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(1 - 14 of 14)
- Title
- DIGITAL CONTROLLER IMPLEMENTATION FOR DISTURBANCE REJECTION IN THE OPTICAL COUPLING OF A MOBILE EXPERIMENTAL LASER TRACKING SYSTEM.
- Creator
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Rhodes, Matthew, Richie, Samuel, University of Central Florida
- Abstract / Description
-
Laser tracking systems are an important aspect of the NASA space program, in particular for conducting research in relation to satellites and space port launch vehicles. Often, launches are conducted at remote sites which require all of the test equipment, including the laser tracking systems, to be portable. Portable systems are more susceptible to environmental disturbances which affect the overall tracking resolution, and consequently, the resolution of any other experimental data being...
Show moreLaser tracking systems are an important aspect of the NASA space program, in particular for conducting research in relation to satellites and space port launch vehicles. Often, launches are conducted at remote sites which require all of the test equipment, including the laser tracking systems, to be portable. Portable systems are more susceptible to environmental disturbances which affect the overall tracking resolution, and consequently, the resolution of any other experimental data being collected at any given time. This research characterizes the optical coupling between two systems in a Mobile Experimental Laser Tracking system and evaluates several control solutions to minimize disturbances within this coupling. A simulation of the optical path was developed in an extensible manner such that different control systems could be easily implemented. For an initial test, several PID controllers were utilized in parallel in order to control mirrors in the optical coupling. Despite many limiting factors of the hardware, a simple proportional control performed to expectations. Although a system implementation was never field tested, the simulation results provide the necessary insight to develop the system further. Recommendations were made for future system modifications which would allow an even higher tracking resolution.
Show less - Date Issued
- 2006
- Identifier
- CFE0001168, ucf:46873
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001168
- Title
- DESIGN AND IMPLEMENTATION OF A DIGITAL CONTROLLER WITH DSP FOR HALF-BRIDGE DC-DC CONVERTERS.
- Creator
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Wen, Yangyang, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
DC-DC power converters play an important role in powering telecom and computing systems. With the speed improvement and cost reduction of digital control, digital controller is becoming a trend for DC-DC converters in addition to existed digital monitoring and management technology. In this thesis, digital control is investigated for DC-DC converters applications. To deeply understand the whole control systems, DC-DC converter models are investigated based on averaged state-space modeling....
Show moreDC-DC power converters play an important role in powering telecom and computing systems. With the speed improvement and cost reduction of digital control, digital controller is becoming a trend for DC-DC converters in addition to existed digital monitoring and management technology. In this thesis, digital control is investigated for DC-DC converters applications. To deeply understand the whole control systems, DC-DC converter models are investigated based on averaged state-space modeling. Considering half-bridge isolated DC-DC converter with a current doublers rectifier has advantages over other topologies especially in the application of low-voltage and high-current DC-DC converters, the thesis take it as an example for digital control modeling and implementation. In Chapter 2, unified steady-state DC models and small-signal models are developed for both symmetric and asymmetric controlled half-bridge DC-DC converters. Based on the models, digital controller design is implemented. In Chapter 3, digital modeling platforms are established based on Matlab, Digital PID design and corresponding simulation results are provided. Also some critical issues and practical requirements are discussed. In Chapter 4, a DSP-based digital controller is implemented with the TI's DSP chip TMS320F2812. Related implementation methods and technologies are discussed. Finally the experimental results of a DSP-based close-loop of HB converter are provided and analyzed in Chapter 5, and thesis conclusions are given in Chapter 6.
Show less - Date Issued
- 2004
- Identifier
- CFE0000246, ucf:46273
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000246
- Title
- BI-DIRECTIONAL DCM DC-TO-DC CONVERTER FOR HYBRID ELECTRIC VEHICLES.
- Creator
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Pepper, Michael, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
With the recent revival of the hybrid vehicle much advancement in power management has been made. The most popular hybrid vehicle, the hybrid electric vehicle, has many topologies developed to realize this hybrid vehicle. From these topologies, as sub set was created to define a particular group of vehicles where the converter discussed in this thesis has the most advantage. This sub set is defined by two electric sources of power coupled together at a common bus. This set up presents many...
