Monday, March 05, 2007

Distribution and Microgrids

Resumen en español más abajo


"A microgrid is an integrated power delivery system consisting of interconnected loads and DER which, as an integrated system, can operate in parallel with the grid or in an intentional island mode. The integrated DER are capable of providing sufficient and continuous energy to a significant portion of the internal demand, and the microgrid possesses independent controls and can island and reconnect with minimal service disruption."
Definition considered for discussion at CERTS’ 2005 Symposium on Microgrids, held on June 17, at UC Berkeley Faculty Club, Berkeley CA. CERTS stands by “Consortium for Electric Reliability Technology Solutions”.


The MicroGrid concept developed by professor Robert H. Lasseter assumes a cluster of loads and microsources operating as a single controllable system that provides both power and heat to its local area. This concept provides a new paradigm for defining the operation of distributed generation. To the utility the MicroGrid can be thought of as a controlled cell of the power system. For example this cell could be controlled as a single dispatchable load, which can respond in seconds to meet the needs of the transmission system. To the customer the MicroGrid can be designed to meet their special needs; such as, enhance local reliability, reduce feeder losses, support local voltages, provide increased efficiency through use waste heat, voltage sag correction or provide uninterruptible power supply functions to name a few.

The microsources of special interest for MicroGrids are small (less than 100kW)units with power electronic interfaces. These sources, (typically microturbines, PV panels, and fuel cells) are placed at customers’sites. They are low cost, low voltage and have high reliable with few emissions. Power electronics provide the control and flexibility required by the MicroGrid concept. Correctly designed power electronics and controls insure that the MicroGrid can meet its customers as well as the utilities needs.

The above characteristics can be achieved using a system architecture with three critical components:

• Local microsource controllers
• System optimizer
• Distributed protection

Figure below illustrates the basic MicroGrid architecture. In this example the electrical system is assumed to be radial with three feeders A, B and C and a collection of loads. The radial system is connected to the distribution system through a separation device, usually a static switch. The feeder voltages at the loads are usually 480 volts or less. Feeder A indicates the presents of several microsources with one providing both power and heat. Each feeder has circuits breakers and power flow controllers. Consider the power flow controller near the heat load in feeder A. This controller regulates feeder power flow at a level prescribed by the Energy Manager. As loads down stream change the local microsources increase or decreases their power output to hold the power flow constant. In this figure feeders A and C are assumed to have critical loads and include microsources, while feed B is assumed to have non-critical loads which can be shed when necessary. For example when there are power quality problems on the distribution system the MicroGrid can island by using the separation device shown in the figure. The non-critical feeder can also be dropped using the breaker at B.

Microgrid  Architecture
Microgrid Architecture

Aditional Info

The Electric Distribution Program of the US DoE Office of Electricity supports distribution grid modernization. Under the GridWise Initiative Topic Area 4 (Microgrid Technology Development and Demonstration) the following proposals have been selected and awarded:

Microgrid Design, Development and Demonstration, GE Global Research. (Click here to see May 2006 project review)

Value and Technology Assessments to Enhance the Business Case for the CERTS Microgrid, University of Wisconsin, Madison. . (Click here to see May 2006 project review)


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Bulk Power System Dynamics and Control - VI, August 22-27, 2004, Cortina d’Ampezzo, Italy



Discussion of Session D1
Distribution and Microgrids

edited by
Peter Sauer
University of Illinois at Urbana-Champaign, Urbana, IL

Contributors

Manuel Burgos Payán University of Seville Spain
Roberto Caldon University of Padova Italy
Rachid Cherkaoui EPFL Switzerland
Gianfranco Chicco Politecnico di Torino Italy
Nijaz Dizdarevic Energy Institute Hrvoje Pozar Croatia
Christiane Eping Technical University of Darmstadt Germany
Alain Germond EPFL Switzerland
Mehdi Karrari Amirkabir University of Technology Iran
Don Koval University of Alberta Canada
Sture Lindahl ABB Power Technologies and Lund University Sweden
A.P. Sakis Meliopoulos Georgia Tech University USA
Peter Sauer University of Illinois at Urbana-Champaign USA
Antonio Simões-Costa UFSC Brazil
Costas Vournas NTUA Greece
Louis Wehenkel University of Liège Belgium

Discussion

Part 1 – Discussion of:
Paper D1-1.- Complex Reliability Constraints Affecting the Isolation and Restoration of Distribution Feeders Following a Blackout (D. O. Koval, J.Qiu, V.Dinavahi and A. A. Chowdhury)

