High-efficiency high voltage hybrid charge pump design with an improved chip area

A hybrid charge pump was developed in a 0.13- $\mu \text{m}$ Bipolar-CMOS-DMOS (BCD) process which utilised high drain-source voltage MOS devices and low-voltage integrated metal-insulator-metal (MIM) capacitors. The design consisted of a zero-reversion loss cross-coupled stage and a new self-biased serial-parallel charge pump design. The latter has been shown to have an area reduction of 60% in comparison to a Schottky diode-based Dickson charge pump operating at the same frequency. Post-layout simulations were carried out which demonstrated a peak efficiency of 38% at the output voltage of 18.5 V; the maximum specified output voltage of 27 V was also achieved. A standalone serial-parallel charge pump was shown to have a better transient response and a flatter efficiency curve; these are preferable for time-sensitive applications with a requirement of a broader range of output currents. These findings have significant implications for reducing the total area of implantable high-voltage devices without sacrificing charge pump efficiency or maximum output voltage

Energy-irrigation nexus in South Asia: Improving groundwater conservation and power sector viability

Tube wells / Energy consumption / Costs / Electricity supplies / Groundwater irrigation / Water policy / Pumps / Water rates

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

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

Analysis and design of switched-capacitor DC-DC converters with discrete event models

Ph. D. Thesis.Switched-capacitor DC-DC converters (SCDDCs) play a critical role in low power integrated systems. The analysis and design processes of an SCDDC impact the performance and power efficiency of the whole system. Conventionally, researchers carry out the analysis and design processes by viewing SCDDCs as analogue circuits. Analogue attributes of an SCDDC, such as the charge flow current or the equivalent output impedance, have been studied in considerable detail for performance enhancement. However, in most existing work, less attention is paid to the analysis of discrete events (e.g. digital signal transitions) and the relationships between discrete events in SCDDCs. These discrete events and the relationships between discrete events also affect the performance of SCDDCs. Certain negative effects of SCDDCs such as leakage current are introduced by unhealthy discrete states. For example, MOS devices in an SCDDC could conduct undesirably under certain combinations of signals, resulting in reversion losses (a type of leakage in SCDDCs). However, existing work only use verbal reasoning and waveform descriptions when studying these discrete events, which may cause confusion and result in an informal design process consisting of intuitive design and backed up merely by validation based on natural language discussions and simulations. There is therefore a need for formalised methods to describe and analyse these discrete events which may facilitate systematic design techniques. This thesis presents a new method of analysing and designing SCDDCs using discrete event models. Discrete event models such as Petri nets and Signal Transition Graphs (STGs) are commonly used in asynchronous circuits to formally describe and analyse the relationships between discrete transitions. Modelling SCDDCs with discrete event models provides a formal way to describe the relations between discrete transitions in SCDDCs. These discrete event models can be used for analysis, verification and even design guidance for SCDDC design. The rich set of existing analysis methods and tools for discrete event models could be applied to SCDDCs, potentially improving the analysis and design flow for them. Moreover, since Petri nets and STGs are generally used to analyse and design asynchronous circuits, modelling and designing SCDDCs with STG models may additionally facilitate the incorporation of positive features of asynchronous circuits in SCDDCs (e.g. no clock skew). In this thesis, the relations between discrete events in SCDDCs are formally described with SC-STG (an extended STG targeting multi-voltage systems, to which SCDDCs belong), which avoids the potential confusion due to natural language and waveform descriptions. Then the concurrency and causality relations described in SC-STG model are extended to Petri nets, with which the presence of reversion losses can be formally determined and verified. Finally, based on the STG and Petri net models, a new design method for reversion-loss-free SCDDCs is proposed. In SCDDCs designed with the new method, reversion losses are entirely removed by introducing asynchronous controls, synthesised with the help of a software synthesis toolkit “Workcraft”. To demonstrate the analysis capabilities of the method, several cross-coupled voltage doublers (a type of SCDDC) are analysed and studied with discrete event models as examples in this thesis. To demonstrate the design capabilities of the method, a new reversion-loss-free cross-coupled voltage doubler is designed. The cross-coupled voltage doubler is widely used in low power integrated systems such as flash memories, LCD drivers and wireless energy harvesting systems. The proposed modelling method is potentially used in both research and industrial area of those applications for a formal and high-efficiency design proces

Sub 1V Charge Pump based Micro Scale Energy Harvesting for Low Power Application

Harvesting energy from our environment is a promising solution to provide power to wireless sensor network, wearable devices and biomedical implantation. Now a days, usage of battery power system has disappeared because of replacement issues, installation costs every periodic year and the possibility of health hazard in the case of biomedical implants. Considering these issues, energy harvesting proves to be the most feasible and convenient option in the case of wearable devices and biomedical implantation. Hence, we have focused on indoor single solar cell energy harvesting to power ultra-low power load. The tree topology DC-DC converter is used for power management circuit with optimized efficiency. High efficiency is achieved by using ZVT MOSCAP. The power management circuit includes DC-DC converter and feed forward maximum power point tracking algorithm to transfer maximum power from the single solar cell. The system has ultra-low power battery protection and input condition sensor circuit to extend the life of the battery by protecting from overcharging and over discharging. Also, cold start up circuit is used to run the system when battery voltage drains out to zero. The objective of this system to make complete energy harvester unit is to drive wide range of ultra-low power applications. We have driven the ZigBee receiver to validate our system and the system works effectively

