Photovoltaic sample-and-hold circuit enabling MPPT indoors for low-power systems

Photovoltaic (PV) energy harvesting is commonly used to power autonomous devices, and maximum power point tracking (MPPT) is often used to optimize its efficiency. This paper describes an ultra low-power MPPT circuit with a novel sample-and-hold and cold-start arrangement, enabling MPPT across the range of light intensities found indoors, which has not been reported before. The circuit has been validated in practice and found to cold-start and operate from 100 lux (typical of dim indoor lighting) up to 5000 lux with a 55cm2 amorphous silicon PV module. It is more efficient than non-MPPT circuits, which are the state-of-the-art for indoor PV systems. The proposed circuit maximizes the active time of the PV module by carrying out samples only once per minute. The MPPT control arrangement draws a quiescent current draw of only 8uA, and does not require an additional light sensor as has been required by previously-reported low-power MPPT circuits

Power Management ICs for Internet of Things, Energy Harvesting and Biomedical Devices

This dissertation focuses on the power management unit (PMU) and integrated circuits (ICs) for the internet of things (IoT), energy harvesting and biomedical devices. Three monolithic power harvesting methods are studied for different challenges of smart nodes of IoT networks. Firstly, we propose that an impedance tuning approach is implemented with a capacitor value modulation to eliminate the quiescent power consumption. Secondly, we develop a hill-climbing MPPT mechanism that reuses and processes the information of the hysteresis controller in the time-domain and is free of power hungry analog circuits. Furthermore, the typical power-performance tradeoff of the hysteresis controller is solved by a self-triggered one-shot mechanism. Thus, the output regulation achieves high-performance and yet low-power operations as low as 12 µW. Thirdly, we introduce a reconfigurable charge pump to provide the hybrid conversion ratios (CRs) as 1⅓× up to 8× for minimizing the charge redistribution loss. The reconfigurable feature also dynamically tunes to maximum power point tracking (MPPT) with the frequency modulation, resulting in a two-dimensional MPPT. Therefore, the voltage conversion efficiency (VCE) and the power conversion efficiency (PCE) are enhanced and flattened across a wide harvesting range as 0.45 to 3 V. In a conclusion, we successfully develop an energy harvesting method for the IoT smart nodes with lower cost, smaller size, higher conversion efficiency, and better applicability. For the biomedical devices, this dissertation presents a novel cost-effective automatic resonance tracking method with maximum power transfer (MPT) for piezoelectric transducers (PT). The proposed tracking method is based on a band-pass filter (BPF) oscillator, exploiting the PT’s intrinsic resonance point through a sensing bridge. It guarantees automatic resonance tracking and maximum electrical power converted into mechanical motion regardless of process variations and environmental interferences. Thus, the proposed BPF oscillator-based scheme was designed for an ultrasonic vessel sealing and dissecting (UVSD) system. The sealing and dissecting functions were verified experimentally in chicken tissue and glycerin. Furthermore, a combined sensing scheme circuit allows multiple surgical tissue debulking, vessel sealer and dissector (VSD) technologies to operate from the same sensing scheme board. Its advantage is that a single driver controller could be used for both systems simplifying the complexity and design cost. In a conclusion, we successfully develop an ultrasonic scalpel to replace the other electrosurgical counterparts and the conventional scalpels with lower cost and better functionality

Ultra-Low Power Circuit Design for Miniaturized IoT Platform

This thesis examines the ultra-low power circuit techniques for mm-scale Internet of Things (IoT) platforms. The IoT devices are known for their small form factors and limited battery capacity and lifespan. So, ultra-low power consumption of always-on blocks is required for the IoT devices that adopt aggressive duty-cycling for high power efficiency and long lifespan. Several problems need to be addressed regarding IoT device designs, such as ultra-low power circuit design techniques for sleep mode and energy-efficient and fast data rate transmission for active mode communication. Therefore, this thesis highlights the ultra-low power always-on systems, focusing on energy efficient optical transmission in order to miniaturize the IoT systems. First, this thesis presents a battery-less sub-nW micro-controller for an always-operating system implemented with a newly proposed logic family. Second, it proposes an always-operating sub-nW light-to-digital converter to measure instant light intensity and cumulative light exposure, which employs the characteristics of this proposed logic family. Third, it presents an ultra-low standby power optical wake-up receiver with ambient light canceling using dual-mode operation. Finally, an energy-efficient low power optical transmitter for an implantable IoT device is suggested. Implications for future research are also provided.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/145862/1/imhotep_1.pd

