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 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.

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The proposed vibration energy harvesting IC harvests energy from a piezoelectric transducer (PZT) to provide power for a wireless sensor node (WSN). With a traditional rectification stage, a two-path three-switch dual-input dual-output architecture is adopted to extract power and regulate the output voltage for the load with one stage. The power stage is controlled with a new maximum power point tracking (MPPT) algorithm, which integrates both fraction open circuit voltage (FOCV) and perturb and observe (PandO). The proposed algorithm was able to extract maximum power from a transducer due to high accuracy on the maxim power point (MPP) and low power dissipation. The proposed circuit is implemented in TSMC 180 nm BCD technology and the post-layout simulation verifies the functionality of the proposed design. The simulation results show that the circuit operates under the maximum power point to extract maximum power from a PZT. / Master of Science / The battery life has always been problematic ever since electronic devices exist. As semiconductor technology advances, more transistors could fit in the same area. Resultantly, portable, and mobile devices become more powerful but usually dissipate more power. Unfortunately, the development of the batteries has not been improved significantly. So, it is necessary to charge portable and mobile devices often or replace batteries frequently. In some applications where a device is hard to reach once installed, charging or replacing the battery is difficult. Under these circumstances, energy harvesting from ambient sources is an effective alternative. There are many types of sources of energy widely available in the environment such as vibration, thermal, solar, RF and etc. Solar energy harvesting is the most popular owing to high power density. However, sunlight is unavailable during night time. Vibration energy, although the power density is lower compared with solar, is a viable solution when solar is not a good source of energy. The proposed work utilizes abundant vibration energy at factories to power wireless sensor nodes (WSNs), which can monitor the temperature, light intensity, pressure, etc.

This dissertation aims to present detailed analysis of the small scale wind energy conversion system (WECS) design and implementation. The dissertation will focus on implementing a hardware prototype to be used for testing different control strategies applied to small scale WECSs. Novel control algorithms will be proposed to the WECS and will be verified experimentally in details. The wind turbine aerodynamics are presented and mathematical modeling is derived which is used then to build wind simulator using motor generator (MG) set. The motor is torque controlled based on the turbine mathematical model and the generator is controlled using the power electronic conversion circuits. The power converter consists of a three phase diode bridge followed by a boost converter. The small signal modeling for the motor, generator, and power converter are presented in details to help building the needed controllers. The main objectives of the small scale WECS controller are discussed. This dissertation focuses on two main regions of wind turbine operation: the maximum power point tracking (MPPT) region operation and the stall region operation. In this dissertation, the concept of MPPT is investigated, and a review of the most common MPPT algorithms is presented. The advantages and disadvantaged of each method will be clearly outlined. The practical implementation limitation will be also considered. Then, a MPPT algorithm for small scale wind energy conversion systems will be proposed to solve the common drawback of the conventional methods. The proposed algorithm uses the dc current as the perturbing variable and the dc link voltage is considered as a degree of freedom that will be utilized to enhance the performance of the proposed algorithm. The algorithm detects sudden wind speed changes indirectly through the dc link voltage slope. The voltage slope is also used to enhance the tracking speed of the algorithm and to prevent the generator from stalling under rapid wind speed slow down conditions. The proposed method uses two modes of operation: A perturb and observe (PandO) mode with adaptive step size under slow wind speed fluctuation conditions, and a prediction mode employed under fast wind speed change conditions. The dc link capacitor voltage slope reflects the acceleration information of the generator which is then used to predict the next step size and direction of the current command. The proposed algorithm shows enhanced stability and fast tracking capability under both high and low rate of change wind speed conditions and is verified using a 1.5-kW prototype hardware setup. This dissertation deals also with the WECS control design under over power and over speed conditions. The main job of the controller is to maintain MPPT while the wind speed is below rated value and to limit the electrical power and mechanical speed to be within the system ratings when the wind speed is above the rated value. The concept of stall region and stall control is introduced and a stability analysis for the overall system is derived and presented. Various stall region control techniques are investigated and a new stall controller is proposed and implemented. Two main stall control strategies are discussed in details and implemented: the constant power stall control and the constant speed stall control. The WECS is expected to work optimally under different wind speed conditions. The system should be designed to handle both MPPT control and stall region control at the same time. Thus, the control transition between the two modes of operation is of vital interest. In this dissertation, the light will be shed on the control transition optimization and stabilization between different operating modes. All controllers under different wind speed conditions and the transition controller are designed to be blind to the system parameters pre knowledge and all are mechanical sensorless, which highlight the advantage and cost effectiveness of the proposed control strategy. The proposed control method is experimentally validated using the WECS prototype developed. Finally, the proposed control strategies in different regions of operation will be successfully applied to a battery charger application, where the constraints of the wind energy battery charger control system will be analyzed and a stable and robust control law will be proposed to deal with different operating scenarios. / Ph. D.

