Modeling and dynamic stability of distributed generations

The objective of this dissertation is to develop dynamic models for distributed generations (DG), to investigate their impacts on dynamic stability of power distribution systems, and to design controllers for DGs to improve the dynamic stability of the integrated power distribution system.;A two-year distributed generation (DG) project at West Virginia University (WVU) evaluated the impact of various DG sources on actual distribution systems by performing computer simulations. The data is supplied by two regional electric utilities of two actual distribution systems each. In this project several important issues were investigated, including the availability of simulation tools and impacts of DGs connected to a distribution line under a variety of line operating conditions. Based on this preliminary research the further most interesting topics for continued research were raised.;The continued research has focused on deeper investigation, such as, modeling DG sources, evaluating their interaction and impacts, and improving the dynamic stability of the integrated power distribution system. Four specific DGs are studied in this dissertation: fuel cell power plant, wind turbine induction generator, gas turbine synchronous generator and diesel engine synchronous generator.;A full-order synchronous generator model represents the generator models of gas turbine generator and diesel engine generator. A simplified gas turbine model has been chosen to be implemented. A practical diesel engine for emergency use is modeled. The generator model of wind turbine induction generator is represented by a full-order induction generator. The rated power operating regime is considered for impacts evaluations and controller design. Two types of fuel cell models are developed. The first one is a model of already operational phosphoric acid fuel cell (PAFC) obtained through data fitting and the second one is dynamic model of solid oxide fuel cell (SOFC). Since fuel cells are connected to the electric power network via inverters, an inverter model has been developed.;Multi-DG controls are investigated in this dissertation. One DG control is fuel cell control, the other one is wind-turbine control. The control of fuel cell (SOFC) plant is through the inverter to adjust active power injection to the network during the transient time. The control of wind turbine generator is through the parallel connected SVC by adjusting reactive power injection to the system. Both control schemes are centralized.;Linear analysis methodologies are utilized in designing the controller. In the fuel cell control design, two pairs of critical modes are screened out using eigenvalue analysis. The participation factors of DGs with respect to the modes are calculated. Two specific lead-lag compensation units are designed to damp each mode separately. The gains of the two compensation units were then obtained via optimal control methodology. In wind turbine DG control design procedure, three rotor speed deviations are used as input signals while the controller outputs are the firing angle for the SVC and the pitch angle for the wind-turbine DG. An output feedback controller is designed. The dynamic load characteristic is also considered by modeling it as a structured uncertainty. mu-analysis is used to evaluate the robust stability of the controllers with respect to the uncertain parameters in the dynamic loads. The IEEE-13 node radial feeder with existing gas turbine and diesel engine DGs is used as a test system to evaluate the multi-DG control. The simulation results demonstrate the effectiveness of the control strategies.;Coordinated operation of all the DGs is investigated. Simulation results show that good configurations within DGs along the system can improve the system stability. Furthermore, the fast acting SVC is very effective in improving damping. Among the DGs investigated in this research, the fuel cell plant control is the best choice for the coordinated operation.;Finally, the approach to model a complete three-phase power distribution system is implemented. The impact of the developed DGs models is evaluated on a three-phase unbalanced distribution system. The three-phase 13-node IEEE system with gas turbine and diesel engine DGs is simulated using MATLAB/Simulink\u27s Power System Blockset (PSB). In the simulation, a three-phase thyristor controlled braking resistor (TCBR) is connected to absorb the surplus energy when the system is subjected to a disturbance. The three-phase dynamic simulation demonstrates the effectiveness of the proposed strategy

Behavioral modelling and identification of power electronics converters and subsystems based on transient response