Show moreWith the recent revival of the hybrid vehicle much advancement in power management has been made. The most popular hybrid vehicle, the hybrid electric vehicle, has many topologies developed to realize this hybrid vehicle. From these topologies, as sub set was created to define a particular group of vehicles where the converter discussed in this thesis has the most advantage. This sub set is defined by two electric sources of power coupled together at a common bus. This set up presents many unique operating conditions which can be handled seamlessly by the DC-to-DC converter when designed properly. The DC-to-DC converter discussed in this thesis is operated in Discontinuous Conduction Mode (DCM) of operation because of its unique advantages over the Continuous Conduction Mode (CCM) operated converter. The most relevant being the reduction of size of the magnetic components such as inductor, capacitor and transformers. However, the DC-to-DC converter operated in DCM does not have the inherent capability of bi-directional power flow. This problem can be overcome with a unique digital control technique developed here. The control is developed in a hierarchical fashion to separate the functions required for this sub set of hybrid electric vehicle topologies. This layered approach for the controller allows for the seamless integration of this converter into the vehicle. The first and lowest level of control includes a group of voltage and controller regulators. The average and small signal model of these controllers were developed here to be stable and have a relatively fast recovery time to handle the transient dynamics of the vehicle system. The second level of control commands and organizes the regulators from the first level of control to perform high level task that is more specific to the operation of the vehicle. This level of control is divided into three modes called hybrid boost, hybrid buck and electric vehicle mode. These modes are developed to handle the specific operating conditions found when the vehicle is operated in the specific mode. The third level of control is used to command the second level of control and is left opened via a communication area network (CAN) bus controller. This level of control is intended to come from the vehicle's system controller. Because the DC-to-DC converter is operated in DCM, this introduces added voltage ripple on the output voltage as well as higher current ripple demand from the input voltage. Since this is generally undesirable, the converter is split into three phases and properly interleaved. The interleaving operation is used to counteract the effects of the added voltage and current ripple. Finally, a level of protection is added to protect the converter and surrounding components from harm. All protection is designed and implemented digitally in DSP.
Show less - Date Issued
- 2008
- Identifier
- CFE0002496, ucf:47676
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002496
- Title
- ADAPTIVE EFFICIENCY OPTIMIZATION FOR DIGITALLY CONTROLLED DC-DC CONVERTERS.
- Creator
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AL-HOOR, WISAM, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
The design optimization of DC-DC converters requires the optimum selection of several parameters to achieve improved efficiency and performance. Some of these parameters are load dependent, line dependent, components dependent, and/or temperature dependent. Designing such parameters for a specific load, input and output, components, and temperature may improve single design point efficiency but will not result in maximum efficiency at different conditions, and will not guarantee improvement...
Show moreThe design optimization of DC-DC converters requires the optimum selection of several parameters to achieve improved efficiency and performance. Some of these parameters are load dependent, line dependent, components dependent, and/or temperature dependent. Designing such parameters for a specific load, input and output, components, and temperature may improve single design point efficiency but will not result in maximum efficiency at different conditions, and will not guarantee improvement at that design point because of the components, temperature, and operating point variations. The ability of digital controllers to perform sophisticated algorithms makes it easy to apply adaptive control, where system parameters can be adaptively adjusted in response to system behavior in order to achieve better performance and stability. The use of adaptive control for power electronics is first applied with the Adaptive Frequency Optimization (AFO) method, which presents an auto-tuning adaptive digital controller with maximum efficiency point tracking to optimize DC-DC converter switching frequency. The AFO controller adjusts the DC-DC converter switching frequency while tracking the converter minimum input power point, under variable operating conditions, to find the optimum switching frequency that will result in minimum total loss and thus the maximum efficiency. Implementing variable switching frequencies in digital controllers introduces two main issues, namely, limit cycle oscillation and system instability. Dynamic Limit Cycle Algorithms (DLCA) is a dynamic technique tailored to improve system stability and to reduce limit cycle oscillation under variable switching frequency operation. The convergence speed and stability of AFO algorithm is further improved by presenting the analysis and design of a digital controller with adaptive auto-tuning algorithm that has a variable step size to track and detect the optimum switching frequency for a DC-DC converter. The Variable-Step-Size (VSS) algorithm is theoretically analyzed and developed based on buck DC-DC converter loss model and directed towered improving the convergence speed and accuracy of AFO adaptive loop by adjusting the converter switching frequency with variable step size. Finally, the efficiency of DC-DC converters is a function of several variables. Optimizing single variable alone may not result in maximum or global efficiency point. The issue of adjusting more than one variable at the same time is addressed by the Multivariable Adaptive digital Controller (MVAC). The MVAC is an adaptive method that continuously adjusts the DC-DC converter switching frequency and dead-time at the same time, while tracking the converter minimum input power, to find the maximum global efficiency point under variable conditions. In this research work, all adaptive methods were discussed, theoretically analyzed and its digital control algorithm along with experimental implementations were presented.
Show less - Date Issued
- 2009
- Identifier
- CFE0002838, ucf:48072
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002838
- Title
- ANALYSIS AND DESIGN OF A MODULAR SOLAR-FED FAULT-TOLERANT POWER SYSTEM WITH MAXIMUM POWER POINT TRACKING.
- Creator
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Al-Atrash, Hussam, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
Solar power is becoming ever more popular in a variety of applications. It is particularly attractive because of its abundance, renewability, and environment friendliness. Solar powered spacecraft systems have ever-expanding loads with stringent power regulation specifications. Moreover, they require a light and compact design of their power system. These constraints make the optimization of power harvest from solar arrays a critical task. Florida Power Electronics Center (FPEC) at UCF set to...