Efficient power management circuits for energy harvesting applications

Low power IoT devices are growing in numbers and by 2020 there will be more than 25 Billion of those in areas such as wearables, smart homes, remote surveillance, transportation and industrial systems, including many others. Many IoT electronics either will operate from stand-alone energy supply (e.g., battery) or be self-powered by harvesting from ambient energy sources or have both options. Harvesting sustainable energy from ambient environment plays significant role in extending the operation lifetime of these devices and hence, lower the maintenance cost of the system, which in turn help make them integral to simpler systems. Both for battery-powered and harvesting capable systems, efficient power delivery unit remains an essential component for maximizing energy efficiency. The goal of this research is to investigate the challenges of energy delivery for low power electronics considering both energy harvesting as well as battery-powered conditions and to address those challenges. Different challenges of energy harvesting from low voltage energy sources based on the limitations of the sources, the type of the regulator used and the pattern of the load demands have been investigated. Different aspects of the each challenges are further investigated to seek optimized solutions for both load specific and generalized applications. A voltage boost mechanism is chosen as the primary mechanism to investigate and to addressing those challenges, befitting the need for low power applications which often rely on battery voltage or on low voltage energy harvesting sources. Additionally, a multiple output buck regulator is also discussed. The challenges analyzed include very low voltage start up issues for an inductive boost regulator, cascading of boost regulator stages, and reduction of the number of external component through reusing those. Design techniques for very high conversion ratio, bias current reduction with autonomous bias gating, battery-less cold start, component and power stage multiplexing for reconfigurable and multi-domain regulators are presented. Measurement results from several silicon prototypes are also presented.Ph.D

Nano-Power Integrated Circuits for Energy Harvesting

The energy harvesting research field has grown considerably in the last decade due to increasing interests in energy autonomous sensing systems, which require smart and efficient interfaces for extracting power from energy source and power management (PM) circuits. This thesis investigates the design trade-offs for minimizing the intrinsic power of PM circuits, in order to allow operation with very weak energy sources. For validation purposes, three different integrated power converter and PM circuits for energy harvesting applications are presented. They have been designed for nano-power operations and single-source converters can operate with input power lower than 1 μW. The first IC is a buck-boost converter for piezoelectric transducers (PZ) implementing Synchronous Electrical Charge Extraction (SECE), a non-linear energy extraction technique. Moreover, Residual Charge Inversion technique is exploited for extracting energy from PZ with weak and irregular excitations (i.e. lower voltage), and the implemented PM policy, named Two-Way Energy Storage, considerably reduces the start-up time of the converter, improving the overall conversion efficiency. The second proposed IC is a general-purpose buck-boost converter for low-voltage DC energy sources, up to 2.5 V. An ultra-low-power MPPT circuit has been designed in order to track variations of source power. Furthermore, a capacitive boost circuit has been included, allowing the converter start-up from a source voltage VDC0 = 223 mV. A nano-power programmable linear regulator is also included in order to provide a stable voltage to the load. The third IC implements an heterogeneous multisource buck-boost converter. It provides up to 9 independent input channels, of which 5 are specific for PZ (with SECE) and 4 for DC energy sources with MPPT. The inductor is shared among channels and an arbiter, designed with asynchronous logic to reduce the energy consumption, avoids simultaneous access to the buck-boost core, with a dynamic schedule based on source priority

Energy Harvesting Solution for the UWASA Node: Applications for Wind Turbine Monitoring

