36 research outputs found
An Input Power-Aware Maximum Efficiency Tracking Technique for Energy Harvesting in IoT Applications
The Internet of Things (IoT) enables intelligent monitoring and management in many applications such as industrial and biomedical systems as well as environmental and infrastructure monitoring. As a result, IoT requires billions of wireless sensor network (WSN) nodes equipped with a microcontroller and transceiver. As many of these WSN nodes are off-grid and small-sized, their limited-capacity batteries need periodic replacement. To mitigate the high costs and challenges of these battery replacements, energy harvesting from ambient sources is vital to achieve energy-autonomous operation. Energy harvesting for WSNs is challenging because the available energy varies significantly with ambient conditions and in many applications, energy must be harvested from ultra-low power levels.
To tackle these stringent power constraints, this dissertation proposes a discontinuous charging technique for switched-capacitor converters that improves the power conversion efficiency (PCE) at low input power levels and extends the input power harvesting range at which high PCE is achievable. Discontinuous charging delivers current to energy storage only during clock non-overlap time. This enables tuning of the output current to minimize converter losses based on the available input power. Based on this fundamental result, an input power-aware, two-dimensional efficiency tracking technique for WSNs is presented. In addition to conventional switching frequency control, clock nonoverlap time control is introduced to adaptively optimize the power conversion efficiency according to the sensed ambient power levels.
The proposed technique is designed and simulated in 90nm CMOS with post-layout extraction. Under the same input and output conditions, the proposed system maintains at least 45% PCE at 4μW input power, as opposed to a conventional continuous system which requires at least 18.7μW to maintain the same PCE. In this technique, the input power harvesting range is extended by 1.5x.
The technique is applied to a WSN implementation utilizing the IEEE 802.15.4- compatible GreenNet communications protocol for industrial and wearable applications. This allows the node to meet specifications and achieve energy autonomy when deployed in harsher environments where the input power is 49% lower than what is required for conventional operation
On-Chip Solar Energy Harvester and PMU With Cold Start-Up and Regulated Output Voltage for Biomedical Applications
This paper presents experimental results from a system that comprises a fully autonomous energy harvester with a solar cell of 1 mm 2 as energy transducer and a Power Management Unit (PMU) on the same silicon substrate, and an output voltage regulator. Both chips are implemented in standard 0.18 μm CMOS technology with total layout areas of 1.575 mm 2 and 0.0126 mm 2 , respectively. The system also contains an off-the-shelf 3.2 mm × 2.5 mm × 0.9 mm supercapacitor working as an off-chip battery or energy reservoir between the PMU and the voltage regulator. Experimental results show that the fast energy recovery of the on-chip solar cell and PMU permits the system to replenish the supercapacitor with enough charge as to sustain Bluetooth Low Energy (BLE) communications even with input light powers of 510 nW. The whole system is able to self-start-up without external mechanisms at 340 nW. This work is the first step towards a self-supplied sensor node with processing and communication capabilities. The small form factor and ultra-low power consumption of the system components is in compliance with biomedical applications requirementsThis work was supported in part by the Spanish Government (Ministerio de Ciencia, Innovación y Universidades) under Project RTI2018-097088-B-C32 and Project RTI2018-095994-B-I00 (MICINN/FEDER), in part by the Xunta de Galicia, in part by the ConsellerÃa de Cultura, Educación e Ordenación Universitaria (accreditation 2016-2019, ED431G/08 and reference competitive group 2017-2020, ED431C 2017/69) and European Regional Development Fund (ERDF), and in part by the Junta de Extremadura and the ERDF, under Grant IB 18079S
Millimeter-Scale and Energy-Efficient RF Wireless System
This dissertation focuses on energy-efficient RF wireless system with millimeter-scale dimension, expanding the potential use cases of millimeter-scale computing devices. It is challenging to develop RF wireless system in such constrained space. First, millimeter-sized antennae are electrically-small, resulting in low antenna efficiency. Second, their energy source is very limited due to the small battery and/or energy harvester. Third, it is required to eliminate most or all off-chip devices to further reduce system dimension. In this dissertation, these challenges are explored and analyzed, and new methods are proposed to solve them. Three prototype RF systems were implemented for demonstration and verification. The first prototype is a 10 cubic-mm inductive-coupled radio system that can be implanted through a syringe, aimed at healthcare applications with constrained space. The second prototype is a 3x3x3 mm far-field 915MHz radio system with 20-meter NLOS range in indoor environment. The third prototype is a low-power BLE transmitter using 3.5x3.5 mm planar loop antenna, enabling millimeter-scale sensors to connect with ubiquitous IoT BLE-compliant devices. The work presented in this dissertation improves use cases of millimeter-scale computers by presenting new methods for improving energy efficiency of wireless radio system with extremely small dimensions. The impact is significant in the age of IoT when everything will be connected in daily life.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147686/1/yaoshi_1.pd