Paper D1.2.- Wind Energy Integration in Distribution Networks: A Voltage-Stability Constrained Case Study (R. Cano Marín, A. Gómez Expósito and M. Burgos Payán)

Paper D1.3.- Control Issues in MV Distribution Systems with Large-scale Integration of Distributed Generation (R. Caldon, R. Turri, V.Prandoni and S.Spelta)

Sture Lindahl
I have a question for the second author (paper D1.2). We have all noticed that the introduction of distributed generation requires recoordination of the relay protection. In order to calculate the settings, we have to calculate the fault currents - both in directly grounded systems and in non-effectively grounded systems. A typical configuration is an induction generator, especially the doubly-fed induction generator. My question is related to the calculation of non-symmetrical fault currents from doubly-fed induction machines. Have you looked into that problem
and have you any solution.

Manuel Burgos Payán
No, we have only considered symmetrical 3-phase faults. In the paper we give some guidance on how to set the distance relay that is proposed to connect in a wind farm. We have only considered the induction generator (not doubly fed) connected directly to the grid and symmetrical faults.

Gianfranco Chicco
I have a question for the first paper (D1.1), about cold load pickup introduction in reliability studies. Cold load pickup depends on lack of load diversity, and is a time-dependent issue. I saw that in the paper the peak load is computed depending on the duration of the interruptions. Is it computed by taking into account that the interruption can occur during nighttime or during daytime, or is it computed by using a “worst” case? What is the effect of the load patterns in this analysis?

Don Koval
For the cold-load pickup, we did the worst case. For some systems, we actually monitored the system before you close the switch. This is to get an idea of the loads. One of the problems with cold-load pickup is the protection on the distribution system. The problem is the settings for faults that they don’t pick for overloads is set too high. For long outages, the feeder load can stay at 2 times for 20 to 30 minutes – it won’t diversify. Even though the media appeals to the people to use less, they use more. They figure they are entitled to their power. Particularly in Toronto there were appeals on TV to please cut power – when the ad went on, the load went up – so they had to dump them –they had to shed them. It’s difficult to get the cold-load pickup as a function of time and season. We have to get some general rule for the crews, so we just used the worst case.

Costas Vournas
I have a couple of questions for the second paper (D1.2). The first is on modeling. It seems from the slides that you modeled the wind generator connected through a transformer to a 132kV bus. In reality, at least in Greece, the wind farms generate at low voltage, and then they are connected at medium voltage with a distribution feeder going all the way to the substation. This may have a significant impact on how they respond. May I have a comment on how the distribution system was modeled?
Second question – on the voltage oscillations, was the system isolated or interconnected? If you have done some work on the analysis of the nature of this (including the controls of voltage regulators and such), have you done eigenvalue analysis?

Manuel Burgos Payán
This is a very preliminary study of the connection. The internal distribution network is really eliminated with the model – we have modeled the wind farm as a cluster – one generator represents all of them. We have not considered any of the real generators in the wind farm. Related to the voltage oscillation – as you have mentioned, it is present in a lot of cases - we haven’t studied the possible control of this oscillation. We have reduced the power of the wind farm eliminated for a fault. We haven’t done any eigenanalysis on the system – but it should be done.

Gianfranco Chicco
Question to prof. Caldon. You showed different modes of operation (PQ and Vf modes) and you can have transitions between these modes. To which local generators is this solution applicable and how is the transition between modes managed? A second comment is on the inclusion of reactive power limits in the analysis. It seems that the example presented refers to a high penetration of local generation (in rated values, the local generation is over 60% of the local load). With small generators, the effect of the reactive power limits becomes more important, and it is difficult to have local generators operating in voltage control mode. In this case, the local generators can be used in voltage following mode, e.g., with imposed power factor, as you suggested.

Roberto Caldon
The simulation demonstrated that it is possible to transition from one mode to the other. In particular the limit that we put on the current of the inverter had this operation. The other was with the voltage control of the distributed generation in the case of large scale integration. Small and large generators – there is a difference between them. Small generators are not in control of the voltage. The large generators (MW) can be controlled by the method we have proposed.

A.P. Sakis Meliopoulos
A general question for the last two papers (D1.2 and D1.3): Considering the fact that the manufacturers of the wind power equipment have interfaces to the system with power electronics with proprietary control, to what extent do you think the models and simulation of these systems would be accurate and credible. Many times we do not know the models because of proprietary control circuits.

Roberto Caldon
It is very difficult to answer this question.

Peter Sauer
But the future is bright for research.