The proposed energy harvesting circuit system is designed for indoor solar environment especially for factories where the light energy is abundant and stable. The designed circuits are intended to power wireless sensor nodes (WSNs) or other computing unit such as microcontrollers or DSPs to provide a power solution for Internet of Things (IoTs). The proposed circuit can extract maximum power from the PV panel by utilizing the maximum power point tracking (MPPT) technique. The power stage is a synchronous dual-input dual-output non-inverting buck-boost converter operating in discontinuous conduction mode (DCM) and constant on-time pulse skipping modulation (COT-PSM) to achieve voltage regulation and maximum power delivery to the load. Battery is used as secondary input also as secondary output to achieve a longer lifecycle, a fast load response time and support higher load conditions. The proposed MPPT technique doesn't require any current sensor or computing units. Fully digitalized simple circuits are used to achieve sampling, store, and comparing tasks to save power. The whole circuits including power stage and control circuits are designed and will fabricate in TSMC BCDMOS 180 nm process. The circuits are verified through schematic level simulations and post-layout simulations. The results are validated to prove the proposed circuit and control scheme work in a manner. / Master of Science / With the growing energy demands, the efficient energy conversion systems caught great attentions. Especially, in the era of Internet of Things, powering those wireless devices can be extremely difficult. Nowadays, lots of devices such as consumer electronics, wireless sensor nodes, computing and mission system etc. are still powered by the batteries. Regular changing the batteries of those devices can be inconvenient or expensive. Energy harvesting provides a good solution to this issue because there are lots of ambient energy source is available. To design an energy efficient energy harvesting circuit system can help extend the device lifecycle per charging cycle. Even with some specific energy source which power scale is high enough, meanwhile the load doesn’t require too much power, the devices can be power-independent or standalone. In this work, the proposed circuit targets for indoor solar energy harvesting via solar panel. The target powering devices are wireless sensor nodes (WSNs). Meanwhile, WSNs can monitor the temperature, humidity, pressure, noise level etc. The proposed circuit design combines the power stage and control circuit on an integrated chip (IC), only few components are off-chip. It provides a very compact, endurable, and economical solution to the current IoT powering issue.

Energy harvesting is becoming increasingly important in low-power applications where energy from the environment is used to power the system alone, or to supplement a battery. For example, pulse oximeter sensors inside helmets of road racing cyclists are powered by the sun. These sensors have become smaller and more practical without the limitation of a finite energy supply. Harvested energy from an energy transducer (solar, piezoelectric, etc.) must be maximized to ensure these devices can survive periods where environmental energy is scarce. The conversion process from the transducer to usable power for the device is not perfectly efficient. Specifically, the output voltage of a solar cell is a function of the light intensity, and by extension the load it powers. A small perturbation of the light source quickly diminishes the available power. The wasted power reduces the energy available for the application, and can be improved using an approach called maximum power point tracking (MPPT). This technique maximizes harvesting efficiency by dynamically impedance matching the transducer to its load. This report introduces the Maximum Efficient Solar Harvester (MESH), an MPPT algorithm tuned for a specific Wireless Sensor Network (WSN) application. MESH specifically controls the operation of the DC-DC converter in a solar power management unit (PMU). The control is done by monitoring the available light and feeding that information to choose the optimal operating point DC-DC converter. This operating point has a direct dependency on the overall efficiency of the system. For MESH to be practical, the cost and power overhead of adding this functionality must be assessed. Empirical results indicate that MESH improves the maximum efficiency of the popular Texas Instruments (TI) RF2500-SEH WSN platform by an average of 20%, which far exceeds the power overhead it incurs. The cost is also found to be minimal, as WSN platforms already include a large portion of the hardware required to implement MESH. The report was done in collaboration with Stephen Kobdish. It covers the software implementation and MESH architecture definition; Kobdish's companion report focuses on hardware components and the bench automation environment. / text

