The demand for increased renewable energy production has led to increased photovoltaic (PV) installations worldwide. As this demand continues to grow, it is important that the costs of PV installations decrease while the power output capability increases. One of the components in PV installations that has lots of room for improvement is the power conditioning system. The power conditioning system is responsible for converting the power output of PV modules into power useable by the utility grid while insuring the PV array is outputting the maximum available power. Modular power conditioning systems, where each PV module has its own power converter, have been proven to yield higher output power due to their superior maximum power point tracking capabilities. However, this comes with the disadvantages of higher costs and lower power conversion efficiencies due to the increased number of power electronics converters. The primary objective of this dissertation is to develop a high-efficiency, low cost microconverter in an effort to increase the output power capability and decrease the cost of modular power conditioning systems. First, existing isolated dc-dc converter topologies are explored and a new topology is proposed based on the highly-efficient series resonant converter operating near the series resonant frequency. Two different hybrid modes of operation are introduced in order to add wide input-voltage regulation capability to the series resonant converter while achieving high efficiency through low circulating currents, zero-current switching (ZCS) of the output diodes, zero-voltage switching (ZVS) and/or ZCS of the primary side active switches, and direct power transfer from the source to the load for the majority of the switching cycle. Each operating mode is analyzed in detail using state-plane trajectory plots. A systematic design approach that is unique to the newly proposed converter is presented along with a detailed loss analysis and loss model. A 300-W microconverter prototype is designed to experimentally validate the analysis and loss model. The converter featured a 97.7% weighted California Energy Commission (CEC) efficiency with a nominal input voltage of 30 V. This is higher than any other reported CEC efficiency for PV microconverters in literature to date. Each operating mode of the proposed converter can be controlled using simple fixed-frequency pulse-width modulation (PWM) based techniques, which makes implementation of control straightforward. Simplified models of each operating mode are derived as well as control-to-input voltage transfer functions. A smooth transition method is then introduced using a two-carrier PWM modulator, which allows the converter to transition between operating modes quickly and smoothly. The performance of the voltage controllers and transition method were verified experimentally. To ensure the proposed converter is compatible with different types of modular power conditioning system architectures, system-level interaction issues associated with different modular applications are explored. The first issue is soft start, which is necessary when the converter is beginning operation with a large capacitive load. A novel soft start method is introduced that allows the converter to start up safely and quickly, even with a short-circuited output. Maximum power point tracking and double line frequency ripple rejection are also explored, both of which are very important to ensuring the PV module is outputting the maximum amount of available power. Lastly, this work deals with efficiency optimization of the proposed converter. It is possible to use magnetic integration so that the resonant inductor can be incorporated into the isolation transformer by way of the transformer leakage inductance in order to reduce parts count and associated costs. This chapter, however, analyzes the disadvantages to this technique, which are increased proximity effect losses resulting in higher conduction losses. A new prototype is designed and tested that utilizes an external resonant inductor and the CEC efficiency was increased from 97.7% to 98.0% with a marginal 1.8% total cost increase. Additionally, a variable frequency efficiency optimization algorithm is proposed which increases the system efficiency under the high-line and low-line input voltage conditions. This algorithm is used for efficiency optimization only and not control, so the previously presented simple fixed-frequency modeling and control techniques can still be utilized. / Ph. D.

Recently, as a promising lighting source, light-emitting diodes (LEDs) have become more and more attractive and have great opportunity to replace traditional lighting sources - incandescent, fluorescent and HID because of the advantages such as high luminous efficacy, long lifetime, quick on/off time, wide color gamut, eco-friendly etc. Based on the research from U.S. Department of Energy, over 30% of total electric consumption in U.S. each year is for lighting, 75% of which are for indoor lighting (including both residential and commercial buildings). In the indoor LED lighting application, to provide multiple current source outputs for multiple LED strings, traditional solutions usually adopt a two-stage structure, which is complicated and cost-ineffective. How to design a simple, low-cost and efficient LED driver with multiple current source outputs is in great demand and really challenging. In this thesis, a single-stage multi-channel constant current (MC3) LED driver structure has been proposed. Multiple transformer structure is utilized to provide multiple current source outputs. The current control scheme is also simple - only one LED string current is sensed and controlled; other strings' currents are cross regulated. Firstly, a PWM half bridge topology is chosen to implement the proposed single-stage MC3 LED driver concept. In order to analyze the current cross regulation, a general model is derived. The circuit has been simulated under various LED load conditions to verify its good current sharing capability. In order to further improve efficiency, simplify the driver's complexity and reduce cost, a LLC resonant topology is also investigated. LLC current gain characteristic has been derived by considering LED's i-v character and a design procedure is developed. A 100 kHz, 200 W, 4-string MC3 LLC LED driver is designed and tested. The experimental results show that the driver can maintain constant current output within the whole input and output variations, achieve good efficiency and realize current sharing under both balanced and unbalanced LED conditions. The dimming function can also be realized through frequency modulation method and burst mode control method. As a conclusion, a single-stage MC3 LED driver concept is proposed and implemented with two topologies. The proposed idea provides a simple, low-cost and efficient solution for indoor LED lighting application with multiple LED string configuration. It also has good current sharing capability and robustness to LED forward voltage variations or short failures. / Master of Science