Power and Energy Student Summit 2019: 9 – 11 July 2019 Otto von Guericke University Magdeburg ; Conference Program

The book includes a short description of the conference program of the "Power and Energy Student Summit 2019". The conference, which is orgaized for students in the area of electric power systems, covers topics such as renewable energy, high voltage technology, grid control and network planning, power quality, HVDC and FACTS as well as protection technology. Besides the overview of the conference venue, activites and the time schedule, the book includes all papers presented at the conference

Conceptual design of thermal energy storage systems for near term electric utility applications. Volume 1: Screening of concepts

Over forty thermal energy storage (TES) concepts gathered from the literature and personal contacts were studied for their suitability for the electric utility application of storing energy off-peak discharge during peak hours. Twelve selections were derived from the concepts for screening; they used as storage media high temperature water (HTW), hot oil, molten salts, and packed beds of solids such as rock. HTW required pressure containment by prestressed cast-iron or concrete vessels, or lined underground cavities. Both steam generation from storage and feedwater heating from storage were studied. Four choices were made for further study during the project. Economic comparison by electric utility standard cost practices, and near-term availability (low technical risk) were principal criteria but suitability for utility use, conservation potential, and environmental hazards were considered

Development of electronics for microultrasound capsule endoscopy

Development of intracorporeal devices has surged in the last decade due to advancements in the semiconductor industry, energy storage and low-power sensing systems. This work aims to present a thorough systematic overview and exploration of the microultrasound (µUS) capsule endoscopy (CE) field as the development of electronic components will be key to a successful applicable µUSCE device. The research focused on investigating and designing high-voltage (HV, < 36 V) generating and driving circuits as well as a low-noise amplifier (LNA) for battery-powered and volume-limited systems. In implantable applications, HV generation with maximum efficiency is required to improve the operational lifetime whilst reducing the cost of the device. A fully integrated hybrid (H) charge pump (CP) comprising a serial-parallel (SP) stage was designed and manufactured for > 20 V and 0 - 100 µA output capabilities. The results were compared to a Dickson (DKCP) occupying the same chip area; further improvements in the SPCP topology were explored and a new switching scheme for SPCPs was introduced. A second regulated CP version was excogitated and manufactured to use with an integrated µUS pulse generator. The CP was manufactured and tested at different output currents and capacitive loads; its operation with an US pulser was evaluated and a novel self-oscillating CP mechanism to eliminate the need of an auxiliary clock generator with a minimum area overhead was devised. A single-output universal US pulser was designed, manufactured and tested with 1.5 MHz, 3 MHz, and 28 MHz arrays to achieve a means of fully-integrated, low-power transducer driving. The circuit was evaluated for power consumption and pulse generation capabilities with different loads. Pulse-echo measurements were carried out and compared with those from a commercial US research system to characterise and understand the quality of the generated pulse. A second pulser version for a 28 MHz array was derived to allow control of individual elements. The work involved its optimisation methodology and design of a novel HV feedback-based level-shifter. A low-noise amplifier (LNA) was designed for a wide bandwidth µUS array with a centre frequency of 28 MHz. The LNA was based on an energy-efficient inverter architecture. The circuit encompassed a full power-down functionality and was investigated for a self-biased operation to achieve lower chip area. The explored concepts enable realisation of low power and high performance LNAs for µUS frequencies