Antonio Simões-Costa
A question to the author of the third paper (D1.3). Your paper emphasizes the importance of coordination of distributed generation. I have a general question about this. In practice, most of those DG plants are owned by independent producers and they are not owned by a single utility, so you have to get the information from a third party – not really involved with the utility directly. You will need to get information on line for this, so there are some practical issues in implementing a coordination as you have proposed. Can you please comment on that.

Roberto Caldon
Yes, you are right. The communication must be increased between the distributor and the producer – especially when the producer is independent. When the distribution system is complex, this communication must be stressed.

Sture Lindahl
I have a question for the author of the third paper (D1.3) and it is concerning the voltage control scheme that you are proposing. I like the idea of doing such a voltage control scheme for a distributed system. But if I understand you right, you have considered synchronous machines. How do you envisage this control scheme if you have induction machines?

Roberto Caldon
Generally the induction generators are small in rating, so it is less important to control. The question is very important for the high-rated generators that are embedded in the network.

Sture Lindahl
Just a follow up - I am thinking of wind farms with some 80 units rated at 2MW connected at the 130kV level - they are by no means insignificant.

Part 2 – Discussion of:
Paper D1.4.- Control of Offshore Wind Farms for a Reliable Power System Management (C.Eping and J.Stenzel)

Paper D1.5.- Small Signal Stability Analysis of the Integrated Power System - MicroGrid Model (A. P. Sakis Meliopoulos and G. J. Cokkinides)

Alain Germond
In the wind farms, what is the distance between two generators?

Christiane Eping
The distance between the generators is dependent on the size of the generators –generally about 750 meters.

Nijaz Dizdarevic
I have question for Ms. Eping concerning the master control units. You are mostly concerned with the shutting down procedures in the wind power plant since it happens abruptly. How about starting up procedures, when wind is coming – perhaps there should be limits there as well. Do you have any intentions to go that way.

Christiane Eping
Up till now I have not done any research on the upcoming of the wind. I think when the wind is coming, it is not in two seconds going from zero to 25 meters per second, so we are not going from zero to 200% of the wind farm. I don’t know how they are doing it now, but I think it is much easier to control that.

Mehdi Karrari
My question goes to paper D1.5. My question is about the concept of inertia-less-ness in microgrids. In megagrids, the thing that affects small signal stability is the inertia. But, you said this is not there in microgrids, so what is it that affects stability the most – parameters or control? You mentioned that by some sort of control strategy, the system may look like a synchronous generator from the outside. Does that system have inertia?

A.P. Sakis Meliopoulos
If I understand your question, you are asking what causes the modes of oscillations – is it the parameters of the network, or the control strategy of the inverter - the answer is both. In this particular case, the two distributed energy resources are 12 miles apart. The controls interact. The control strategy depends on the impedances between the resources. If the controls changed, the modes of oscillation change. The case I mentioned is that a certain manufacturer basically works on a control methodology that uses the storage on the DC bus to make the inverter behave as an inertia device. In many cases in static VAR compensators and so on it is desirable to have the inverter behave as an inertia device. In many cases the generator saves the day because of its inertia.

Gianfranco Chicco
Question to Sakis Meliopoulos: you showed examples with microturbine models. Did you find any unstable case with these models?

A.P. Sakis Meliopoulos
With this particular model with generic segregated phase inverters, there were no unstable modes in all the cases considered.

Sture Lindahl
A simple question to the author of the fourth paper (D1.4). I am a little bit puzzled by the requirements from the TSO concerning the smooth shut down of a 500 MVA wind farm in the central European system where there are at least two generating units with a rated capacity of 1640 MW that can trip immediately and you have a large fleet of 1300 and 900MW nuclear units in France that can trip immediately. Why is it necessary to smoothly shut down a 500MW unit?

Christiane Eping
I am looking in the future. Today it is not necessary, but the wind energy is expected to triple in coming years – mainly offshore. If we have that offshore, there may be many wind farms that will all shut down. This might be a problem. We also only have 3.6MW turbines today, but we plan to have 4.5MW turbines offshore, so the size of the wind farms will go up. So, we will have 1000MW wind farms rather than
500MW.

Louis Wehenkel
Concerning these interactions among generators, I was wondering about the range of frequencies when they start to be unstable.

A.P. Sakis Meliopoulos
Depending on the type of distributed energy resource, the frequency may not be relevant – for example, the fuel cell generates DC, so the frequency deviation is the same as the grid. On a wind farm if the interface is through power electronics, the frequency deviation on the wind side could be tremendous, but on the AC side it would be a small deviation – I hope I understood your question correctly.