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
Energy processing circuits for low-power applications
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 199-205).Portable electronics have fueled the rich emergence of new applications including multi-media handsets, ubiquitous smart sensors and actuators, and wearable or implantable biomedical devices. New ultra-low power circuit techniques are constantly being proposed to further improve the energy efficiency of electronic circuits. A critical part of these energy conscious systems are the energy processing and power delivery circuits that interface with the energy sources and provide conditioned voltage and current levels to the load circuits. These energy processing circuits must maintain high efficiency and reduce component count for the final solution to be attractive from an energy, size and cost perspective. The first part of this work focuses on the development of on-chip voltage scalable switched capacitor DC-DC converters in digital CMOS processes. The converters are designed to deliver regulated scalable load voltages from 0.3V up to the battery voltage of 1.2V for ultra-dynamic voltage scaled systems. The efficiency limiting mechanisms of these on-chip DC-DC converters are analyzed and digital circuit techniques are proposed to tackle these losses. Measurement results from 3 test-chips implemented in 0.18pm and 65nm CMOS processes will be provided. The converters are able to maintain >75% efficiency over a wide range of load voltage and power levels while delivering load currents up to 8mA. An embedded switched capacitor DC-DC converter that acts as the power delivery unit in a 65nm subthreshold microcontroller system will be described. The remainder of the thesis deals with energy management circuits for battery-less systems. Harvesting ambient vibrational, light or thermal energy holds much promise in realizing the goal of a self-powered system. The second part of the thesis identifies problems with commonly used interface circuits for piezoelectric vibration energy harvesters and proposes a rectifier design that gives more than 4X improvement in output power extracted from the piezoelectric energy harvester. The rectifier designs are demonstrated with the help of a test-chip built in a 0.35pm CMOS process. The inductor used within the rectifier is shared efficiently with a multitude of DC-DC converters in the energy harvesting chip leading to a compact, cost-efficient solution. The DC-DC converters designed as part of a complete power management solution achieve efficiencies of greater than 85% even in the micro-watt power levels output by the harvester. The final part of the thesis deals with thermal energy harvesters to extract electrical power from body heat. Thermal harvesters in body-worn applications output ultra-low voltages of the order of 10's of milli-volts. This presents extreme challenges to CMOS circuits that are powered by the harvester. The final part of the thesis presents a new startup technique that allows CMOS circuits to interface directly with and extract power out of thermoelectric generators without the need for an external battery, clock or reference generators. The mechanically assisted startup circuit is demonstrated with the help of a test-chip built in a 0.35pm CMOS process and can work from as low as 35mV. This enables load circuits like processors and radios to operate directly of the thermoelectric generator without the aid of a battery. A complete power management solution is provided that can extract electrical power efficiently from the harvester independent of the input voltage conditions. With the help of closed-loop control techniques, the energy processing circuit is able to maintain efficiency over a wide range of load voltage and process variations.by Yogesh Kumar Ramadass.Ph.D
Power management systems based on switched-capacitor DC-DC converter for low-power wearable applications
The highly efficient ultra-low-power management unit is essential in powering low-power wearable electronics. Such devices are powered by a single input source, either by a battery or with the help of a renewable energy source. Thus, there is a demand for an energy conversion unit, in this case, a DC-DC converter, which can perform either step-up or step-down conversions to provide the required voltage at the load. Energy scavenging with a boost converter is an intriguing choice since it removes the necessity of bulky batteries and considerably extends the battery life.