The yield from a solar photovoltaic (PV) source is dependent on factors such as light and temperature. A control system called a maximum power point tracker (MPPT) ensures that the yield from a solar PV source is maximized in spite of these factors. This thesis presents a novel implementation of a perturb and observe (PO) MPPT. The implementation uses a switched capacitor step down converter and a custom digital circuit implementation of the PO algorithm. Working in tandem, the switched capacitor step down converter and the custom digital circuit implementation were able to successfully track the maximum power point of a simulated solar PV source. This implementation is free of the overhead encountered with general purpose processor based MPPT implementations. This makes this MPPT system a valid candidate for applications where general purpose processors are undesirable. This document will begin by discussing the current state of MPPT research. Afterward, this thesis will present studies done to be able to use the chosen switched capacitor step down converter. Then the digital circuit PO implementation will be discussed in detail. Simulations of the architecture will be presented. Finally, experimental validation using a hardware prototype will be shown.

A energia fotovoltaica oferece conhecidas vantagens, entretanto, ainda deve vencer alguns desafios, principalmente a baixa eficiência de conversão dos painéis fotovoltaicos. Além do desenvolvimento de novos materiais, ainda continua muito importante aumentar a eficiência de conversão através da maximização da entrada de radiação solar e da otimização do ponto de operação do painel fotovoltaico. Este trabalho apresenta uma nova abordagem de rastreamento do ponto de máxima potência, adequada a qualquer configuração de conversores e capaz de seguir as rápidas mudanças de insolação e temperatura. É um método de perturbação e observação que mede apenas a corrente de saída do painel e que mantém a perfeita busca do ponto de máxima potência, mesmo durante as bruscas variações atmosféricas, com o simples emprego de flags. O trabalho apresenta ainda, como objetivo secundário, informações básicas a respeito de sistemas fotovoltaicos: células, painéis, conversores e suas técnicas de controle. O desempenho das simulações utilizando o software Matlab foram muito bons, confirmando a robustez, simplicidade, rápida convergência e facilidade de implementação do algoritmo. / The photovoltaic energy offers known advantages, however, it has yet to overcome some challenges, mainly the low efficiency of conversion of the photovoltaic panels. Besides the development of new materials, it still continues very important to increase the conversion efficiency through the maximization of the input solar radiation and the optimization of the photovoltaic panel operating point. This work presents a new approach for tracking the maximum power point, appropriate for any configuration of converters and capable to follow the fast changes in irradiance and temperature. It is a method of perturbation and observation that measures only the panel output current and that maintains a perfect search of the maximum power point, even during abrupt atmospheric variations, by simply using flags. The work still presents, as secondary objective, basic information regarding photovoltaic systems: cells, panels, converters and their control techniques. The performance of the simulations using the software Matlab proved to be very good, confirming the robustness, simplicity, rapid convergence and ease of implementation of the algorithm.

