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Indiana University-Purdue University Indianapolis (IUPUI) / The inner structural characteristics of non-minimum phase DC-DC converters pose a severe limitation in direct regulation of voltage when addressed from a control perspective. This constraint is reflected by the presence of right half plane zeros or the unstable zero dynamics of the output voltage of these converters. The existing controllers make use of one-to-one correspondence between the voltage and current equilibriums of the non-minimum phase converters and exploit the property that when the average output of these converters is the inductor current, the system dynamics are stable and hence they indirectly regulate the voltage. As a result, the system performance is susceptible to circuit parameter and load variation and require additional controllers, which in turn increase the system complexity. In this thesis, a novel approach to this problem is proposed for second order non-minimum phase converters such as Boost and Buck-Boost Converter. Different solutions have been suggested to the problem based on whether the converter is modeled as a linear system or as a nonlinear system. For the converter modeled as a linear system, the non-minimum phase part of the system is decoupled and its transfer function is converted to minimum phase using a parallel compensator. Then the control action is achieved by using a simple proportional gain controller. This method accelerates the transient response of the converter, reduces the initial undershoot in the response, and considerably reduces the oscillations in the transient response. Simulation results demonstrate the effectiveness of the proposed approach. When the converter is modeled as a bilinear system, it preserves the stabilizing nonlinearities of the system. Hence, a more effective control approach is adopted by using Passivity properties. In this approach, the non-minimum phase converter system is viewed from an energy-based perspective and the property of passivity is used to achieve stable zero dynamics of the output voltage. A system is passive if its rate of energy storage is less than the supply rate i.e. the system dissipates more energy than stores. As a result, the energy storage function of the system is less than the supply rate function. Non-minimum phase systems are not passive, and passivation of non-minimum phase power converters is an attractive solution to the posed problem. Stability of non-minimum phase systems can also be investigated by defining the passivity indices. This research approaches the problem by characterizing the degree of passivity i.e. the amount of damping in the system, from passivity indices. Thus, the problem is viewed from a system level rather than from a circuit level description. This method uses feed-forward passivation to compensate for the shortage of passivity in the non-minimum phase converter and makes use of a parallel interconnection to the open-loop system to attain exponentially stable zero dynamics of the output voltage. Detailed analytical analysis regarding the control structure and passivation process is performed on a buck-boost converter. Simulation and experimental results carried out on the test bed validate the effectiveness of the proposed method.

A series of studies were initiated to investigate growth responses of Kentucky bluegrass (Poa praetensis L.) and creeping bentgrass (Agrostis palustris Huds.) to foliar applications of two plant growth regulators (PGR) and/or chelated Fe (Na Fe diethylene triamine pentaacetate). Environmental variables considered were N levels, soil moisture regimes, and saline irrigations. The two materials investigated for PGR properties were a commercial product called Roots (a cold-water extract of seaweed and peat humus fortified with "intermediate metabolites" and thiamine) and the systemic fungicide propiconazole, trade name: (Banner) and chemical name: [1- {(2-(2,4-dichlorophenyl)-4-propyl-l,3-dioxolan-2yl}methyl-l H-1,2,4-triazole]. Fortified seaweed extract (FSE) was applied at 9.3 L/ha, and propiconazole (PPC) was applied at 0.93 L a.i/ha. Each was applied alone or in conjunction with chelated Fe at 0.11 kg a.i/ha. Kentucky bluegrass foliage height, root and shoot dry weight, and several foliar nutrients increased following PGR treatments when grown under either limited soil moisture or saline irrigation. Foliar applications of PGR and/or chelated Fe to creeping bentgrass reduced wilting and evapotranspiration, and increased leaf water status, root strength, and shoot dry matter at two levels of N during and after drought stress. / Ph. D.

