# Three-level Neutral-point-clamped matrix converter Neutral-point-clamped Matrix Converter ... Matrix converter is a direct AC-AC ... 2.1 Conventional three-phase to three-phase direct matrix converter

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Lee, Meng Yeong (2009) Three-level neutral-point-clamped matrix converter topology. PhD thesis, University of Nottingham.

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Three-level Neutral-point-clamped Matrix Converter

Topology

By

Meng Yeong Lee, MSc in Electrical Engineering

Submitted to the University of Nottingham for the degree of Doctor of Philosophy,

March 2009.

- i -

Acknowledgement

I would like to thank my supervisors, Prof. Patrick Wheeler and Dr. Christian

Klumpner, of the Power Electronics, Machines and Control (PEMC) group at the

University of Nottingham for their guidance and continuous support throughout the

course of this research.

Thanks are due to all my friends and colleagues in the PEMC group for their continuous

support and for providing such a pleasant working environment. I would like to

especially thank Dr. Lee Empringham, Dr. Qiang Gao, Dr. M. Imayavaramban and Dr.

James Campbell for their advices on practical issues.

Last but not least, my minds and thanks always go to my beloved wife and parents, who

have always been enriching my life with their continuous support and love.

- ii -

Abstract

Matrix converter is a direct AC-AC converter topology that is able to directly convert

energy from an AC source to an AC load without the need of a bulky and limited

lifetime energy storage element. Due to the significant advantages offered by matrix

converter, such as adjustable power factor, capability of regeneration and high quality

sinusoidal input/output waveforms, matrix converter has been one of the AC AC

topologies that receive extensive research attention for being an alternative to replace

traditional AC-DC-AC converters in the variable voltage and variable frequency AC

drive applications.

Multilevel matrix converter is an emerging topology that integrates the multilevel

concept into the matrix converter topology. Having the ability to generate multilevel

output voltages, the multilevel matrix converter is able to produce better quality output

waveforms than conventional matrix converter in terms of harmonic content, but at the

cost of higher number of power semiconductor device requirement and more

complicated modulation strategy.

In this research work an indirect three-level sparse matrix converter is proposed. The

proposed converter is a hybrid combination between a simplified three-level neutral-

point-clamped voltage source inverter concept and an indirect matrix converter

topology. This multilevel matrix converter topology has a simpler circuit configuration

and is able to generate three-level output voltages, making this topology an attractive

option in industrial applications.

In this work a comprehensive simulation study is carried out to investigate the operation

of the proposed converter. The performance of the proposed converter is compared to

the conventional indirect matrix converter topology and a multilevel neutral-point-

clamped matrix converter in order to identify the advantages and disadvantages offered

by the proposed converter. A study of the semiconductor losses in the indirect three-

level sparse matrix converter is also included. Finally, the operation of the proposed

converter is experimentally validated using a laboratory prototype.

