Modular Multilevel Converter (MMC) has become the most concerned converter topology in the High Voltage Direct Current (HVDC) transmission system, in recent times. The low switching frequency, low converter losses and flexible control made it most attractive topology. It is important to make a research on the loss calculation method of MMC and state formulae for the losses as it is a vital step during the design stage of the MMC based HVDC system.
In this research work, the structure of MMC based HVDC system is discussed. Three sub module topologies’; half bridge, full bridge and clamp double sub module, are discussed. A method based on the average and root mean square (RMS) values of the current passing through the sub module is discussed. The conversion losses in the switching devices of the sub modules are calculated using the method.
A cases study is taken into consideration then with certain parameters. Using these parameters a MATLAB program is developed. With the help of the program the losses and efficiency curves for each switching device by taking each sub module separately are obtained respectively. A comparison of the losses and efficiency of each sub module is also discussed. At the end those factors which effect the losses and efficiency of the sub module are discussed along with the certain aspects for the directions of future work.
Table of Contents
Chapter 1: Introduction
1.1 Problem Statement
1.2 Aim and Objective
1.3 Scope of Work
1.4 Organisation of Thesis
Chapter 2: Literature Review
2.1 Introduction
2.2 Literature Review
Chapter 3: Modular Multilevel Converter
3.1 Introduction
3.2 Modular Multilevel Converter (MMC).
3.2.1 Features of Modular Multilevel Converter (MMC).
3.2.2 Advantages of Modular Multilevel Converter (MMC).
3.2.3 Working of Modular Multilevel Converter (MMC).
3.3 Sub Module Topologies
3.3.1 Half Bridge Sub Module.
3.3.2 Full Bridge Sub Module.
3.3.3 Clamp Double Sub Module.
Chapter 4: Average and RMS Values Calculation
4.1 Introduction
4.2 Circuit Ananlysis
4.3 Conversion Losses.
4.3.1 Conduction Losses.
4.3.2 Switching Losses.
4.4 Half Bridge Sub Module Calculations
4.4.1 Average Value of the Current.
4.4.2 RMS Value of the Current.
4.5 Full Bridge Sub Module Calculations
4.5.1 Average Value of the Current.
4.5.2 RMS Value of the Current.
4.6 Clamp Double Sub Module Calculations.
4.6.1 Average Value of the Current.
4.6.2 RMS Value of the Current.
Chapter 5: Power Losses Estimation
5.1 Introduction
5.2 Half Bridge Sub Module
5.2.1 Conduction Losses.
5.2.2 Switching Losses.
5.3 Full Bridg Sub Module.
5.3.1 Conduction Losses.
5.3.2 Switching Losses.
5.4 Clamp Double Sub Module.
5.4.1 Conduction Losses.
5.4.2 Switching Losses.
Chapter 6: Solution based on MATLAB Simulation: Case Study.
6.1 Introduction
6.2 Half Bridge Sub Module
6.3 Full Bridge Sub Module.
6.4 Clamp Double Sub Module.
6.5 Summary
Chapter 7: Conclusion.
7.1 Conclusion of Research Work.
7.2 Future Directions.
Research Objectives and Focus
The primary aim of this research is to develop an analytical method for calculating conversion losses and efficiency of various sub-module topologies used in Modular Multilevel Converter (MMC) based HVDC systems, providing engineers with a reliable tool for system design and optimization.
- Analysis of MMC sub-module topologies including half bridge, full bridge, and clamp double configurations.
- Derivation of mathematical models for conduction and switching losses based on average and RMS current values.
- Development of a MATLAB-based simulation program to evaluate performance metrics under varying parameters.
- Comparative study of efficiency and power loss characteristics for different sub-module designs.