Louis Wehenkel
Sorry, I was not clear - I was wondering about the eigenfrequency of the unstable modes. What is the order of magnitude?

A.P. Sakis Meliopoulos
Oh, I see. I don’t remember the range, but basically through the method that I mentioned where you can go from the discrete eigenvalues into an equivalent analog system eigenvalues, you can compute the modes of oscillation –typically they are in the low range – on the case of the Chesterton system they are below 1200 Hz.

Don Koval
A quick one on the wind farms. Each unit has a different output. The generator output of each unit is unique because of the separation of the units. So, when you report to the transmission operator, do you take into account that the outputs of the individual units are different over time?

Christiane Eping
I don’t know if I understood your question right, but I give the operator only the total wind farm output. It is not about the individual units.

Rachid Cherkaoui
I have a question concerning the stability of the microgrid. In your paper the last figure shows some eigenvalues that are poorly damped. What kind of device can be used to damp them – can you use the standard PSS?

A.P. Sakis Meliopoulos
The paper shows that as more units are added to the system there are more modes of oscillations in the system. In my opinion, the best way to damp these oscillations is to rethink the controllers of the inverters. These inverters can utilized as a compensator to mitigate the oscillations. Whenever we sense the oscillations, we might switch to a different control mechanism. We might use additional static VAR compensators, or something that will have a negative feedback. Why not use the inverter themselves as the control? The University of Illinois has a center on this type of thing.

Selected bibliography.

From The Economist print edition: The dawn of micropower Aug 3rd 2000

Robert H. Lasseter, Paolo Piagi. Industrial Application of MicroGrids PSERC: October 2001.

Robert Lasseter, A. P. Sakis Meliopoulos, Giri Venkataramanan, Microgid Operation and Control HICSS-34 Tutorial 14. January 3, 2001.

Robert Lasseter, Abbas Akhil, Chris Marnay, John Stevens, Jeff Dagle, Ross Guttromson, A. Sakis Meliopoulous, Robert Yinger, and Joe Eto. The CERTS Microgrid Concept Consortium for Electric Reliability Technology Solutions.
White Paper on Integration of Distributed Energy Resources. April, 2002

Sakis Meliopoulos, A.P. (2003), Cokkinides, George J., and Lasseter, Robert. A MultiPhase Power Flow Model for µGrid Analysis36th Hawaii International Conference on System Sciences.

Robert H. Lasseter, Paolo Piagi. University of Wisconsin-Madison. Madison, Wisconsin
Microgrid: A Conceptual Solution. PESC’04 Aachen, Germany 20-25 June 2004

Chris Marnay, Ernest and Owen C Bailey, Orlando Lawrence Berkeley National Laboratory.The CERTS Microgrid and the Future of the Macrogrid. ACEEE 2004 Summer Study on Energy Efficiency in Buildings, Asilomar Conference Center, Pacific Grove CA, 22-27 Aug 2004

Suleiman Abu-Sharkh, Rachel Li, Tom Markvart,
Neil Ross, Peter Wilson, Runming Yao,
Koen Steemers, Jonathan Kohler and Ray Arnold. Microgrids: distributed on-site generation Tyndall Centre for Climate Change Research. March 2005.

California PIER. Energy Systems Integration. Presentations from the June 17, 2005 CERTS Berkeley 2005 Symposium on Microgrids

J. A. Peças Lopes, C. L. Moreira, F. O. Resende. Microgrids Blackstart and Islanded operation 15th Power Systems Computation Conference August 22-26, 2005 Liège, Belgium.

Lars Gertmar, Per Karlsson, Olof Samuelsson. (Lund University - Sweden) On DC Injection to AC Grids from Distributed Generation EPE 2005 - Dresden

Femmy M Combrink, Peter T M Vaessen, KEMA, Low voltage, but high tension. www.leonardo-energy.org. June 2006.

Paolo Piagi. Autonomous Control of Microgrids. IEEE PES Meeting, Montreal, June 2006

Poonum Agrawal, U.S. Department of Energy; Mark Rawson, California Energy Commission; and Stan Blazewicz and Forrest Small, Navigant Consulting Inc. How ‘Microgrids’ are Poised To Alter The Power Delivery Landscape Utility Automation Engineering T&D August, 2006.