This dissertation presents various systematic design techniques for photovoltaic (PV) source simulators to serve as a convenient tool for the dynamic performance evaluation of solar power conditioning systems and their maximum power point tracking algorithms. A well-designed PV source simulator should accurately emulate the static and the dynamic characteristic of actual PV generator. Four major design features should be adopted in any PV source simulator: (i) high power-stage efficiency, (ii) fast transient response-time, (iii) output impedance matching with actual PV generator, and (iv) precise reference generation technique. Throughout this research, two different PV source simulator systems are designed, modeled, and experimentally verified. The design of the first system focuses mainly on creating new reference generation techniques where the PV equivalent circuit is used to precisely generate the current-voltage reference curves. A novel technique is proposed and implemented with analog components to simplify the reference signal generator and to avoid computation time delays in digital controllers. A two-stage LC output filter is implemented with the switching power-stage to push the resonant frequency higher and thus allowing a higher control-loop bandwidth design while keeping the same switching ripple attenuation as in the conventional one-stage LC output filter. With typical control techniques, the output impedance of the proposed simulator did not  match the closed-loop output impedance of actual PV generator due to the double resonant peaks of the two-stage LC output filter. Design procedures for both control and power-stage circuits are explained. Experimental results verify the steady-state and transient performance of the proposed PV source simulator at around 2.7 kW output. The design concept of the first simulator system is enhanced with a new type of PV source simulator that incorporates the advantages of both analog and digital based simulators. This simulator is characterized with high power-stage efficiency and fast transient response-time. The proposed system includes a novel three-phase ac-dc dual boost rectifier cascaded with a three-phase dc-dc interleaved buck converter. The selected power-stage topology is highly reliable and efficient. Moreover, the multi-phase dc-dc converter helps improve system transient response-time though producing low output ripple, which makes it adequate for PV source simulators. The simulator circuitry emulates precisely the static and the dynamic characteristic of actual PV generator under different environmental conditions including different irradiance and temperature levels. Additionally, the system allows for the creation of the partial shading effect on PV characteristic. This dissertation investigates the dynamic performance of commercial and non-commercial solar power conditioning systems using the proposed simulator in steady-state and transient conditions. Closed-loop output impedance of the proposed simulator is verified at different operating conditions. The impedance profile --magnitude and phase- matches the output impedance of actual PV generator closely. Mathematical modeling and experimental validation of the proposed system is thoroughly presented based on a 2.0 kW hardware prototype. The proposed simulator efficiency including the active-front-end rectifier and the converter stages at the maximum power point is 96.4%. / Ph. D.

Indiana University-Purdue University Indianapolis (IUPUI) / With the increasing demand of economy and environmental pollutions, more and more renewable energy systems with clean sources appear and have attracted attention of systems involving solar power, wind power and hybrid new energy powers[1]. However, there are some difficulties associated with combined utilization of solar and wind, such as their intermittent behavior and their peak hours mismatch in generation and consumption[1]. For this purpose, advanced network of a variety of renewable energy systems along with controllable load and storage units have been introduced[1-3]. This thesis proposes some configurations of hybrid energy harvesting systems, including wind-wind-storage DC power system with BOOST converters, solar-solar-storage DC power system with cascade BOOST converters, wind-solar-storage DC power system with BOOST converter and cascade BOOST converter, and wind-solar DC power system with SEPIC converter and BOOST converter. The models of all kinds of systems are built in Matlab/Simulink and the mathematical state-space models of combined renewable energy systems are also established. Several MPPT control strategies are introduced and designed to maximize the simultaneous power capturing from wind and solar, such as Perturb & Observe (P&O) algorithm for solar and wind, Tip Speed Ratio (TSR) control and Power Signal Feedback (PSF) control for wind, and Sliding Mode Extremum Seeking Control (SM-ESC) for wind and solar systems[4]. The control effects of some of these MPPT methods are also compared and analyzed. The supervisory control strategies corresponding to each configurations are also discussed and implemented to maximize the simultaneous energy harvesting from both renewable sources and balance the energy between the sources, battery and the load[2]. Different contingencies are considered and categorized according to the power generation available at each renewable source and the state of charge in the battery[2]. Applying the system architectures and control methods in the proposed hybrid new energy systems is a novel and significant attempt, which can be more general in the practical applications. Simulation results demonstrate accurate operation of the supervisory controller and functionality of the maximum power point tracking algorithm in each operating condition both for solar and for wind power[3]