abstract: The demand for cleaner energy technology is increasing very rapidly. Hence it is important to increase the eciency and reliability of this emerging clean energy technologies. This thesis focuses on modeling and reliability of solar micro inverters. In order to make photovoltaics (PV) cost competitive with traditional energy sources, the economies of scale have been guiding inverter design in two directions: large, centralized, utility-scale (500 kW) inverters vs. small, modular, module level (300 W) power electronics (MLPE). MLPE, such as microinverters and DC power optimizers, oer advantages in safety, system operations and maintenance, energy yield, and component lifetime due to their smaller size, lower power handling requirements, and module-level power point tracking and monitoring capability [1]. However, they suer from two main disadvantages: rst, depending on array topology (especially the proximity to the PV module), they can be subjected to more extreme environments (i.e. temperature cycling) during the day, resulting in a negative impact to reliability; second, since solar installations can have tens of thousands to millions of modules (and as many MLPE units), it may be dicult or impossible to track and repair units as they go out of service. Therefore identifying the weak links in this system is of critical importance to develop more reliable micro inverters. While an overwhelming majority of time and research has focused on PV module eciency and reliability, these issues have been largely ignored for the balance of system components. As a relatively nascent industry, the PV power electronics industry does not have the extensive, standardized reliability design and testing procedures that exist in the module industry or other more mature power electronics industries (e.g. automotive). To do so, the critical components which are at risk and their impact on the system performance has to be studied. This thesis identies and addresses some of the issues related to reliability of solar micro inverters. This thesis presents detailed discussions on various components of solar micro inverter and their design. A micro inverter with very similar electrical specications in comparison with commercial micro inverter is modeled in detail and veried. Components in various stages of micro inverter are listed and their typical failure mechanisms are reviewed. A detailed FMEA is conducted for a typical micro inverter to identify the weak links of the system. Based on the S, O and D metrics, risk priority number (RPN) is calculated to list the critical at-risk components. Degradation of DC bus capacitor is identied as one the failure mechanism and the degradation model is built to study its eect on the system performance. The system is tested for surge immunity using standard ring and combinational surge waveforms as per IEEE 62.41 and IEC 61000-4-5 standards. All the simulation presented in this thesis is performed using PLECS simulation software. / Dissertation/Thesis / Masters Thesis Electrical Engineering 2015

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With the decrease in availability of non-renewable energy sources coupled with the increase in the amount of energy required for the operation of personal electronic devices there has been an increased focus on developing systems that take advantage of renewable energy sources. Renewal energy sources such as photovoltaic (PV) panels have become more popular due to recent developments in PV panel manufacturing that decreases material costs and improves energy harvesting efficiency. Since PV sources are DC sources power conversion stages have to be used in order to interface this power to the existing electrical utility system. The structure of large scale PV systems usually consists of several PV panels connected in series to achieve a high input source voltage that can be fed into a high power centralized DC-AC inverter. The drawback to this approach is that when the PV panels are subjected to less than ideal conditions. If a single PV panel is subjected to drastically less solar irradiation during cloud conditions, then its output power will drop dramatically. Since this panel is series connected with the other PV panels, their current output is also dragged low decreasing the power output of the system. Algorithms that have the power converter operate at different input conditions allow the system to operate at a maximum power point (MPP), however this only allows the system to operate at a higher power point and not the true MPP. To get around this limitation a new PV system implementation was created by giving each panel its own DC-AC power conversion system. This configuration gives each panel the ability to operate at its own MPP increasing the total system energy harvest. Another advantage of the single panel DC-AC microinverter power conversion stage is that the outputs are parallel connected to the utility grid easily allowing the ability to expand the system without having to shut down the entire system. The most prevalent implementation of the microinverter consists of a single power converter that uses the PV low voltage DC and outputs high voltage AC. In order to ensure that the double line AC ripple does not propagate to the PV panel a large bank of electrolytic capacitors are used to buffer the ripple. There is concern that the electrolytic capacitor will degrade over time and affect the system efficiency. To get around having to use electrolytic capacitors a two stage microinverter has been proposed. The two stage microinverter consists of a DC-DC converter that steps up the low DC voltage of the PV panel to high voltage DC and the second stage is a DC-AC inverter that takes the high voltage DC and converts it to high voltage AC. There is a capacitor that connects the two power converter stages called the DC link capacitor which can buffer the double line energy ripple without using electrolytic capacitors. This thesis focuses on the review of several DC-AC inverter topologies suitable for use in PV microinverter systems. Operation capabilities such as common mode noise and efficiency are compared. The main focus of the review is to determine the optimal DC-AC inverter using the performance metrics of cost, efficiency and common mode performance. A 250 W prototype is built for each inverter topology to verify its performance and operation. / Master of Science