Wearable devices are typically powered by a monolithic battery. The commonly available battery such as Alkaline or Lithium-ion, degrade over time due to their life spans as it is limited by the number of charge cycles- which depend highly on the environmental and loading condition. Thus, once it reaches the maximum number of life cycles, the battery needs to be replaced. The operation of the wearable devices is limited by usable duration, which depends on the energy density of the battery. Once the stored energy is depleted, the operation of wearable devices is also affected, and hence it needs to be recharged. The energy harvesters- which gather the available energy from the surroundings, however, have no limitation on operating life. The application can become battery-less given that harvestable energy is sufficiently powering the low-power devices. Although the energy harvester may not completely replace the battery source, it ensures the maximum duration of use and assists to become autonomous and self-sustain devices.
The photovoltaic (PV) cell is a promising candidate as a hypothetical input supply source among the energy harvesters due to its smaller area and high power density over other harvesters. Solar energy use PV harvester can convert ambient light energy into electrical energy and keep it in the storage device. The harvested output of PV cannot directly connect to wearable loads for two main reasons. Depending on the incoming light, the harvested current result in varying open-circuit voltage. It requires the power management circuit to deal with unregulated input variation. Second, depending on the PV cell's material type and an effective area, the I-V characteristic's performance varies, resulting in a variation of the output power. There are several works of maximum power point tracking (MPPT) methods that allow the solar energy harvester to achieve optimal harvested power. Therefore, the harvested power depends on the size and usually small area cell is sufficient for micro-watt loads low-powered applications. The available harvested voltage, however, is generally very low-voltage range between 0.4-0.6 V. The voltage ratings of electronics in standard wearable applications operate in 1.8-3 V voltages as described in introduction’s application example section. It is higher than the supply source can offer. The overcome the mismatch voltage between source and supply circuit, a DC-DC boost converter is necessary.
The switch-mode converters are favoured over the linear converters due to their highly efficient and small area overhead. The inductive converter in the switch-mode converter is common due to its high-efficiency performance. However, the integration of the inductor in the miniaturised integrated on-chip design tends to be bulky. Therefore, the switched-capacitor approach DC-DC converters will be explored in this research. In the switched-capacitor converter universe, there is plenty of work for single-output designs for various topologies. Most converters are reconfigurable to the different DC voltage levels apart from Dickson and cross-coupled charge pump topologies due to their boosting power stage architecture through a number of stages. However, existing multi-output converters are limited to the fixed gain ratio. This work explores the reconfigurable dual-output converter with adjustable gain to compromise the research gap.
The thesis's primary focus is to present the inductor-less, switched-capacitor-based DC-DC converter power management system (PMS) supplied by a varying input of PV energy harvester input source. The PMS should deliver highly efficient regulated voltage conversion ratio (VCR) outputs to low-power wearable electronic devices that constitute multi-function building blocks
Energy efficient control for power management circuits operating from nano-watts to watts
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 163-172).Energy efficiency and form factor are the key driving forces in today's power electronics. All power delivery circuits, irrespective of the magnitude of power, basically consists of power trains, gate drivers and control circuits. Although the control circuits are primarily required for regulation, these circuits can play a crucial role in achieving high efficiency and/or minimizing overall system form-factor. In this thesis, power converter circuits, spanning a wide operating range- from nano-watts to watts, are presented while highlighting techniques for using digital control circuits not just for regulation but also to achieve high system efficiency and smaller system form-factor. The first part of the thesis presents a power management unit of an autonomous wireless sensor that sustains itself by harvesting energy from the endo-cochlear potential (EP), the 70-100mV electrochemical potential inside the mammalian inner ear. Due to the anatomical constraints, the total extractable power from the EP is limited to 1.1-6.3nW. A low switching frequency boost converter is employed to increase the input voltage to a higher voltage usable by CMOS circuits in the sensor. Ultra-low power digital control circuits with timers help keep the quiescent power of the power management unit down to 544pW. Further, a charge-pump is used to implement leakage reduction techniques in the sensor. This work demonstrates how digital low power control circuit design can help improve converter