Nowadays, electrical engineers face significant changes in the way the electrical energy is generated and distributed to the consumers. On the one hand, the number of electronic and electrical loads in power distribution systems is continuously growing. Developments in power electronics technology during last decades have enabled the use of power-electronics-based subsystems as an alternative to mechanical, hydraulic and pneumatic subsystems, looking for more reliable and light systems, and a reduction in maintenance costs and environmental impact. On the other hand, due to the growth of alternative energy sources, power distribution systems supply the load not only from a single source but from a variety of energy sources such as batteries, fuel cells, solar panels and electromechanical generators. Consequently, power distribution systems are incorporating more and more power electronics converters, thus moving from traditional centralized architectures to distributed ones, where a variety of interconnected power converters supply a number of electrical and electronic loads with different voltage levels and dynamic requirements from a variety of energy sources. Current trends in power distribution systems for aircrafts, naval ships, hybrid/electric vehicles, telecommunications, datacenters, satellites as well as initiatives in micro-grids illustrate this concept. Such increase of power converters means increasing complexity of the power distribution architecture, at system-level rather than at converter-level. Dynamic interactions between regulated converters, activation of protections, connections and disconnections of load and sources are some problems to be faced by system engineers. Hence, modeling and simulation becomes a powerful system integration tool to ensure proper performance of the whole system at all operating conditions. However, modeling in power electronics have been traditionally focused on the design of the converters itself, rather than the integration of systems comprised of multiple converters. Most modeling approaches provide a detailed description of the internal signals of the power converter as well as requires detailed knowledge of its internal structure. However, new power distribution systems are comprised of a number of power converters provided by a variety of manufacturers. Companies need to protect their know-how, so they provide limited information about their products which is rarely sufficient to build a conventional average model or switching model. Also, excessively detailed models lead to unacceptable simulation time when large power distribution systems are analyzed. In order to cope with this lack of models, first proposals on system-level modeling of power converters have been recently proposed. The models are referred to as “behavioral models” since they only reproduces the behavior of the input-output voltages and currents and do not represent in detail the internal structure of the converter. Hence, they can be provided by the manufacturer while keeping confidential information. Moreover, behavioral models can be fully parameterized from a set of experimental measurements by the end user. However, the reported references so far are focused on DC-DC converters, either un-regulated or output voltage-regulated. The aim of this thesis is to propose novel system-level behavioral modeling and identification methods for several types of power electronics converters and other power-electronics-based subsystems typically integrated in power distribution architectures. The main characteristics of the proposed methods are the following ones: · The models are fully parameterized from a set of experimental tests and do not represent details about the internal structure of the modeled converter/subsystem. The models are simple, are built using dynamic transfer functions combined with nonlinear static functions, and reproduce the large-signal behavior of the converter/subsystem in terms of the signals required for system-level analysis, typically input-output voltage and currents. · The proposed identification method is based on the transient response of the input-output signals under a set of step tests. The tests are simple and can be carried out using low-cost equipment: switches, passive loads and a data acquisition system (e.g. an oscilloscope). From the transient response, a parametric identification algorithm is applied to identifiy transfer function models. --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------En la actualidad, los ingenieros eléctricos están haciendo frente a cambios significativos en la manera en que la energía eléctrica se genera y distribuye a los consumidores. Por una parte, el número de cargas eléctricas y electrónicas en los sistemas de distribución de potencia está creciendo significativamente. Los desarrollos en electrónica de potencia durante las últimas décadas permiten la utilización de subsistemas basados en electrónica de potencia como una alternativa a subsistemas mecánicos, hidráulicos y neumáticos. Ello permite obtener sistemas más robustos y ligeros así como menores costes de mantenimiento e impacto medioambiental. Por otra parte, debido al crecimiento de las fuentes de energía alternativas, las cargas en los sistemas de distribución de potencia son suministradas con energía proveniente de múltiples fuentes de energía, tales como baterías, paneles solares, generadores electromecánicos, pilas de combustible, etc. En consecuencia, los sistemas de distribución de potencia están incorporando más y más convertidores electrónicos de potencia, pasando de las tradicionales estructuras centralizadas a estructuras distribuidas. En estas últimas, una variedad de convertidores interconectados suministran potencia a varias cargas eléctricas y electrónicas, con distintos niveles de tensión y requerimientos dinámicos, desde varias fuentes de energía. Las tendencias actuales en sistemas para aviones, barcos, vehículos híbridos y eléctricos, telecomunicaciones, centros de datos, así como las microrredes ilustran este concepto. Tal incremento en el número de convertidores de potencia significa un incremento en la complejidad del comportamiento de los sistemas. Interacciones dinámicas entre convertidores regulados, activación de protecciones, conexión y desconexión de cargas y fuentes son algunos problemas a los que los ingenieros deben hacer frente. El modelado y la simulación son herramientas potentes para asegurar buenas prestaciones de los sistemas bajo todas las condiciones de funcionamiento. Sin embargo, el modelado en electrónica de potencia se ha enfocado tradicionalmente al diseño de los convertidores en sí mismo, en vez de a la integración de sistemas compuestos por múltiples convertidores. La mayoría de las técnicas de modelado dan una descripción detallada de las señales internas de los convertidores, y requieren un profundo conocimiento de la estructura interna de los mismos. Sin embargo, los nuevos sistemas de distribución de potencia están compuestos por convertidores y subsistemas suministrados por una variedad fabricantes. Las compañías necesitan proteger su “know-how”, y debido a ello dan información limitada de sus productos a los usuarios, la cual habitualmente es insuficiente para poder construir un modelo convencional (por ejemplo, un modelo promediado o un modelo conmutado). Por otra parte, utilizar modelos excesivamente detallados suele llevar a tiempos de simulación inaceptables cuando se simulan sistemas de potencia grandes. Con el fin de hacer frente a esta carencia de modelos, se han propuesto las primeras propuestas de modelado a nivel de sistema de convertidores de potencia en los últimos años. Estos modelos se denominan “modelos comportamentales” debido a que sólo reproducen el comportamiento de las señales de entrada/salida de los convertidores y además no representan en detalle su estructura interna. Esto permite que puedan ser suministrados por los fabricantes sin revelar información confidencial. Por otra parte, los modelos comportamentales pueden ser identificados a partir de ensayos eléctricos y medidas de la respuesta de entrada-salida, con lo cual los usuarios pueden obtener modelos de los equipos si el fabricante no los suministra. Sin embargo, por el momento las técnicas existentes se centran en convertidores CC-CC, bien no regulados o con tensión de salida regulada. El objetivo de esta tesis es proponer nuevas técnicas de modelado e identificación a nivel de sistema para convertidores electrónicos de potencia y otros subsistemas basados en convertidores, que típicamente se integran en arquitecturas de distribución. Las principales características de los métodos propuestos son las siguientes. · Los modelos no representan detalles sobre la estructura interna del convertidor/subsistema modelado. Los modelos son sencillos y se componen básicamente de funciones de transferencia dinámicas combinadas con funciones estáticas no lineales. Estos modelos reproducen el funcionamiento de gran señal del convertidor/subsistema modelado en términos de las señales requeridas para análisis a nivel de sistema, típicamente tensiones y corrientes de entrada/salida. · Los parámetros de los modelos se identifican completamente a partir de ensayos experimentales. El método de de identificación propuesto está basado en la respuesta transitoria de las señales de entrada/salida de los convertidores/subsistemas ante una serie de ensayos sencillos de tipo escalón. Los tests son sencillos y se pueden llevar a cabo utilizando equipos de bajo coste, tales como interruptores, cargas pasivas y un sistema de adquisición de datos (por ejemplo, un osciloscopio). A partir de la respuesta transitoria, se aplican algoritmos de identificación paramétrica para identificar modelos de función de transferencia

