Archive for the ‘AC Grid’ Category

Conferencia “Motivación en Ingeniería Mecánica Eléctrica, Biomédica y Espacial”. Ciclo de Charlas de Motivación – Lugar Polideportivo Colegio Nacional San Juan de Chota, Chota – Perú. Lunes 20 Junio 2016 – 9 am. Organiza: Promoción Bodas de Plata 1987-1991 “Horacio Zeballos Gamez” – CN San Juan de Chota (in spanish)


Información en detalle disponible en:

https://radiotelescopesnanosatellite.wordpress.com/2016/06/17/conferencia-motivacion-en-ingenieria-mecanica-electrica-biomedica-y-espacial-ciclo-de-charlas-de-motivacion-lugar-polideportivo-colegio-nacional-san-juan-de-chota-chota-peru-lunes-20-junio/

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Single doubly fed induction machine with two fully controlled ac–dc power converters

Variable-Speed Concept Utilizing Doubly Fed Induction Generator (DFIG):In a variable-speed turbine with DFIG, the converter feeds the rotor winding, while the stator winding is connected directly to the grid. This converter, thus decoupling mechanical and electrical frequencies and making variable-speed operation possible, can vary the electrical rotor frequency. This turbine cannot operate in the full range from zero to the rated speed, but the speed range is quite sufficient. This limited speed range is caused by the fact that a converter that is considerably smaller than the rated power of the machine is used. In principle, one can say that the ratio between the size of the converter and the wind-turbine rating is half of the rotor-speed span. In addition to the fact that the converter is smaller, the losses are also lower. The control possibilities of the reactive power are similar to the full power-converter system. For instance, the Spanish company Gamesa supplies this kind of variable-speed wind turbines to the market. The forced switched power-converter scheme is shown in Figure. The converter includes two three-phase ac–dc converters linked by a dc capacitor battery. This scheme allows, on one hand, a vector control of the active and reactive powers of the machine, and on the other hand, a decrease by a high percentage of the harmonic content injected into the grid by the power converter.

Source:
Juan Manuel Carrasco, Leopoldo García Franquelo, Jan T. Bialasiewicz, Eduardo Galván, Ramón C. Portillo Guisado, Ángeles Martín Prats, José Ignacio León and Narciso Moreno-Alfonso “Power-Electronic Systems for the Grid integration of Renewable Energy Sources: A Survey”. IEEE Transactions on Industrial Electronics, Vol. 53, No. 4, August 2006


Other example of microgrid con cell fuel wind turbine PV microturbine battery bank and loads

This microgrid have different elements: wind turbine, photovoltaics, fuel cell, battery bank, microturbine and interconection with main grifd. The level power is little but it is a interesting microgrid for study. It is a typical AC microgrid with load distribuited in many locations into microgrid. Main grind is a sub-transmission network in 20 kV.

Image Source:
Aris L. Dimeas, Nikos D. Natziargyriou “Operation of Multiagent System for Microgrid Control” IEEE Transactions on Power Systems, Vol. 20, No. 3, August 2005.


Actions sequence for the market operation in the time domain and Powerflows and bids in the microgrid

The overall procedure is the following:

1. The Market Operator (MO) announces the prices for selling (SP) or buying (BP) energy to the Microgrid. Normally it is SP>BP.
2. The local loads announce their demands for the next 15 minutes and an initial price (DP) for the kWh. It is DP>BPand DP<SP.
3. The production units accept or decline the load offer according to an Auction Price (AP).
4. The negotiation continues for a specific time (5 min).
5. After the end of the negotiation time, all the units have adjusted their set points. If there is no production unit within the Microgrid to satisfy the load demand, the power is bought from the grid. In addition, the grid can be considered as a load too, so the production or storage units can sell energy to the grid.

Source:
Aris L. Dimeas, Nikos D. Natziargyriou “Operation of Multiagent System for Microgrid Control” IEEE Transactions on Power Systems, Vol. 20, No. 3, August 2005.


Example of General hybrid power system model

A simple block diagram of a hybrid power system is shown in Figure. The sources of electric power in this hybrid system consist of a diesel generator, a battery bank, a PV array, and a wind generator. The diesel generator is the main source of power around the world. The output of the diesel generator is regulated ac voltage, which supplies the load directly through the main distribution transformer. The battery bank, the PV array, and the wind turbine are interlinked through a dc bus. The RTU (Remote Terminal Unit) regulates the flow of power to and from the different units, depending on the load. The integration of a RTU into a hybrid power system is important to enhance the performance of the system. The overall purpose of the RTU is to give knowledgeable personnel the ability to monitor and control the hybrid system from an external control center. Since the hybrid systems of interest in this research are located in remote areas, the ability for external monitoring and control is of utmost importance. The RTU is interfaced with a variety of sensors and control devices located at key locations within the hybrid system. The RTU processes the data from these sensors and transmits it to a control center. In addition, the RTU is also capable of receiving control signals and adjusting parameters within the system without the physical presence of the operating personnel.

