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 Non-Invasive Thermal Drift Compensation Technique Applied to a Spin-Valve Magnetoresistive Current Sensor

A compensation method for the sensitivity drift of a magnetoresistive (MR) Wheatstone bridge current sensor is proposed. The technique was carried out by placing a ruthenium temperature sensor and the MR sensor to be compensated inside a generalized impedance converter circuit (GIC). No internal modification of the sensor bridge arms is required so that the circuit is capable of compensating practical industrial sensors. The method is based on the temperature modulation of the current supplied to the bridge, which improves previous solutions based on constant current compensation. Experimental results are shown using a microfabricated spin-valve MR current sensor. The temperature compensation has been solved in the interval from 0 °C to 70 °C measuring currents from −10 A to +10 A

Advanced control architectures for grid connected and standalone converter systems

This dissertation proposes new control algorithms dedicated towards improving the reliability, computational burden and stability in grid-connected and stand-alone based power electronic converter systems applicable for ac microgrids. Two voltage sensorless control architectures, one for stand-alone applications and the other for grid-connected application are established in this thesis. The output voltage of a standalone single-phase inverter is controlled directly by controlling the output filter capacitor current without using a dedicated output voltage sensor. A method to estimate the output filter capacitance is also presented. For the grid connected converter, a novel closed loop estimation is presented to estimate the grid voltage. In addition to the estimation of the grid voltage, the proposed method also generates the unit vectors and frequency information similar to a conventional phase-locked loop structure. The voltage sensorless algorithm is then extended to LCL filter based grid connected converters thereby proposing a new indirect method of controlling the grid current. Furthermore, addressing the stability issues in current-controlled grid tied converters, this dissertation also analyzes the power angle synchronization control of grid-tied bidirectional converters for low voltage grids. The power flow equations for the low voltage grid are analyzed and compensators are designed to ensure the decoupled control of active and reactive power. It is demonstrated that the proposed compensators are immune to grid fluctuations and ensure stable operation controlling the desired power flow to and from the grid. Detailed plant modeling, controller design, simulation and experimental results are presented for all of the proposed schemes --Abstract, page iv

Current-Source DC-DC Converter for Fiber-Optic Communication Systems

In this thesis, a proof of concept for a current-source DC-DC converter for powering sensors used in an underwater communications system is presented. The proposed converter steps down an input current of 0.9 A to 0.625 A, while maintaining an output voltage of 24 V and output power of 15 W. The complete steady-state analysis and design of the proposed converter in its single-stage form is also explained in detail. Performance evaluation of the proposed converter was carried out using LTspice. Results of the simulation demonstrate that the design was able to produce average output current of 0.639 A at maximum output power of 15.292 W while maintaining 24.39 V regulated output voltage. The overall efficiency of the converter was determined to be 88.73% and the output voltage ripple was calculated to be 0.4%, meeting the original specifications of the design

Adaptive Boundary Control Using the Natural Switching Surfaces for Flyback Converters

The derivation and implementation of the natural switching surfaces (NSS) considering certain parametric uncertainties for a flyback converter operating in the boundary conduction mode (BCM) is the main focus of this paper. The NSS with nominal parameters presents many benefits for the control of nonlinear systems; for example, fast transient response under load-changing conditions. However, the performance worsens considerably when the converter actual parameters are different from the ones used in the design process. Therefore, a novel control strategy for NSS considering the effects of parameter uncertainties is proposed. This control law can estimate and adapt the control trajectories in a minimum number of switching cycles to obtain excellent performances even under extreme parameter uncertainties. The analytical derivation of the proposed adaptive switching surfaces is presented together with simulations and experimental results showing adequate performance under different tests, including comparisons with a standard PI controller

Pregled različitih tehnologija upravljanja naprednim mrežama za povećanje fleksibilnosti elektroenergetskih sustava i omogućavanje masovne integracije obnovljivih izvora energije

