ABSTRACT
This proposes a switching for cascaded H-Bridge (CHB) cells. Single Sinusoidal PWM (SCSPWM) scheme is employed in the generation of the gating signals.
A sequential switching and base PWM circulation schemes are presented for this fundamental cascaded multilevel inverter . With these proposed concepts, it is now possible to generate equal switching signal patterns in all the constituting power semiconductor switches.
This results in equal switching loss dissipation and equal power sharing in CHB multilevel inverter modules; and therefore technically modularizes the cascaded system. A 4-cell cascaded structure has been used to exemplify the proposed switching technique.
Outlines with switching functions are given for the proposed modulation strategy. For a modulation index of 0.9, a Total Harmonic Distortion (THD) value of 14.61% has been achieved in the output voltage waveform of the exemplanary 4- cell cascaded configuration.
Simulations for single phase cascaded multilevel inverters (five-level, seven-level and nine-level) and their Total Harmonic Distortion (THD) is compared.
The THD for the five-level, seven-level and nine-level are 21.92%, 9.51, and 5.30% for different topologies with different modulation techniques for single phase.
When compared with the cascaded H-Bridge Cell, there is an improvement compared with the single phase cells. Verification of the performance of the proposed control technique is done through simulations.
TABLE OF CONTENTS
Title Page i
Approval Page ii
Certification iii
Dedication iv
Acknowledgement v
Abstract vi
Table of Contents vii
List of Tables xi
List of Figures xii
List of Abbreviations xvii
Chapter One
- Introduction 1
- Overview 1
- Significance of the Study 2
- Objective of the Study 3
- Features of Multilevel Inverter 4
Chapter Two
- Multilevel Inverter to Hybrid Multilevel Inverter 7
- Multilevel Inverter Configuration 7
- Working Principle of Multilevel Inverter 9
- H-bridge Inverter 9
- Bipolar Pulse-Width Modulation 11
- Unipolar Pulse-Width Modulation 12
- Diode Clamped Multilevel Inverter 14
- Flying Capacitor Multilevel Inverter 18
- Cascaded Multilevel Inverter 21
- Modulation Control Techniques 23
- Classification of Different Modulation Techniques 23
- Multi Carrier Pulse width Modulation 24
- Carrier Disposition (CD) Techniques 25
- Phase Disposition (PD) Technique 26
- Phase opposition disposition (pod) technique 27
- Alternative Phase Opposition Disposition (APOD) Technique 28
- Phase Shifted (PS) Technique 30
- Hybrid Modulation Techniques Hybrid PWM (H-PWM) 31
- Hybrid Modulation Strategy 31
- Hybrid Multilevel Inverter 33
- Classification of Hybrid Multilevel Inverter 33
- Asymmetric Hybrid Multilevel Inverter 34
- Hybrid Multilevel Inverter Based on Half-Bridge Modules 36
- New Symmetrical Hybrid Multilevel Inverters 38
- Hybrid Clamped Five-Level Inverter Topology 40
- Distinct Series Connected Cells Hybrid Multilevel Inverter 41
- Hybrid Medium-Voltage Based on a NPC Inverter 43
- Hybrid Multilevel Inverter Based on Main Inverter and
Conditioning Inverter 44
- New Hybrid Asymmetrical Multilevel H-Bridge Inverter 46
- Hybrid Multilevel Inverter with Single DC Source 47
Chapter Three
3.0 Proposed Hybrid Modulation Strategy for Cascaded H-Bridge Multilevel Inverter 51
3.1. Base Switching Signal Generator 54
- Module Signal Equalizing Generator 54
- Gating Signal Sequence Generator 55
Chapter Four
- Simulation Results for Multilevel Inverter and Hybrid strategy for cascaded H-bridge 59
- Five-Level cascaded multilevel inverter 59
- Five-Level Cascaded Multilevel Inverter with Staircase Technique 59
- Five-Level Cascaded Multilevel Inverter with Phase Disposition Modulation Technique 61
- Seven-Level Cascaded Multilevel Inverter 62
- Seven-Level Cascaded Multilevel Inverter with Staircase Technique Using Three H Bridges 62
- Seven Level Cascaded Multilevel inverter with phase Disposition Modulation Technique 65
- Nine-Level Cascaded Multilevel Inverter 67
- Nine-Level Cascaded Multilevel Inverter with Staircase Technique Using Three H Bridges 67
- Hybrid Strategy for Cascaded H-bridge Multilevel Inverter 70
Chapter Five
- Experimental Results 74
- Single Carrier Sinusoidal Pulse Width Modulation (SCSPWM) 75
- Rectified Single Carrier Sinusoidal Pulse Width Modulation (SCSPWM) 76
- Triangular Carrier Signal 77
- Comparing of a Rectified Sine wave with a Triangular Wave Signal 78
- comparing of Offset of the Rectified Sine Wave with Triangular wave signal 78
- Logic Output Pulse Signals a, b, c, d, A, B, C and 81
- Base Switching Signal Generators U4, V4, U3, V3, U2, V2, U1, V1. 84
Chapter Six
- Conclusion 88
- Recommendation 89
Reference 90
INTRODUCTION
Multilevel inverters (MLI) have very significant development for medium voltage and high power application due to their ability to synthesize waveforms with better harmonic spectrum.
Multilevel inverters refer to the inverters with output which have more than two voltage levels possible with respect to pole. The attribute of having an output voltage level that is higher than those of the power semiconductor switching devices’ ratings puts the MLIs in high power inverters class.
The application of MLIs has been extended to the medium power range due the advantages of reduced distortion, dv/dt stress and common mode voltage [1]–[3].
Overview
Cascaded H-bridge (CHB) multilevel inverter is one of the popular converter topologies used in high-power medium-voltage (MV) drives [1–3]. It is composed of a multiple units of single- phase H-bridge power cells.
The H-bridge cells are normally connected in cascade on their ac side to achieve medium-voltage operation and low harmonic distortion.
In practice, the number of power cells in a CHB inverter is mainly determined by its operating voltage and manufacturing cost. For instance, in the MV drives with a rated line-to-line voltage of 3300 V, a nine-level inverter can be used, where the CHB inverter has a total of 12 power cells using 600V class components [1].
The use of identical power cells leads to a modular structure, which is an effective means for cost reduction. The CHB multilevel inverter requires a number of isolated dc supplies, each of which feeds an H-bridge power cell.
REFERENCES
Nabae, I. Takahashi, and H. Akagi, “A new neutral-point-clamped PWM inverter,” IEEE Trans.Ind. Appl., vol. 17, no. 5, pp. 518–523,Sep./Oct. 1981.
S. Choi, J. G. Cho, and G. H. Cho, “A general circuit topology of multilevel inverter,” in Conf. Rec. 1991 IEEE PESC, pp. 96–103
A. Meynard and H. Foch, “Multi-level conversion: high-voltage chopper and voltage-source inverters,” in Conf.Rec. 1992 IEEE PESC,pp. 397–403.
W. Menzies, P. Steimer, and J. K. Steike, “Five-level GTO inverters for large induction motor drives,” in Conf.Rec. 1993 IEEE-IAS Annu.Meeting, pp. 595–601
Marchesoni and M. Mazzucchelli, “Multilevel converters for high power AC drives: a review,” in Proc. IEEE ISIE’93, Budapest, Hungary, 1993, pp. 38–43.
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