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

A Biofuel-Cell-Based Energy Harvester With 86% Peak Efficiency and 0.25-V Minimum Input Voltage Using Source-Adaptive MPPT

This article presents an efficient cold-starting energy harvester system, fabricated in 65-nm CMOS. The proposed harvester uses no external electrical components and is compatible with biofuel-cell (BFC) voltage and power ranges. A power-efficient system architecture is proposed to keep the internal circuitry operating at 0.4 V while regulating the output voltage at 1 V using switched-capacitor dc–dc converters and a hysteretic controller. A startup enhancement block is presented to facilitate cold startup with any arbitrary input voltage. A real-time on-chip 2-D maximum power point tracking with source degradation tracing is also implemented to maintain power efficiency maximized over time. The system performs cold startup with a minimum input voltage of 0.39 V and continues its operation if the input voltage degrades to as low as 0.25 V. Peak power efficiency of 86% is achieved at 0.39 V of input voltage and 1.34 μW of output power with 220 nW of average power consumption of the chip. The end-to-end power efficiency is kept above 70% for a wide range of loading powers from 1 to 12 μW. The chip is integrated with a pair of lactate BFC electrodes with 2 mm of diameter on a prototype-printed circuit board (PCB). Integrated operation of the chip with the electrodes and a lactate solution is demonstrated

A cost effective computational design of maximum power point tracking for photo-voltaic cell

Maximum Power Point Tracking (MPPT) is one of the essential controller operations of any Photo-Voltaic (PV) cell design. Developing an efficient MPPT system includes a significant challenge as there are various forms of uncertainty factors that results in higher degree of fluctuation in current and voltage in PV cell. After reviewing existing system, it has been found that there is no presence of any benchmarked model to ensure a better form of computational model. Hence, this paper presents a novel and very simple design of MPPT without using any form of complex design mechanism nor including any form of frequently used iterative approach. The proposed model is completely focused on developing an algorithm that takes the input of voltage (open circuit), current (short circuit), and max power in order to obtain the peak power to be extracted from the PV cells. The study outcome shows faster response time and better form of analysis of current-voltage-power for given state of PV cells

CMOS indoor light energy harvesting system for wireless sensing applications

Dissertação para obtenção do Grau de Doutor em Engenharia Electrotécnica e de ComputadoresThis research thesis presents a micro-power light energy harvesting system for indoor environments. Light energy is collected by amorphous silicon photovoltaic (a-Si:H PV) cells, processed by a switched-capacitor (SC) voltage doubler circuit with maximum power point tracking (MPPT), and finally stored in a large capacitor. The MPPT Fractional Open Circuit Voltage (VOC) technique is implemented by an asynchronous state machine (ASM) that creates and, dynamically, adjusts the clock frequency of the step-up SC circuit, matching the input impedance of the SC circuit to the maximum power point (MPP) condition of the PV cells. The ASM has a separate local power supply to make it robust against load variations. In order to reduce the area occupied by the SC circuit, while maintaining an acceptable efficiency value, the SC circuit uses MOSFET capacitors with a charge reusing scheme for the bottom plate parasitic capacitors. The circuit occupies an area of 0.31 mm2 in a 130 nm CMOS technology. The system was designed in order to work under realistic indoor light intensities. Experimental results show that the proposed system, using PV cells with an area of 14 cm2, is capable of starting-up from a 0 V condition, with an irradiance of only 0.32 W/m2. After starting-up, the system requires an irradiance of only 0.18 W/m2 (18 mW/cm2) to remain in operation. The ASM circuit can operate correctly using a local power supply voltage of 453 mV, dissipating only 0.085 mW. These values are, to the best of the authors’ knowledge, the lowest reported in the literature. The maximum efficiency of the SC converter is 70.3% for an input power of 48 mW, which is comparable with reported values from circuits operating at similar power levels.Portuguese Foundation for Science and Technology (FCT/MCTES), under project PEst-OE/EEI/UI0066/2011, and to the CTS multiannual funding, through the PIDDAC Program funds. I am also very grateful for the grant SFRH/PROTEC/67683/2010, financially supported by the IPL – Instituto Politécnico de Lisboa

POWER DISTRIBUTION ANALYSIS IN COMPLEX SYSTEMS

Electronic systems are continuously growing nowadays in every ambit and application; concepts like mobile systems, domotic, wireless monitoring are becoming very common, and the reason is the continuous reduction of the energy and time needed to collect, process and send information and data to the end user. The energy management complexity of these systems is increasing in parallel both in terms of efficiency and reliability, in order to increase the lifetime of the application and try to make it energy-autonomous, thus also the power management should not be seen only as an efficient energy conversion stage, but as a complex system which can now manage different energy sources, and ensure an uninterrupted power supply to the application. The problems that must be overcome increase as the number of scenarios where the end applications have to be used: this thesis aims to present some complex power distribution systems and provide a detailed analysis of the strategies necessary to make the solution reliable and efficient

Analysis, design and implementation of high performance control schemes in renewable energy source based DC/AC inverter for micro-grid application

Ph.DDOCTOR OF PHILOSOPH

A Charge-Recycling Scheme and Ultra Low Voltage Self-Startup Charge Pump for Highly Energy Efficient Mixed Signal Systems-On-A-Chip