Show moreSolar power is becoming ever more popular in a variety of applications. It is particularly attractive because of its abundance, renewability, and environment friendliness. Solar powered spacecraft systems have ever-expanding loads with stringent power regulation specifications. Moreover, they require a light and compact design of their power system. These constraints make the optimization of power harvest from solar arrays a critical task. Florida Power Electronics Center (FPEC) at UCF set to develop a modular fault-tolerant power system architecture for space applications. This architecture provides a number of very attractive features including Maximum Power Point Tracking (MPPT) and uniform power stress distribution across the system. MPPT is a control technique that leads the system to operate its solar sources at the point where they provide maximum power. This point constantly moves following changes in ambient operating conditions. A digital controller is setup to locate it in real time while optimizing other operating parameters. This control scheme can increase the energy yield of the system by up to 45%, and thus significantly reduces the size and weight of the designed system. The modularity of the system makes it easy to prototype and expand. It boosts its reliability and allows on-line reconfiguration and maintenance, thus reducing down-time upon faults. This thesis targets the analysis and optimization of this architecture. A new modeling technique is introduced for MPPT in practical environments, and a novel digital power stress distribution scheme is proposed in order to properly distribute peak and thermal stress and improve reliability. A 2kW four-channel prototype of the system was built and tested. Experimental results confirm the theoretical improvements, and promise great success in the field.
Show less - Date Issued
- 2005
- Identifier
- CFE0000469, ucf:46357
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000469
- Title
- MODELING AND DIGITAL CONTROL OF HIGH FREQUENCY DC-DC POWER CONVERTERS.
- Creator
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Wen, Yangyang, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
The power requirements for leading edge digital integrated circuits have become increasingly demanding. Power converter systems must be faster, more flexible, more precisely controllable and easily monitored. Meanwhile, in addition to control process, the new functions such as power sequencing, communication with other systems, voltage dynamic programming,load line specifications, phase current balance, protection, power status monitoring and system diagnosis are going into today's power...
Show moreThe power requirements for leading edge digital integrated circuits have become increasingly demanding. Power converter systems must be faster, more flexible, more precisely controllable and easily monitored. Meanwhile, in addition to control process, the new functions such as power sequencing, communication with other systems, voltage dynamic programming,load line specifications, phase current balance, protection, power status monitoring and system diagnosis are going into today's power supply systems. Digital controllers, compared withanalog controllers, are in a favorable position to provide basic feedback control as well as those power management functions with lower cost and great flexibility. The dissertation gives an overview of digital controlled power supply systems bycomparing with conventional analog controlled power systems in term of system architecture,modeling methods, and design approaches. In addition, digital power management, as one of the most valuable and "cheap" function, is introduced in Chapter 2. Based on a leading-edge digital controller product, Chapter 3 focuses on digital PID compensator design methodologies, design issues, and optimization and development of digital controlled single-phase point-of-load (POL)dc-dc converter. Nonlinear control is another valuable advantage of digital controllers over analogcontrollers. Based on the modeling of an isolated half-bridge dc-dc converter, a nonlinear control method is proposed in Chapter 4. Nonlinear adaptive PID compensation scheme is implemented based on digital controller Si8250. The variable PID coefficient during transients improves power system's transient response and thus output capacitance can be reduced to save cost. In Chapter 5, another nonlinear compensation algorithm is proposed for asymmetric flybackforward half bridge dc-dc converter to reduce the system loop gain's dependence on the input voltage, and improve the system's dynamic response at high input line. In Chapter 6, a unified pulse width modulation (PWM) scheme is proposed to extend the duty-cycle-shift (DCS) control, where PWM pattern is adaptively generated according to the input voltage level, such that the power converter's voltage stress are reduced and efficiency is improved. With the great flexibility of digital PWM modulation offered by the digital controller Si8250, the proposed control scheme is implemented and verified. Conclusion of the dissertation work and suggestions for future work in related directions are given in final Chapter.
Show less - Date Issued
- 2007
- Identifier
- CFE0001612, ucf:47172
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001612
- Title
- NEW OPTIMAL HIGH EFFICIENCY DSP-BASED DIGITAL CONTROLLER DESIGN FOR SUPER HIGH-SPEED PERMANENT MAGNET SYNCHRONOUS MOTOR.
- Creator
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zhao, limei, Wu, Thomas, University of Central Florida
- Abstract / Description
-
This dissertation investigates digital controller and switch mode power supply design for super high-speed permanent magnet synchronous motors (PMSM). The PMSMs are a key component for the miniaturic cryocooler that is currently under development at the University of Central Florida with support from NASA Kennedy Space Center and the Florida Solar Energy Center. Advanced motor design methods, control strategies, and rapid progress in semiconductor technology enables production of a highly...