Floors have traditionally been designed only for strength and deflection serviceability. As technological advances have been made in medical, scientific and micro-electronics manufacturing, many types of equipment have become sensitive to vibration of the supporting floor. Thus, vibration serviceability has become a routinely evaluated limit state for floors supporting sensitive equipment. Equipment vibration tolerance limits are sometimes expressed as waveform peak acceleration, and are more often expressed as narrowband spectral acceleration, or one-third octave spectral velocity. Current floor vibration prediction methods, such as those found in the American Institute of Steel Construction Design Guide 11, Floor Vibrations Due to Human Activity, the British Steel Construction Institute P354, Design of Floors for Vibration: a New Approach and the British Concrete Centre CCIP-016 A Design Guide for Footfall Induced Vibration of Structures, have limitations. It has been observed that non-structural components such as light-weight partitions could significantly change floor dynamic properties. Current prediction methods do not provide a fundamental frequency manual prediction method nor finite element modeling guidance for floors with non-structural components. Current prediction methods only predict waveform peak acceleration and do not provide predictions for frequency domain response including narrowband spectral acceleration or one-third octave spectral velocity. Also, current methods are not calibrated to provide a specific level of conservatism. This research project provides (1) a fundamental frequency manual prediction method for floors with lightweight partitions; (2) an improved finite element modeling procedure for floors with light-weight partitions; (3) a procedure to predict the vibration response in narrow-band spectrum and one-third octave band spectrum which can be directly compared with vibration tolerance limits; and (4) a simplified experimental procedure to estimate the floor natural frequencies. An experimental program including four steel-framed building floors and a concrete was completed. Modal tests were performed on two of the steel-framed buildings and the concrete building using an electrodynamic shaker. Experimental modal analysis techniques were used to estimate the modal properties: natural frequencies, mode shapes, and damping ratios. Responses to walking excitation were measured several times in each tested bay for individuals walking at different walking speeds. During each test, the walker crossed the middle of the bay using a metronome to help maintain the intended cadence. The proposed method was used to predict the modal properties and responses to walking. The measurements are used to assess the precision of the proposed methods and to calibrate the prediction methods to provide a specific probability that the actual response will exceed the predicted response. Comparison of measurements and predictions shows the proposed methods are sufficiently accurate for design usage.

This thesis is concerned with various methods for the control and investigation of pulse dynamics in a Photonic Crystal Fibre (PCF) and of the radiation driven by a short pulse. In particular the focus is on pulses in the anomalous dispersion region which would form solitons in the absence of higher order effects. Several different types of radiation can be driven by such pulses if they are perturbed by higher order dispersive and non-linear effects - for example Resonant Radiation (RR) and Negative Resonant Radiation (NRR) two dispersive waves which gain energy at the expense of the pulse. The feature of NRR which is of particular importance is that it is the first observed example of a coupling between positive and negative frequencies in optics. This has only been possible due to recent advances in fields such as PCFs, lasers and analogue systems. As with many scientific discoveries, NRR was found by bringing together ideas and techniques from these different fields. Both the pulse and the driven radiation are investigated using a number of different pulse and PCF parameters. These include power, chirp, polarisation and PCF dispersion. These are used to vary the wavelengths at which the driven radiation occurs as well as its generation efficiency. Furthermore the power and chirp are used to vary where in the PCF the driven radiation is generated by controlling where the driving pulse compresses and spectrally expands. This property is used to investigate different stages in the evolution of the pulse and driven radiation as well as to optimise the generation efficiency of the driven radiation.

