The first ICASE/LARC industry roundtable: Session proceedings

The first 'ICASE/LaRC Industry Roundtable' was held on October 3-4, 1994, in Williamsburg, Virginia. The main purpose of the roundtable was to draw attention of ICASE/LaRC scientists to industrial research agendas. The roundtable was attended by about 200 scientists, 30% from NASA Langley; 20% from universities; 17% NASA Langley contractors (including ICASE personnel); and the remainder from federal agencies other than NASA Langley. The technical areas covered reflected the major research programs in ICASE and closely associated NASA branches. About 80% of the speakers were from industry. This report is a compilation of the session summaries prepared by the session chairmen

Design of module level converters in photovoltaic power systems

The application of distributed maximum power point tracking (DMPPT) technology in solar photovoltaic (PV) systems is a hot topic in industry and academia. In the PV industry, grid integrated power systems are mainstream. The main objective for PV system design is to increase energy conversion efficiency and decrease the levelized cost of electricity of PV generators. This thesis firstly presents an extensive review of state-of-the-art PV technologies. With focus on grid integrated PV systems research, various aspects covered include PV materials, conventional full power processing DMPPT architectures, main MPPT techniques, and traditional partial power processing DMPPT architectures. The main restrictions to applying traditional DMPPT architectures in large power systems are discussed. A parallel connected partial power processing DMPPT architecture is proposed aiming to overcome existing restrictions. With flexible ‘plug-and-play’ functionality, the proposed architecture can be readily expanded to supply a downstream inverter stage or dc network. By adopting smaller module integrated converters, the proposed approach provides a possible efficiency improvement and cost reduction. The requirements for possible converter candidates and control strategies are analysed. One representative circuit scheme is presented as an example to verify the feasibility of the design. An electromagnetic transient model is built for different power scale PV systems to verify the DMPPT feasibility of the evaluated architecture in a large-scale PV power system. Voltage boosting ability is widely needed for converters in DMPPT applications. Impedance source converters (ISCs) are the main converter types with step-up ability. However, these converters have a general problem of low order distortion when applied in dc-ac applications. To solve this problem, a generic plug-in repetitive control strategy for a four-switch three-phase ISC type inverter configuration is developed. Simulation and experimental results confirm that this control strategy is suitable for many ISC converters.The application of distributed maximum power point tracking (DMPPT) technology in solar photovoltaic (PV) systems is a hot topic in industry and academia. In the PV industry, grid integrated power systems are mainstream. The main objective for PV system design is to increase energy conversion efficiency and decrease the levelized cost of electricity of PV generators. This thesis firstly presents an extensive review of state-of-the-art PV technologies. With focus on grid integrated PV systems research, various aspects covered include PV materials, conventional full power processing DMPPT architectures, main MPPT techniques, and traditional partial power processing DMPPT architectures. The main restrictions to applying traditional DMPPT architectures in large power systems are discussed. A parallel connected partial power processing DMPPT architecture is proposed aiming to overcome existing restrictions. With flexible ‘plug-and-play’ functionality, the proposed architecture can be readily expanded to supply a downstream inverter stage or dc network. By adopting smaller module integrated converters, the proposed approach provides a possible efficiency improvement and cost reduction. The requirements for possible converter candidates and control strategies are analysed. One representative circuit scheme is presented as an example to verify the feasibility of the design. An electromagnetic transient model is built for different power scale PV systems to verify the DMPPT feasibility of the evaluated architecture in a large-scale PV power system. Voltage boosting ability is widely needed for converters in DMPPT applications. Impedance source converters (ISCs) are the main converter types with step-up ability. However, these converters have a general problem of low order distortion when applied in dc-ac applications. To solve this problem, a generic plug-in repetitive control strategy for a four-switch three-phase ISC type inverter configuration is developed. Simulation and experimental results confirm that this control strategy is suitable for many ISC converters

Analysis And Simulation Tools For Solar Array Power Systems

This dissertation presents simulation tools developed specifically for the design of solar array power systems. Contributions are made in several aspects of the system design phases, including solar source modeling, system simulation, and controller verification. A tool to automate the study of solar array configurations using general purpose circuit simulators has been developed based on the modeling of individual solar cells. Hierarchical structure of solar cell elements, including semiconductor properties, allows simulation of electrical properties as well as the evaluation of the impact of environmental conditions. A second developed tool provides a co-simulation platform with the capability to verify the performance of an actual digital controller implemented in programmable hardware such as a DSP processor, while the entire solar array including the DC-DC power converter is modeled in software algorithms running on a computer. This virtual plant allows developing and debugging code for the digital controller, and also to improve the control algorithm. One important task in solar arrays is to track the maximum power point on the array in order to maximize the power that can be delivered. Digital controllers implemented with programmable processors are particularly attractive for this task because sophisticated tracking algorithms can be implemented and revised when needed to optimize their performance. The proposed co-simulation tools are thus very valuable in developing and optimizing the control algorithm, before the system is built. Examples that demonstrate the effectiveness of the proposed methodologies are presented. The proposed simulation tools are also valuable in the design of multi-channel arrays. In the specific system that we have designed and tested, the control algorithm is implemented on a single digital signal processor. In each of the channels the maximum power point is tracked individually. In the prototype we built, off-the-shelf commercial DC-DC converters were utilized. At the end, the overall performance of the entire system was evaluated using solar array simulators capable of simulating various I-V characteristics, and also by using an electronic load. Experimental results are presented

