Distributed generation (DG) is getting more and more popular due to the environmentally-friendly feature, the new generation unit developments, and the ability to operate in a remote area. By clustering the paralleled DGs, storage system and loads, a microgrid (MG) can offer a power system with increased reliability, flexibility, cost effectiveness, and energy efficient feature. Popular energy sources like photovoltaic modules (PV), wind turbines, and fuel cells require the power-electronic interface as the bridge to connect to the utility grid for usable transmission. The inverter-based microgrid system, however, suffers more challenges than traditional rotational power system. Those challenges, including much less over current capability, the nature of the intermittent renewable energy sources, a wide-band dynamic of generation units, and a large grid impedance variation, call for more careful system hardware and control designs to ensure a reliable system operation. Major design interests are found in (i) precision power flow control, (ii) proper current sharing, (iii) smooth transition between grid-tie and islanding modes, and (iv) stability analysis. This dissertation will cover a complete design and implementation of an experimental microgrid with paralleled power conditioning systems operating in the gridtie mode, islanding mode, and mode transfers. A universal inverter is proposed with the LCL filter to operate in both grid-tie and standalone mode without any hardware modification. Next, controllers of individual inverters running in basic microgrid modes will be discussed to ensure high quality output characteristics. The admittance compensation will also be proposed to avoid reverse power flow during the grid-tie connection transient. Combining previous designed single inverters, a CAN-bus multiinverter microgrid system will be established. The current sharing with the proposed frequency-decoupled transmission will be implemented to extend the transmission distance. Next, smooth mode transfer procedures between grid-tie mode and islanding mode will be suggested based on the circuit principles to minimize the excessive electrical stresses. Finally, the state-space analysis of the proposed multi-inverter microgrid system will be conducted to investigate the stability under system variations and optimize the system performance. Experimental and simulation results show that the designed universal inverter can provide stable outputs in different basic microgrid operation modes. With the proposed current sharing scheme, the output current is equally shared among paralleled inverters without a noticeable circulating current. Both the simulation and experimental results of mode transfer show that the multi-inverter based microgrid system is able to switch between grid-tie and islanding modes smoothly to guarantee an uninterrupted power supply to the critical loads. Based on eigenvalue analysis, the study of stability analysis also shows the agreement of the design, simulation and test results which further verifies the reliability of the designed multi-inverter microgrid system. / Ph. D.

Renewable energy and distributed generation are getting more and more popular, including photovoltaic modules (PV), wind turbines, and fuel cells. The renewable energy sources need the power electronics interface to the utility grid because of different characteristics between the sources and the grid. No matter what renewable energy source is utilized, inverters are essential in the microgrid system. Thanks to flexible modular design, transformerless connection, extended voltage and power output, less maintenance and higher fault tolerance, the cascade inverters are good candidates for utility interface of various renewable energy sources. This dissertation proposes a new type of cascade inverters based on dual-buck topology and phase-shift control scheme. Compared to traditional cascade inverters, they have enhanced system reliability thanks to no shoot-through problems and lower switching loss with the help of using power MOSFETs. With phase-shift control, it theoretically eliminates the inherent current zero-crossing distortion of the single-unit dual-buck type inverter. In addition, phase-shift control can greatly reduce the ripple current or cut down the size of passive components by increasing the equivalent switching frequency. An asymmetrical half-cycle unipolar (AHCU) PWM technique is proposed for dual-buck full-bridge inverter. The proposed approach is to cut down the switching loss of power MOSFETs by half. At the same time, this AHCU PWM leads to current ripple reduction, and thus reducing ripple-related loss in filter components. Therefore, the proposed PWM strategy results in significant efficiency improvement. Additionally, the AHCU PWM also compensates for the zero-crossing distortion problem of dual-buck full-bridge inverter. Several PWM techniques are analyzed and compared, including bipolar PWM, unipolar PWM and phase-shifted PWM, when applied to the proposed cascade dual-buck full-bridge inverter. It has been found out that a PWM combination technique with the use of two out of the three PWMs leads to better performance in terms of less output current ripple and harmonics, no zero-crossing distortion, and higher efficiency. A grid-tie control system is proposed for cascade dual-buck inverter with both active and reactive power flow capability in a wide range under two types of renewable energy and distributed generation sources. Fuel cell power conditioning system (PCS) is Type I system with active power command generated by balance of plant (BOP) of each unit; and photovoltaic or wind PCS is Type II system with active power harvested by each front-end unit through maximum power point tracking (MPPT). Reactive power command is generated by distributed generation (DG) control site for both systems. Selective harmonic proportional resonant (PR) controller and admittance compensation controller are first introduced to cascade inverter grid-tie control to achieve better steady-state and dynamic performances. / Ph. D.