Show moreThis dissertation investigates digital controller and switch mode power supply design for super high-speed permanent magnet synchronous motors (PMSM). The PMSMs are a key component for the miniaturic cryocooler that is currently under development at the University of Central Florida with support from NASA Kennedy Space Center and the Florida Solar Energy Center. Advanced motor design methods, control strategies, and rapid progress in semiconductor technology enables production of a highly efficient digital controller. However, there are still challenges for such super high-speed controller design because of its stability, high-speed, variable speed operation, and required efficiency over a wide speed range. Currently, limited research, and no commercial experimental analysis, is available concerning such motors and their control system design. The stability of a super high-speed PMSM is an important issue particularly for open-loop control, given that PMSM are unstable after exceeding a certain applied frequency. In this dissertation, the stability of super high-speed PMSM is analyzed and some design suggestions are given to maximize this parameter. For ordinary motors, the V/f control curve is a straight line with a boost voltage because the stator resistance is negligible and only has a significant effect around the DC frequency. However, for the proposed super high-speed PMSM the situation is quite different because of the motor's size. The stator resistance is quite large compared with the stator reactive impedance and cannot be neglected when employing constant a V/f control method. The challenge is to design an optimal constant V/f control scheme to raise efficiency with constant V/f control. In the development, test systems and prototype boards were built and experimental results confirmed the effectiveness of the dissertation system.
Show less - Date Issued
- 2005
- Identifier
- CFE0000856, ucf:46651
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000856
- Title
- Optimization and design of photovoltaic micro-inverter.
- Creator
-
Zhang, Qian, Batarseh, Issa, Shen, Zheng, Wu, Xinzhang, Lotfifard, Saeed, Kutkut, Nasser, University of Central Florida
- Abstract / Description
-
To relieve energy shortage and environmental pollution issues, renewable energy, especially PV energy has developed rapidly in the last decade. The micro-inverter systems, with advantages in dedicated PV power harvest, flexible system size, simple installation, and enhanced safety characteristics are the future development trend of the PV power generation systems. The double-stage structure which can realize high efficiency with nice regulated sinusoidal waveforms is the mainstream for the...
Show moreTo relieve energy shortage and environmental pollution issues, renewable energy, especially PV energy has developed rapidly in the last decade. The micro-inverter systems, with advantages in dedicated PV power harvest, flexible system size, simple installation, and enhanced safety characteristics are the future development trend of the PV power generation systems. The double-stage structure which can realize high efficiency with nice regulated sinusoidal waveforms is the mainstream for the micro-inverter.This thesis studied a double stage micro-inverter system. Considering the intermittent nature of PV power, a PFC was analyzed to provide additional electrical power to the system. When the solar power is less than the load required, PFC can drag power from the utility grid.In the double stage micro-inverter, the DC/DC stage was realized by a LLC converter, which could realize soft switching automatically under frequency modulation. However it has a complicated relationship between voltage gain and load. Thus conventional variable step P(&)O MPPT techniques for PWM converter were no longer suitable for the LLC converter. To solve this problem, a novel MPPT was proposed to track MPP efficiently. Simulation and experimental results verified the effectiveness of the proposed MPPT.The DC/AC stage of the micro-inverter was realized by a BCM inverter. With duty cycle and frequency modulation, ZVS was achieved through controlling the inductor current bi-directional in every switching cycle. This technique required no additional resonant components and could be employed for low power applications on conventional full-bridge and half-bridge inverter topologies. Three different current mode control schemes were derived from the basic theory of the proposed technique. They were referred to as Boundary Current Mode (BCM), Variable Hysteresis Current Mode (VHCM), and Constant Hysteresis Current Mode (CHCM) individually in this paper with their advantages and disadvantages analyzed in detail. Simulation and experimental results demonstrated the feasibilities of the proposed soft-switching technique with the digital control schemes.The PFC converter was applied by a single stage biflyback topology, which combined the advantages of single stage PFC and flyback topology together, with further advantages in low intermediate bus voltage and current stresses. A digital controller without current sampling requirement was proposed based on the specific topology. To reduce the voltage spike caused by the leakage inductor, a novel snubber cell combining soft switching technique with snubber technique together was proposed. Simulation and experimental waveforms illustrated the same as characteristics as the theoretical analysis.In summary, the dissertation analyzed each power stage of photovoltaic micro-inverter system from efficiency and effectiveness optimization perspectives. Moreover their advantages were compared carefully with existed topologies and control techniques. Simulation and experiment results were provided to support the theoretical analysis.
Show less - Date Issued
- 2013
- Identifier
- CFE0005286, ucf:50540
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005286
- Title
- DIGITAL PULSE WIDTH MODULATOR TECHNIQUES FOR DC - DC CONVERTERS.
