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3-L DC Link ML Converter Properties 67 any of the upper six states in the table with FC balancing result in +i a/2, a combination of any of the six lower states in the table with FC balancing results in –i a/2. TABLE 22, REDUNDANT STATES FOR VECTOR {100} 2D AND COMBINATIONS OF STATES FOR BALANCED FC VOLTAGES States Levels Currents Total a b c a b c i-NP i-FC-a i-FC-b i-FC-c {1}DS 1 0 0 1 0 0 0 ia 0 0 {2}DS 2 0 0 1 0 0 ia -ia 0 0 {75}DS 3 1 1 2 1 1 ia 0 ib Ic {83}DS 3 2 1 2 1 1 -ic 0 -ib Ic {139}DS 3 1 2 2 1 1 -ib 0 ib -ic {147}DS 3 2 2 2 1 1 0 0 -ib -ic {221}DS 5 3 3 3 2 2 0 ia 0 0 {222}DS 6 3 3 3 2 2 -ia -ia 0 0 {367}DS 7 5 5 4 3 3 -ia 0 ib Ic {375}DS 7 6 5 4 3 3 ic 0 -ib Ic {431}DS 7 5 6 4 3 3 ib 0 ib -ic {439}DS 7 6 6 4 3 3 0 0 -ib -ic - States are defined as {c 1c 2c 3b 1b 2b 3a 1a 2a 3} BS (c 1 = MSB, a 3 = LSB). - Output levels are numbered from 0 to 4. - Currents are defined as positive when flowing out of the converter. Positive values indicate discharge of either NP and / or FC, negative currents are correspondingly charging NP or FC. Any linear combination of states in the upper half and the lower half can be implemented, leading to any average NP current value between –i a/2 and +i a/2. This corresponds with what has been found in paragraph 4.7.1.2, the NP current can be described as a piecewise linear function of the CM voltage also in the operating point of a discrete vector. The same kind of behavior can be shown for any of the other space vectors. The same principles apply to any other 3-L DC link topology. Redundant states can be combined to balance the flying capacitors and the resulting groups of states can be combined again to control the NP current. 4.5.4 Interaction of NP and FC control All 3-L DC link ML converters need both NP control and FC control. The two can be decoupled in all topologies in the following way: - FC control by choice of redundant states - NP control with CM based 3-L NP control schemes However, when they are combined, there is a higher degree of freedom. Suitable combinations of redundant states act both on FC and NP at the same time, but there may also be conflicting targets. This is topology specific and is discussed in more detail in paragraph 5.3 and chapter 0 where control schemes acting on NP and FC at the same time are proposed. 4.5.5 Natural balancing The split DC link converters have natural balancing properties for the flying capacitors and / or the NP voltage at least in some operating points. This has been analytically analyzed in various publications for NPC [93, 94], MC [95, 96, 97, 98, 99, 100], and SMC [101, 102]. [103] proposes a SVM scheme extending the natural balance capability of the NPC, allowing for smooth operation in
68 3-L DC Link ML Converter Properties steady state. No publications on the natural balance properties of the ML ANPC are available so far. A self balancing feature is nice, as it allows applying optimal modulation schemes regarding harmonic performance without sacrificing that property for NP control. On the other hand, active balancing features are not very effective and in reality, all topologies may require active NP control during transients, with distorted or unbalanced loads or in specific operating point. Active NP control schemes can dramatically improve dynamics and steady state error in NP and FC voltages. The remainder of this thesis focuses fully on active methods and does not investigated natural balance any further. 4.6 NP current in function of output voltage in single phase legs The neutral point current depends on the output currents and the duty cycles of the relevant switching cells. Many publications on NP control include an analysis of the NP current, however, this is usually limited to certain operating ranges and a limited set of topologies. The following paragraphs investigate the NP current for different topologies in detail to determine, whether the topology has an impact on the NP controllability and the control concepts to be applied. 4.6.1 NP current in the NPC In the NPC, there are two commutation cells. The upper cell is controlled by S1 and S3, the lower cell is controlled by S2 and S4. The NP current can be calculated based on (32) and (33) on page 53. The corresponding duty cycles and the resulting NP current are indicated in Figure 57. Cell duty cycle S1: α1 S2: α2 1 α2 α1 Phase leg duty cycle 1 NP current ratio S3: 1 − α1 S4: 1 − α2 1 I-NP/ I-out Phase leg duty cycle (a) (b) 1 Figure 57, 3-L NPC with duty cycles of the individual switches and the resulting normalized NP current, b) also valid for standard SMC modulation 4.6.2 NP current in the 3-L ANPC The ANPC allows for several different modulation schemes [22]. The different schemes are indicated in Figure 58. To calculate the NP current, the following equation can be derived from (32) and (33), assuming cell 1 and cell 2 to be operated in phase and cell 3 with a phase shift of π. α2 must always be larger than α1 to not violate any blocking voltage constraints.
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THÈSE En vue de l'obtention du DOC
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Acknowledgements i ACKNOWLEDGEMENTS
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iv Table of Contents 3.4 Generic ML
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vi Table of Contents 7.1 General mo
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viii Résumé français (French sum
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x Résumé français (French summar
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xiv Résumé français (French summ
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xvi Résumé français (French summ
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xviii Résumé français (French su
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Introduction 1 2 INTRODUCTION This
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Introduction 3 tighter capacitor di
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Introduction 5 TABLE 1, OPERATING R
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Introduction 7 2.3 Glossary Note th
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Introduction 9 2.4 Nomenclature Not
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Introduction 11 DPC DSP DTC FC FPGA
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ML Converter Topologies 13 3 ML CON
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ML Converter Topologies 15 The four
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Page 58 and 59: ML Converter Topologies 37 TABLE 17
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NP Control with Carrier based PWM 1
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NP Control with Optimal Sequence SV
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Application and Verification 149 7
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Application and Verification 151 TA
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Application and Verification 153 Th
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Application and Verification 155 7.
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170 Conclusions and Outlook 8.1.2 M
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172 Conclusions and Outlook 8.2 Out
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174 Conclusions and Outlook 8.3 Sum
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176 Appendix I = 1− ) (99) ( C 2
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178 Appendix TABLE 78, FLYING CAPAC
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180 Appendix 9.3 Single phase NP cu
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182 Appendix 9.4 States of the ANPC
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184 Appendix 9.5 NP currents as a f
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186 Appendix 9.5.3 Maximum and mini
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188 Appendix 9.6 NP current functio
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190 Appendix TABLE 91, NP CURRENT I
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192 Appendix TABLE 93, NP CURRENT I
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Bibliography 195 10 BIBLIOGRAPHY [1
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Bibliography 197 [33] P. Steimer,
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Bibliography 199 neutral point bala
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Bibliography 201 [88] J. Pou, J. Za
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Christoph Haederli - Les thÃ¨ses en ligne de l'INP - Institut National ...

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