The aim of this thesis was to develop an energy harvesting solution for the UWASA Node for wind power station applications. Energy harvesting is the process by which small amounts of ambient energy is collected for use by electronics such as wireless sensor nodes. The developed energy harvesting solution is capable of supplying enough energy for the UWASA Node to perform a wide variety of tasks indefinitely, without the need for changing its battery. The wireless sensor node can for example read sensors at high sampling rates and store or wirelessly transmit these readings. It can also perform complex computations and react to changes in its environment. One intended use was monitoring vibrations of wind turbines blades, but field tests have yet to be done. This master’s thesis builds on the findings of my bachelor’s thesis, Höglund (2014) in the references. In the bachelor’s thesis different methods of energy harvesting were in-vestigated to find the most suitable methods for this project. In this master’s thesis a prototype energy harvester and energy management circuit was developed and tested. The prototype is capable of harvesting tens of milliwatts from a small solar cell. It could also be modified to harvest another ambient energy source or several sources at once. Every part of the energy harvester and energy management circuit is discussed in detail and laboratory tests are presented. Different means of maximum power point tracking were tested and evaluated. The prototype energy harvester was built using a modular approach so that energy harvesting from multiple sources of energy easily can be ac-complished by adding a few components for each source to the harvesting circuit. The programming of the sensor node also needs to be adapted so that it runs optimally from the harvested energy by scheduling measurements and wireless communication. A low-power real-time clock and a latching switch were included on the prototype PCB for switching on and off the power to the sensor node completely in order to consume as little energy as possible when the sensor node is inactive.fi=Opinnäytetyö kokotekstinä PDF-muodossa.|en=Thesis fulltext in PDF format.|sv=Lärdomsprov tillgängligt som fulltext i PDF-format

Energy harvesting system design and optimization for wireless sensor networks

Wireless sensor networks (WSN) are becoming widely adopted for many applications including complicated tasks like building energy management. However, one major concern for WSN technologies is the short lifetime and high maintenance cost due to the limited battery energy. One of the solutions is to scavenge ambient energy, which is then rectified to power the WSN. The objective of this thesis was to investigate the feasibility of an ultra-low energy consumption power management system suitable for harvesting sub-mW photovoltaic and thermoelectric energy to power WSNs. To achieve this goal, energy harvesting system architectures have been analyzed. Detailed analysis of energy storage units (ESU) have led to an innovative ESU solution for the target applications. Battery-less, long-lifetime ESU and its associated power management circuitry, including fast-charge circuit, self-start circuit, output voltage regulation circuit and hybrid ESU, using a combination of super-capacitor and thin film battery, were developed to achieve continuous operation of energy harvester. Low start-up voltage DC/DC converters have been developed for 1mW level thermoelectric energy harvesting. The novel method of altering thermoelectric generator (TEG) configuration in order to match impedance has been verified in this work. Novel maximum power point tracking (MPPT) circuits, exploring the fractional open circuit voltage method, were particularly developed to suit the sub-1mW photovoltaic energy harvesting applications. The MPPT energy model has been developed and verified against both SPICE simulation and implemented prototypes. Both indoor light and thermoelectric energy harvesting methods proposed in this thesis have been implemented into prototype devices. The improved indoor light energy harvester prototype demonstrates 81% MPPT conversion efficiency with 0.5mW input power. This important improvement makes light energy harvesting from small energy sources (i.e. credit card size solar panel in 500lux indoor lighting conditions) a feasible approach. The 50mm × 54mm thermoelectric energy harvester prototype generates 0.95mW when placed on a 60oC heat source with 28% conversion efficiency. Both prototypes can be used to continuously power WSN for building energy management applications in typical office building environment. In addition to the hardware development, a comprehensive system energy model has been developed. This system energy model not only can be used to predict the available and consumed energy based on real-world ambient conditions, but also can be employed to optimize the system design and configuration. This energy model has been verified by indoor photovoltaic energy harvesting system prototypes in long-term deployed experiments