- Creator
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Batarseh, Majd, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
Recent research activities focused on improving the steady-state as well as the dynamic behavior of DC - DC converters for proper system performance, by proposing different design methods and control approaches with growing tendency to using digital implementation over analog practices. Because of the rapid advancement in semiconductors and microprocessor industry, digital control grew in popularity among PWM converters and is taking over analog techniques due to availability of fast speed...
Show moreRecent research activities focused on improving the steady-state as well as the dynamic behavior of DC - DC converters for proper system performance, by proposing different design methods and control approaches with growing tendency to using digital implementation over analog practices. Because of the rapid advancement in semiconductors and microprocessor industry, digital control grew in popularity among PWM converters and is taking over analog techniques due to availability of fast speed microprocessors, flexibility and immunity to noise and environmental variations. Furthermore, increased interest in Field Programmable Gate Arrays (FPGA) makes it a convenient design platform for digitally controlled converters. The objective of this research is to propose new digital control schemes, aiming to improve the steady-state and transient responses of a high switching frequency FPGA-based digitally controlled DC-DC converters. The target is to achieve enhanced performance in terms of tight regulation with minimum power consumption and high efficiency at steady-state, as well as shorter settling time with optimal over- and undershoots during transients. The main task is to develop new and innovative digital PWM techniques in order to achieve: 1. Tight regulation at steady-state: by proposing high resolution DPWM architecture,based on Digital Clock Management (DCM) resources available on FPGA boards. The proposed architecture Window-Masked Segmented Digital Clock Manager-FPGA based Digital Pulse Width Modulator Technique, is designed to achieve high resolution operating at high switching frequencies with minimum power consumption. 2. Enhanced dynamic response: by applying a shift to the basic saw-tooth DPWM signal, in order to benefit from the best linearity and simplest architecture offered by the conventional counter-comparator DPWM. This proposed control scheme will help the compensator reach the steady-state value faster. Dynamically Shifted Ramp Digital Control Technique for Improved Transient Response in DC-DC Converters, is projected to enhance the transient response by dynamically controlling the ramp signal of the DPWM unit.
Show less - Date Issued
- 2010
- Identifier
- CFE0003055, ucf:48314
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003055
- Title
- The Diffusion of Digital Dashboards: An Examination of Dashboard Utilization and the Managerial Decision Environment.
- Creator
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Reinking, Jeffrey, Arnold, Vicky, Roberts, Robin, Sutton, Steven, Hampton, Clark, University of Central Florida
- Abstract / Description
-
This dissertation consists of three related studies examining the diffusion of digital dashboard technology throughout today's organizations. Dashboards, once reserved for the executive level, are now available to managers at the lower levels of the organization. For these managers, dashboards have become an integral part of their work life to support their decision environment, to provide consistency in measures, to monitor performance, and to communicate information throughout the...
Show moreThis dissertation consists of three related studies examining the diffusion of digital dashboard technology throughout today's organizations. Dashboards, once reserved for the executive level, are now available to managers at the lower levels of the organization. For these managers, dashboards have become an integral part of their work life to support their decision environment, to provide consistency in measures, to monitor performance, and to communicate information throughout the organization. Prior research in the practice literature has shown that dashboards improve managerial performance and organizational performance as well as communicate organizational goals and objectives; however, empirical research has not been conducted in this area to confirm this anecdotal evidence. Using three theories, the phenomenon surrounding the diffusion of dashboards to the lower levels of the organization are examined based on 1) dashboards as a source of interactive management control and strategy alignment, 2) the impact of dashboard quality on strategy alignment, decision environment, and performance, and 3) the impacts on dashboard utilization from the antecedents of information content and task uncertainty and the consequences of user satisfaction and managerial performance. The first study investigates why dashboards have been diffused to the lowers levels of today's organizations. The primary focus of this study is to develop an understanding about the extent of dashboard utilization by decision-makers and the antecedents and consequences of utilization that is responsible for the widespread acceptance of this technology. The data for this study is collected and analyzed through an explanatory cross-sectional field study utilizing a semi-structured questionnaire. Using data from interviews with 27 managers, a framework is developed that indicates strategy alignment and dashboards associated with interactive management control are the primary antecedents that drive dashboard diffusion. The dimensions of dashboard system quality and dashboard information quality mediate the relationship between an interactive dashboard and the extent of dashboard utilization, which leads to higher levels of managerial performance and organizational performance. This study contributes to the dashboard, strategy, and MCS literature by revealing that dashboards are not isolated technologies, rather they play an important role in the execution of strategy at the operational levels of an organization. In addition, dashboards can also function as an interactive management control, which leads to high levels of diffusion of dashboards throughout organizations. Prior strategy literature has examined strategy alignment at the higher levels and this study extends this research stream by investigating strategy alignment at the lower operational levels of the organization.The second study utilizes the IS Success Model to explore the impacts of the antecedents of dashboard system quality and dashboard information quality on the managerial decision environment in addition to the resulting consequences or 'net benefit' of managerial performance and organizational performance. A field survey is used to collect data from 391 dashboard using