Contenido

Son necesarias arquitecturas y herramientas para gestionar el flujo de energía de distintos tipos de fuentes hacia la red eléctrica. Por tanto, la microrgrid se puede clasificar en tres topologías:.

Microgrid AC

As for the AC type microgrid, the power supplies with AC output are interconnected with the AC bus through the AC/AC converter which will transform the variable AC frequency and voltage into an AC waveform with another frequency at another voltage. While power supplies with DC output use DC/AC converters for connection to the AC bus.[9]​.

DC Microgrid

In DC microgrid topology, power supplies with DC output are connected to the DC bus directly or via DC/DC converters. On the other hand, power supplies with AC output are connected to the DC bus through the AC/DC converter.[9]​.

Hybrid microgrid

The hybrid microgrid has a topology for the AC and DC output of the power supply. Additionally, the AC and DC buses are connected to each other through a bidirectional converter,[10]​ allowing power to flow in both directions between the two buses.[9]​.

Campus environment or institutional microgrids

The approach to campus microgrids is to aggregate existing on-site generation to support multiple loads located in a narrow geographic area,[11]​ where an owner can easily and quickly manage them[12]​.

Community microgrids

Community microgrids can serve thousands of customers and support local energy integration (electricity, heating and cooling). Some homes may have some renewable sources that can meet their demand as well as that of their neighbors within the same community. It can also have centralized or distributed energy storage. These microgrids can take the form of an AC and DC microgrid (as explained in the typologies) coupled together through a bidirectional power electronic converter.[13]​[14]​.

Remote off-grid microgrids

These microgrids are never connected to the macrogrid and instead operate in island mode at all times due to economic issues or geographic position. Typically, an “off-grid” microgrid is built in areas that are very far from any transmission and distribution infrastructure and therefore have no connection to the utility grid. Operating in a remote area that is dominated by renewable sources will reduce the levelized cost of electricity production over the life of such microgrid projects.[15]​.

Several independent microgrids can supply large remote areas, each with a different owner. Although these microgrids are designed to be self-sufficient in energy, intermittent renewable sources and their unexpected variations can cause unexpected power shortfalls or excessive generation in those microgrids. This will cause an unacceptable voltage or frequency deviation in the microgrids. To remedy such situations, it is possible to interconnect such microgrids provisionally to a nearby one to exchange power and improve voltage and frequency deviations. This can be achieved by a power electronics based switch after proper synchronization of two power electronic converters. Determining the need to interconnect neighboring microgrids and finding the appropriate microgrid to couple with can be achieved through optimization or decision-making approaches[16].

Military base microgrids

These microgrids are being actively deployed with a focus on physical and cyber security for military installations to ensure reliable power without relying on the macrogrid.[1]​[17]​.

Commercial and industrial (C&I) microgrids

This category of microgrids is maturing rapidly in North America and East Asia, specifically in the world's leading technological powers; However, the lack of standards limits it worldwide, which is why Europe has barely experimented with this category of microgrid yet.[18]​ The main reason for the installation of an industrial microgrid is due to the security of the energy supply. There are many manufacturing processes where a power supply disruption can cause large revenue losses and prolonged start-up time.[14]​ Industrial microgrids can be designed to supply near-zero emission circular economy industrial processes and can integrate combined heat and power (CHP) generation, powered by both renewable sources and waste processing.[19]​[20]​.

Local generation

One of the first fundamental components for the microgrid are the different types of generation sources that supply electricity, heating and cooling to the user. These sources are divided into two main groups:

Consumption

The second fundamental component of a microgrid consists of consumption, which simply refers to the elements that use electricity, heat and cooling, ranging from individual devices to the lighting and heating systems of buildings, shopping centers, etc. In the case of controllable loads, electricity consumption can be modified according to the demands of the network.

Energy storage

In microgrid, energy storage can perform multiple functions, which is why it is another of its fundamental components:.

