Analysis and Design of Multicell DC/DC Converters Using Vectorized Models

Thierry Meynard is Directeur de Recherches CNRS at Laboratoire LAPLACE, ENSEEIHT, INPT, University of Toulouse, France and part-time consultant at CIRTEM (Centre d'ingénierie et de recherche en technologies de l'électrotechnique moderne). He is the co-inventor of various topologies of series multicell (multilevel) converters and has been involved in the transfer of several of these topologies to industry, especially in the field of medium voltage drives (typ. 1-10kV, 1-10MW). In recent years his research interests have focused on parallel multicell (interleaved) converters for application in low voltage embedded applications (<1kV) and on the design of corresponding magnetic components.

CHAPTER 1. GENERAL PROPERTIES OF MULTILEVEL CONVERTERS 1

1.1. Time-domain: multilevel waveform and apparent switching frequency 1

1.2. Frequency domain: harmonic cancellation 4

1.3. Transient response 5

1.4. Conclusion 6

CHAPTER 2. TOPOLOGIES OF MULTILEVEL DC/DC CONVERTERS 9

2.1. Series connection 9

2.1.1. Direct series connection with isolated sources 9

2.1.2. Flying capacitor 11

2.2. Parallel connection 14

2.2.1. Interleaved choppers with star-connected inductors 14

2.2.2. Interleaved choppers with InterCell Transformers (ICTs) 17

2.3. Series-parallel connection 20

CHAPTER 3. CONCEPT OF VECTORIZATION IN PLECS 23

3.1. Vectorized components 23

3.2. Star-connection block and parallel multicell converter 25

3.3. Series connection block and series multicell converter 27

3.4. Generalized multicell commutation cell 28

3.5. Practice 34

3.5.1. How to? 34

3.5.2. Basic blocks 34

CHAPTER 4. VECTORIZED MODULATOR FOR MULTILEVEL CHOPPERS 37

4.1. General principle 37

4.2. xZOH: equalizing multisampler for multilevel choppers 38

4.2.1. Control as the main source of perturbation 38

4.2.2. Handling duty cycle variation 38

4.2.3. Frequency response of the equalizing sampler and modulator 51

4.3. Practice 53

CHAPTER 5. VOLTAGE BALANCE IN SERIES MULTILEVEL CONVERTERS 57

5.1. Basic principles 57

5.2. Linear circuits 58

5.2.1. Internal balancers 58

5.2.2. External balance boosters 59

5.2.3. Pros and cons of internal/external balance boosters 64

5.3. Nonlinear variants 65

5.3.1. Internal balance boosters 65

5.3.2. External balance boosters 66

5.4. Loss-based design 67

5.4.1. Introduction 67

5.4.2. Internal balance boosters 68

5.4.3. External balance boosters 68

5.5. Vectorized models of balance boosters 69

CHAPTER 6. FILTER DESIGN 75

6.1. Requirements 75

6.1.1. Steady state: current ripple, voltage ripple and standards 75

6.1.2. Transients 83

6.1.3. Extra design constraints 84

6.2. Design process 85

CHAPTER 7. DESIGN OF MAGNETIC COMPONENTS FOR MULTILEVEL CHOPPERS 89

7.1. Requirements and problem formulation 89

7.2. Area product 92

7.2.1. Low frequency – low ripple formulation for filtering inductors 92

7.2.2. General formulation for filtering inductors 94

7.2.3. Application to inductors for interleaved converters 95

7.2.4. Extension to InterCell Transformers 97

7.3. Optimal area product of magnetic components for interleaved converters 99

7.3.1. Optimal area product for inductors 99

7.3.2. Optimal area product for InterCell Transformers 101

7.4. Weight-optimal dimensions for a given area product 101

7.4.1. For inductors 101

7.4.2. For InterCell Transformers 107

7.5. Volume-optimal dimensions for a given area product 118

7.6. Number of turns and air gap 120

7.7. Accounting for current overload 123

7.8. Optimal phase sequence for InterCell Transformers 123

7.9. Vectorized reluctance model of magnetics 125

7.9.1. Inductors 125

7.9.2. Cyclic cascade InterCell Transformers 126

7.9.3. Monolithic InterCell Transformers 128

7.10. Design process 130

CHAPTER 8. CLOSED-LOOP CONTROL OF MULTILEVEL DC/DC CONVERTERS 131

8.1. Principle 131

8.2. Corresponding PLECS block 133

8.3. Average model of the macrocommutation cell for transient studies 136

8.4. Conclusion 140

BIBLIOGRAPHY 141

INDEX 145