Experimental evaluation of a CPT-based 4-leg active power compensator For distributed generation

Four-wire microgrids (MGs) and distribution systems are inherently unbalanced with the presence of negative and zero sequence components in voltages and currents. In small autonomous systems, the imbalance, in addition to the harmonic distortion produced by nonlinear loads, can significantly affect the power quality, loadability, and stability of the system. Furthermore, in isolated networks with significant generation from intermittent renewable energy sources, the stiffness of the system is reduced and this could amplify the effects of imbalance on the stability and power quality. To mitigate some of these problems, a novel methodology based on the application of a four-leg active power filter is proposed in this paper. The control of the compensator is based on the conservative power theory augmented by resonant controllers. The behavior of the proposed system is demonstrated using an experimental prototype deployed in a laboratory scale MG

Electronic/electric technology benefits study

The benefits and payoffs of advanced electronic/electric technologies were investigated for three types of aircraft. The technologies, evaluated in each of the three airplanes, included advanced flight controls, advanced secondary power, advanced avionic complements, new cockpit displays, and advanced air traffic control techniques. For the advanced flight controls, the near term considered relaxed static stability (RSS) with mechanical backup. The far term considered an advanced fly by wire system for a longitudinally unstable airplane. In the case of the secondary power systems, trades were made in two steps: in the near term, engine bleed was eliminated; in the far term bleed air, air plus hydraulics were eliminated. Using three commercial aircraft, in the 150, 350, and 700 passenger range, the technology value and pay-offs were quantified, with emphasis on the fiscal benefits. Weight reductions deriving from fuel saving and other system improvements were identified and the weight savings were cycled for their impact on TOGW (takeoff gross weight) and upon the performance of the airframes/engines. Maintenance, reliability, and logistic support were the other criteria

Key technologies of active power filter for aircraft: a review

Active Power Filter (APF) is not only an advanced technology to improve power quality and purify power system pollution but also a good approach to solve electrical problems of an advanced aircraft such as harmonic, reactive power and unbalanced load. However, there are still some specific problems for the application of aeronautic APF in practice. Based on current research on aeronautic APF, this paper reviews three key technologies where APF can be used in aircraft AC power supply system, including the acquisition method of reference current, the strategy of APF current control and the main circuit topology.  Consecutively, the features of current aeronautic APF research are summarized, and the future research directions are also suggested

Index to 1981 NASA Tech Briefs, volume 6, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1981 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Megawatt solar power systems for lunar surface operations

Lunar surface operations require habitation, transportation, life support, scientific, and manufacturing systems, all of which require some form of power. As an alternative to nuclear power, the development of a modular one megawatt solar power system is studied, examining both photovoltaic and dynamic cycle conversion methods, along with energy storage, heat rejection, and power backup subsystems. For photovoltaic power conversion, two systems are examined. First, a substantial increase in photovoltaic conversion efficiency is realized with the use of new GaAs/GaSb tandem photovoltaic cells, offering an impressive overall array efficiency of 23.5 percent. Since these new cells are still in the experimental phase of development, a currently available GaAs cell providing 18 percent efficiency is examined as an alternate to the experimental cells. Both Brayton and Stirling cycles, powered by linear parabolic solar concentrators, are examined for dynamic cycle power conversion. The Brayton cycle is studied in depth since it is already well developed and can provide high power levels fairly efficiently in a compact, low mass system. The dynamic conversion system requires large scale waste heat rejection capability. To provide this heat rejection, a comparison is made between a heat pipe/radiative fin system using advanced composites, and a potentially less massive liquid droplet radiator system. To supply power through the lunar night, both a low temperature alkaline fuel cell system and an experimental high temperature monolithic solid-oxide fuel cell system are considered. The reactants for the fuel cells are stored cryogenically in order to avoid the high tankage mass required by conventional gaseous storage. In addition, it is proposed that the propellant tanks from a spent, prototype lunar excursion vehicle be used for this purpose, therefore resulting in a significant overall reduction in effective storage system mass