Source:
Richard W. Wies, Ron A. Johnson, Ashish N. Agrawal and Tyler J. Chubb “Simulink Model for Economic Analysis and Environmental Impacts of a PV With Diesel-Battery System for Remote Villages” IEEE Transactions on Power Systems, Vol. 20, No. 2, May 2005


Example de AC Microgrid with Diesels CHPs PVs Boilers and conextion with Main Grid

This a example of a AC microgrid with differents equipment from usually photovoltaic solar plant (PV), CHPs, boilers and diesel generators. Many electric lines and loads placed on a characteristic topology of new tendence in market electrical

Source:
In-Su Bae and Jin-O Kim “Phasor Discrete Particle Swarm Optimization Algorithm to Configure Micro-grids” Journal of Electrical Engineering & Technology, Vol. 7, No.1, pp. 9 -16, 2012


A block diagram of grid interconnection unit

There is a significative difference storage system and electric power system interconnection unit. The microgrid usually has as high power from grid point of view that it is connected to medium voltage fine, typically 15 kV in Poland. Although the power system interconnection unit has almost the structure as storage system, its primary voltage is in range of kilovolts and is sinusoidal. So, it requires different power electronic converter. It is assumed in Poland that all devices connected to 15 kV lines have to be joined using 50 Hz transformer. Hence, the grid interconnection unit can have a structure shown in Figure.

Source:
Piotr Biczel. “Power Electronic Converters in DC Microgrid”. IEEE 5th International Conference – Workshop, Compatibility in Power Electronics, CPE 2007. Poland.


Typical Power Plant Power Output and End-Use Power Demands

In addition to economic benefits, other motivations helping to drive the transition toward small-scale, decentralized energy systems include increased concern for environmental impacts of generation, most especially those related to climate change, increased concern for the vulnerability of our centralized energy systems to terrorist attacks, and increased demands for electricity reliability in the digital economy.
A sense of the dramatic decrease in scale that is underway is provided in Table (top), in which a number of generation technologies are listed along with typical power outputs. For comparison, some examples of power demands of typical end uses are also shown. While the power ratings of some of the distributed generation options may look trivially small, it is the potentially large numbers of replicated small units that will make their contribution significant. For example, the U.S. auto industry builds around 6 million cars each year. If half of those were 60-kW fuel-cell vehicles, the combined generation capacity of
5-year’s worth of automobile production would be greater than the total installed capacity of all U.S. power plants.

Source:
Gilbert M. Masters. “Renewable and Efficient Electric Power Systems”. Jhon Wiley & Sons, Inc., New Jersey. ISBN 0-471-28060-7. 2004


Characteristics of Copper Wire

Wire size in the United States with diameter less than about 0.5 in. is specified by its American Wire Gage (AWG) number. The AWG numbers are based on wire resistance, which means that larger AWG numbers have higher resistance and hence smaller diameter. Conversely, smaller gage wire has larger diameter and, consequently, lower resistance. Ordinary house wiring is usually No. 12 AWG, which is roughly the diameter of the lead in an ordinary pencil. The largest wire designated with an AWG number is 0000, which is usually written 4/0, with a diameter of 0.460 in. For heavier wire, which is usually stranded (made up of many individual wires bundled together), the size is specified in the United States in thousands of circular mills (kcmil). For example, 1000-kcmil stranded copper wire for utility transmission lines is 1.15 in. in diameter and has a resistance of 0.076 ohms per mile. In countries using the metric system, wire size is simply specified by its diameter in millimeters. In Table gives some
values of wire resistance, in ohms per 100 feet, for various gages of copper wire at 68◦F. Also given is the maximum allowable current for copper wire clad in the most common insulation

Source:
Gilbert M. Masters. “Renewable and Efficient Electric Power Systems”. Jhon Wiley & Sons, Inc., New Jersey. ISBN 0-471-28060-7. 2004


FACTS devices can enhance the power flow on existing power lines. For the transmission line shown in figure, the sending end voltage isVS∠δS, the receiving end voltage is VR∠δR and the equivalent impedance of parallel connected lines isX. The power transfer through the lines is given by:

FACTS equation

the figure also shows how FACTS devices act on the power transfer equation. The TCSC can change the impedance of the line, the STATCOM can control the voltage magnitude at

FACTS applications for increased power transfer

the terminal to which it is connected by injecting or absorbing reactive power and the UPFC can alter the phase angle of the sending end voltage, thus power flow through a line can be controlled in a number of ways.