On the other hand, when multiple energy storages with various capacities are available on a *microgrid, it is preferred to coordinate their charging and discharging so that a smaller energy storage is not discharged faster than those with larger capacities. Likewise, it is preferred that a smaller one not be fully charged before those with a larger capacity. This can be achieved under coordinated control of energy stores based on their state of charge. If multiple energy storage systems are used (working on different technologies) and controlled by a single supervisory unit (an energy management system) and hierarchical control based on a master-slave architecture can ensure the best operations.[21]​.

Point Common Coupling (PCC)

Finally we have the PCC which is the point in the electrical circuit where a microgrid is connected to a main grid. They also highlight a series of microgrids that do not have a PCC and are called isolated microgrids that are generally present in remote sites where an interconnection with the main network is not feasible due to technical or economic limitations.[20]​.

Advantages

A microgrid is capable of operating in grid-connected and autonomous mode and handling the transition between the two:.

Microgrids offer an option to balance the need to reduce carbon emissions with continuing to provide reliable electrical power in periods of time when renewable energy sources are not available. They also offer the security of being reinforced for severe weather and natural disasters by not having large assets and miles of above-ground cables and other electrical infrastructure that must be maintained or repaired after such events.[22]​.

Additionally, you can switch between these two modes due to:.

By modifying the flow of energy through the components of microgrids, they facilitate the integration of renewable energies, such as photovoltaic, wind and fuel cell generations, without the need to redesign the national distribution system. Modern optimization methods can also be incorporated into the microgrid energy management system to improve efficiency and economics.[23]​[24]​.

Challenges

Microgrids, and the integration of DER units, introduce a series of operational challenges that must be addressed in the design of control and protection systems, with the aim of ensuring that current levels of reliability are not affected and the benefits of Distributed Generation (DG) units are fully exploited. Some of these challenges arise from assumptions normally applied to conventional distribution systems that are no longer valid, while others are the result of stability problems that were previously only observed at the transmission system level.[22]​ The most relevant challenges in the protection and control of microgrids include:.

Modeling tools

To plan and install microgrids correctly, an engineering model is necessary. There are multiple simulation and optimization tools to model the economic and electrical effects of microgrids. A widely used economic optimization tool is the Distributed Energy Resources Customer Adoption Model (DER-CAM) from Lawrence Berkeley National Laboratory.[26] Another is Homer Energy, designed by the National Renewable Energy Laboratory. There are also some electrical and power flow design tools that guide microgrid developers.[23]​ The Pacific Northwest National Laboratory designed the publicly available GridLAB-D tool and the Electric Power Research Institute (EPRI) did the same with OpenDSS. A European tool that can be used for electrical, cooling, heating and process heat demand simulation is EnergyPLAN from Aalborg University in Denmark. The open source network planning tool OnSSET has been implemented to investigate microgrids using a three-level analysis starting with settlement archetypes[22].

It should be noted that control and protection are difficulties for microgrids, since all auxiliary services for system stabilization must be generated within the microgrid and low short circuit levels can be a challenge for the selective operation of protection systems. An important characteristic is also the proportion of multiple useful energy needs, such as heating and cooling in addition to electricity, because it allows the substitution of energy carriers and greater energy efficiency thanks to the waste heat that is intended for heating, hot water and cooling.[18]​.

With respect to the control architecture of microgrids, or any control problem, there are two different approaches that can be identified:.

Advanced Microgrid Montgomery, USA

Montgomery County in Maryland (USA) is making important advances in sustainability and energy security through the use of microgrids that improve the resilience of the county, in order to keep its residents safe and provide necessary services even in the case of prolonged power outages such as those that are occurring in several municipalities in China in late 2021. The Advanced Microgrid solution, from Schneider Electric and Duke Energy Renewables, installed at the Public Safety Headquarters in Gaithersburg, has received the maximum PEER certification (Performance Excellence in Electricity Renewal). They have achieved that 33% of total consumption comes from solar energy, 66% from a local cogeneration system and the wiring network is 100% underground.