managers to enable the analysis of the relationships predicted in the theoretical model. The theoretical model is analyzed utilizing PLS. The results show that two dimensions of dashboard quality, system flexibility and information currency, have a positive effect the managerial decision environment. The model indicates support for the consequences of managerial performance and organizational performance resulting from higher levels of decision quality in the managerial decision environment. The model also reveals that when the dashboard measures are strategy aligned, lower levels of dashboard system flexibility are associated with improved managerial decision environment. Therefore, when organizations design their dashboard systems to support strategy alignment, managers should not be afforded high levels of system flexibility to maintain their attention on the key performance indicators selected to align with strategy. This result is a primary contribution to the strategy literature that reveals that strategy aligned dashboards are more effective in environments where the dashboard flexibility is lower. Additionally, study two also extends the strategy literature by examining strategy alignment at the lower levels of the organization, since prior research has concentrated on the higher level strategic outcomes.As dashboards become highly diffused and more managers utilize the technology, the likelihood that dashboard designers cannot provide dashboard content that fits the tasks performed by managers is higher. The third study investigates this fit between dashboard information content and task uncertainty to understand if the fit between the technology and task impacts the extent of dashboard utilization by managers based on the theory of task-technology fit (TTF). TTF predicts higher levels of utilization will increase user satisfaction and managerial performance. Data is collected from 391 managers that utilize dashboards in their weekly work life to analyze the relationships predicted in the theoretical model. PLS is utilized to analyze the theoretical model and indicates weak support of TTF impacting the extent of dashboard utilization. The model supports the hypotheses for the links between the extent of dashboard utilization and user satisfaction and managerial performance. Based on the weak findings from this theoretical model, a second model is developed and analyzed. The second model measures TTF through the mediation of task uncertainty between dashboard information content and the extent of dashboard utilization, while the first model measured TTF through interacting task uncertainty and dashboard information content. The results of the second model show strong support that TTF, as measured through mediation, increases the extent of dashboard utilization. This study contributes to the literature by empirically showing that more extensive levels of dashboard utilization are achieved through the antecedent of TTF, resulting in increased managerial satisfaction and managerial performance.
Show less - Date Issued
- 2013
- Identifier
- CFE0005052, ucf:49969
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005052
- Title
- INTEGRATED TOPOLOGIES AND DIGITAL CONTROL FOR SATELLITE POWER MANAGEMENT AND DISTRIBUTION SYSTEMS.
- Creator
-
Al-Atrash, Hussam, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
This work is focused on exploring advanced solutions for space power management and distribution (PMAD) systems. As spacecraft power requirements continue to increase, paralleled by the pressures for reducing cost and overall system weight, power electronics engineers will continue to face major redesigns of the space power systems in order to meet such challenges. Front-end PMAD systems, used to interface the solar sources and battery backup to the distribution bus, need to be designed with...
Show moreThis work is focused on exploring advanced solutions for space power management and distribution (PMAD) systems. As spacecraft power requirements continue to increase, paralleled by the pressures for reducing cost and overall system weight, power electronics engineers will continue to face major redesigns of the space power systems in order to meet such challenges. Front-end PMAD systems, used to interface the solar sources and battery backup to the distribution bus, need to be designed with increased efficiency, reliability, and power density. A new family of integrated single-stage power converter structures is introduced here. This family allows the interface and control of multiple power sources and storage devices in order to optimize utilization of available resources. Employing single-stage power topologies, these converters control power flow efficiently and cost-effectively. This is achieved by modifying the operation and control strategies of isolated soft-switched half-bridge and full-bridge converters--two of the most popular two-port converter topologies. These topologies are reconfigured and utilized to realize three power processing paths. These paths simultaneously utilize the power devices, allowing increased functionality while promising reduced losses and enhanced power densities. Each of the proposed topologies is capable of performing simultaneous control of two of its three ports. Control objectives include battery or ultra-capacitor charge regulation, solar array maximum power point tracking (MPPT), and/or bus voltage regulation. Another advantage of the proposed power structure is that current engineering design concepts can be used to optimize the new topologies in a fashion similar to the mother topologies. This includes component selection and magnetic design procedures, as well as achieving soft-switching for increased efficiency at higher switching frequencies. Galvanic isolation of the load port through high-frequency transformers provides design flexibility for high step-up/step-down conversion ratios. It further allows the converters to be used as power electronics building blocks (PEBB) with outputs connected in different series/parallel combinations to meet different load requirements. Utilizing such converters promises significant savings in size, weight, and costs of the power management system as well as the devices it manages. Chapter 1 of this dissertation provides an introduction to the requirements, challenges, and trends of space PMAD. A review of existing multi-port converter technologies and digital control techniques is given in Chapter 2. Chapter 3 discusses different PMAD system architectures. It outlines the basic concepts used for PMAD integration and discusses the potential for improvement. Chapters 4 and 5 present and discuss the operation and characteristics of three different integrated multi-port converters. Chapter 6 presents improved methods for practical digital control of switching converters, which are especially useful in complex multi-objective controllers used for PMAD. This is followed by conclusions and suggested future work.