The demand for electricity is increasing daily due to technological advancement, and ?luxurious lifestyles. Increasing utilization of electricity means the depletion of fossil fuel ?reserves. Thus, governments around the world are seeking alternative and sustainable ?sources of energy such as the solar powered system. The main purpose of this research is ?to develop a knowledge base on residential electric generation from the grid and solar ?energy. This paper examined the economic feasibility of using grid-tied residential ?photovoltaic (GRPV) system in Saudi Arabia with the HOMER software. Models ?forecasting the price of oil barrels through artificial neural networks (ANN) were also ?employed in the analysis. The study shows that an oil-rich country like Saudi Arabia has ?potential to utilize the GRPV system as an alternative source of energy. / This paper examined the economic feasibility of using grid-tied residential photovoltaic ??(GRPV) system in Saudi Arabia with the HOMER software. Models forecasting the ?price of oil barrels through artificial neural networks (ANN) were also employed in the ?analysis. The study shows that an oil-rich country like Saudi Arabia has potential to ?utilize the GRPV system as an alternative source of energy. This study provides a ?discussion of the potential for applying solar-powered and an assessment of the ?performance of existing systems based on collecting output data.?

Master of Science / Department of Electrical Engineering / William B. Kuhn / During the development of an educational renewable energy production platform, it was found that there were no low-cost, efficient grid-tie interfaces for a 160 W DC wind turbine. Typically, a small DC wind turbine is used in conjunction with a rechargeable battery bank or, if the wind turbine is directly interfaced with a grid-tie inverter, a regulator with a diversion-load. The use of batteries is undesirable due to their high-cost and high-maintenance characteristics. Diversion loads by nature waste power, as any excess energy that cannot be accepted by a battery or inverter is usually converted into heat through a resistive element. Initially, a 24 V DC, 160 W Air Breeze small wind turbine was directly connected to an Enphase Energy M190 grid-tie micro-inverter. The 24 V DC Air Breeze wind turbine is designed to charge a battery or bank of batteries while the M190 micro-inverter is designed to convert the DC output of a 200 W solar panel to grid-tied AC power. As expected, the power-production response time associated with the small wind turbine and the power-accepting, load-matching response time of the micro-inverter were not compatible. The rapidly changing power output of the small wind turbine conflicted with the slow response time of the micro-inverter resulting in little power production. Ultimately, the response time mismatch also produced sufficiently large voltage spikes to damage the turbine electronics. In this thesis, a solution for a low-cost, efficient grid-tie interface using no batteries and no diversion load is presented. A capacitance of eight Farads is placed in parallel with the small wind turbine and the micro inverter. The large capacitance sufficiently smoothes the potential abrupt voltage changes produced by the wind turbine, allowing the micro-inverter adequate time to adjust its load for optimal power conversion. Laboratory experiments and data from an implementation of such a parallel super capacitor wind turbine to grid-tie micro-inverter configuration are provided along with DC and AC power production monitoring circuits interfaced with a micro controller.

This thesis compares two methods of designing grid-tie inverters. The first design topology is a traditional two stage approach consisting of an isolated DC-DC converter on the input followed by a high switching frequency SPWM (Sinusoidal Pulse Width Modulation) stage to produce the required low frequency sine wave output. The novel second design approach employs a similar DC-DC input stage capable of being modulated to provide a rectified sine wave output voltage/current waveform. This stage is followed by a simple low frequency switched Unfolding Stage to recreate the required sine wave output. Both of the above designs have advantages and disadvantages depending on operating parameters. The following work will compare the Unfolding Output Stage and the SPWM Output Stage at various power levels and power densities. Input stage topologies are similarly examined in order to determine the best design approach for each output stage under consideration.

No description available.