New Trends in Active Power Filter for Modern Power Grids

From harmonic compensation to interface with renewable energy sources, active filters are capable to improve power quality, increase the reliability of the power grid, and contribute to make feasible the implementation of decentralized microgrids. In this scenario, this chapter provides a discussion involving new trends on distribution power grids, with active power filters playing an important key role. Considering the aforementioned explanation, part of the chapter covers active filter applications for power grids. In sequence, we discuss time domain control algorithms to identify power quality disturbances or other problems that may compromise the power grid reliability, with simulation results to evaluate the performance of the active filters for compensating power quality problems under transient- and steady-state conditions. Next, we discuss the integration of active filters with renewable energy sources (RENs) including a brief explanation of maximum power point tracking (MPPT) algorithms and other controllers considering a decentralized microgrid scenario with several active filters connected at the same grid circuit

Controle coordenado em microrredes de baixa tensão baseado no algoritmo power-based control e conversor utility interface

Orientadores: José Antenor Pomilio, Fernando Pinhabel MarafãoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: Esta tese apresenta uma possível arquitetura e sua respectiva estratégia de controle para microrredes de baixa tensão, considerando-se a existência de geradores distribuídos pela rede. A técnica explora totalmente a capacidade dos geradores distribuídos em ambos os modos de operação: conectado à rede e ilhado. Quando conectado à rede, sob o modo de otimização global, o controle busca a operação quase ótima da microrrede, reduzindo as perdas de distribuição e os desvios de tensão. Quando em modo ilhado, a técnica regula de forma eficaz os geradores distribuídos disponíveis, garantindo a operação autônoma, segura e suave da microrrede. A estratégia de controle é aplicada a uma estrutura de microrrede completamente despachável, baseada em uma arquitetura de controle mestre-escravo, em que as unidades distribuídas são coordenadas por meio do recém-desenvolvido algoritmo Power-Based Control. As principais vantagens da arquitetura proposta são a expansividade e a capacidade de operar sem sincronização ou sem conhecimento das impedâncias de linha. Além disso, a microrrede regula as interações com a rede por meio do conversor chamado de Utility Interface, o qual é um inversor trifásico com armazenador de energia. Esta estrutura de microrrede permite algumas vantagens como: compensação de desbalanço e reativo, rápida resposta aos transitórios de carga e de rede, e suave transição entre os modos de operação. Em contrapartida, para compartilhar a potência ativa e reativa proporcionalmente entre as unidades distribuídas, controlar a circulação de reativos, e maximizar a operação, a comunicação da microrrede requer em um canal de comunicação confiável, ainda que sem grandes exigências em termos de resolução ou velocidade de transmissão. Neste sentido, foi demonstrado que uma falha na comunicação não colapsa o sistema, apenas prejudica o modo de otimização global. Entretanto, o sistema continua a operar corretamente sob o modo de otimização local, que é baseado em um algoritmo de programação linear que visa otimizar a compensação de reativos, harmônicos e desbalanço de cargas por meio dos gerador distribuído, particularmente, quando sua capacidade de potência é limitada. Esta formulação consiste em atingir melhores índices de qualidade de energia, definidos pelo lado da rede e dentro de uma região factível em termos de capacidade do conversor. Baseado nas medições de tensão e corrente de carga e uma determinada função objetiva, o algoritmo rastreia as correntes da rede ótima, as quais são utilizadas para calcular os coeficientes escalares e finalmente estes são aplicados para encontrar as referências da corrente de compensação. Finalmente, ainda é proposta uma técnica eficiente para controlar os conversores monofásicos conectados arbitrariamente ao sistema de distribuição trifásico, sejam conectados entre fase e neutro ou entre fase e fase, com o objetivo de compensar o desbalanço de carga e controlar o fluxo de potência entre as diferentes fases da microrrede. Isto melhora a qualidade da energia elétrica no ponto de acoplamento comum, melhora o perfil de tensão nas linhas, e reduz as perdas de distribuição. A arquitetura da microrrede e a estratégia de controle foi analisada e validada através de simulações computacionais e resultados experimentais, sob condições de tensão senoidal/simétrica e não-senoidal/assimétrica, avaliando-se o comportamento em regime permanente e dinâmico do sistema. O algoritmo de programação linear que visa otimizar a compensação foi analisado por meio de resultados de simulaçãoAbstract: This thesis presents a flexible and robust architecture and corresponding control strategy for modern low voltage microgrids with distributed energy resources. The strategy fully exploits the potential of distributed energy resources, under grid-connected and islanded operating modes. In grid-connected mode, under global optimization mode, the control strategy pursues quasi-optimum operation of the microgrid, so as to reduce distribution loss and voltage deviations. In islanded mode, it effectively manages any available energy source to ensure a safe and smooth autonomous operation of the microgrid. Such strategy is applied to a fully-dispatchable microgrid structure, based on a master-slave control architecture, in which the distributed units are coordinated by means of the recently developed power-based control. The main advantages of the proposed architecture are the scalability (plug-and-play) and capability to run the distributed units without synchronization or knowledge of line impedances. Moreover, the proposed microgrid topology manages promptly the interaction with the mains by means of a utility interface, which is a grid-interactive inverter equipped with energy storage. This allows a number of advantages, including compensation of load unbalance, reduction of harmonic injection, fast reaction to load and line transients, and smooth transition between operating mode. On the other hand, in order to provide demand response, proportional power sharing, reactive power control, and full utilization of distributed energy resources, the microgrid employs a reliable communication link with limited bit rate that does not involve time-critical communications among distributed units. It has been shown that a communication failure does not jeopardize the system, and just impairs the global optimization mode. However, the system keeps properly operating under the local optimization mode, which is managed by a linear algorithm in order to optimize the compensation of reactive power, harmonic distortion and load unbalance by means of distributed electronic power processors, for example, active power filters and other grid-connected inverters, especially when their capability is limited. It consists in attain several power quality performance indexes, defined at the grid side and within a feasible power region in terms of the power converter capability. Based on measured load quantities and a certain objective function, the algorithm tracks the expected optimal source currents, which are thereupon used to calculate some scaling coefficients and, therefore, the optimal compensation current references. Finally, the thesis also proposes an efficient technique to control single-phase converters, arbitrarily connected to a three-phase distribution system (line-to-neutral or line-to-line), aiming for reduce unbalance load and control the power flow among different phases. It enhances the power quality at the point-of-common-coupling of the microgrid, improve voltage profile through the lines, and reduce the overall distribution loss. The master-slave microgrid architecture has been analyzed and validated by means of computer simulations and experimental results under sinusoidal/symmetrical and nonsinusoidal/asymmetrical voltage conditions, considering both the steady-state and dynamic performances. The local optimization mode, i.e., linear algorithm for optimized compensation, has been analyzed by simulation resultsDoutoradoEnergia EletricaDoutor em Engenharia Elétrica2012/24309-8, 2013/21922-3FAPES