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yes / Background/Aims: Personalised nutrition has potential to revolutionise dietary health promotion if accepted by the general public. We studied trust and preferences regarding personalised nutrition services, how they influence intention to adopt these services, and cultural and social differences therein. Methods: A total of 9381 participants were quota sampled to be representative for each of nine EU countries (Germany, Greece, Ireland, Poland, Portugal, Spain, Netherlands, UK, Norway) and surveyed by questionnaire assessing their intention to adopt personalised nutrition, trust in service regulators and information sources, and preferences for service providers and information channels. Results: Trust and preferences significantly predicted intention to adopt personalised nutrition. Higher trust in the local department of healthcare was associated with lower intention to adopt personalised nutrition. General practitioners were the most trusted of service regulators, except for in Portugal, where consumer organisations and universities were most trusted. In all countries, family doctors were the most trusted information providers. Trust in the National Health Service as service regulator and information source showed high variability across countries. Despite its highest variability across countries, personal meeting was the preferred communication channel except in Spain (where an automated internet service was preferred). General practitioners were the preferred service providers, except in Poland, where dietitians and nutritionists were preferred. The preference for dietitians and nutritionists as service providers highly varied across countries. Conclusion: These results may assist in informing local initiatives to encourage acceptance and adoption of country specific tailored personalised nutrition services therefore benefiting individual and public health.

This thesis investigates the use of real-time phasor measurements for voltage and transient stability monitoring and control. Taking advantage of the ability of a Phasor Measurement Unit (PMU) placed at a bus to sample at a fast rate the voltage and current phasors of that bus) various schemes for placing PMU's are considered and evaluated. These schemes include coherency based methods and pilot point placement techniques for system controllability. A novel scheme is proposed which places a minimal set of PMU's so as to make the system measurement model observable, and thereby linear. This placement scheme is derived from the topological observability theory. It concerns the building of a spanning measurement sub-graph across the system with actual or pseudo-measurement assigned to each of its branches. The minimal PMU set is found through a dual search algorithm which uses both a modified bisecting search and a simulated annealing-based method. The former fixes the number of PMU's while the latter look for a placement set that leads to an observable network. In order to accelerate the procedure, an initial PMU placement is provided by a graph-theoretic procedure which builds a spanning measurement sub-graph according to a depth-first search. From computer simulation results performed on various test systems, it appears that only one fourth of the system buses need to be provided with PMU's in order to make the system observable. In an effort to reduce the computing time of transient stability assessment, a dynamic equivalent is presented, which results from the elimination of the load buses provided with voltage--dependent loads. The elimination is performed through a new version of the Ward equivalencing method. In this approach, the equivalent current injections are expressed in terms of the retained bus angles and a sensitivity matrix. The non-linearity of the load flow model is accounted for through piecewise linear approximations by updating the sensitivity matrix whenever the operating point moves beyond the validity of the linearization. The expressions of the incremental changes in the generator electric power is derived. The study also investigates the possibility of using the telemetered data provided by the PMU's during pre-fault and post-fault operating conditions in conjunction with a. new version of the Extended Equal Area Criterion (EEAC) method. The latter is able to handle complex loads through the dynamic Ward equivalencing method. The performance of the approach is illustrated on three test systems which have been reduced to the internal generator nodes. / Ph. D.

The primary objective of this research was to identify practices by which specialty cut flower growers can extend the vase life of cut delphinium, sunflower, and dahlia. Experiments investigated the effects of nitrogen fertilization rate on delphinium 'Guardian Mix' and the effects of deficit irrigation on delphinium 'Guardian Blue.' 'Guardian Mix' plants produced marketable cut stems at nitrogen rates as low as 50 mg/L. Deficit irrigation did not change vase life, stomatal conductance, or transpiration rates of delphinium 'Guardian Blue.' Studies tested the effects of foliar calcium applications or benzyladenine application on sunflower 'Moulin Rouge' and 'Procut Lemon.' Calcium did not change the vase life, stomatal conductance, or transpiration rates of either sunflower cultivar. Benzyladenine applied as a preharvest spray or a postharvest dip did not alter vase life of sunflower 'Moulin Rouge' or 'Procut Lemon.' Transpiration rate and conductance rates of sunflowers significantly decreased in the first three days after harvest. In both sunflower experiments, vase life of 'Moulin Rouge' was shorter than vase life of 'Procut Lemon.' Benzyladenine was also applied to dahlia 'Park Princess' and 'Karma Yin Yang' cut flowers. Benzyladenine did not change dahlia vase life. Dahlia 'Park Princess,' 'Bride to Be,' 'Cherish,' and 'Lollipop' cut flowers were not sensitive to exogenous ethylene. Further experiments tested the effect of flower stage at harvest, vase water temperature, or preharvest fungicide application on dahlia 'Park Princess' and 'Karma Yin Yang' cut flowers. Vase life of 'Park Princess' flowers was extended when flowers were harvested before fully open, but 'Park Princess' flowers harvested at budbreak failed to open completely after harvest. 'Karma Yin Yang' cut flower vase life did not differ when flowers were harvested at different stages. Placing cut dahlias in hot vase water had varied effects, but did not extend vase life of either cultivar. Fungicide applications extended vase life of 'Park Princess' flowers. However, the use of fungicide is not necessary to prevent postharvest fungal infection in cut dahlias. The results of all experiments indicate that optimal handling practices vary between cut flower taxa and that factors determining cut flower vase life are complex. / Master of Science