Hassan Nikkhajoei and Robert H. Lasseter, Microgrid Fault Protection Based on Symmetrical and Differential Current Components". February 5, 2007. PSERC



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Micro-Redes

El concepto de MicroGrid implica la existencia de una agregación ("cluster") de cargas y microfuentes que operan como un único sistema controlable para suministrar potencia eléctrica y energía calorífica en su área local. Este concepto introduce un nuevo paradigma en la definición de la operación de la generación distribuida que aporta ventajas tanto a la empresa eléctrica de distribución como al cliente. Para la empresa eléctrica de distribución la MicroGrid es como una "celda controlada" del sistema de distribución. Por ejemplo esta celda podría controlarse como una sola carga despachable que puede responder en segundos para cumplir con los requerimientos del sistema de distribución. Para el cliente la MicroGrid puede proyectarse para que proporcione la calidad de potencia que requieran sus cargas o atienda sus necesidades especiales, como pueden ser la mejora de la fiabilidad local, la reducción de las pérdidas en los circuitos, el mantenimiento de las tensiones locales, obtener mayor eficiencia a partir del calor residual, eliminar los huecos de tensión, etc., solo por mencionar algunas.

Las microfuentes de las MicroGrids son pequeñas unidades Las microfuentes de las MicroGrids son pequeñas unidades (menos de 100 kW) con interfaces de electrónica de potencia. Estas fuentes (típicamente microturbinas, paneles fotovoltaicos, y pilas de combustible) están colocadas en los sitios de los clientes. Son baratas, de baja tensión, fiables y de bajas emisones. La electrónica de potencia facilita el control y la flexibilidad que exige el concepto de MicroGrid. Diseñados correctamente, la electrónica de potencia y los controles garantizan que la MicroGrid puede cumplir con las necesidades de sus clientes y de la compañía eléctrica. Las características descritas se pueden lograr empleando una arquitectura del sistema con tres componentes críticos:

• Los controladores de las microfuentes locales
• El optimizador del sistema
• La protección distribuida

Microgrid  Architecture
Arquitectura de una Micro-Red


La figura de arriba ilustra la arquitectura básica de la MicroGrid: En este ejemplo se supone que la MicroGrid es un sistema eléctrico radial de tres alimentadores A, B, y C, y una serie de cargas. El sistema radial está acoplado al sistema de distribución de la compañía eléctrica mediante un dispositivo de separación, normalmente un conmutador estático. Las tensiones de los alimentadores y de las cargas son normalmente de 480 V o inferiores. El alimentador A tiene varias microfuentes, una de las cuales suministra electricidad y calor. Cada alimentador tiene interruptores y controladores del flujo de potencia. Considérese el controlador del flujo de potencia que hay al lado de la carga calorífica en el alimentador A. Este controlador regula el flujo de potencia como le prescribe el Gestor de Energía. Cuando las cargas aguas abajo varían, las microfuentes aumentan o disminuyen su entrega de potencia para mantener el flujo de potencia constante. En esta figura se ha supuesto que los alimentadores A y C tienen cargas críticas y también microfuentes, mientras que el alimentador B tiene cargas que no son críticas que se pueden deslastrar cuando sea necesario. Por ejemplo cuando se presenten problemas de calidad de onda en el sistema de distribución la MicroGrid se puede aislar como una isla empleando el dispositivo de separación mostrado en la figura. El alimentador que no es crítico también se puede separar con el interruptor en B.

El Controlador de la Microfuente
Es un elemento importante de la infraestructura de la MicroGrid. Este controlador responde en milisegundos y utiliza información local para controlar la microfuente durante todos los eventos. Un factor clave es que no se necesitan comunicaciones entre las microfuentes para la operación básica. Cada inversor es capaz de responder a los cambios de carga de una manera predeterminada sin comunicación de datos desde otras fuentes o localizaciones, lo cual habilita las capacidades de “plug and play”. El “plug and play” (reconocimiento automático de un dispositivo por el sistema) implica que se puede añadir una microfuente a la MicroGrid sin hacer cambios en la protección y el control de las unidades que ya son parte del sistema. Los "inputs" básicos a este controlador son los puntos de consigna de régimen permanente para la potencia de salida, P, y la tensión del bus local, V.

