A 400 nW single-inductor dual-input–tri-output DC–DC buck–boost converter with maximum power point tracking for indoor photovoltaic energy harvesting

This paper presents a single-inductor dual-input- tri-output buck-boost (DITOBB) converter that manages energy harvesting, energy storage, and power rail regulation of an indoor remote sensor system. The converter operates in discontinuous conduction mode (DCM) and regulates the outputs with a combination of pulse-skipping modulation (PSM) and constant-ON-time pulse-frequency modulation (PFM). To reduce the quiescent power, all the circuit blocks are turned OFF when the outputs are within regulation, except a system clock generator. A newly designed relaxation oscillator provides the main clock of the system, which requires neither reference voltages nor comparators. The frequency of the system clock doubles or halves based on the states of the sources and outputs following a proposed algorithm. The DITOBB converter has been designed and fabricated using 0.18 μm CMOS process. With a quiescent power of 400 nW, the designed DITOBB converter shows a measured peak efficiency of 83% at 100 μW output power

An Energy Harvesting Solution for IoT Sensors Using MEMS Technology

The significant development of IoT sensors will play a critical role in a large number of applications. It is predicted that billions of IoT sensors will be used worldwide by 2020 [1]. Batteries are commonly utilized to power on sensors, but they are depleted and they require maintenance and replacement. Battery replacement for billions of sensors is a daunting task and battery disposal for IoT sensors can become an environmental problem. Energy harvesting from ambient sources presents a viable solution to overcome these problems. Among all energy sources, light is considered as one of the best sources due to its high energy density and availability in both indoor and outdoor environments. In order to make an energy harvesting system efficient, many methods have been proposed in the literature to extract the maximum energy while minimizing the power consumption by the energy harvesting circuitry. In this work, a boost converter circuit is designed using MEMS-based switches to reduce the leakage current and power loss caused by conventional transistor-based switches. A light energy harvesting method is also proposed utilizing available components of a typical IoT sensor. The reuse of available components in the proposed solution reduces the overall power consumption and the area overhead of the energy harvesting solution

Power Management Techniques for Supercapacitor Based IoT Applications

University of Minnesota Ph.D. dissertation. January 2018. Major: Electrical Engineering. Advisor: Ramesh Harjani. 1 computer file (PDF); xi, 89 pages.The emerging internet of things (IoT) technology will connect many untethered devices, e.g. sensors, RFIDs and wearable devices, to improve health lifestyle, automotive, smart buildings, etc. This thesis proposes one typical application of IoT: RFID for blood temperature monitoring. Once the blood is donated and sealed in a blood bag, it is required to be stored in a certain temperature range (+2~+6°C for red cell component) before distribution. The proposed RFID tag is intended to be attached to the blood bag and continuously monitor the environmental temperature during transportation and storage. When a reader approaches, the temperature data is read out and the tag is fully recharged wirelessly within 2 minutes. Once the blood is distributed, the tag can be reset and reused again. Such a biomedical application has a strong aversion to toxic chemicals, so a batteryless design is required for the RFID tag. A passive RFID tag, however, cannot meet the longevity requirement for the monitoring system (at least 1 week). The solution of this thesis is using a supercapacitor (supercap) instead of a battery as the power supply, which not only lacks toxic heavy metals, but also has quicker charge time (~1000x over batteries), larger operating temperature range (-40~+65°C), and nearly infinite shelf life. Although nearly perfect for this RFID application, a supercap has its own disadvantages: lower energy density (~30x smaller than batteries) and unstable output voltage. To solve the quick charging and long lasting requirements of the RFID system, and to overcome the intrinsic disadvantages of supercaps, an overall power management solution is proposed in this thesis. A reconfigurable switched-capacitor DC-DC converter is proposed to convert the unstable supercap's voltage (3.5V~0.5V) to a stable 1V output voltage efficiently to power the subsequent circuits. With the help of the 6 conversion ratios (3 step-ups, 3 step-downs), voltage protection techniques, and low power designs, the converter can extract 98% of the stored energy from the supercap, and increase initial energy by 96%. Another switched-inductor buck-boost converter is designed to harvest the ambient RF energy to charge the supercap quickly. Because of the variation of the reader distance and incident wave angle, the input power level also has large fluctuation (5uW~5mW). The harvester handles this large power range by a power estimator enhanced MPPT controller with an adaptive integration capacitor array. Also, the contradiction between low power and high tracking speed is improved by adaptive MPPT frequency

Module autonome pour l’évaluation du potentiel photovoltaïque en intérieur

L’alimentation de dispositifs électroniques à faible consommation énergétique est un sujet qui connait beaucoup d’intérêt. Dans le contexte de la mise en place de l’Internet des objets, un nombre important de capteurs sans fil de type Wireless sensor node (WSN) devront être installés. Ces derniers ne consommant que peu d’énergie, des solutions sont envisagées pour assurer leur alimentation autrement que par une pile. Il est ainsi intéressant d’utiliser les faibles énergies présentes dans un environnement pour les convertir en électricité. Ce principe se retrouve par exemple dans les capteurs piézoélectriques, utilisant les déformations mécaniques de leur environnement, ou dans les capteurs photovoltaïques, utilisant la lumière, afin de générer un signal électrique. Dans le cas des capteurs WSN utilisés en intérieur, la lumière artificielle combinée à un capteur photovoltaïque pourrait être est une source d’énergie adaptée. Ce principe se nomme Indoor Photovoltaic, ou plus généralement Energy Harvesting. Le courant produit par une cellule photovoltaïque utilisée en intérieur varie selon les types de cellules et d’éclairages utilisés, de l’éclairement lumineux et de sa position spatiale par rapport à la source lumineuse utilisée dans la pièce. Plusieurs montages issus de la littérature ont permis d’évaluer le courant généré selon ces paramètres. À notre connaissance, il n’existe cependant pas de dispositifs commerciaux compacts dédiés à la mesure de ces paramètres en conditions réelles. Un tel outil permettrait de réaliser une mesure du potentiel photovoltaïque en tout lieu. La connaissance précise de la quantité d’énergie disponible dans un environnement permettrait de mieux appréhender l’autonomie énergétique de ces capteurs sans fil. Le projet de recherche portera sur la conception d’un module de mesure compact et autonome, permettant d’évaluer les performances de plusieurs cellules photovoltaïques dans tous types d’environnements internes. Cet outil de mesure, couplé à une application mobile Android, offre la possibilité d’estimer la quantité d’énergie photovoltaïque disponible. Ce capteur intelligent permettra d’évaluer le potentiel d’utilisation et donc l’installation de capteurs sans fil de type WSN, autonomes en énergie, en intérieur