Distributed photovoltaic systems: Utility interface issues and their present status

Major technical issues involving the integration of distributed photovoltaics (PV) into electric utility systems are defined and their impacts are described quantitatively. An extensive literature search, interviews, and analysis yielded information about the work in progress and highlighted problem areas in which additional work and research are needed. The findings from the literature search were used to determine whether satisfactory solutions to the problems exist or whether satisfactory approaches to a solution are underway. It was discovered that very few standards, specifications, or guidelines currently exist that will aid industry in integrating PV into the utility system. Specific areas of concern identified are: (1) protection, (2) stability, (3) system unbalance, (4) voltage regulation and reactive power requirements, (5) harmonics, (6) utility operations, (7) safety, (8) metering, and (9) distribution system planning and design

Power Quality

Electrical power is becoming one of the most dominant factors in our society. Power generation, transmission, distribution and usage are undergoing signifi cant changes that will aff ect the electrical quality and performance needs of our 21st century industry. One major aspect of electrical power is its quality and stability – or so called Power Quality. The view on Power Quality did change over the past few years. It seems that Power Quality is becoming a more important term in the academic world dealing with electrical power, and it is becoming more visible in all areas of commerce and industry, because of the ever increasing industry automation using sensitive electrical equipment on one hand and due to the dramatic change of our global electrical infrastructure on the other. For the past century, grid stability was maintained with a limited amount of major generators that have a large amount of rotational inertia. And the rate of change of phase angle is slow. Unfortunately, this does not work anymore with renewable energy sources adding their share to the grid like wind turbines or PV modules. Although the basic idea to use renewable energies is great and will be our path into the next century, it comes with a curse for the power grid as power fl ow stability will suff er. It is not only the source side that is about to change. We have also seen signifi cant changes on the load side as well. Industry is using machines and electrical products such as AC drives or PLCs that are sensitive to the slightest change of power quality, and we at home use more and more electrical products with switching power supplies or starting to plug in our electric cars to charge batt eries. In addition, many of us have begun installing our own distributed generation systems on our rooft ops using the latest solar panels. So we did look for a way to address this severe impact on our distribution network. To match supply and demand, we are about to create a new, intelligent and self-healing electric power infrastructure. The Smart Grid. The basic idea is to maintain the necessary balance between generators and loads on a grid. In other words, to make sure we have a good grid balance at all times. But the key question that you should ask yourself is: Does it also improve Power Quality? Probably not! Further on, the way how Power Quality is measured is going to be changed. Traditionally, each country had its own Power Quality standards and defi ned its own power quality instrument requirements. But more and more international harmonization efforts can be seen. Such as IEC 61000-4-30, which is an excellent standard that ensures that all compliant power quality instruments, regardless of manufacturer, will produce of measurement instruments so that they can also be used in volume applications and even directly embedded into sensitive loads. But work still has to be done. We still use Power Quality standards that have been writt en decades ago and don’t match today’s technology any more, such as fl icker standards that use parameters that have been defi ned by the behavior of 60-watt incandescent light bulbs, which are becoming extinct. Almost all experts are in agreement - although we will see an improvement in metering and control of the power fl ow, Power Quality will suff er. This book will give an overview of how power quality might impact our lives today and tomorrow, introduce new ways to monitor power quality and inform us about interesting possibilities to mitigate power quality problems. Regardless of any enhancements of the power grid, “Power Quality is just compatibility” like my good old friend and teacher Alex McEachern used to say. Power Quality will always remain an economic compromise between supply and load. The power available on the grid must be suffi ciently clean for the loads to operate correctly, and the loads must be suffi ciently strong to tolerate normal disturbances on the grid