Newly proposed strategies to increase the energy efficiency of water systems

One of the main challenges in the water industry consists of the reduction of environmental impacts, as well as the containment of energy use. In this research work, new solutions to achieve a sustainable management of water networks have been developed and organized in three lines of research. The main line of research is based on the optimal location of hydraulic devices within a water distribution network in order to maximize the energy production and water savings, as well as to minimize the investment cost. Firstly, the installation of only Pumps As Turbines (PATs) has been analyzed within a literature synthetic network and a new Mixed Integer Non-Linear Programming (MINLP) model has been developed to perform the optimization. Such an optimization model has been defined by a thorough mathematical formulation in order to deal with the extremely hard technical and computational complexities affecting the optimization procedure. In this research, only deterministic solvers have been employed to search the optima, and a comparison of their performance has been also carried out. Most of the computations have been performed by a global optimization solver, which potentially finds the global optimum in both convex and non-convex problems, but is also used to find good quality local optima in very complex problems, where the achievement of the exact solution may require infinite computational time. Compared to other studies in literature on the same network, the proposed study accounts for crucial hydraulic aspects, such as the phenomenon of flow reversion during the day affecting the installation and the operation of the devices, as well as the need for installing machines generating a power above a minimum fixed value. A comparison with such previous literature works has been carried out in order to highlight the effectiveness of the newly proposed optimization procedure. Moreover, to develop a more realistic and comprehensive mathematical model, the simultaneous installation of PATs and Pressure Reducing Valves (PRVs) has been also modeled by the introduction of new variables and mathematical constraints. Indeed, in presence of large water savings but small energy recovery, a PRV might be a more viable solution than a PAT. Compared to other studies in literature optimizing the only location of PATs within the same synthetic network, the simultaneous installation of valves and turbines, as well as the formulation of new hydraulic constraints, has significantly increased the value of the optimization model. In addition, the optimization has been extended to a real water distribution network serving the Blackstairs region (IE), with the aim of testing the robustness of the model and of the optimization procedure in more complex and larger problems. Indeed, the computational complexity affecting the optimization procedure increases according to the size of the network and the mathematical formulation proposed for the synthetic network might be not suitable for such a more complex case study. Compared to the synthetic network where the pressure reduction up to defined minimum requirements has not compromised the hydraulic operation of the system, in the analyzed real water network the exploitation of the available excess pressure to save both water and energy raises the need for employing also pumping systems to supply the most remote nodes of the network. The installation of pumping systems within the network has been therefore included within the optimization procedure and the outcome has been a new model for a Global Optimization of Hydraulic Devices Location (GOHyDeL), suitable for any water distribution network. Such a new model has been the result of progressive findings and hard attempts to deal with the enormous complexities arising during the computation. In all the performed optimization, the maximized water and energy savings and the minimized installation costs have been assessed according to a cost model used by previous authors in literature, in order to make a more straightforward comparison with such literature works. However, more recent cost models available in literature have been also employed to achieve more reasonable and realistic values of the results. According to the comparison between results obtained by using different cost models, despite the employment of more recent models leading to significantly larger investment costs and, thus, smaller values of NPV, the solutions are quite similar in terms of location of installed devices, and the achieved savings are comparable as well. However, among all the devices, the PRVs have resulted to be more affected by the choice of the cost model, due to the strong dependency of the valve costs on the pipe diameter. On the whole, beyond the large feasibility of the model within the optimal location field, a remarkable value of the proposed research also results from the new formulation of mathematical constraints and variables, which requires less computational effort and could find application also in more general optimization problems. The second line of research defines and compares two alternative strategies to supply a real water distribution network. The first solution consists of an elevated reservoir, which is located upstream of a water distribution network and is supplied from the water source by a pumping system. In this scheme, the excess pressure is not dissipated by a traditional valve, but rather a pump as turbine is installed to contain the pressure, thus water leakage, and also recover energy. The second hydraulic scheme instead consists of a pump supplying the downstream network directly from the source. In this scheme there is not an excess pressure to convert in energy, since the elevated reservoir is bypassed and the flow is pumped to the network with lower head. Such new schemes represent two different strategies to increase the energy efficiency of a supply system, as alternatives to the use of elevated reservoir with dissipation of the excess pressure by means of pressure reducing valves. The two schemes have been properly designed in order to find the devices, in terms of diameter and rotational speed, minimizing the energy requirements, thus maximizing the energy efficiency of the whole system. Given the water network supplying a small village in Ballacolla area (IE), the direct supply of the network has resulted a more efficient strategy than the indirect supply scheme with energy recovery. Moreover, the two schemes have been compared by varying the operating conditions, thus considering different combinations of distance and elevation of the source from the water distribution network. The energy audit of the two schemes has been assessed by new energy efficiency indices and also by literature indices. The comparison has showed that the convenience of a scheme over the other significantly depends on the operating conditions. However, with equal values of pumping head in both the schemes, the indirect scheme with energy recovery is up to 5 % more convenient than the direct pumping scheme, which is instead more efficient if the pumping head could be reduced up to 6 %. In the third line of research a new strategy to save energy in the urban water management is presented. The proposed solution consists of a mixed PAT-pump turbocharger, that is a PAT-equipped turbopump exploiting an excess pressure within the fresh water network to produce energy, which is entirely used to carry a wastewater stream towards a treatment plant. In this system, the excess pressure is converted by the PAT in a mechanical torque, which in turn supplies the pump mounted on the same shaft. Such a plant arises whenever wastewater pumping station and excess pressure point could be co-located, thus in low ground areas where high clean-water pressures occur and sewage networks are equipped with pumping systems due to the need to treat the wastewater. In this application, the water distribution network serving Ballacolla area (IE) has been assumed as case study, since it is suitable for the installation of this kind of plant. A preliminary geometric selection of the devices has been performed by a new selection method based on the maximum daily averaged values of fresh and wastewater discharge. Then, the behavior of the plant has been simulated for several wastewater hydrographs by a new mathematical model. The benefits of the plants have been assessed and compared with a conventional wastewater pumping system working in ON/OFF mode. According to the comparison, the higher Net Present Value (NPV) of the MPP plant proves the advantage of this scheme over the conventional system, at least until the useful life of the plant is reached