Multilevel Inverters

Conventional and Emerging Topologies and Their Control

Krishna Kumar Gupta, Pallavee Bhatnagar

• Publisher: Academic Press
• Year: 2017
• ISBN:
  9780128124499
• Topic: Technology & Engineering
• Subtopic: Engineering General
• Index: Technology & Engineering

Multilevel Inverters: Conventional and Emerging Topologies and Their Control is written with two primary objectives: (a) explanation of fundamentals of multilevel inverters (MLIs) with reference to the general philosophy of power electronics; and (b) enabling the reader to systematically analyze a given topology with the possibility of contributing towards the ongoing evolution of topologies. The authors also present an updated status of current research in the field of MLIs with an emphasis on the evolution of newer topologies. In addition, the work includes a universal control scheme, with which any given topology can be modulated. Extensive qualitative and quantitative evaluations of emerging topologies give researchers and industry professionals suitable solutions for specific applications with a systematic presentation of software-based modeling and simulation, and an exploration of key issues.

Topics covered also include power distribution among sources, voltage balancing, optimization switching frequency and asymmetric source configuration. This valuable reference further provides tools to model and simulate conventional and emerging topologies using MATLAB®/Simulink® and discusses execution of experimental set-up using popular interfacing tools.

The book includes a Foreword by Dr. Frede Blaabjerg, Fellow IEEE, Professor and VILLUM Investigator, Aalborg University, Denmark.

• Includes a universal control scheme to help the reader learn the control of existing topologies and those which can be proposed in the future
• Presents three new topologies. Systematic development of these topologies and subsequent simulation and experimental studies exemplify an approach to the development of newer topologies and verification of their working and experimental verification.
• Contains a systematic and step-by-step approach to modelling and simulating various topologies designed to effectively employ low-power applications

Chapter 1

Basics of Inverters

Abstract

In this chapter, fundamental concepts related to power electronics and inverters are discussed. Popular terminology is defined so that understanding multilevel inverters becomes much easier.

Keywords

Converters; electricity; energy; inverters; voltage

1.1 Introduction

While the demand for electrical energy continues to grow throughout the world, it is estimated that 100% of electrical energy will flow through power electronics, especially in developed countries [1]. It is anticipated that the role of power electronics in this era will be as crucial as that of computers and communication technologies. Power electronics has changed the face of electrical engineering. Applications of power electronics include regulated power supplies, uninterruptible power supplies (UPS), electrochemical processes, heating and lighting control, welding, reactive power compensation, flexible AC transmission systems, active filters, energy storage, motor drives, and so on. Of all power electronics converters, DC to AC converters (i.e. “inverters”) are most widely employed in the modern set-up of electric power generation, transmission, distribution, utilization, and protection.

This chapter deals with the fundamentals of inverters, however before that, there is a discussion on the power electronics technology. Throughout this book, concepts are discussed mainly in the context of voltage source inverters because the voltage-fed class of inverters is becoming universal, replacing the current-fed class [1]. While you might already have a good understanding of inverters, we would still recommend you read this chapter. This chapter serves as the base for building up a case for multilevel inverters. It will help you understand and appreciate the concept behind multilevel inverters from various angles. Moreover, it will help you understand the popular terminology for multilevel inverters in research publications.

In addition to the basics of the so-called H-bridge inverter, we also discuss the philosophy behind waveform analysis and filtering needs. This discussion sets up the scene for the pulse-width modulation (PWM) technique. In the final part, power switch requirements are discussed for inverters in general. Some more specific cases in the context of multilevel inverters will be taken up in subsequent chapters.

1.2 Power Electronics as a Technology

The purpose of this section is to understand the philosophy of power electronics in a simplified manner. Once this philosophy is understood, it will be extremely easy to introduce and analyze various concepts related to inverters at this stage and those related to multilevel inverters at later stages.

Before defining power electronics, let us consider a hypothetical problem (without considering practical application, as of now): you have a resistance of 10 Ω which is to be supplied with a voltage of 8 V, while you have a battery of 12 V at your disposal. What do you do? Well, you visualize the problem as shown in Fig. 1.1. You recognize that the battery (the “source”) is, of course, to be connected to the resistance (the “load”), but since the required voltage and the available voltage do not match, you need to do “something” in between! And that “something” should “step-down” the voltage from 12 to 8 V.

Figure 1.1 A hypothetical problem where a resistance is to be supplied with a voltage of 8 V while a source of 12 V is available.

Conventional wisdom tells you to connect another resistance of 5 Ω “in between” and voila! You do get the required voltage at the load terminals, as shown in Fig. 1.2. But there is a catch. The 5 Ω resistance dissipates a power of 3.2 W, while the source delivers a power of 6.4 W. So, the power loss is 50% of delivered power!

Figure 1.2 While putting another resistance in series helps to obtain the desired load voltage, it also leads to power loss.

So you now look for another solution which fulfills two requirements: it steps down voltage and it does so without any power loss (ideally). You connect a “switch S” in between the source and the load, as shown in Fig. 1.3A. And, you repeatedly operate the switch S in ON and OFF states. When S is ON, the instantaneous voltage v_R(t) across the load is 12 V and when S is OFF, v_R(t) is 0 V. These modes are shown in Fig. 1.3B and C, respectively. Your logic of doing so is simple: you are controlling the “average” voltage across the load. That is, if you keep S ON for a time duration T, then next you keep it OFF for a duration T/2 and you keep repeating it. You get a voltage waveform across the load resistance as shown in Fig. 1.3D and you calculate the average value of voltage to be 8 V (=V_R)! Also, when ON, the switch carries a current of 1.2 A but the voltage...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Foreword
• About the Authors
• Preface
• Acknowledgments
• Chapter 1. Basics of Inverters
• Chapter 2. Basics of Multilevel Inverters
• Chapter 3. Advent of New Topologies
• Chapter 4. Universal Control Scheme with Voltage-Level-Based Methods
• Chapter 5. Multilevel Inverter Based on Bridge-Type Connected Sources
• Chapter 6. Cross-Connected Sources-Based Multilevel Inverter
• Chapter 7. Comparison of Multilevel Inverter Topologies
• Index