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CHAPTER 7: FILTER DESIGN AND REALIZATION Frequency [kHz] Attenuation required [dB] Resulting f0 [kHz] 150 25 36 230 28 46 300 10 170 Table 7.4: Attenuation for crucial points in CM output emissions 7.5 CM output filter implementation The DM filter, once inserted into the system, will provide on its own a CM inductance, that may or may not be enough to be used for the CM emissions filtering. The actual inductance that couples with the path of CM currents is the parallel of the three DM inductors, which is approximately 3mH. To see if this value will be enough, a CM filter design procedure has been followed, in the same way as fot the DM filter. Table 7.4 represents the attenuation required according to standards for crucial frequency points in Fig. 5.10, considering 10dB margin. Considering 3mH for the inductance, using expression 7.3.2, and designing the filter to attenuate 25dB at 150kHz, the required capacitance is 6.7nF. Therefore a commercial value of 10nF was used, which is below the 20nF limit of the 787 power-quality standard. This capacitor has been connected in the central point of the three DM capacitors in order to limit the number of capacitors connected from line to ground and to keep the capacitance connected on the three phases as low as possible. The actual capacitance that the CM currents will cross is composed of the parallel of the three 68nF DM capacitors in series with the single 10nF CM capacitor and this value is actually 9.5nF. This because the CM capacitor is much smaller compared to the value of 204nF resulting from the parallel of the DM capacitors, so the actual DM capacitors will not affect much the total CM capacitance value. Other than the estimation method used in Fig. 7.1, the emissions can be estimated more accurately adding the actual Filter’s frequency response, calculated with Matlab "Ø" function for the actual values of L and C, to the emissions before the filter insertion. Fig. 7.12 represents the results obtained using this method compared with the actual emissions measured once the complete filter has been inserted in the circuit. It can be seen that the estimation is very accurate for frequencies up to 1MHz; after that limit the filter attenuation remains constant rather than keep rolling-off, with a resulting emission behaviour parallel to the original without filter, roughly 70dB lower. As it is possible to notice in Fig. 7.13, the total output DM emissions after filter insertion presents a range of frequency around 10MHz in which a resonant peak still brings the EMI above the limit. To reduce the peak, some ferrite tubes made of material Fer- 93
CHAPTER 7: FILTER DESIGN AND REALIZATION I[dBµA] I[dBµA] 100 80 60 40 20 0 −20 w/o filter Estmated emissions Actual CM emissions after filter insertion −40 0.1 1 Frequency [MHz] 80 60 40 20 0 Figure 7.12: Output CM emissions after DM filter insertion −20 w/o filter with filter Limit Cat L −40 0.1 1 10 Frequency [MHz] Figure 7.13: Output DM emissions after DM filter insertion roxcube 3S4, a material designed to properly handle frequencies higher than 100 MHz, have been inserted on the output three-phase conductors; once again the saturation has been checked showing that only one turn was allowed. So two tubes CST 17/9.5/29- 3S4 have been used for each phase for a DM configuration, plus a single one across all the conductors to reduce the CM emissions too. The final schematic of the filter can be seen in Fig. 7.14, where the ferrite beads are highlited, while Table 7.5 report the complete list of used components. 94
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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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CHAPTER 3: HF MODELLING STRATEGY Re
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CHAPTER 3: HF MODELLING STRATEGY De
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CHAPTER 3: HF MODELLING STRATEGY C2
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CHAPTER 4: MOTOR AND MATRIX CONVERT
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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
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