of EMI problem during design process. To complete the analysis on reduction methods, the suppression at noise source is also studied. Methods using different modulation strategies are analyzed. With simulation and experimental verification, their influences on conducted EMI and operational performances are compared and evaluated.
