Powering Autonomous Sensors

Transcription

1 Powering Autonomous Sensors

2 María Teresa Penella-López Manuel Gasulla-Forner Powering Autonomous Sensors An Integral Approach with Focus on Solar and RF Energy Harvesting

3 María Teresa Penella-López Electrical Engineering Univ. Politecnica de Catalunya (UPC) Isabena 15 Monzon, Huesca, Spain Manuel Gasulla-Forner Electronic Engineering Univ. Politecnica de Catalunya (UPC) c/ Esteve Terradas 7 Castelldefels, Barcelona, Spain manel.gasulla@upc.edu ISBN e-isbn DOI / Springer Dordrecht Heidelberg London New York Library of Congress Control Number: Springer Science+Business Media B.V No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Cover design: VTeX UAB, Lithuania Printed on acid-free paper Springer is part of Springer Science+Business Media (

4 A mi familia María Teresa Penella A la meva família Manuel Gasulla

5 Preface Autonomous sensors do not use cables either for transmitting data or for powering electronics. They can be found in wireless sensor networks (WSNs) or in remote acquisition systems. Primary batteries provide a simple design for the powering of autonomous sensors. However, batteries must be replaced when depleted, which can lead to unacceptable maintenance costs whenever the number of autonomous sensors is very large or their accessibility is difficult or impractical. An alternative is to extract energy from the ambient, which is usually known as energy harvesting. However, the reduced dimensions of most autonomous sensors lead to a low available power from the energy transducer. Thus, efficient methods and circuits to manage and gather the energy are a must. This book tackles the powering of autonomous sensors, providing an integral approach by considering both primary batteries and energy harvesting. Two rather different forms of energy harvesting are further dealt with: optical (solar) and radiofrequency (RF). Optical energy presents high energy density, especially outdoors, whereas RF remote powering can be the most feasible option for autonomous sensors embedded into the soil or within structures. Throughout the different chapters, devices such as primary and secondary batteries, supercapacitors, and the energy transducers are extensively reviewed. Then, circuits and methods found in the literature to efficiently extract and gather the energy are presented. Finally, new proposals based in our own research are analyzed and tested. Each chapter is written to be rather independent, incorporating the related literature references into each one. Chapter 1 first presents autonomous sensors and the feasible energy sources. Both primary batteries and energy harvesters are considered and basic concepts to take into account are detailed. The chapter also provides a general overview of the main problems that appear when designing the power supply of autonomous sensors and refers to some of the most important previous works on this topic. Chapter 2 analyzes the power consumption of an autonomous sensor and adds some remarks on voltage regulators. In particular, a review is presented, from the point of view of power consumption, on some of the typical devices found in autonomous sensors such as microcontrollers and transceivers. A short introduction to sensors and their signal conditioners is also presented. Finally, a general model based on a pulsed current sink is proposed and experimentally validated. vii

6 viii Preface Chapter 3 reviews the ambient energy sources amenable to powering autonomous sensors: radiant, mechanical, thermal, magnetic, and biochemical. The associated energy transducers are also described and some of the most relevant literature is referenced. Chapter 4 presents the electrical characteristics and models of primary and secondary batteries, and supercapacitors. Low capacity batteries (up to 3 Ah), both primary and secondary, were experimentally characterized and the parameters of a simplified Randles model are fitted. Several types of supercapacitors were also characterized, obtaining the equivalent series resistances. One of them was further tested to obtain its leakage resistance. Temperature tests, both for batteries and supercapacitors were also carried out. On the other hand, the use of hybrid storage units is proposed in order to reduce the power waste and voltage drop caused by high-resistance batteries. Design criteria for choosing a suitable value of the accompanying supercapacitor are presented. Runtime extensions between 16% and 33% are reported. Chapter 5 considers optical energy for powering autonomous sensors. A generic model for optical energy transducers, namely solar cells or photovoltaic (PV) panels, is employed to compute the I V and P V curves as well as their dependency on optical power and on temperature. Based on this model, the efficiency of directcoupled solutions was also computed, ranging from 70% to 90%. With respect to maximum power point trackers (MPPTs), a new open-circuit voltage (OCV) method has been proposed and tested, providing a tracking efficiency greater than 99.5%, higher than that reported for current implementations of OCV methods. Additionally, we devised and tested a novel MPPT method that provides a tracking efficiency greater than 99.6% and an overall efficiency greater than 92% for a PV panel power greater than 100 mw. Chapter 6 is dedicated to remote RF powering of autonomous sensors and in particular to RF energy harvesters. The RF energy transducer (antenna), matching networks, and ensuing rectifiers are presented. Based on circuits proposed in the literature, extensive simulations for several incoming power levels at the antenna (from 10 dbm to 10 dbm) were performed. We determine that circuit efficiency slightly depends on the number of stages used for the voltage rectifier multiplier, but varies widely with the received power (ranging, when using a shunt-inductor matching network, from 10% at 10 dbm to 80% at 10 dbm). Additionally, as the power level increases, so does the output voltage corresponding to maximum efficiency. For low power levels, LC matching networks provided higher efficiencies than shunt-inductor networks, at the cost of greater sensitivity to output voltage variations and to the value of the inductor. Experimental tests were performed with a folded dipole antenna (about 300 ), shunt inductor matching, a three-stage rectifier, and a storage unit composed of two series connected NiMH batteries. María Teresa Penella-López Manuel Gasulla-Forner