efficiency and ensure system sustainability. All circuits have been implemented on a 0.18[mu]m CMOS process. The second part of the thesis discusses an energy harvesting architecture that combines energy from multiple energy harvesting sources- photovoltaic, thermoelectric and piezoelectric sources. Digital control circuits that configure the power trains to new efficient system architectures with maximum power point tracking are presented, while using a single inductor to combine energy from the aforementioned energy sources all at the same time. A dual-path architecture for energy harvesting systems is proposed. This provides a peak efficiency improvement of 11-13% over the traditional two stage approach. The system can handle input voltages from 20mV to 5V and is also capable of extracting maximum power from individual harvesters all at the same time utilizing a single inductor. A proposed completely digital timebased power monitor is used for achieving maximum power point tracking for the photovoltaic harvester. This has a peak tracking efficiency of 96%. The peak efficiencies achieved with inductor sharing are 83%, 58% and 79% for photovoltaic boost, thermoelectric boost and piezoelectric buck-boost converters respectively. The switch matrix and the control circuits are implemented on a 0.35pm CMOS process. This part of the thesis highlights how digital control circuits can help reconfigure power converter architectures for improving efficiency and reducing form-factors. The last part of the thesis deals with a power management system for an offline 22W LED driver. In order to reduce the system form factor, Gallium Nitride (GaN) transistors capable of high frequency switching have been utilized with a Quasi-Resonant Inverted Buck architecture. A burst mode digital controller has been used to perform dimming control and power factor correction (PFC) for the LED driver. The custom controller and driver IC was implemented in a 0.35[mu]m CMOS process. The LED driver achieves a peak efficiency of 90.6% and a 0.96 power factor. Due to the high power level of the driver, the digital controller is primarily used for regulation purposes in this system, although the digital nature of the controller helps remove the passives that would be normally present in analog controllers. In this thesis, apart from regulation, control circuit enabled techniques have been used to improve efficiency and reduce system form factor. Low power design and control for reconfigurable power train architectures help improve the overall power converter efficiency. Digital control circuits have been used to reduce the form factor by enabling inductor sharing in a system with multiple power converters or by removing the compensator passives.by Saurav Bandyopadhyay.Ph.D
A gravitational torque energy harvesting system for rotational motion
This thesis describes a novel, single point-of-attachment, gravitational torque energy harvesting system
powered from rotational motion. The primary aim of such a system is to scavenge energy from a continuously
rotating host in order to power a wireless sensor node. In this thesis, a wireless tachometer was
prototyped.
Most published work on motion-driven energy harvesters has used ambient vibrations in the environment
as the energy source. However, none of the reported devices have been designed to harvest energy
directly from continuous ambient rotation. There are important applications such as tire pressure sensing
and condition monitoring of machinery where the host structure experiences continuous rotation. In this
work, it is shown that in many applications, a rotational energy harvester can offer significant improvements
in power density over its vibration-driven counterparts.
A prototype single point-of-attachment rotational energy harvester was conceived using a simple direct-current
generator. The rotational source was coupled to the stator and an offset mass was anchored on the
rotor to create a counteractive gravitational torque. This produces a relative angular speed between rotor and
stator which causes power to be generated. Power transfer from the generator to a load was maximised by
enforcing an input impedance match between the generator’s armature resistance and the input impedance
of a boost converter which in this case, functioned as a resistance emulator. Energy storage and output
voltage regulation were implemented using supercapacitors and a wide-input buck regulator respectively.
When excess power was generated, it was stored in the supercapacitors and during low source rotation
speeds, i.e. insufficient harvested power, the supercapacitors will discharge to maintain operation of the
interface electronics.
A detailed optimisation procedure of a boost converter was conducted in Matlab in order to minimise
the power loss, resulting in a maximum voltage gain of 11.1 and measured circuit efficiency of 96 %. A
state-space control model of the harvester electronics was developed in the analogue domain using classical
control techniques and this showed the system to be closed-loop stable. A final prototype of the rotational
energy harvesting system was built and this comprised an input impedance controller, wireless transmitter
and tachometer. The entire system has a measured end-to-end efficiency which peaked at 58 % from a
source rotation of 1400 RPM with the generator producing 1.45 W under matched load conditions