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication

 


Evolution of electricity metering

Electricity meters are used to measure the quantity of electricity supplied to customers as well as to calculate energy and transportation charges for electricity retailers and network operators. The most common type of meter is an accumulation meter, which records energy consumption over time. Accumulation meters in consumer premises are read manually to assess how much energy has been used within a billing period. In recent years, industrial and commercial consumers with large loads have increasingly been using more advanced meters, for example, interval meters which record energy use over short intervals, typically every half hour. This allows the energy suppliers to design tariffs and charging structures that reflect wholesale prices and helps the customers understand and manage their pattern of electricity demand. Smart meters are even more sophisticated as they have two-way communications and provide a real-time display of energy use and pricing information, dynamic tariffs and facilitate the automatic control of electrical appliances

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication


Possible communication infrastructure for the Smart Grid

The communication infrastructure of a power system typically consists of SCADA systems with dedicated communication channels to and from the System Control Centre and a Wide Area Network (WAN). Some long-established power utilities may have private telephone networks and other legacy communication systems. The SCADA systems connect all the major power system operational facilities, that is, the central generating stations, the transmission grid substations and the primary distribution substations to the System Control Centre. The WAN is used for corporate business and market operations. These form the core communication networks of the traditional power system. However, in the Smart Grid,it is expected that these two elements of communication infrastructure will merge into a Utility WAN.
An essential development of the Smart Grid (see figure ) is to extend communication throughout the distribution system and to establish two-way communications with customers through Neighbourhood Area Networks (NANs) covering the areas served by distribution substations. Customers’ premises will have Home Area Networks (HANs). The interface of the Home and Neighbourhood Area Networks will be through a smart meter or smart interfacing device.

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication


Architecture of a DMSC

 

The figure shows the DMSC controller building blocks that assess operating conditions and find the control settings for devices connected to the network. The key functions of the DMSC are state estimation, bad data detection and the calculation of optimal control settings. The DMSC receives a limited number of real-time measurements at set intervals from the network nodes. The measurements are normally voltage, load injections and power flow measurements from the primary substation and other secondary substations. These measurements are used to calculate the network operating conditions. In addition to these real-time measurements, the DMSC uses load models to forecast load injections at each node on the network for a given period that coincides with the real-time measurements. The network topology and impedances are also supplied to the DMSC.
The state estimator uses this data to assess the network conditions in terms of node voltage magnitudes, line power flows and network injections. Bad measurements coming to the system will be filtered using bad data detection and identification methods.

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication


Distribution network active management scheme

The Figure is a schematic of a simple distribution network with distributed generation (DG).There are many characteristics of this network that differ from a typical passive distribution network. First, the power flow is not unidirectional. The direction of power flows and the voltage magnitudes on the network depend on both the demand and the injected generation. Second, the distributed generators give rise to a wide range of fault currents and hence complex protection and coordination settings are required to protect the network. Third, the reactive power flow on the network can be independent of the active power flows. Fourth, many types of DGs are interfaced through power electronics and may inject harmonics into the network. The Figure also shows a control scheme suitable for achieving the functions of active control. In this scheme a Distribution Management System Controller (DMSC) assesses the network conditions and takes action to control the network voltages and flows. The DMSC obtains measurements from the network and sends signals to the devices under its control. Control actions may be a transformer tap operation, altering the DG output and injection/absorption
of reactive power.

Source:
SMART GRID
TECHNOLOGY AND APPLICATIONS
Janaka Ekanayake
Cardiff University, UK
Kithsiri Liyanage
University of Peradeniya, Sri Lanka
Jianzhong Wu
Cardiff University, UK
Akihiko Yokoyama
University of Tokyo, Japan
Nick Jenkins
Cardiff University, UK
A John Wiley & Sons, Ltd., Publication

 


charge and discharge battery

The present post describe the charge and discharge process of a battery bank of a microgrid. This microgrid have a aleatory voltage with inferior and superior limit. The current and electric power of charge and discharge is in picture. This simulation has writing and processing on Matlab/Simulink of MathaWorth Inc. Actually my interest is the control, optimization and management of microgrid DC. Greetings from Perú.