Over the last 15 years, major changes have taken place in the electricity sector. A significant increase in the share of renewable energy sources (RES) with variable generation, followed by the decommissioning of conventional power plants based on fossil fuels, has dramatically changed the way of the power system (EPS) operation. During this time, there has been inadequate and untimely investment in the transmission infrastructure. This occurred partly due to the lack of funding, and partly due to the climate change and the rising environmental awareness, as well as the influence of green activists making it difficult to obtain permits to build electrical grid facilities. Additionally, electricity consumption is steadily increasing due to population growth in the undeveloped and developing countries, and due to the rising living standard in the developed countries. Therefore, global electricity consumption is expected to triple by 2050. To meet the new demands, Transmission System Operators (TSOs) are deploying advanced transmission technologies based on a comprehensive application of information and communication solutions. These technologies increase the capacity, efficiency, and reliability of both the existing and new elements of the transmission system. These solutions applied vary from system to system and depend on many influencing factors. The application of these advanced technologies is particularly important for congestion management, as the power system operates closer and closer to stability limits, increasing the risk of collapse. The paper describes the technologies that transform the existing network into smart grids, primarily from the point of view of increasing the capacity of the existing infrastructure through different smart grid investments.U posljednjih 15 godina u elektroenergetskom sektoru dogodile su se velike promjene. Značajno povećanje udjela obnovljivih izvora energije (OIE) s varijabilnom proizvodnjom, praćeno gašenjem konvencionalnih elektrana na fosilna goriva, dramatično je promijenilo način rada elektroenergetskog sustava (EES). Tijekom tog vremena bilo je neodgovarajućih i nepravovremenih ulaganja u prijenosnu infrastrukturu. To se dogodilo dijelom zbog nedostatka financijskih sredstava, a dijelom zbog klimatskih promjena i porasta ekološke svijesti, kao i utjecaja zelenih aktivista koji su otežali dobivanje dozvola za izgradnju energetskih objekata. Osim toga, potrošnja električne energije u stalnom je porastu zbog rasta stanovništva u nerazvijenim zemljama i zemljama u razvoju te zbog povećanja životnog standarda u razvijenim zemljama. Stoga se očekuje da će se globalna potrošnja električne energije utrostručiti do 2050. Kako bi zadovoljili nove zahtjeve, operatori prijenosnih sustava (TSO) uvode napredne tehnologije prijenosa temeljene na sveobuhvatnoj primjeni informacijskih i komunikacijskih rješenja. Ove tehnologije povećavaju kapacitet, učinkovitost i pouzdanost postojećih i novih elemenata prijenosnog sustava. Ova primijenjena rješenja razlikuju se od sustava do sustava i ovise o mnogim utjecajnim čimbenicima. Primjena ovih naprednih tehnologija posebno je važna za upravljanje zagušenjima jer elektroenergetski sustav radi sve bliže i bliže granicama stabilnosti, povećavajući rizik od njegovog sloma. U radu su opisane tehnologije koje transformiraju postojeću mrežu u napredne elektroenergetske mreže, prvenstveno sa stajališta povećanja kapaciteta postojeće infrastrukture kroz različite investicije u napredne tehnologije

Modeling and Analysis of Active Front-End Induction Motor Drive for Reactive Power Compensation

In this thesis, an active front end induction motor drive for reactive power compensation is analyzed. The classical vector control approach for high performance control of an induction motor drive is a well established industry standard today. The same idea of decoupled control is extended to the line-side PWM converter for achieving better dynamic performance. The system model is obtained using d-q rotating frame theory. The iqe component of line currents is used to control the reactive power. The idecomponent is used to control the dc-link voltage and also to supply active power required by the motor. A high gain feedback controller with input-output linearization is presented to remove coupling between iqe and ide currents. A load power feed-forward loop is added to the dc-link voltage controller for fast dynamic response. The drive performance is analyzed to define system specifications. The motor acceleration, deceleration, and variable power factor operation (reactive power compensation) of the active drive system are demonstrated. The motor load is varied from no load to full load in steps of 10% each. For each step the device currents, switching power loss, line harmonics, and dc-link ripples are plotted. This data is used to derive conclusions that define system specifications and also state operating limits. The control of the drive system is implemented in MATLAB-SIMULINK. The complete system hardware is implemented in commercially available simulation tool, PSIM. The two software packages are interlinked using an interface module

Transformerless Microinverter with Low Leakage Current Circulation and Low Input Capacitance Requirement for PV Applications

The inevitable depletion of limited fossil fuels combined with their harmful footprint on the environment led to a global pursuit for alternative energy sources that are clean and inexhaustible. Renewable energies such as wind, biomass and solar are the best alternative energy candidates, with the latter being more suitable for GCC countries. Besides, the energy generated from photovoltaic (PV) modules is one of the elegant examples of harnessing solar energy, as it is clean, pollutant-free and modular. Furthermore, recent advances in PV technology, especially grid-connected PV systems revealed the preeminence of using multiple small inverters called (Microinverters) over using the conventional single inverter configuration. Specifically, the break-even cost point can be reached faster and the system modularity increases with microinverters usage. Nonetheless, due to microinverter’s small ratings designers prefer transformerless designs because transformer removal achieves higher efficiency and power density. However, the transformer removal results in loss of galvanic isolation that leads to dangerous leakage current circulation that affects system safety. Another issue with microinverters is that since they are installed outside their bulky DC-Link electrolytic capacitor lifetime deteriorates the system reliability because electrolytic capacitor failure rate increases as temperature increases. Moreover, the DC-Link capacitor is used to decouple the 2nd order power harmonic ripples that appear in single-phase systems. Thus, the objective of this thesis is to design an efficient transformerless microinverter that has low leakage current circulation and low input capacitance requirement with a minimum number of active switches. In other words, the objective is to increase the safety and the reliability of the system while maintaining the high efficiency. Eventually, the configuration selected is the transformerless differential buck microinverter with LCL filter and it is modeled with passive resonance damping and active resonance damping control