Advances in transistor-integration technology and multi-core technology of the latest microprocessors have driven transient requirements to become more and more stringent. Rather than relying on the bulky output capacitors as energy-storage devices, increasing the control bandwidth (BW) of the multiphase voltage regulator (VR) is a more cost-effective and space-saving approach. However, it is found that the stability margin of current-mode control in high-BW design is very sensitive to operating conditions and component tolerance, depending on the performance of the current-sensing techniques, modulation schemes, and interleaving approaches. The primary objective of this dissertation is to investigate an advanced multiphase current-mode control, which provides accurate current sensing, enhances the stability margin in high-BW design, and adaptively compensates the parameter variations. Firstly, an equivalent circuit model for generic current-mode controls using DCR current sensing is developed to analyze the impact of component tolerance in high-BW design. Then, the existing state-of-the-art auto-tuning method used to improve current-sensing accuracy is reviewed, and the deficiency of using this method in a multiphase VR is identified. After that, enlightened by the proposed model, a novel auto-tuning method is proposed. This novel method features better tuning performance, noise-insensitivity, and simpler implementation than the state-of-the-art method. Secondly, the current state-of-the-art adaptive current-mode control based on constant-frequency PWM is reviewed, and its inability to maintain adequate stability margin in high-BW design is recognized. Therefore, a new external ramp compensation technique is proposed to keep the stability margin insensitive to the operating conditions and component tolerance, so the proposed high-BW constant-frequency control can meet the transient requirement without the presence of bulky output capacitors. The control scheme is generic and can be used in various kinds of constant-frequency controls, such as peak-current-mode, valley-current-mode, and average-current-mode configurations. Thirdly, an interleaving technique incorporating an adaptive PLL loop is presented, which enables the variable-frequency control to push the BW higher than proposed constant-frequency control, and avoids the beat-frequency input ripple. A generic small-signal model of the PLL loop is derived to investigate the stability issue caused by the parameter variations. Then, based on the proposed model, a simple adaptive control is developed to allow the BW of the PLL loop to be anchored at the highest phase margin. The adaptive PLL structure is applicable to different types of variable-frequency control, including constant on-time control and ramp pulse modulation. Fourthly, a hybrid interleaving structure is explored to simplify the implementation of the adaptive PLL structure in an application with more phases. It combines the adaptive PLL loop with a pulse-distribution technique to take the advantage of the high-BW design and fast transient response without adding a burden to the controller implementation. As a conclusion, based on the proposed analytical models, effective control concepts, systematic optimization strategies, viable implementations are fully investigated for high-BW current-mode control using different modulation techniques. Moreover, all the modeling results and the system performance are verified through simulation with a practical output filter model and an advanced mixed-signal experimental platform based on the latest MHz VR design on the laptop motherboard. In consequence, the multiphase VRs in future computation systems can be scalable easier with proposed multiphase configurations, increase the system reliability with proposed adaptive loop compensation, and minimize the total system footprint of the VR with the superior transient performance. / Ph. D.

Open-loop stability analysis of multi-loop current-injected switching regulator is performed using a small signal model containing a power stage, an error processor and a duty cycle pulse modulator. Two design constraints and the effects of various critical control circuit parameters are pinpointed and the analysis-based design guidelines are established in order to optimize the switching regulator performances. In addition, an external ramp slope is proposed to obtain the optimal performance and eliminate the 50% duty cycle instability when operated in constant frequency mode. The effects of the second stage output filter are also examined. / Master of Science