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3.1 Introduction CHAPTER 3 HF Modelling Strategy In literature some works have been presented with the aim to reduce EMI emission on inverter driven motors, some of which use a Finite Elements (FE) analysis approach to fully understand the stray components and so the current paths, as in [41]. Such FE simulations can provide a very accurate result, but they are time consuming and they are very specific for the chosen system. This will hinder a fast design for the EMI filter and will largely reduce the portability of the model eventually created. For these reasons the FE approach has been considered not of interest in this work, instead modelling and parametrization using experimental impedance measurements has been chosen in this thesis. This chapter describes the high frequency modelling strategy proposed, based on automated impedance measurements matching; however without going into details of the HF models yet. The experimental impedance measurement techniques used and how the measurements have been chosen will be firstly described. Then a brief introduction on the Genetic Algorithms, used to identify the model’s parameters to match the experimental measurements, together with a description of the fitness function that weights how the results are close to the reference values provided, is given. A discussion on the way the HF impedance simulations have been carried out, trying to optimize the calculation time and still providing a good flexibility if some changes in the model are needed. 3.2 Impedance measurements During the HF filter design process an accurate HF model is needed for the whole system. In order to do so, in this thesis, the starting point for the HF modelling is the actual 29
CHAPTER 3: HF MODELLING STRATEGY impedance measurement of every single component of the drive, along the frequencies of interest. To obtain these values an Impedance Analyzer (HP4194A with a 41941- 61001 probe) has been used. It provides reliable measurements in the range 10kHz – 100MHz, of which we are interested only in the first 30MHz because the Conducted Emission specifications in [1] apply only in this range. This instrument can perform linear or logarithmic sweeps in the specified range of frequencies, storing internally up to 401 points of the measured complex impedance. The instrument also features an HP interface bus, interconnected with a pc to allow the download of the stored data. When the measurement has taken place, a LabVIEW program was used to read the internal registers and save them into an excel file, to be imported into the Matlab’s environment for use as a reference during the HF modelling. This whole process is very straightfor- ward and does not take long; it is a much faster approach than a Finite Element study that would have to be carried out on every component; even though the latter will be more accurate. This lack of high precision is unavoidable with this system, besides, it is a necessary trade-off in order to obtain results good enough for a quick start of the EMI filter design. Configurations of measurements done To characterize the whole system, every single component has to be measured; in more detail there is the AC motor, the matrix converter, the cables and the Line Impedance Stabilization Network (LISN). This latter component becomes part of the circuit because it must be used during the emissions measurements, as it is described by the reference standard [1], to provide a nominal line impedance no matter which voltage source is in use. The impedance measurement configurations have to match the emissions to be reduced, in more detail we need common and differential mode measurements. Starting with the motor, for the common mode all the input terminals need to be shorted together, and the impedance measured between this point and the ground. For the differential mode, instead, the measure needs to take place among one terminal and the others 2 shorted, leaving the ground connection floating. Some considerations need to be made, because of the high frequency in play: over the last part of the interest range, 10 – 30MHz the parasitics play a dominant role in the impedance, and all the capacitive coupling will come into play dominating the impedance’s behaviour. Therefore if, for the measurements, any external wire has been used, its impedance needs to be measured on its own and afterwards subtracted from the global measurement to get only the data of interest. For the measurements, wher- ever possible, all the data has been taken using no extra wires, to avoid the differences 30
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CHAPTER 6: SIMULATIONS OF INPUT AND
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CHAPTER 7 Filter Design and realiza
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CHAPTER 7: FILTER DESIGN AND REALIZ
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CHAPTER 8 Filter realization and ex
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CHAPTER 8: FILTER REALIZATION AND E
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CHAPTER 9 Conclusions and Further w
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APPENDIX A Scientific Publications
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B.1 C code APPENDIX B External DLL
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APPENDIX B: EXTERNAL DLL Tseq_Pulse
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APPENDIX B: EXTERNAL DLL B.2 MAST c
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References [1] RTCA Incorporated. R
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REFERENCES nious drives. In Europea
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REFERENCES [48] D.F. Knurek. Reduci
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