Contributions to the efficiency and safety of stand-alone DC microgrids

Currently, the distributed generation based on renewable energy sources is mainly DC. Those DC systems are used diverse applications such as airplanes, automobiles, ships, spaceships, computers, servers, telecommunications stations, among others. This thesis considers an isolated DC microgrid architecture composed of a renewable source, an energy storage system, and a DC load. The thesis is aimed at identifying and solving efficiency and safety problems at the source, the DC bus, and the load. During the development of this Thesis, six contributions to the state-of-the-art of DC microgrids were obtained. The first contribution is the mathematical model of a distributed maximum power point platform formed by multiple module-converter sets connected in series, which can be implemented in different programming languages and deployed on multiple platforms to evaluate optimization strategies. The second contribution is a vectorial MPPT algorithm for a distributed photovoltaic system, based in the perturb and observe algorithm. This algorithm provides a satisfactory trade-off between implementation cost and energy production since it uses a single I/V sensor. The third contribution is a reconfiguration algorithm that optimizes the electrical connections of a commercial photovoltaic array, which enables to maximize the energy extraction under arbitrary shading conditions. The fourth and fifth contributions are two control strategies, based on sliding-modes, designed for a charger/discharger DC/DC converter. Those solutions enable to regulate the voltage on the DC-bus of the microgrid to improve the microgrid safety. One of the strategies considers the current of the DC-bus into the sliding surface, which gives a better performance in terms of overshoot and settling time of the DC bus voltage. The final contribution concerns a control strategy, also based on sliding modes, to regulate a point-of-load DC/DC converter. Such a contribution enables to improve the conversion efficiency, and at the same time, to improve the load safety by reducing the current and voltage ripples delivered by the converter. Finally, those contributions improve the electrical efficiency and operational safety of DC microgrids based on renewable sources. The results obtained in this thesis were published in five journals articles and three communications to conferences. From those, three articles were published in Q1 journals, one article was published in Q3 journal, and another one was published in a Colombian journalResumen: Actualmente, la generación distribuida basada en fuentes de energía renovable es principalmente DC. Estos sistemas DC son utilizados en aviones, automóviles, barcos, naves espaciales, computadores, servidores, estaciones de telecomunicaciones, etc. Esta Tesis considera una arquitectura de microrred DC aislada compuesta por una fuente renovable, un sistema de almacenamiento de energía y una carga DC. La tesis tiene como objetivo identificar y solucionar problemas de eficiencia y seguridad de operación en la fuente, en el bus DC y en la carga. Durante el desarrollo de esta Tesis se obtuvieron seis aportes al estado del arte en microrredes DC. La primera contribución es el modelo matemático de una plataforma de seguimiento del punto de máxima potencia formada por múltiples conjuntos panel-convertidor conectados en serie, el cual se puede implementar en diferentes lenguajes de programación y desplegar en múltiples plataformas para evaluar estrategias de optimización. La segunda contribución es un algoritmo MPPT vectorial para un sistema fotovoltaico distribuido, basado en el algoritmo de perturbar y observar. Este algoritmo proporciona una compensación satisfactoria entre el costo de implementación y la producción de energía, ya que utiliza un solo sensor de I/V. La tercera contribución es un algoritmo de reconfiguración que optimiza las conexiones eléctricas de un arreglo de paneles fotovoltaicos comercial, el cual permite maximizar la extracción de energía bajo condiciones arbitrarias de sombreado. La cuarta y quinta contribución son dos estrategias de control, basadas en modos deslizantes, diseñadas para un convertidor DC/DC cargador/descargador. Estas soluciones permiten regular el voltaje del bus DC de la microrred para mejorar la seguridad de su operación. Una de las estrategias considera la corriente del bus DC en la superficie deslizante, lo cual da un mejor desempeño en cuanto al sobreimpulso y el tiempo de establecimiento del voltaje del bus DC. La contribución final es una estrategia de control, también basada en modos deslizantes, para regular un convertidor DC/DC point-of-load. Esta contribución permite mejorar la eficiencia de la conversión y al mismo tiempo mejorar la seguridad operativa de la carga reduciendo el rizado de voltaje y corriente entregado por el convertidor. Finalmente, estas contribuciones mejoran la eficiencia eléctrica y la seguridad operativa de microrredes DC basadas en fuentes de energía renovable. Los resultados obtenidos en esta Tesis fueron publicados en cinco artículo de revista y tres ponencias en conferencias. De estos, tres artículos fueron publicados en revistas clasificadas en Q1, un artículo fue publicado en una revista con clasificación Q3 y otro en una revista colombianaDoctorad

Technology 2004, Vol. 2

Proceedings from symposia of the Technology 2004 Conference, November 8-10, 1994, Washington, DC. Volume 2 features papers on computers and software, virtual reality simulation, environmental technology, video and imaging, medical technology and life sciences, robotics and artificial intelligence, and electronics

You are what you measure! But are we measuring it right? An empiric analysis of energy access metrics based on a multi-tier approach in Bangladesh

Measuring energy access through binary indicators is insufficient, and often, even misleading. In this work, the SE4ALL global tracking framework, and the recently introduced ESMAP multi-tier approach, is critically discussed analyzing questionnaire based primary data from rural Bangladesh. The performance of different energy interventions is evaluated using the new tier framework. The challenges in its application lie in reliable data collection, adequate gradation of indicators, and an effective algorithm for the tier assignment based on the specified set of attributes. The study showcases very high sensitivities to parameter changes, different algorithms, and data requirements. The results reveal a clear trade-off between capturing the multi-dimensionality of energy access and the simplicity of an easy to use global framework. Suggestions to improve the measuring approach are made and conclusions are drawn for possible implications of the tier framework for different energy service offers in the market. Strengths and weaknesses of the present measurement scheme are discussed and country specific results interpreted through targeted gap analysis for future policy advice

Advanced Operation and Maintenance in Solar Plants, Wind Farms and Microgrids

This reprint presents advances in operation and maintenance in solar plants, wind farms and microgrids. This compendium of scientific articles will help clarify the current advances in this subject, so it is expected that it will please the reader