This dissertation aims to present a detailed analysis of the grid voltage disturbance in frequency domain for the current control design in the grid-tie inverter applications and to propose current control techniques in order to minimize its impact and maximize feasibility of the power conditioning system in distributed generations. Because the grid voltage is constantly changing, the inverter must be able to response to it. If the inverter is unable to respond properly, then the grid voltage power comes back to the system and damages the fuel cell power conditioning systems. A closed-loop dynamic model for the current control loop of the grid-tie inverter has been developed. The model explains the structure of the inverter admittance terms. The disturbance of the grid voltages has been analyzed in frequency domain. The admittance compensator has been proposed to prevent the grid voltage effect. The proposed lead-lag current control with admittance compensator transfers current properly without system failure. In order to get rid of the steady-state error of the feedback current, a proportional-resonant controller (PR) has been adopted. A PR control with admittance compensation provides great performance from zero power to full power operation. In addition, active and reactive power flow controller has been proposed based on the PR controller with admittance compensation. The proposed active and reactive power flow control scheme shows a wide range power flow control from pure leading power to pure lagging power. Finally, the proposed controller scheme has been verified its feasibility in three phase grid-tie inverter applications. First of all, a half-bridge grid-tie inverter has been designed with PR controller and admittance compensation. Then three individual grid-tie inverters has been combined and produced three phase current to the three phase grid in either balanced condition or unbalanced condition. The proposed control scheme can be applied not only single phase grid-tie inverter application, but also three phase grid-tie inverter application. This research can be applicable to the photovoltaic PCS as well. This technology makes renewable energy source more plausible for distributed generations. / Ph. D.

Submitted by Simone Souza (simonecgsouza@hotmail.com) on 2017-10-06T15:12:15Z No. of bitstreams: 1 DISS_2014_Daniel Moussalem Apolonio.pdf: 7540330 bytes, checksum: 1d1c94a7cce19da52ea4511636e5f609 (MD5) / Approved for entry into archive by Jordan (jordanbiblio@gmail.com) on 2017-11-06T13:59:30Z (GMT) No. of bitstreams: 1 DISS_2014_Daniel Moussalem Apolonio.pdf: 7540330 bytes, checksum: 1d1c94a7cce19da52ea4511636e5f609 (MD5) / Made available in DSpace on 2017-11-06T13:59:30Z (GMT). No. of bitstreams: 1 DISS_2014_Daniel Moussalem Apolonio.pdf: 7540330 bytes, checksum: 1d1c94a7cce19da52ea4511636e5f609 (MD5) Previous issue date: 2014-08-25 / A crescente utilização da energia solar fotovoltaica decorrente do aumento da competitividade econômica na instalação de sistemas fotovoltaicos conectados à rede (SFCR) demanda estudos de aplicabilidade e inovações tecnológicas e de processos nessa área do conhecimento. A evolução da aplicação de geração solar dos países pioneiros demonstra a grande possibilidade de investimentos no setor em um futuro próximo, principalmente após a possibilidade de conexão à rede e de geração distribuída regularizada e normatizada pela ANEEL no Brasil. O objetivo deste trabalho é o estudo de sistemas solares fotovoltaicos conectados à rede no que tange ao seu dimensionamento, funcionamento, operação, qualidade da energia gerada, eficiência energética do sistema e quantidade de energia gerada, obtida por medição e simulação, através de um estudo de caso de um sistema instalado na Universidade Federal de Mato Grosso (UFMT), campus Cuiabá. O sistema de 510 Wp gerou 583,66 kWh de energia elétrica durante um ano de medição e apresentou performance ratio de 0,657 frente aos 0,731 definido como padrão pela NREL (2005). Algumas características técnicas do sistema foram averiguadas e comparadas com os valores de placa. Os resultados obtidos com o uso dos programas computacionais mostram-se apropriados na etapa de elaboração dos projetos, previsão de geração de energia e retorno financeiro dos sistemas a serem instalados. O retorno financeiro para o sistema instalado se dará em aproximadamente 20 anos e para sistemas de 3 kWp em que 100% da carga é utilizada na própria edificação com tarifa B a viabilidade financeira será alcançada em 2016. O retorno financeiro de investimentos em SFCR varia de acordo com o sistema a ser aplicado, e tende a ser suscetível a mudanças bruscas devido principalmente às legislações, incentivos tributários por parte do governo e variações no preço dos componentes dos sistemas e das tarifas de energia. / The increasing usage of solar photovoltaic systems because of the growth of economic competitiveness demands studies in applications and technological or process innovations in this field of knowledge. The evolution of the application of solar generation by the pioneers countries demonstrate the possibility of large investments in the sector in a near future, especially after the possibility of grid connection and distributed generation regulated by ANEEL in Brazil. The objective of this work is to study on-grid solar photovoltaic systems regarding its project, operation, power quality, system efficiency and the amount of energy generated, obtained by simulations and measurements, through a case study of an installed system working at the Federal University of Mato Grosso (UFMT), Cuiabá campus. The 510 Wp system generated 583,66 kWh of electric energy during a year of measurements and presented performance ratio of 0,657 in comparison to the 0,731 standard for PV systems of NREL (2005). Some system technical characteristics were checked and compared with nominal values on the manual. The results obtained by the softwares are appropriated as an assistant for projecting, energy generation prediction e financial feasibility for the incoming systems. The payback for the installed system is predicted to approximately 20 years and for 3 kWp systems in which the generation is used in the building before injected with B energy fee the viability is going to be reached in 2016. The payback of the investment on on-grid photovoltaic systems vary from each system, and tend to be susceptible to harsh variations, mainly due to legislations and government support and changes in the photovoltaics equipment prices and the electric energy rates.

