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ELEC-6411 Bi-directional Cascaded Buck-Boost ConverterFall 2015


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ELEC-6411 Project Final ReportBi-directional Cascaded Buck-Boost Converter

Design, Simulation and Analysis

Submitted to: Dr Luiz A. C. Lopes

Submitted by:

Andrew Jensson, 40009961

Rajendra Thike, 27833040

Date of Submission: , 2015

Term: Fall 2015


Table of Contents

List of Given Parameters ........................................................................................... 3

List of Tables .............................................................................................................. 3

Acknowledgement ..................................................................................................... 7

Abstract ..................................................................................................................... 7

Introduction ............................................................................................................... 8

Machine Design .......................................................................................................... 8

Parameter Selection ................................................................................................... 8

Adjustments ............................................................................................................. 11

Conclusions ............................................................................................................. 14

References ............................................................................................................... 15

Abstract

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Buck-Boost converters have a wide range of functionality and application within the renewable energy field; from motor drives of electric vehicles to wind turbine energy generation. Matching the required dc voltage output with a variable dc source can make for a difficult task without the use of commonplace electronic devices such as the Buck-Boost converter; which has also been coloquially referred to as the “dc transformer”. This project will look at the design, application, analysis and overview of a functional Buck-Boost converter with a specific design called the “cascade” in which an inductor couples the sections of the converter to allow for voltage regulation of a variable source that can vary from much less than the desired output voltage to much greater. The Buck-Boost Cascaded converter is truly a robust and useful design that will be explored in the following sections.

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Introduction

In many applications, the need for a regulated output dc voltage is a necessity. Applying an unregulated dc voltage to certain loads may lead to component unintended operation, deterioration, failure or worse. Another important factor to consider is that many dc loads and sources may deteriorate and prematurely fail if acurrent ripple or alternating component is present under operating conditions. Whena designer is implementing a converter for a specific task, much consideration is required to meet the specific design requirements, specifications and features as well as provide a robust, efficient and adequately designed system.

The Bi-directional Cascaded Buck-Boost Converter, for simplicity will be referred to as the BBC from herein, is one topography of dc-dc converters that has unique features and function that make it an attractive option for certain applications. When variable power must be sent and returned to a dc source (hence bi-directional), a dc-dc converter may be selected; even providing a more stable operating dc source for critical loads, a BBC may be utilized. The “cascaded” component stems from the series connection of both types of converters. The BBC presented in this project offers an efficient, relatively simple and robust topology to operate under varying conditions. To further understand the operation and principles of this BBC, some applications are:

Electric Vehicle Drive and Regenerative Brakingi

Back-up Power Supplyii

Grid-connected Fuel-cell Energy Storage

Photo-voltaic Systems

Energy Recovery Systems

Back-to-back Wind Power Systems

For the purpose of this project, the BBC will be modeled in an electric vehicle inspired application, with the load of the BBC being a super-capacitor. Depending onthe status of the super-capacitor, it will be charged using a Buck or Boost configuration.

The following schematic illustrates the circuit that is used for this project:

Operation

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Before designing a functional BBC, one must understand the fundamentals of operation of the circuit, as well as fundamental components and concepts individually.

MOSFETiii

For the purpose of design and analysis of the BBC, the MOSFET operates as an idealized switch. This means that the MOSFET will have not voltage drop across it when closed, and no current will leak through when opened. The idealized MOSFET will also have an instantaneous turn-on and turn-off time and is capable of operating under all voltage and current conditions present in the BBC. To operate the MOSFET, a gate signal will be applied to the “G” node when a closed switch is desired; under all other conditions, the gate signal will be grounded with 0 v.

Inductor

The inductor plays a vital role in the BBC circuit; namely to act as the energy storage medium while the MOSFETs are switching to provide the desired output voltage. The basic inductor is a simple component in that it has a magnetic or air core with a wire coiled around. There are many other types of inductors, but the scope of this project will only explore these configurations of inductors. When current passes through the coil of wire, the inductor presents an “inertia”, or resists the change of current, depending upon the current applied and the inductance, measured in henries.

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Capacitor

The capacitor is an important part of the BBC to aid in reducing the voltage ripple and are often applied on the supply and output of a BBC. For the design of the BBC within the scope of this project, the capacitor will be considered ideal, meaning that it contains no parasitic resistance. A capacitor acts as an energy storage device andwill oppose the change in voltage by drawing in the ripple currents, so the current that is supplied to the capacitor is dependent on the rate of change of the voltage applied, and the capacitance, measured in farads.

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Steady-state Analysis

Steady-state analysis is an important tool used by designers and engineers to allow for certain assumptions that simplify the design process. The assumptions presume that all analyses of the circuit will be done after any transient or sub-transient responses of the components have been cleared. This is done to allow for designers to accurately calculate critical parameters and components while utilizing simplifiedequations and processes.

Continuous Conduction Mode

Also known as CCM, this describes the operation principle of the BBC when the inductor is not allowed to fully discharge its stored energy. This state of operation, like steady-stay analysis above, is used to simplify the design procedure and analysis of the circuit. The current flowing through the inductor never reaches a zero-value and this allows for a designer to use common analysis and design equations to create a BBC that operates as expected.

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Buck Converter

The

Design

List the design equations and methodology/process/assumptions

Simulation

Show the simulation results

Discussion

Compare the simulation results with the expected and calculated values from the Design section.

Conclusion

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References

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iStudy of Bi-Directional Buck-Boost Converter Topologies for Application in Electrical Vehicle Motor Drives. F. Caricchi (*), F. Crescimbini (*), F. Giulii Capponi (*), L. Solero (**)

iiModeling and Control for a Bidirectional Buck–Boost Cascade Inverter. Honglin Zhou, Shuai Xiao, Geng Yang, Hua Geng.

iii http://wps.prenhall.com/chet_paynter_introduct_6/6/1664/426188.cw/index.html

iv https://en.wikipedia.org/wiki/Inductor#/media/File:InductorSignalFilter1.png

v http://www.electronics-tutorials.ws/capacitor/cap_1.html

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