Ultra-Low-Voltage IC Design Methods

The emerging nanoscale technologies inherently offer transistors working with low voltage levels and are optimized for low-power operation. However, these technologies lack quality electronic components vital for reliable analog and/or mixed-signal design (e.g., resistor, capacitor, etc.) as they are predominantly used in high-performance digital designs. Moreover, the voltage headroom, ESD properties, the maximum current densities, parasitic effects, process fluctuations, aging effects, and many other parameters are superior in verified-by-time CMOS processes using planar transistors. This is the main reason, why low-voltage, low-power high-performance analog and mixed-signal circuits are still being designed in mature process nodes. In the proposed chapter, we bring an overview of main challenges and design techniques effectively applicable for ultra-low-voltage and low-power analog integrated circuits in nanoscale technologies. New design challenges and limitations linked with a low value of the supply voltage, the process fluctuation, device mismatch, and other effects are discussed. In the later part of the chapter, conventional and unconventional design techniques (bulk-driven approach, floating-gate, dynamic threshold, etc.) to design analog integrated circuits towards ultra-low-voltage systems and applications are described. Examples of ultra-low-voltage analog ICs blocks (an operational amplifier, a voltage comparator, a charge pump, etc.) designed in a standard CMOS technology using the unconventional design approach are presented

Robustness and durability aspects in the design of power management circuits for IoT applications

With the increasing interest in the heterogeneous world of the “Internet of Things” (IoT), new compelling challenges arise in the field of electronic design, especially concerning the development of innovative power management solutions. Being this diffusion a consolidated reality nowadays, emerging needs like lifetime, durability and robustness are becoming the new watchwords for power management, being a common ground which can dramatically improve service life and confidence in these devices. The possibility to design nodes which do not need external power supply is a crucial point in this scenario. Moreover, the development of autonomous nodes which are substantially maintenance free, and which therefore can be placed in unreachable or harsh environments is another enabling aspect for the exploitation of this technology. In this respect, the study of energy harvesting techniques is increasingly earning interest again. Along with efficiency aspects, degradation aspects are the other main research field with respect to lifetime, durability and robustness of IoT devices, especially related to aging mechanisms which are peculiar in power management and power conversion circuits, like for example battery wear during usage or hot-carrier degradation (HCD) in power MOSFETs. In this thesis different aspects related to lifetime, durability and robustness in the field of power management circuits are studied, leading to interesting contributions. Innovative designs of DC/DC power converters are studied and developed, especially related to reliability aspects of the use of electrochemical cells as power sources. Moreover, an advanced IoT node is proposed, based on energy harvesting techniques, which features an intelligent dynamically adaptive power management circuit. As a further contribution, a novel algorithm is proposed, which is able to effectively estimate the efficiency of a DC/DC converter for photovoltaic applications at runtime. Finally, an innovative DC/DC power converter with embedded monitoring of hot-carrier degradation in power MOSFETs is designed

Design of Low-Cost Energy Harvesting and Delivery Systems for Self-Powered Devices: Application to Authentication IC

This thesis investigates the development of low-cost energy harvesting and delivery systems for low-power low-duty-cycle devices. Initially, we begin by designing a power management scheme for on-demand power delivery. The baseline implementation is also used to identify critical challenges for low-power energy harvesting. We further propose a robust self-powered energy harvesting and delivery system (EHDS) design as a solution to achieve energy autonomy in standalone systems. The design demonstrates a complete ecosystem for low-overhead pulse-frequency modulated (PFM) harvesting while reducing harvesting window confinement and overall implementation footprint. Two transient-based models are developed for improved accuracy during design space exploration and optimization for both PFM power conversion and energy harvesting. Finally, a low-power authentication IC is demonstrated and projected designs for self-powered System-on-Chips (SoCs) are presented. The proposed designs are proto-typed in two test-chips in a 65nm CMOS process and measurement data showcase improved performance in terms of battery power, cold-start duration, passives (inductance and capacitance) needed, and end-to-end harvesting/conversion efficiency.Ph.D