POWER MANAGEMENT CIRCUITS FOR ENERGY HARVESTING APPLICATIONS A Dissertation by SALVADOR CARREON-BAUTISTA Submitted to the Office of Graduate and Professional Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Chair of Committee, Edgar Sánchez-Sinencio Committee Members, Kamran Entesari Arum Han Kenith Meissner Head of Department, Miroslav M. Begovic May 2015 Major Subject: Electrical Engineering Copyright 2015 Salvador Carreon-Bautista ABSTRACT Energy harvesting is the process of converting ambient available energy into usable electrical energy. Multiple types of sources are can be used to harness environmental energy: solar cells, kinetic transducers, thermal energy, and electromagnetic waves. This dissertation proposal focuses on the design of high efficiency, ultra-low power, power management units for DC energy harvesting sources. New architectures and design techniques are introduced to achieve high efficiency and performance while achieving maximum power extraction from the sources. The first part of the dissertation focuses on the application of inductive switching regulators and their use in energy harvesting applications. The second implements capacitive switching regulators to minimize the use of external components and present a minimal footprint solution for energy harvesting power management. Analysis and theoretical background for all switching regulators and linear regulators are described in detail. Both solutions demonstrate how low power, high efficiency design allows for a self-sustaining, operational device which can tackle the two main concerns for energy harvesting: maximum power extraction and voltage regulation. Furthermore, a practical demonstration with an Internet of Things type node is tested and positive results shown by a fully powered device from harvested energy. All systems were designed, implemented and tested to demonstrate proof-of-concept prototypes. ii DEDICATION Para mis padres Salvador y Marisa, cuyo apoyo y ejemplo me han fortalecido cuando lo necesitaba. Para mi esposa Pilar, que estuvo conmigo todo el camino sin yo darme cuenta. iii ACKNOWLEDGEMENTS I am enormously grateful for the people that have helped me accomplish what is presented in this dissertation. I thank my advisor, Dr. Edgar Sanchez-Sinencio, for his knowledge, advice, and friendship throughout my studies here at Texas A&M. If it not for his invitation to visit College Station, I would not be writing this today. I would like to thank my committee members, Dr. Kamran Entesari, Dr. Arum Han, and Dr. Kenith Meissner, for their guidance and support throughout the course of this research. I would like to thank Professors Ahmed Emira Eladawy and Ahmed Mohieldin for their help and insight for our projects. Thanks also go to my friends and colleagues and the department faculty and staff for making my time at Texas A&M University a great experience. Special thanks to the friends I had the privilege of meeting and working alongside. I would like to greatly thank Joselyn Torres and Jorge Zarate, for being both great friends and mentors throughout my time at the AMSC. I would also like to thank Efrain Gaxiola, Miguel Rojas, Xiaosen Liu, Roland Ribeiro, Judy Amanor-Boadu, Jiayi Jin, Carlos Briseño, Fernando Lavalle, Alfredo Costilla, Congyin Shi, Mohamed Abouzied, Felix Fernandez, Roland Ribeiro, as well as Celal Erbay for putting up with my incessant emails and texts asking if we could perform tests on the fuel cells. I would also like to thank Ms. Ella Gallagher for her help and humor throughout my time at the AMSC. iv Furthermore, I would like to extend my thanks to the National Council on Science and Technology of Mexico for the economic support during my doctoral studies. Finally, I am forever thankful for my mother and father, for their encouragement and support; my brother and sister for their own perspective and outlook on things; and to my wife Pilar for her patience, love, and understanding. v TABLE OF CONTENTS Page ABSTRACT .......................................................................................................................ii DEDICATION ................................................................................................................. iii ACKNOWLEDGEMENTS .............................................................................................. iv TABLE OF CONTENTS .................................................................................................. vi LIST OF FIGURES ............................................................................................................ x LIST OF TABLES ....................................................................................................... xviii CHAPTER I INTRODUCTION ....................................................................................... 1 Energy harvesting ....................................................................................... 1 Applications and need for power management .......................................... 2 Energy harvesting sources .......................................................................... 6 Thermoelectric generators .............................................................. 6 Photovoltaic cells ......................................................................... 13 Radiofrequency harvesting ........................................................... 18 Kinetic energy harvesting ............................................................. 24 Alternative energy harvesting sources ......................................... 29 Voltage regulators .................................................................................... 33 Inductive switching regulators ..................................................... 33 Capacitive switching regulators ................................................... 36 Linear regulators .......................................................................... 38 Energy storage elements ........................................................................... 40 Power management’s significance on energy harvesting technology ...... 41 Proposed solution ..................................................................................... 42 CHAPTER II FUNDAMENTALS OF POWER MANAGEMENT SYSTEMS FOR ENERGY HARVESTING ............................................................................................... 47 Introduction .............................................................................................. 47 Switching converter fundamentals ........................................................... 50 Step-up (boost converter) ............................................................. 50 Operating modes .......................................................................... 55 Boost converter control Loop for Pulse Width Modulation ......... 63 Boost converter Control Loop for Pulse Frequency Modulation ................................................................................... 64 vi Step-up (switched capacitor) ........................................................ 67 Switched capacitor control loop for pulse width modulation .................................................................................... 73 Switched capacitor control loop for pulse frequency modulation .................................................................................... 75 Performance comparison .......................................................................... 77 Voltage gain ratio ......................................................................... 77 Power efficiency ........................................................................... 78 Integration .................................................................................... 81 Trade-offs ..................................................................................... 82 Linear regulators ...................................................................................... 84 Low dropout regulators ................................................................ 84 Principles ...................................................................................... 86 Digital LDO approach .................................................................. 89 Performance comparison and state-of-the-art .............................. 93 CHAPTER III A BOOST CONVERTER WITH DYNAMIC INPUT IMPEDANCE MATCHING FOR DC ENERGY HARVESTING SOURCES ...................................... 95 Introduction .............................................................................................. 95 Maximum power point tracking ............................................................... 98 Proposed dynamic matching for boost converter ................................... 100 Block diagram for dynamic MPPT ............................................ 102 Algorithm for pseudo zero current switching ............................ 110 Output voltage setting ................................................................ 111 Building block circuit implementation ................................................... 112 Divider (extraction of Voc/2) ...................................................... 112 Comparators (KP) and charge pump (KCP) ................................. 113 Voltage controlled oscillator ...................................................... 114 Filter ........................................................................................... 114 Pseudo