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CHAPTER 7: FILTER DESIGN AND REALIZATION I[dBµA] 80 60 40 20 0 −20 Limit for category L Estimated DM emissions after filter insertion −40 0.1 1 10 Frequency [MHz] Figure 7.1: Output DM filter design L = C = 1 (2π f0) 2 · C 1 (2π f0) 2 · L (7.3.1) (7.3.2) The filter so designed, however, presented some flaws that will later on be reported and the final filter design will be eventually described. 7.3.1 DM inductor design with Ferrites To build the DM inductors the choice went initially for ferrite cores, because of their capabilities of handling high frequencies, and this section will provide the reasons and reference about their choice. Each manufacturer has several different materials specif- ically designed for EMI filtering; unfortunately these have proven not to be all easily obtainable as it may seem looking at catalogues. This is because distributors have only a limited set of materials and toroids available, and usually the available ones are not the best ones for an EMI application, but just the ones more requested for general application. Some attempts were made to obtain materials properly suited for high frequency, like Ferroxcube 3S4 cores, but the available size was not a fit for the needed current level and attenuation. Having the restriction to choose only from off-the-shelf components that were available from distributors, a very narrow span of materials was therefore possible: it mainly consisted of N30 for Epcos, 3E27 for Ferroxcube and J material for Magnetics. Among these the worst is probably the Epcos 3E27, of which the permeability drops sharply just after 300kHz, that will not provide a sufficient attenuation for the high frequen- 85
CHAPTER 7: FILTER DESIGN AND REALIZATION cies. In Fig. 7.2 and 7.3 it is possible to see and compare the permeability of these materials. Figure 7.2: Permeability of Ferroxcube 3E27[5] and Epcos N30[6] materials To design the inductors there are two main aspects to be taken under consideration: the Inductance factor A l that will determine the number of turns needed to reach the desired inductance and the maximum magnetic field strength allowed before having saturation. Avoiding saturation in inductors is an important issue, if not observed the component inductance will drop significantly, thus loosing the filtering capabilities. The allowed maximum field density changes from material to material, and it can be obtained from the relative datasheet on the B/H curve; in ferrites it varies significantly, for example for an EPCOS ferrite N30 its 100A/m (Fig. 7.4), for a N87 ferrite is 250A/m, for harder ferrites it can even be greater than 2000 A/m. Because of the limited number of ferrites available, a collection of the data for the available ones was carried out to populate a table with the useful parameters, to guide the Figure 7.3: Permeability of Magnetics J material[7] 86
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EMI Filter Design for Matrix Conver
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that may involve long Finite Elemen
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CONTENTS 3.1 Introduction . . . . .
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CONTENTS B External DLL 118 B.1 C c
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LIST OF FIGURES 2.10 Measurement at
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LIST OF FIGURES 6.9 CM Conducted EM
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LIST OF FIGURES 8.18 Input CM and D
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LIST OF TABLES 7.9 Attenuation for
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CHAPTER 1: INTRODUCTION the receive
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CHAPTER 1: INTRODUCTION Abs. Magnit
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CHAPTER 1: INTRODUCTION Figure 1.5:
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CHAPTER 1: INTRODUCTION • Make th
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CHAPTER 1: INTRODUCTION Figure 1.10
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CHAPTER 1: INTRODUCTION the filters
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CHAPTER 1: INTRODUCTION experimenta
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CHAPTER 2 Experimental implementati
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CHAPTER 2: EXPERIMENTAL IMPLEMENTAT
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CHAPTER 3: HF MODELLING STRATEGY im
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CHAPTER 3: HF MODELLING STRATEGY ci
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Page 131 and 132: APPENDIX A Scientific Publications
Page 133 and 134: B.1 C code APPENDIX B External DLL
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Page 139 and 140: References [1] RTCA Incorporated. R
Page 141 and 142: REFERENCES nious drives. In Europea
Page 143: REFERENCES [48] D.F. Knurek. Reduci
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