Excerpt from the Book
3.3.1 Half Bridge Sub Module
Structure of half bridge sub module (chopper cell) is shown in Figure 3-2. Half bridge sub module consists of two IGBTs; T1 and T2, two freewheeling diodes; D1 and D2 and a capacitor. As mentioned early, a sub module is a two terminal device. The voltage across the sub module is VAB, which is equal to the voltage across the capacitor, Vcap. The switching states and the sub module voltages are shown in Table I. For positive arm current (bridge current), ib, either the diode D1 or IGBT T2 is conducting. For the conduction of diode, D1 the capacitor will charge, giving the sub module voltage equal to capacitors voltage. While for IGBT, T2 the sub module is by passed, resulting in zero sub module voltage.
For negative arm current, either diode D2 or IGBT T1 is conducting. For IGBT T1 conduction, the capacitor is discharged, resulting in the sub module voltage equal to the capacitor’s voltage. While for the conduction of Diode D2, the voltage across the sub module is equal to zero, by-passing the sub module.
Summary of Chapters
Chapter 1: Introduction: Provides an overview of HVDC systems, identifies the design challenges in MMC technology, and outlines the thesis objectives and structure.
Chapter 2: Literature Review: Surveys existing research on MMC loss estimation techniques from 2003 onwards, establishing the need for the proposed analytical method.
Chapter 3: Modular Multilevel Converter: Details the construction, working principles, and specific features of MMC, comparing various sub-module topologies like half-bridge and full-bridge.
Chapter 4: Average and RMS Values Calculation: Derives the mathematical relationships for average and RMS currents flowing through switching devices under different operating conditions.
Chapter 5: Power Losses Estimation: Calculates conversion losses for each sub-module topology using the derived current equations from the previous chapter.
Chapter 6: Solution based on MATLAB Simulation: Case Study: Presents simulation results, including efficiency curves and loss analysis, to validate the derived analytical models.
Chapter 7: Conclusion: Summarizes the key findings of the research regarding sub-module efficiency and provides recommendations for future investigative work.
Keywords
Modular Multilevel Converter, MMC, HVDC, Power Electronics, Conduction Losses, Switching Losses, Half Bridge, Full Bridge, Clamp Double Sub Module, MATLAB Simulation, Efficiency, IGBT, Current Analysis, RMS Value, Transmission System.
Frequently Asked Questions
What is the main focus of this research?
The research focuses on accurately calculating and comparing conversion losses and efficiency for different sub-module topologies within MMC-based HVDC transmission systems.
What are the primary sub-module topologies discussed?
The thesis examines the half bridge, full bridge, and clamp double sub-module topologies.
What is the primary objective of this work?
The goal is to provide design engineers with a robust analytical method and a MATLAB-based tool to estimate semiconductor power losses during the design phase of MMC systems.
What scientific methodology is employed?
The study utilizes an analytical approach based on the calculation of average and root mean square (RMS) values of currents flowing through semiconductor devices to derive loss and efficiency formulas.
What is covered in the main body of the thesis?
The main body covers the theoretical background of MMC, the mathematical derivation of current-based loss models, and the numerical verification of these models through MATLAB simulations.
Which keywords best characterize this work?
Key terms include Modular Multilevel Converter (MMC), HVDC, semiconductor power losses, efficiency estimation, and sub-module topologies.
Why is MMC preferred over traditional VSC topologies in this context?
MMC is noted for its low switching frequency, low converter losses, flexible control, and easier scalability, making it ideal for modern HVDC applications.
What effect does the junction temperature have on losses?
The research acknowledges that junction temperature significantly impacts semiconductor device performance and incorporates it into loss considerations using temperature coefficients.
How does the clamp double sub-module compare to the full bridge?
The analysis indicates that the clamp double sub-module has higher total power losses compared to the full bridge due to the inclusion of additional transistors and diodes.
- Arbeit zitieren
- Ehtasham Mustafa (Autor:in), 2014, Analytical Efficiency Evaluation of Modular Multilevel Converter (MMC) for High Voltage Direct Current System (HVDC), München, GRIN Verlag, https://www.grin.com/document/316343