Table of Contents

- iii -

Table of Contents

1 Introduction

1.1 Power Electronics... 1

1.2 The DC AC Conversion.. 3

1.2.1 Diode Clamped Multilevel Converter. 5

1.3 The AC AC Conversion.. 8

1.3.1 Indirect AC AC Converter 8

1.3.2 Direct AC AC Converter.. 9

1.4 Motivation and objectives of the project. 12

1.5 Thesis Plan.. 13

2 Matrix Converter Topologies

2.1 Introduction..... 15

2.2 Direct Matrix Converter.. 15

2.2.1 Overview.. 15

2.2.2 Modulation strategies for the direct matrix converter.. 20

2.3 Indirect Matrix Converter... 23

2.3.1 Overview. 23

2.3.2 Space vector modulation for the indirect matrix converter

topology 26

2.3.2.1 The rectification stage... 26

2.3.2.2 The inversion stage 32

2.3.2.3 Synchronisation between the rectification and

inversion stages. 36

Table of Contents

- iv -

2.3.2.4 Simulation results of the indirect matrix

converter... 38

2.4 Hardware Implementation of the Indirect Matrix Converter. 40

2.4.1 Bi-directional switches... 40

2.4.2 Commutation techniques for the indirect matrix converter. 42

2.4.2.1 Output current direction based commutation

technique.... 43

2.4.2.2 Relative input voltage magnitude based

commutation technique. 45

2.4.3 Input filter design of the indirect matrix converter.. 46

2.4.4 Protection issues for the indirect matrix converter.. 48

2.4.4.1 Over-voltage protection. 48

2.4.4.2 Clamp circuit. 48

2.4.4.3 Protection against over-voltage caused by LC filter. 50

2.5 Advantages of the indirect matrix converter over the direct matrix

converter. 50

2.5.1 Overview.. 50

2.5.2 Safer commutation... 50

2.5.3 Reduced number of switches... 51

2.5.4 Cost effective multi-drive system 52

2.6 Conclusions. 54

3 Three-level Neutral-point-clamped Voltage Source Inverter

3.1 Introduction. 55

3.2 Circuit Topology. 55

3.3 Space Vector Modulation.... 60

Table of Contents

- v -

3.3.1 The neutral-point balancing problem... 65

3.3.1.1 The nearest three virtual space vector modulation.... 67

3.3.2 The switching sequences.. 72

3.4 Simulation results.... 72

3.5 Conclusions. 76

4 Simplified Three-level Neutral-point-clamped Voltage

Source Inverter

4.1 Introduction. 77

4.2 Circuit Topology. 77

4.3 Space Vector Modulation.... 82

4.3.1 The switching sequences.. 90

4.4 Simulation Results... 92

4.5 Conclusions. 94

5 Three-level-output-stage Matrix Converter

5.1 Introduction. 95

5.2 Circuit Topology. 96

5.3 Space Vector Modulation... 98

5.3.1 The Rectification Stage.... 99

5.3.2 The Inversion Stage. 100

5.3.3 Synchronization between the rectification and inversion

stages 111

5.4 Simulation Results.. 112

5.5 Conclusions. 120

Table of Contents

- vi -

6 Indirect Three-level Sparse Matrix Converter

6.1 Introduction. 121

6.2 Circuit Topology. 122

6.3 Space Vector Modulation.... 126

6.3.1 The Rectification Stage.... 126

6.3.2 The Inversion Stage. 130

6.3.3 Synchronization between the rectification and inversion

stages... 138

6.4 Simulation Results.. 140

6.5 Performance evaluation of the indirect three-level sparse matrix

converter. 144

6.6 Conclusions. 153

7 Converter Implementation and Experimental Results

7.1 Introduction. 154

7.2 Hardware Implementation.. 154

7.2.1 Overall structure of the prototype converter.... 154

7.2.2 Control platform.. 156

7.2.2.1 The three-step relative voltage magnitude based

commutation strategy 158

7.2.3 Measurement circuits... 161

7.2.4 Gate drive circuits.... 163

7.2.4.1 The bi-directional switch cell.... 165

7.2.4.2 The unidirectional switch.. 167

7.2.5 The power and protection circuits... 168

7.3 Experimental Validation. 172

Table of Contents

- vii -

7.3.1 Output performance evaluation... 173

7.3.2 Input performance evaluation.. 183

7.4 Conclusions 187

8 Semiconductor losses in the three-level matrix converters

8.1 Introduction. 188

8.2 Modeling of conduction losses 189

8.3 Modeling of switching losses.. 190

8.4 Semiconductor loss calculations for the three-level matrix converter

topologies 196

8.4.1 The three-level-output-stage matrix converter. 196

8.4.2 The indirect three-level sparse matrix converter.. 203

8.4.3 Comparison of semiconductor losses between the three-level

matrix converters and the indirect matrix converter 207

8.5 Conclusions. 212

9 Conclusions

9.1 Conclusions. 213

9.2 Future Work 215

Appendixes

A Parameters Used. 216

B List of Symbols... 219

C Published Papers 224

List of Figures

- ix -

List of Figures

1.1 The power electronic interface between the source and the load .. 2

1.2 (a) A conventional three-phase two-level inverter (b) The output

voltage waveform generated by a voltage source inverter based on a

pulse-width modulation (sinusoidal reference voltage is included)... 4

1.3 Output terminal voltage waveforms .. 5

1.4 One phase leg of a three-level neutral-point-clamped voltage

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