<p align="justify">Many different active control techniques can be used to control the vibrations of a mechanical structure: they however require at least a sensitive signal amplifier (for the sensor), a power amplifier (for the actuator) and an analog or digital filter (for the controller). The use of all these electronic devices may be impractical in many applications and has motivated the use of the so-called shunt circuits, in which an electrical circuit is directly connected to a transducer embedded in the structure. The transducer acts as an energy converter: it transforms mechanical (vibrational) energy into electrical energy, which is in turn dissipated in the shunt circuit. No separate sensor is required, and only one, generally simple electronic circuit is used. The stability of the shunted structure is guaranteed if the electric circuit is passive, i.e., if it is made of passive components such as resistors and inductors.</p> <p align="justify">This thesis compares the performances of the electric shunt circuits with those of classical active control systems. It successively considers the use of piezoelectric transducers and that of electromagnetic (moving-coil) transducers.</p> <p align="justify">In a first part, the different damping techniques are applied on a benchmark truss structure equipped with a piezoelectric stack transducer. A unified formulation is found and experimentally verified for an active control law, the Integral Force Feedback (IFF), and for various passive shunt circuits (resistive and resistive-inductive). The use of an active shunt, namely the negative capacitance, is also investigated in detail. Two different implementations are discussed: they are shown to have very different stability limits and performances.</p> <p align="justify">In a second part, vibration isolation with electromagnetic (moving-coil) transducers is introduced. The effects of an inductive-resistive shunt circuit are studied in detail; an equivalent mechanical representation is found. The performances are compared with that of resonant shunts and with that of active isolation with IFF. Next, the construction of a six-axis isolator based on a Stewart Platform is presented: the key parameters and the main limitations of the system are highlighted.</p>

The telecommunications market is one of the large rapidly growing fields in today’s power supply industry due to the increasing demand for telecom distributed power supply (DPS) systems. The half-bridge LLC (Inductor-Inductor-Capacitor) resonant converter is currently the most attractive topology for the design and implementation of 24V/48V DC telecom power converters. The current doubler rectifier (CDR) converter topology was invented and described in the early 1950s which can offer the unique characteristic of halving the output voltage while doubling the output current compared to a standard rectifier. In this thesis, the current doubler converter topology with its unique characteristic is evaluated as a complementary solution to improve the LLC resonant converter performance, especially for the low output voltage and high output current telecommunication applications. A novel half-bridge LLC resonant current doubler converter (LLC-CDR) is proposed in this thesis which can offer several performance benefits compared to conventional LLC-standard rectifier design . The unique characteristics of the LLC-CDR topology can offer significant improvements by transformation of a 48V converter into a 24V converter with the same power density. This thesis introduces a new SPICE-based simulation model to analyse the operation of this novel LLC-CDR converter circuit design. This model can be used to define the critical component parameters for the LLC -CDR circuit output inductor values. It can also be used to predict the circuit overall performance under different load conditions. Both time-domain based transient simulation analysis and frequency-domain based AC analysis provided by this simulation model showed favourable results in comparison to bench measurement results on a prototype. The model provides a valuable insight to reveal some of the unique characteristics of this LLC -CDR topology. It demonstrates a proof of concept that the conventional LLC resonant converter can be easily redesigned for low voltage, high current applications by using the LLC-CDR topology without requiring a new design for the LLC resonant stage components and the power transformer. A new magnetic integration solution was proposed to significantly improve the overall performance in the LLC-CDR topology that had not been published before. The LLC-CDR converter hardware prototypes with two output inductors coupled and uncoupled configurations were extensively modelled, constructed and bench tested.Test results demonstrated the suitability of an integrated coupled inductors design for the novel LLC-CDR converter application. The integrated coupled inductors design can significantly improve the LLC-CDR converter frequency-domain based AC simulation analysis results. In addition, these results also illustrate the potential benefit of how the magnetic integration design in general could reduce the magnetic component size, cost, and weight compared to the uncoupled inductors design. Finally, a hardware prototype circuit was constructed based on a commercial 1800 W single phase telecom power converter to verify the operation of this novel half bridge LLC-CDR topology. The converter prototype successfully operated at both no load and full load conditions with the nominal output voltage halved from 48VDC to 24VDC, and doubled the output current to match the same output power density. It also demonstrates that the efficiency of this novel half bridge LLC –CDR is 92% compares to 90% of EATON’s commercial 24VDC LLC resonant converter, which can fulfill the research goals.