This project is part of a larger one, which has been initiated to implement two Advanced Microgrids, one at PSHQ and another at the Montgomery County Correctional Facility in Boyds (Washington), two facilities that require continuous access to power to ensure their security and operational integrity.[29]​.

Hajjah and Lahj, Yemen

The UNDP project “Enhanced Rural Resilience in Yemen” uses community-owned solar microgrids reducing energy costs by about 2 cents per hour. It won the Ashden Humanitarian Energy Awards in 2020.[30][31]​.

Île d'Yeu

A two-year pilot program, called Harmon'Yeu, was started in 2020 during the Coronavirus pandemic lockdowns to interconnect 23 houses in the Ker Pissot neighborhood and surrounding areas with a microgrid that was automated as a smart grid with software from Engie. The process led to the installation of 64 solar panels with a maximum capacity of 23.7 kW in five houses and a battery with a storage capacity of 15 kWh was installed in one house. Six homes store excess solar energy in their water heaters. A dynamic system distributes the energy provided by the solar panels and stored in the battery and water heaters to the 23-home system. The smart grid software updates power supply and demand at 5-minute intervals, deciding whether to draw power from the battery or panels and when to store it in the water heaters. This program was the first project of its kind in France.[32]​.

Les Anglais, Haiti

A wirelessly managed microgrid is installed in rural Les Anglais, Haiti. The system consists of a three-tier architecture:

Non-technical loss represents a significant challenge when providing reliable electrical service in developing countries, where it often represents 11-15% of total generating capacity.[33]​ An extensive data-driven simulation on seventy-two days of wireless meter data from a 430-home microgrid deployed in Les Anglais investigated how to distinguish it from total energy losses, aiding in the detection of energy theft.[34]​.

Mpeketoni, Kenya

The Mpeketoni Electricity Project is a community-based diesel power microgrid system, which was established in rural Kenya near Mpeketoni. Due to the installation of these microgrids, Mpeketoni has experienced tremendous growth in its infrastructure. This growth includes an increase in productivity per worker, in values ​​of 100% to 200%, and an increase in the level of income from 20 to 70% depending on the product.

Stone Edge Farm Winery

A micro-turbine consists of a series of components:

All this enabled for PV in Sonoma, California.[35]​.

Schneider Electric, Barcelona

Iberdrola has installed a microgrid at the Schneider Electric plant in Barcelona, ​​with 990 solar panels, 5 electric vehicle charging points and a battery system, with a storage capacity of 216 kWh. Schneider Electric has also managed to convert the plant located in Molins de Rei into a Zero CO2 factory. [36][37]​.

Contenido

Son necesarias arquitecturas y herramientas para gestionar el flujo de energía de distintos tipos de fuentes hacia la red eléctrica. Por tanto, la microrgrid se puede clasificar en tres topologías:.

Microgrid AC

As for the AC type microgrid, the power supplies with AC output are interconnected with the AC bus through the AC/AC converter which will transform the variable AC frequency and voltage into an AC waveform with another frequency at another voltage. While power supplies with DC output use DC/AC converters for connection to the AC bus.[9]​.

DC Microgrid

In DC microgrid topology, power supplies with DC output are connected to the DC bus directly or via DC/DC converters. On the other hand, power supplies with AC output are connected to the DC bus through the AC/DC converter.[9]​.

Hybrid microgrid

The hybrid microgrid has a topology for the AC and DC output of the power supply. Additionally, the AC and DC buses are connected to each other through a bidirectional converter,[10]​ allowing power to flow in both directions between the two buses.[9]​.

Campus environment or institutional microgrids

The approach to campus microgrids is to aggregate existing on-site generation to support multiple loads located in a narrow geographic area,[11]​ where an owner can easily and quickly manage them[12]​.