 

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cargas residencial comercial

Cargas residenciales o domiciliarias, dado que tienen el mismo comportamiento junto con las cargas comerciales son simuladas en Matlab/Simulink  de MathWork Inc. y los resultados se muestran en el presente post. Se ha considerado un tiempo de simulación de 72 horas, para el cual se ha cargado los datos de registro de ambos tipos de cargas. Sirve como parte de un sistema mucho más grande en que las cargas eléctricas son una parte de los equipos y elementos que lo constituyen. Estamos hablando de redes de distribución o también microredes. Uno de los problemas que se tiene a simular es calibrar el eje horizontal a la escala de tiempo de simulación, dado que Matlab/Simulink cuenta estados, esta cantidad de estados resueltos por las ecuaciones tiene que luego ser escalados al tiempo de simulación. Redes eléctricas, microredes y SmartGrid son las cosas que me interesan.


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a hybrid ac-dc microgrid system

La figura muestra el concepto de un sistema híbrido ac/dc donde varias fuentes y cargas ac y dc son conectadas a sus correspondientes redes ac y dc. Las redes ac y dc están conectadas a través de dos transformadores y conversores trifásicos ac/dc bidireccionales. Pueden observar la diversidad de micro fuentes que se está utilizando en la descripción de la microred, incluye los diferentes dispositivos de electrónica de potencia que sirven para adecuar la energía eléctrica desde fuentes y para cargas eléctricas. Hay vehículos eléctricos conectados a la microred. Los generadores eólicos tienen diferentes configuración de control (diferentes tipos de turbinas eólicas). Un grupo electrógeno diesel también se da, dado que estos grupos se consideran los que en último caso darán energía a la microred eléctrica en situaciones ya críticas pero a la vez rentables en lo posible en economía. Para todo esto se crea modelos matemáticos de cada elemento y luego se integran en un solo programa en que se puedan cambiar las condiciones de trabajo y analizar las variables de respuesta de lo que se desea estudiar. Yo lo hago en Matlab/Simulink para quienes deseen que les brinde el servicio de asesoramiento.


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Limits of Harmonic Distortion

La distorción armónica total de la corriente de salida en el rango de operación de un generador debe ser menor que 5 % de la corriente fundamental. La tabla muestra el valor de los armónicos que no deben exceder esos límites, expresados en relación a la corriente fundamental. Se habla de armónicos pares e impares, interesan todos dado que dependiendo del armónicos los efectos son diferentes, algunos de ellos se les puede reconocer con los cinco sentidos, otros requieren equipos como Analizadores de Redes Eléctricas. Que hacer en lugares con alta distorción armónica?. Una de las formas más fáciles es colocar un transformador de impedancia y un transformador de aislamiento (corregirme si me equivoco). Sin embargo, estas cosas para instalaciones medianas y grandes resultan bastante caras y espaciosas, considerando también las pérdidas asociadas a su funcionamiento. Por lo tanto, como cliente es pararse bien frente a las empresas de electricidad y como autoproductor de electricidad es comprar un buen generador que cumpla las exigencias de calidad de energía eléctrica, de esta manera proteges tu inversión y obtienes una fiabilidad alta y rentabilidad bastante ya que el beneficio es para toda la instalación (máquinas y sistemas de iluminación que en condiciones adecuadas brinda clima laboral adecuado sin flickers y/o baja iluminación).


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Recommended Service Voltage Variation Limits

La tabla que se presenta acá son lo recomendados límites de variación de voltaje para circuitos que operan con voltajes de hasta 1000 voltios. Hay los límites en condiciones normales y los límites de operación extremos. Quiere decir que los diseñadores de equipos consideran estos valores para el cálculo, selección de materiales y condiciones de trabajo de los equipos eléctricos, electrónicos y electromecánicos que pudieran haber en cualquier instalación. Obviamente que equipos construidos con normas locales, en la vida van a cumplir las exigencias, así mismo, equipos que por cuestión de marca ponen exigencias a los usuarios para mantener el voltaje dentro de un valor determinado y el usuario tiene que hacer inversión en UPS, transformadores de aislamiento y demás cosas (“son las niñas bonitas estas marcas del mercado”). Por lo tanto, al ingreso del circuito estos valores son los recomendados, implica de ahí aguas adentro, el diámetro de los conductores, la topología de la red eléctrica, calidad de empalmes, calidad de contactos, conductores en ductos o bandejas, condiciones ambientales, etc.


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