The advent of battery operated sensor-based electronic systems has provided a pressing need to design energy-efficient, ultra-low power integrated circuits as a means to improve the battery lifetime. This dissertation describes a scheme to lower the power requirement of a digital circuit through the use of charge-recycling and dynamic supply-voltage scaling techniques. The novel charge-recycling scheme proposed in this research demonstrates the feasibility of operating digital circuits using the charge scavenged from the leakage and dynamic load currents inherent to digital design. The proposed scheme efficiently gathers the “ground-bound” charge into storage capacitor banks. This reclaimed charge is then subsequently recycled to power the source digital circuit. The charge-recycling methodology has been implemented on a 12-bit Gray-code counter operating at frequencies of less than 50 MHz. The circuit has been designed in a 90-nm process and measurement results reveal more than 41% reduction in the average energy consumption of the counter. The total energy savings including the power consumed for the generation of control signals aggregates to an average of 23%. The proposed methodology can be applied to an existing digital path without any design change to the circuit but with only small loss to the performance. Potential applications of this scheme are described, specifically in wide-temperature dynamic power reduction and as a source for energy harvesters. The second part of this dissertation deals with the design and development of a self-starting, ultra-low voltage, switched-capacitor (SC) DC-DC converter that is essential to an energy harvesting system. The proposed charge-pump based SC-converter operates from 125-mV input and thus enables battery-less operation in ultra-low voltage energy harvesters. The charge pump does not require any external components or expensive post-fabrication processing to enable low-voltage operation. This design has been implemented in a 130-nm CMOS process. While the proposed charge pump provides significant efficiency enhancement in energy harvesters, it can also be incorporated within charge recycling systems to facilitate adaptable charge-recycling levels. In total, this dissertation provides key components needed for highly energy-efficient mixed signal systems-on-a-chip

Analysing integrated renewable energy and smart-grid systems to improve voltage quality and harmonic distortion losses at electric-vehicle charging stations

Due to environmental impacts of fossil fuels, a move towards using Electric-Vehicles (EV) to reduce carbon emissions and fossil fuels is regarded as a good solution to the climate change problem. In recent years, a dramatic increase of EV and charging stations has raised voltage quality and harmonic distortion issues that are affecting the electrical grid network. To address these issues there is a need to redesign the integrated renewable energy and smart grid network by applying new methodologies. The aim of this work is to propose an isolated smart micro grid, which connects renewable energy generation units to the electric vehicles charging station without degrading voltage quality or causing harmonic distortion losses. A topology has been identified for the smart grid that is simulated with the intention of implementing it with the integration of modern communication technologies that enables the components to produce and reflect data in an efficient way to assist better regulation in the power flow. The power flow is investigated by simulating unpredictable renewable energy and by using car batteries at the electric vehicle charging station. It is investigated how micro grid parameters are affected in the presence of super capacitors, car batteries and the use of larger power electronic converters. In the simulations, an electrical power control system is implemented at power conversion units which generates the correct duty cycle of the converter switches and controls the power flow operation at the smart grid. Then the proposed electrical power control system is compared with other systems such as maximum power point tracking (MPPT) algorithm and space vector pulse width modulation (SVPWM). A smart sensor system and smart protection are connected to protect the grid and to maintain system stability over a long time. The research focuses on developing a smart grid that performs the communication among the converters, performs power sharing, and does preventive management. It also monitors the energy efficiently and balances the energy in the grid irrespective of load or power generation variations. A mathematical model is developed to predict grid behaviour and is validated via MATLAB simulation of the grid. It is noticed that an improvement is made in the efficiency of renewable energy transmission to the electric-vehicle charging station

Automated Synthesis Tool for Design Optimization of Power Electronic Converters

Designers of power electronic converters usually face the challenge of having multiple performance indices that must be simultaneously optimized, such as maximizing efficiency while minimizing mass or maximizing reliability while minimizing cost. The experienced engineer applies his or her judgment to reduce the number of possible designs to a manageable number of feasible designs for which to prototype and test; thus, the optimality of this design-space reduction is directly dependent upon the experience, and expertise and biases of the designer. The practitioner is familiar with tradeoff analysis; however, simple tradeoff studies can become difficult or even intractable if multiple metrics are considered. Hence a scientific and systematic approach is needed. In this dissertation, a multi-objective optimization framework is presented as a design tool. Optimization of power electronic converters is certainly not a new subject. However, when limited to off-the-shelf components, the resulting system is really optimized only over the set of commercially available components, which may represent only a subset of the design space; the reachable space limited by available components and technologies. While this approach is suited to cost-reduce an existing design, it offers little insight into design possibilities for greenfield projects. Instead, this work uses the Technology Characterization Methods (TCM) to broaden the reachable design space by considering fundamental component attributes. The result is the specification for the components that create the optimal design rather than an evaluation of an apriori selected set of candidate components. A unique outcome of this approach is that new technology development vectors may emerge to develop optimized components for the optimized power converter. The approach presented in this work uses a mathematical descriptive language to abstract the characteristics and attributes of the components used in a power electronic converter in a way suitable for multi-objective and constrained optimization methods. This dissertation will use Technology Characterization Methods (TCM) to bridge the gap between high-level performance attributes and low-level design attributes where direct relationship between these two does not currently exist. The loss and size models for inductors, capacitors, IGBTs, MOSFETs and heat sinks will be used to form objective functions for the multi-objective optimization problem. A single phase IGBT-based inverter is optimized for efficiency and volume based on the component models derived using TCM. Comparing the obtained designs to a design, which can be made from commercial off-the-shelf components, shows that converter design can be optimized beyond what is possible from using only off-the-shelf components. A module-integrated photovoltaic inverter is also optimized for efficiency, volume and reliability. An actual converter is constructed using commercial off-the-shelf components. The converter design is chosen as close as possible to a point obtained by optimization. Experimental results show that the converter modeling is accurate. A new approach for evaluation of efficiency in photovoltaic converter is also proposed and the front-end portion of a photovoltaic converter is optimized for this efficiency, as well as reliability and volume