Indiana University-Purdue University Indianapolis (IUPUI) / This thesis proposes two new topologies for Uninterrupted Power Supply (UPS), and a grid-tie microinverter. The first topic will discuss an on-line transformerless UPS system based on the integrated power electronics converters that is able to control the input power factor, charge the battery, and guarantee backup operation of the system. The main advantages of the proposed UPS are active power factor correction (PFC) without the need of a complex control scheme, and integrated functions of the battery charger circuit and PFC with only three power switches. Operation modes of the system and the PWM strategy is presented in detail. The second topic discussed is of a proposed circuitry for a single-phase back-to-back converter for UPS applications. The main advantages of this topology is higher number of levels at the rectifier side, less number of power switches, and no need for a boost inductor at the input side of the converter. The last topic discussed is of a proposed patent pending microinverter. This topic was a project funded by the National Science Foundation, and its aim was to help commercialize the research. This project proposes a solution for a solar inverter called Delta Microinverter that allows easier and faster installation as well as power conversion with higher efficiency. Delta Microinverters innovation is found in its patent-pending shape and in its patent-pending circuitry, i.e., electronics mounted inside of the Delta Microinverter. The Delta Microinverters shape has a housing configured for rapid mounting using a single fastener and its power electronics configuration offers an optimized relationship between the number of levels and number of power switches.

Este trabalho estuda a interação entre os métodos anti-ilhamento aplicados em sistemas fotovoltaicos residenciais, operando simultaneamente em uma rede de distribuição de baixa tensão. Os sistemas fotovoltaicos em geral interagem entre si, com a rede de distribuição da concessionária e com outras fontes de geração distribuída. Uma consequência importante dessa interação é a ocorrência do ilhamento, que acontece quando as fontes de geração distribuída fornecem energia ao sistema elétrico de potência mesmo quando esta se encontra eletricamente isolada do sistema elétrico principal. A função anti-ilhamento é uma proteção extremamente importante, devendo estar presente em todos os sistemas de geração distribuída. Atualmente, são encontradas diversas técnicas na literatura. Muitas delas oferecem proteção adequada quando um inversor está conectado à linha de distribuição, mas podem falhar quando dois ou mais funcionam simultaneamente, conectados juntos ou próximos entre si. Dois destes métodos são analisados detalhadamente nesse estudo, avaliados em uma rede de distribuição residencial de baixa tensão. Os resultados obtidos mostram que a influência de um método sobre o outro é dependente da predominância de cada um deles dentro do sistema elétrico. Contudo, nas condições analisadas o ilhamento foi detectado dentro do limite máximo estabelecido pelas normas pertinentes. / This work studies the interaction between islanding detection methods applied in residential photovoltaic systems, operating simultaneously in a low voltage distribution network. Photovoltaic systems, in general, interact with themselves, with the utility grid and other distributed generation sources. An important consequence of this interaction is the islanding occurrence, which happens when distributed generation sources supply energy to the electrical power system even when it is electrically isolated from the main electrical system. The anti-islanding function is an extremely important protection, and should be present in all distributed generation systems. Actually, many techniques are found in the literature. Most of them provide suitable protection when one inverter is connected to the distribution line, but can fail when two or more work simultaneously, connected at the same point or close to each other. Two of these methods are analyzed in detail in this study and evaluated in a residential low voltage distribution line. The obtained results show that the influence of a method over another one is dependent of the predominance of each one within the electrical system. However, in the analyzed condition the islanding was detected within the maximum allowed time established by applicable rules.