Community microgrids

Community microgrids can serve thousands of customers and support local energy integration (electricity, heating and cooling). Some homes may have some renewable sources that can meet their demand as well as that of their neighbors within the same community. It can also have centralized or distributed energy storage. These microgrids can take the form of an AC and DC microgrid (as explained in the typologies) coupled together through a bidirectional power electronic converter.[13]​[14]​.

Remote off-grid microgrids

These microgrids are never connected to the macrogrid and instead operate in island mode at all times due to economic issues or geographic position. Typically, an “off-grid” microgrid is built in areas that are very far from any transmission and distribution infrastructure and therefore have no connection to the utility grid. Operating in a remote area that is dominated by renewable sources will reduce the levelized cost of electricity production over the life of such microgrid projects.[15]​.

Several independent microgrids can supply large remote areas, each with a different owner. Although these microgrids are designed to be self-sufficient in energy, intermittent renewable sources and their unexpected variations can cause unexpected power shortfalls or excessive generation in those microgrids. This will cause an unacceptable voltage or frequency deviation in the microgrids. To remedy such situations, it is possible to interconnect such microgrids provisionally to a nearby one to exchange power and improve voltage and frequency deviations. This can be achieved by a power electronics based switch after proper synchronization of two power electronic converters. Determining the need to interconnect neighboring microgrids and finding the appropriate microgrid to couple with can be achieved through optimization or decision-making approaches[16].

Military base microgrids

These microgrids are being actively deployed with a focus on physical and cyber security for military installations to ensure reliable power without relying on the macrogrid.[1]​[17]​.

Commercial and industrial (C&I) microgrids

This category of microgrids is maturing rapidly in North America and East Asia, specifically in the world's leading technological powers; However, the lack of standards limits it worldwide, which is why Europe has barely experimented with this category of microgrid yet.[18]​ The main reason for the installation of an industrial microgrid is due to the security of the energy supply. There are many manufacturing processes where a power supply disruption can cause large revenue losses and prolonged start-up time.[14]​ Industrial microgrids can be designed to supply near-zero emission circular economy industrial processes and can integrate combined heat and power (CHP) generation, powered by both renewable sources and waste processing.[19]​[20]​.

Local generation

One of the first fundamental components for the microgrid are the different types of generation sources that supply electricity, heating and cooling to the user. These sources are divided into two main groups:

Consumption

The second fundamental component of a microgrid consists of consumption, which simply refers to the elements that use electricity, heat and cooling, ranging from individual devices to the lighting and heating systems of buildings, shopping centers, etc. In the case of controllable loads, electricity consumption can be modified according to the demands of the network.

Energy storage

In microgrid, energy storage can perform multiple functions, which is why it is another of its fundamental components:.

On the other hand, when multiple energy storages with various capacities are available on a *microgrid, it is preferred to coordinate their charging and discharging so that a smaller energy storage is not discharged faster than those with larger capacities. Likewise, it is preferred that a smaller one not be fully charged before those with a larger capacity. This can be achieved under coordinated control of energy stores based on their state of charge. If multiple energy storage systems are used (working on different technologies) and controlled by a single supervisory unit (an energy management system) and hierarchical control based on a master-slave architecture can ensure the best operations.[21]​.

Point Common Coupling (PCC)

Finally we have the PCC which is the point in the electrical circuit where a microgrid is connected to a main grid. They also highlight a series of microgrids that do not have a PCC and are called isolated microgrids that are generally present in remote sites where an interconnection with the main network is not feasible due to technical or economic limitations.[20]​.

Advantages

A microgrid is capable of operating in grid-connected and autonomous mode and handling the transition between the two:.

Microgrids offer an option to balance the need to reduce carbon emissions with continuing to provide reliable electrical power in periods of time when renewable energy sources are not available. They also offer the security of being reinforced for severe weather and natural disasters by not having large assets and miles of above-ground cables and other electrical infrastructure that must be maintained or repaired after such events.[22]​.