La integración de muchas microfuentes que implica el concepto de MicroGrid no es posible sin controles P-Q básicos. La regulación de tensión es necesaria para la estabilidad y fiabilidad locales. Sin un control de tensión local, los sistemas con una alta penetración de microfuentes pueden experimentar oscilaciones de tensión y de potencia reactiva. El control de tensión exige cuidado para asegurar que no se producen grandes circulaciones de reactiva entre fuentes. Se trata de aspectos idénticos a los que encontramos en el control de los grandes generadores síncronos. En la red de alta, la impedancia entre generadores es normalmente lo bastante alta como para reducir la posibilidad de corrientes de circulación. En una MicroGrid, que es típicamente radial, el problema de grandes circulaciones de reactiva es inmenso. Con pequeños errores en los puntos de consigna de tensión la corriente de circulación puede sobrepasar los valores nominales de las microfuentes. Esta situación exige un controlador V-Q. Básicamente, cuando la corriente reactiva generada por la microfuente se vuelve más capacitiva se reduce el punto de consigna de la tensión local: y recíprocamente, cuando la corriente se vuelve más inductiva se aumenta el punto de consigna.

Funcionamiento de la MicroGrid
Las microrredes pueden proporcionar potencia de calidad por su capacidad de pasar suavemente de la modalidad de operación de despacho de potencia (cuando están acopladas a la red de distribución de la compañía eléctrica), a la modalidad de seguimiento de la carga (cuando operan en isla desacopladas de la red de distribución de la empresa eléctrica). Bajo la modalidad de operación en isla, asuntos que implicarían la necesidad de disponer de un sistema de comunicaciones complejo, como la corrección de las pequeñas variaciones de frecuencia de generación en cada convertidor en torno a su valor nominal y los cambios de los puntos de consigna ("set points" en la jerga SCADA) para adecuar la generación a los cambios de la carga, se pueden enfocar empleando funciones de control frecuencia-potencia en cada microfuente sin necesidad de disponer de una red de comunicaciones dedicada.

Cuando está acoplada a la red, las cargas de la MicroGrid reciben potencia tanto de la red de distribución de la compañía eléctrica como de las microfuentes locales, dependiendo de la situación del cliente. Cuando se producen pérdidas en la red de distribución de la empresa eléctrica debido a caídas de tensión, faltas, cortes, etc., la MicroGrid pasa suavemente a operar bajo la modalidad en isla. Cuando la MicroGrid se desacopla de la red de distribución de la empresa eléctrica, los ángulos de fase de la tensión en cada microfuente de la MicroGrid varían originando una reducción aparente de la frecuencia local. Esta reducción de frecuencia lleva aparejada un aumento de potencia aportada por microfuentes locales que se reparte entre las microfuentes de manera que cada una de ellas proporciona una parte de la variación de la carga que experimenta la MicroGrid sin que sea necesaria la intervención del Gestor de Energía para despachar nueva carga. De hecho en la operación en isla no se usa el Gestor de Energía excepto para reacoplar la MicroGrid a la red de distribución de la compañía eléctrica.

El Gestor de Energía
El Gestor de Energía se encarga de la optimización del sistema. Valiéndose de la información local referente a las necesidades de electricidad y energía calorífica, exigencias de calidad de onda, precios de la electricidad y el gas, requisitos especiales de la red, requerimientos de gestión de la demanda, etc., el Gestor de Energía determina la cantidad de potencia que debe absorber la MicroGrid del sistema de distribución de la compañía eléctrica. Algunas de sus funciones más importantes son:

• Facilitar el set point de potencia y tensión a cada controlador de microfuente y de flujo de potencia
• Garantizar que se atienden las cargas eléctricas y caloríficas
• Garantizar que la MicroGrid cumple los contratos de funcionamiento establecidos con el sistema de distribución de la compañía eléctrica
• Reducir las emisiones y las pérdidas del sistema
• Optimizar el rendimiento de las microfuentes.
• Facilitar la lógica y el control para desacoplar la MicroGrid de la red de distribución de la empresa eléctrica y ponerla a operar en isla, así como para realizar el proceso inverso de reacoplar la MicroGrid a la red de distribución.

Protecciones
Tienen que responder tanto a las faltas de la red de distribución de la compañía eléctrica como a las de la MicroGrid. Si la falta se produce en aquella, la respuesta deseada debe ser desacoplar la MicroGrid de ella tan rápidamente como sea necesario para proteger las cargas de la MicroGrid. La velocidad de desacoplamiento depende de las cargas específicas de cliente que tenga la MicroGrid.

En algunos casos se pueden compensar los huecos de tensión para proteger cargas críticas sin desacoplar la MicroGrid. Si la falta se produce en el interior de la MicroGrid, la coordinación de protecciones aisla la sección más pequeña posible del alimentador radial afectado para eliminar la falta.

En el texto en inglés de arriba se facilita más información, referencias y una bibliografía.

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