Conceptual design study for an advanced cab and visual system, volume 2

The performance, design, construction and testing requirements are defined for developing an advanced cab and visual system. The rotorcraft system integration simulator is composed of the advanced cab and visual system and the rotorcraft system motion generator, and is part of an existing simulation facility. User's applications for the simulator include rotorcraft design development, product improvement, threat assessment, and accident investigation

Superfluid Helium Tanker (SFHT) study

Replenishment of superfluid helium (SFHe) offers the potential of extending the on-orbit life of observatories, satellite instruments, sensors and laboratories which operate in the 2 K temperature regime. A reference set of resupply customers was identified as representing realistic helium servicing requirements and interfaces for the first 10 years of superfluid helium tanker (SFHT) operations. These included the Space Infrared Telescope Facility (SIRTF), the Advanced X-ray Astrophysics Facility (AXAF), the Particle Astrophysics Magnet Facility (Astromag), and the Microgravity and Materials Processing Sciences Facility (MMPS)/Critical Point Phenomena Facility (CPPF). A mixed-fleet approach to SFHT utilization was considered. The tanker permits servicing from the Shuttle cargo bay, in situ when attached to the OMV and carried to the user spacecraft, and as a depot at the Space Station. A SFHT Dewar ground servicing concept was developed which uses a dedicated ground cooling heat exchanger to convert all the liquid, after initial fill as normal fluid, to superfluid for launch. This concept permits the tanker to be filled to a near full condition, and then cooled without any loss of fluid. The final load condition can be saturated superfluid with any desired ullage volume, or the tank can be totally filed and pressurized. The SFHT Dewar and helium plumbing system design has sufficient component redundancy to meet fail-operational, fail-safe requirements, and is designed structurally to meet a 50 mission life usage requirement. Technology development recommendations were made for the selected SFHT concept, and a Program Plan and cost estimate prepared for a phase C/D program spanning 72 months from initiation through first launch in 1997