Innovative electronic device concepts that use polarization charges to provide improved performance were validated. The strength of the electric fields created by polarization charges (PCs) was suggested to act as an additional design parameter in the creation of devices using III-nitride and other highly polar materials. Results indicated that polarization induced electric fields can replace conventional doping schemes to create the charge separation region of solar cells and would allow for a decoupling of device performance from doping requirements. Additionally, a model for calculating current through polarization induced tunnel diodes was proposed. The model was found to agree well with experimental current values. Several polarization induced tunnel junction (PTJ) designs were analyzed. A novel double-barrier PTJ was conceived that would allow for the creation of a multi-junction solar cell using strained InGaN absorption layers. Future research would include the fabrication of these devices and the inclusion of thermal effects in the model for calculating current through PTJs.

An innovative approach for characterization of one dimensional Photonic Band Gap structures comprised of metallic inclusions (i.e. subwavelength dipole elements or resonant ring elements) is presented. Through an efficient S- to T-parameters conversion technique, a detailed analysis has been performed to investigate the variation of the dispersion characteristics of 1-D PBG structures as a function of the cell element configuration. Also, for the first time, the angular sensitivity of the structure has been studied in order to obtain the projected band diagrams for both TE and TM polarizations. Polarization sensitivity of the subwavelength cell element is exploited to propose a novel combination of elements which allows achieving PBGs with simultaneous frequency and polarization selectivity. The proposed approach demonstrates that the dispersion characteristic of each orthogonal polarization can be independently adjusted with dipole elements parallel to that same polarization. Generally, the structure has potential applications in orthomode transducer, and generally whenever the polarization of the incoming signal is to be used as a means of separating it from another signal in the same frequency band that is of orthogonal polarization. The current distribution and the resonance behavior of the ring element is studied and the effect of resonance on dispersion characteristics of 1-D PBGs composed of rings is investigated for the first time, for both individual and coupled rings. Interestingly, it is observed that 1-D PBG composed of resonant elements consistently has a bandgap around the resonant frequency of the single layer structure.

The objective of this doctoral thesis is to study three different innovative noise control techniques in ducts namely: acoustic metamaterials, porous absorbers and microperforates. There has been a lot of research done on all these three topics in the context of duct acoustics. This research will assess the potential of the acoustic metamaterial technique and compare to the use of conventional methods using microperforated plates and/or porous materials.  The objective of the metamaterials part is to develop a physical approach to model and synthesize bulk moduli and densities to feasibly control the wave propagation pattern, creating quiet zones in the targeted fluid domain. This is achieved using an array of locally resonant metallic patches. In addition to this, a novel thin slow sound material is also proposed in the acoustic metamaterial part of this thesis. This slow sound material is a quasi-labyrinthine structure flush mounted to a duct, comprising of coplanar quarter wavelength resonators that aims to slow the speed of sound at selective resonance frequencies. A good agreement between theoretical analysis and experimental measurements is demonstrated. The second technique is based on acoustic porous foam and it is about modeling and characterization of a novel porous metallic foam absorber inside ducts. This material proved to be a similar or better sound absorber compared to the conventional porous absorbers, but with robust and less degradable properties. Material characterization of this porous absorber from a simple transfer matrix measurement is proposed.The last part of this research is focused on impedance of perforates with grazing flow on both sides. Modeling of the double sided grazing flow impedance is done using a modified version of an inverse semi-analytical technique. A minimization scheme is used to find the liner impedance value in the complex plane to match the calculated sound field to the measured one at the microphone positions. / <p>QC 20160923</p>

The work of this dissertation has been to prove that the coherence of multiphoton excitation can be studied by an appropriately phased and time delayed sequence of pulses. An application of this fundamental study of coherence has been made for the enhancement of third harmonic generation. The coherent recovery of the energy lost to the two photon absorption process enalled a larger propagation distance for the fundamental than in an interaction which is incoherent or coherent, but not using a 90 degree phase shifted pulse pair. Phase matching over this longer propagation distance gave an enhancement of third harmonic generation.