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2015-10-26T16:05:56Z No. of bitstreams: 1 Gabriela Schenkel_.pdf: 3048283 bytes, checksum: cd479115e88afd207554abd627ee1c17 (MD5) / Made available in DSpace on 2015-10-26T16:05:56Z (GMT). No. of bitstreams: 1 Gabriela Schenkel_.pdf: 3048283 bytes, checksum: cd479115e88afd207554abd627ee1c17 (MD5) Previous issue date: 2015-02 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Os sistemas fotovoltaicos conectados à rede tem como finalidade a conversão da energia solar em energia elétrica. No Brasil, recentemente foi dado o primeiro passo efetivo com a publicação pela ANEEL da Resolução Normativa n° 482. Esta resolução, publicada em 17 de abril de 2012, possibilita à um consumidor doméstico e comercial possuir um sistema de microgeração de energia (hidráulica, solar, eólica, biomassa ou cogeração qualificada) conectado à rede elétrica e fazer compensação de energia. Neste trabalho foi instalado em caráter experimental, no Laboratório de Energias Renováveis da Unisinos, um sistema fotovoltaico conectado à rede com uso de um modelo de microinversor, e buscou-se por meio desta instalação e do monitoramento, analisar o comportamento elétrico e energético do sistema. O sistema é composto por um módulo monocristalino LG255S1C de 255 Wp conectado a um microinversor ENPHASE M215 de 215 W. O período de monitoramento foi de 1° de agosto até 20 de dezembro de 2014. Uma central de aquisição de dados Agilent HP 34970A foi empregada para coletar dados de irradiância no plano do gerador fotovoltaico, corrente e tensão na entrada e saída do microinversor, temperatura de uma célula FV no centro do módulo fotovoltaico e temperatura no dissipador do microinversor. Também foi utilizado como medidor o analisador de energia Fluke 43B, que coleta os dados de potência ativa, potência reativa e potência aparente injetada na rede elétrica pelo sistema. Índices de qualidade de energia como a distorção harmônica total de corrente e fator de deslocamento também foram medidos. A eficiência média diária máxima, considerando a incerteza, medida no microinversor empregado foi de 95,18 % e é semelhante aos valores de eficiência média diária dos microinversores de primeira e segunda geração. O sistema fotovoltaico monitorado com o uso do microinversor atingiu o valor máximo de desempenho global de 0,93. A produção de energia máxima diária em corrente alternada foi de 1,49 kWh. Estima-se, levando em consideração este valor, que a produção mensal pode ser de até 44,7 kWh. Isto significa uma redução de 58 % no consumo de energia em uma residência, levando em consideração o custo de disponibilidade e o sistema instalado em uma residência com consumo médio mensal da região nordeste que é de 120 kWh. / Photovoltaic grid-connected systems aims the conversion of solar energy into electrical energy. In Brazil, was recently given the first effective step with the publication by ANEEL Normative Resolution No. 482. This resolution published on 17 th April, 2012, enables domestic and commercial consumers have an energy microgeneration system (hydro, solar, wind, biomass or qualified cogeneration) connected to mains power and make compensation. In this work was mounted on an experimental character, in the Renewable Energy Laboratory of Unisinos, a photovoltaic grid-connected system that uses a microinverter model, and through this installation and monitoring, analyse the electrical and energetical behavior of the system. The system consists of a 255 Wp LG255S1C monocrystalline module, connected to a 215 W ENPHASE M215 microinverter. The monitoring period was 1 st August to 20 th December, 2014. A central acquisition of Agilent HP 34970A data was used to collect data irradiance in the plane of the PV array, current and voltage at the input and output of microinverter, temperature of a PV cell in the center of the PV module and the microinverter sink. It was also used as a measuring the energy analyzer Fluke 43B, which collects the data of active power, reactive power and apparent power injected into the grid by the system. Power quality indices as the total harmonic current distortion and displacement factor were also measured. The maximum daily average efficiency, considering the uncertainty, measured on the employed microinverter was 95.18 % and is similar than the daily average efficiency values of microinverters of first and second generation. The photovoltaic system monitored using the microinverter peaked overall performance of 0.93. The production maximum daily energy into alternating current was 1.49 kWh. It is estimated taking into account the value that the monthly production can achieved 44.7 kWh. This means a reduction of 58 % in the consumption of a residence considering the availability cost and that the system is installed in a residence with the northest comsumption whose the average monthly consumption is 120.00 kWh.

Multilevel inverters offer many well-known advantages for use in high-voltage and high-power applications, but they are also well suited for low-power applications. A single phase inverter is developed in this paper to deliver power from a residential-scale system of Photovoltaic panels to the utility grid. The single-stage inverter implements a novel control technique for the reversing voltage topology to produce a stepped output waveform. This approach increases the granularity of control over the PV systems, modularizing key components of the inverter and allowing the inverter to extract the maximum power from the systems. The adaptive controller minimizes harmonic distortion in its output and controls the level of reactive power injected to the grid. A computer model of the controller is designed and tested in the MATLAB program Simulink to assess the performance of the controller. To validate the results, the performance of the proposed inverter is compared to that of a comparable voltage-sourced inverter.

Energy Harvesting from Exercise Machines (EHFEM) is an ongoing project pursuing alternate forms of sustainable energy for Cal Poly State University. The EHFEM project seeks to acquire user-generated DC power from exercise machines and sell that energy back to the local grid as AC power. The end goal of the EHFEM project aims to integrate a final design with existing elliptical fitness trainers for student and faculty use in Cal Poly’s Recreational Center. This report examines whether including the DC-DC converter in the EHFEM setup produces AC power to the electric grid more efficiently and consistently than an EHFEM system that excludes a DC-DC converter. The project integrates an overvoltage protection circuit, a DC-DC converter, and a DC-AC microinverter with an available elliptical trainer modified to include an energy converting circuit. The initial expectation was that a DC-DC converter would increase, when averaged over time, the overall energy conversion efficiency of the EHFEM system, and provide a stable voltage and current level for the microinverter to convert DC power into AC power. In actuality, while including a DC-DC converter in a test setup allows the EHFEM system to function with less frequent interruptions, this occurs at the cost of lower efficiency. Testing demonstrates the EHFEM project can convert user-generated DC mechanical power into usable AC electrical power. Retrofitting existing equipment with the EHFEM project can reduce Cal Poly’s energy cost.

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