Show less - Date Issued
- 2007
- Identifier
- CFE0001784, ucf:47283
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001784
- Title
- DIGITAL CONTROL OF HALF-BRIDGE DC-DC CONVERTERS WITH CURRENT DOUBLER RECTIFICATION.
- Creator
-
Yao, Liangbin, Batarseh, Issa, University of Central Florida
- Abstract / Description
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DC-DC power converters play an important role in powering telecom and computing systems. Complex systems, including power electronics systems, are increasingly using digital controllers because of the major advancements in digital controllers and DSP as well as there ability to perform sophisticated and enhanced control schemes. In this thesis, the digital controller is investigated for DC-DC converters in high current low voltage applications. For an optimal design of a regulated DC-DC...
Show moreDC-DC power converters play an important role in powering telecom and computing systems. Complex systems, including power electronics systems, are increasingly using digital controllers because of the major advancements in digital controllers and DSP as well as there ability to perform sophisticated and enhanced control schemes. In this thesis, the digital controller is investigated for DC-DC converters in high current low voltage applications. For an optimal design of a regulated DC-DC converter, it is necessary to derive a valid model. The current doubler rectified half bridge (CDRHB) DC-DC converter is suitable for high current low voltage applications. In this thesis, the topology operations are analyzed and then the unified state space model, analog small signal model and digital small signal model are derived. Then the digital compensator design is discussed as well as the analog-digital converter (ADC) and the digital pulse-width-modulator (DPWM) design rules. In addition, voltage driving optimization is proposed for the benefit of the digital controller. Finally, experimental results based on the CDRHB are presented and analyzed.
Show less - Date Issued
- 2005
- Identifier
- CFE0000706, ucf:46626
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000706
- Title
- The Response of American Police Agencies to Digital Evidence.
- Creator
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Yesilyurt, Hamdi, Wan, Thomas, Potter, Roberto, Applegate, Brandon, Lang, Sheau-Dong, University of Central Florida
- Abstract / Description
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Little is known about the variation in digital forensics practice in the United States as adopted by large local police agencies. This study investigated how environmental constraints, contextual factors, organizational complexity, and organizational control relate to the adoption of digital forensics practice. This study integrated 3 theoretical perspectives in organizational studies to guide the analysis of the relations: institutional theory, contingency theory, and adoption-of-innovation...
Show moreLittle is known about the variation in digital forensics practice in the United States as adopted by large local police agencies. This study investigated how environmental constraints, contextual factors, organizational complexity, and organizational control relate to the adoption of digital forensics practice. This study integrated 3 theoretical perspectives in organizational studies to guide the analysis of the relations: institutional theory, contingency theory, and adoption-of-innovation theory. Institutional theory was used to analyze the impact of environmental constraints on the adoption of innovation, and contingency theory was used to examine the impacts of organizational control on the adoption of innovation. Adoption of innovation theory was employed to describe the degree to which digital forensics practice has been adopted by large municipal police agencies having 100 or more sworn police officers.The data set was assembled primarily by using Law Enforcement Management and Administrative Statistics (LEMAS) 2003 and 1999. Dr. Edward Maguire`s survey was used to obtain 1 variable. The joining up of the data set to construct the sample resulted in 345 large local police agencies. The descriptive results on the degree of adoption of digital forensics practice indicate that 37.7% of large local police agencies have dedicated personnel to address digital evidence, 32.8% of police agencies address digital evidence but do not have dedicated personnel, and only 24.3% of police agencies have a specialized unit with full-time personnel to address digital evidence. About 5% of local police agencies do nothing to address digital evidence in any circumstance. These descriptive statistics indicate that digital evidence is a matter of concern for most large local police agencies and that they respond to varying degrees to digital evidence at the organizational level. Agencies that have not adopted digital forensics practice are in the minority. The structural equation model was used to test the hypothesized relations, easing the rigorous analysis of relations between latent constructs and several indicator variables. Environmental constraints have the largest impact on the adoption of innovation, exerting a positive influence. No statistically significant relation was found between organizational control and adoption of digital forensic practice. Contextual factors (task scope and personnel size) positively influence the adoption of digital forensics. Structural control factors, including administrative weight and formalization, have no significant influence on the adoption of innovation. The conclusions of the study are as follows. Police agencies adopt digital forensics practice primarily by relying on environmental constraints. Police agencies exposed to higher environmental constraints are more frequently expected to adopt digital forensics practice. Because organizational control of police agencies is not significantly related to digital forensics practice adoption, police agencies do not take their organizational control extensively into consideration when they consider adopting digital forensics practice. The positive influence of task scope and size on digital forensics practice adoption was expected. The extent of task scope and the number of personnel indicate a higher capacity for police agencies to adopt digital forensics practice. Administrative weight and formalization do not influence the adoption of digital forensics practice. Therefore, structural control and coordination are not important for large local police agencies to adopt digital forensics practice.The results of the study indicate that the adoption of digital forensics practice is based primarily on environmental constraints. Therefore, more drastic impacts on digital forensics practice should be expected from local police agencies' environments than from internal organizational factors. Researchers investigating the influence of various factors on the adoption of digital forensics practice should further examine environmental variables. The unexpected results concerning the impact of administrative weight and formalization should be researched with broader considerations.