7 Acknowledgements This book is the result of the research carried out by the authors during the last five years at the ISI group of the Universitat Politècnica de Catalunya, BarcelonaTech. First, we would like to thank all the technical and economical support from our research group. In particular we want to thank our colleague Oscar López for his inestimable help during the design, implementation and testing of solar maximum power point trackers. His knowledge in power electronics and his enthusiasm have been very inspiring. Gracias a todos. Gràcies a tots. Part of the work on RF energy harvesting was developed during a short stay of Maria Teresa Penella at EPFL, in Lausanne (Switzerland). She would like to thank Michel Declerq, Catherine Dehollain, Nicolas Pillin and Norbert Joehl. Merci de votre aide. We would also like to acknowledge all the institutions and people that supported economically this research. Maria Teresa Penella enjoyed first an FI grant from AGAUR (Agència de Gestió d Ajuts Universitaris i de Recerca) ofthecatalan government and afterwards an FPU grant (FPU AP ) from the Spanish Ministry of education during most of the part of her research. This research has been also funded in part by the Spanish Ministry of Science and Innovation through projects TEC and TEC /MIC and by the European Regional Development Union, and by the Spanish-Tunisian cooperation project (AECI-A/ ). Maria Teresa Penella has been working during the last year at Urbiotica. She would like to thank them the support during the final stage of this research. Finally, we would like to thank all the people that in one way or another made this book possible: colleagues, friends, and family. Without them this book would be incomplete. The last thing one knows in constructing a work is what to put first Blaise Pascal ( ) French mathematician and physicist. ix

8 Contents 1 Introduction Autonomous Sensors Power Sources for Autonomous Sensors Challenges References Load and Power Conditioning Load Sensors and Signal Conditioning Microcontrollers Transceiver Load Model PowerConditioning Linear Regulators SwitchingRegulators ChargePumps ControlStrategy Conclusions References Ambient Energy Sources RadiantEnergy OpticalEnergy Radiofrequency Energy Mechanical Energy ThermalEnergy Magnetic Energy Biochemical Energy Conclusions References xi

9 xii Contents 4 Primary Batteries and Storage Elements Batteries General Characteristics Batteries and Autonomous Sensors PrimaryBatteries Secondary Batteries BatteryCharacterization Proposed Approach Materials and Methods Experimental Results Model Validation Supercapacitors Supercapacitor Characterization Materials and Methods Experimental Results HybridSystems ProblemStatement Theoretical Analysis Materials and Methods Experimental Results Conclusions References Optical Energy Harvesting SolarCells PVArraySimulator Direct-Coupled Circuits Analysis Experimental Results MPPT Circuits and Methods Dc/dc Converters Based on PFM Techniques Analysis LOCVMethod Efficiency Experimental Characterization Implementation and Time Response AssigningParameterValues A Novel Closed-Loop MPPT Technique Theoretical Approach Implementation Analysis AssigningtheParameterValues Materials and Methods Experimental Results Conclusions References

10 Contents xiii 6 Radiofrequency Energy Harvesting Background Antenna Impedance Matching Filters Rectifier Post-rectificationEnergyConditioning Radiofrequency Energy Harvesting for Autonomous Sensors Analysis Rectifier Simulations Experimental Results MeasurementSetup Results Conclusions References