Systems design study of the Pioneer Venus spacecraft. Appendices to volume 1, sections 8-11 (part 3 of 3)

Power subsystem cost/weight tradeoffs are discussed for the Venus probe spacecraft. The cost estimations of power subsystem units were based upon DSCS-2, DSP, and Pioneer 10 and 11 hardware design and development and manufacturing experience. Parts count and degree of modification of existing hardware were factored into the estimate of manufacturing and design and development costs. Cost data includes sufficient quantities of units to equip probe bus and orbiter versions. It was based on the orbiter complement of equipment, but the savings in fewer slices for the probe bus balance the cost of the different probe bus battery. The preferred systems for the Thor/Delta and for the Atlas/Centaur are discussed. The weights of the candidate designs were based upon slice or tray weights for functionally equivalent circuitry measured on existing hardware such as Pioneers 10 and 11, Intelsat 3, DSCS-2, or DSP programs. Battery weights were based on measured cell weight data adjusted for case weight or off-the-shelf battery weights. The solar array weight estimate was based upon recent hardware experience on DSCS-2 and DSP arrays

Development of controllers using FPGA for fuel cells in standalone and utility applications

In the recent years, increase in consumption of energy, instability of crude oil price and global climate change has forced researchers to focus more on renewable energy sources.Though there are different renewable energy sources available (such as photovoltaic and wind energy), they have some major limitations. The potential techniques which can provide renewable energy are fuel cell technology which is better than other renewable sources of energy. Solid oxide fuel cell (SOFC) is more efficient, environmental friendly renewable energy source. This dissertation focuses on load/grid connected fuel cell power system (FCPS) which can be used as a backup power source for household and commercial units. This backup power source will be efficient and will provide energy at an affordable per unit cost. Load/grid connected fuel cell power system mainly comprises of a fuel cell module, DCDC converter and DC-AC inverter. This thesis primarily focuses on solid oxide fuel cell (SOFC) modelling, digital control of DC-DC converter and DC-AC inverter. Extensive simulation results are validated by experimental results. Dynamic mathematical model of SOFC is developed to find out output voltage, efficiency, over potential loss and power density of fuel cell stack. The output voltage of fuel cell is fed to a DC-DC converter to step up the output voltage. Conventional Proportional-Integral (PI) controller and FPGA based PI controller is implemented and experimentally validated. The output voltage of DC-DC converter is fed to DC-AC inverter. Different pulse width modulation-voltage source inverter (PWM-VSI) control strategy (such as Hysteresis Current Controller (HCC), Adaptive-HCC, Fuzzy-HCC, Adaptive Fuzzy-HCC, Triangular Carrier Current Controller (TCCC) and Triangular Periodical Current Controller (TPCC)) for DC-AC inverter are investigated and validated through extensive simulations using MATLAB/SIMULINK. This work also focuses on number of fuel cells required for application in real time and remedy strategies when one or few fuel cells are malfunctioning. When the required numbers of fuel cells are not available, DC-DC converter is used to step up the output voltage of fuel cell. When there is a malfunction in fuel cell or shortage of hydrogen then a battery is used to provide backup power

Integrated Power/Attitude Control System (IPACS) study. Volume 2: Conceptual designs

For abstract, see N74-22706

Distributed photovoltaic systems: Utility interface issues and their present status. Intermediate/three-phase systems

The interface issues between the intermediate-size Power Conditioning Subsystem (PCS) and the utility are considered. A literature review yielded facts about the status of identified issues