Show less - Date Issued
- 2011
- Identifier
- CFE0004181, ucf:49081
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004181
- Title
- HIGH CURRENT DENSITY LOW VOLTAGE ISOLATED DC-DC CONVERTERSWITH FAST TRANSIENT RESPONSE.
- Creator
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Yao, Liangbin, Batarseh, Issa, University of Central Florida
- Abstract / Description
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With the rapid development of microprocessor and semiconductor technology, industry continues to update the requirements for power supplies. For telecommunication and computing system applications, power supplies require increasing current level while the supply voltage keeps decreasing. For example, the Intel's CPU core voltage decreased from 2 volt in 1999 to 1 volt in 2005 while the supply current increased from 20A in 1999 to up to 100A in 2005. As a result, low-voltage high-current...
Show moreWith the rapid development of microprocessor and semiconductor technology, industry continues to update the requirements for power supplies. For telecommunication and computing system applications, power supplies require increasing current level while the supply voltage keeps decreasing. For example, the Intel's CPU core voltage decreased from 2 volt in 1999 to 1 volt in 2005 while the supply current increased from 20A in 1999 to up to 100A in 2005. As a result, low-voltage high-current high efficiency dc-dc converters with high power-density are demanded for state-of-the-art applications and also the future applications. Half-bridge dc-dc converter with current-doubler rectification is regarded as a good topology that is suitable for high-current low-voltage applications. There are three control schemes for half-bridge dc-dc converters and in order to provide a valid unified analog model for optimal compensator design, the analog state-space modeling and small signal modeling are studied in the dissertation and unified state-space and analog small signal model are derived. In addition, the digital control gains a lot of attentions due to its flexibility and re-programmability. In this dissertation, a unified digital small signal model for half-bridge dc-dc converter with current doubler rectifier is also developed and the digital compensator based on the derived model is implemented and verified by the experiments with the TI DSP chip. In addition, although current doubler rectifier is widely used in industry, the key issue is the current sharing between two inductors. The current imbalance is well studied and solved in non-isolated multi-phase buck converters, yet few discusse this issue in the current doubler rectification topology within academia and industry. This dissertation analyze the current sharing issue in comparison with multi-phase buck and one modified current doubler rectifier topology is proposed to achieve passive current sharing. The performance is evaluated with half bridge dc-dc converter; good current sharing is achieved without additional circuitry. Due to increasing demands for high-efficiency high-power-density low-voltage high current topologies for future applications, the thermal management is challenging. Since the secondary-side conduction loss dominates the overall power loss in low-voltage high-current isolated dc-dc converters, a novel current tripler rectification topology is proposed. Theoretical analysis, comparison and experimental results verify that the proposed rectification technique has good thermal management and well-distributed power dissipation, simplified magnetic design and low copper loss for inductors and transformer. That is due to the fact that the load current is better distributed in three inductors and the rms current in transformer windings is reduced. Another challenge in telecommunication and computing applications is fast transient response of the converter to the increasing slew-rate of load current change. For instance, from Intel's roadmap, it can be observed that the current slew rate of the age regulator has dramatically increased from 25A/uS in 1999 to 400A/us in 2005. One of the solutions to achieve fast transient response is secondary-side control technique to eliminate the delay of optocoupler to increase the system bandwidth. Active-clamp half bridge dc-dc converter with secondary-side control is presented and one industry standard 16th prototype is built and tested; good efficiency and transient response are shown in the experimental section. However, one key issue for implementation of secondary-side control is start-up. A new zero-voltage-switching buck-flyback isolated dc-dc converter with synchronous rectification is proposed, and it is only suitable for start-up circuit for secondary-side controlled converter, but also for house-keeping power supplies and standalone power supplies requiring multi-outputs.
Show less - Date Issued
- 2007
- Identifier
- CFE0001814, ucf:47336
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001814