Additionally, you can switch between these two modes due to:.

By modifying the flow of energy through the components of microgrids, they facilitate the integration of renewable energies, such as photovoltaic, wind and fuel cell generations, without the need to redesign the national distribution system. Modern optimization methods can also be incorporated into the microgrid energy management system to improve efficiency and economics.[23]​[24]​.

Challenges

Microgrids, and the integration of DER units, introduce a series of operational challenges that must be addressed in the design of control and protection systems, with the aim of ensuring that current levels of reliability are not affected and the benefits of Distributed Generation (DG) units are fully exploited. Some of these challenges arise from assumptions normally applied to conventional distribution systems that are no longer valid, while others are the result of stability problems that were previously only observed at the transmission system level.[22]​ The most relevant challenges in the protection and control of microgrids include:.

Modeling tools

To plan and install microgrids correctly, an engineering model is necessary. There are multiple simulation and optimization tools to model the economic and electrical effects of microgrids. A widely used economic optimization tool is the Distributed Energy Resources Customer Adoption Model (DER-CAM) from Lawrence Berkeley National Laboratory.[26] Another is Homer Energy, designed by the National Renewable Energy Laboratory. There are also some electrical and power flow design tools that guide microgrid developers.[23]​ The Pacific Northwest National Laboratory designed the publicly available GridLAB-D tool and the Electric Power Research Institute (EPRI) did the same with OpenDSS. A European tool that can be used for electrical, cooling, heating and process heat demand simulation is EnergyPLAN from Aalborg University in Denmark. The open source network planning tool OnSSET has been implemented to investigate microgrids using a three-level analysis starting with settlement archetypes[22].

It should be noted that control and protection are difficulties for microgrids, since all auxiliary services for system stabilization must be generated within the microgrid and low short circuit levels can be a challenge for the selective operation of protection systems. An important characteristic is also the proportion of multiple useful energy needs, such as heating and cooling in addition to electricity, because it allows the substitution of energy carriers and greater energy efficiency thanks to the waste heat that is intended for heating, hot water and cooling.[18]​.

With respect to the control architecture of microgrids, or any control problem, there are two different approaches that can be identified:.

Advanced Microgrid Montgomery, USA

Montgomery County in Maryland (USA) is making important advances in sustainability and energy security through the use of microgrids that improve the resilience of the county, in order to keep its residents safe and provide necessary services even in the case of prolonged power outages such as those that are occurring in several municipalities in China in late 2021. The Advanced Microgrid solution, from Schneider Electric and Duke Energy Renewables, installed at the Public Safety Headquarters in Gaithersburg, has received the maximum PEER certification (Performance Excellence in Electricity Renewal). They have achieved that 33% of total consumption comes from solar energy, 66% from a local cogeneration system and the wiring network is 100% underground.

This project is part of a larger one, which has been initiated to implement two Advanced Microgrids, one at PSHQ and another at the Montgomery County Correctional Facility in Boyds (Washington), two facilities that require continuous access to power to ensure their security and operational integrity.[29]​.

Hajjah and Lahj, Yemen

The UNDP project “Enhanced Rural Resilience in Yemen” uses community-owned solar microgrids reducing energy costs by about 2 cents per hour. It won the Ashden Humanitarian Energy Awards in 2020.[30][31]​.

Île d'Yeu

A two-year pilot program, called Harmon'Yeu, was started in 2020 during the Coronavirus pandemic lockdowns to interconnect 23 houses in the Ker Pissot neighborhood and surrounding areas with a microgrid that was automated as a smart grid with software from Engie. The process led to the installation of 64 solar panels with a maximum capacity of 23.7 kW in five houses and a battery with a storage capacity of 15 kWh was installed in one house. Six homes store excess solar energy in their water heaters. A dynamic system distributes the energy provided by the solar panels and stored in the battery and water heaters to the 23-home system. The smart grid software updates power supply and demand at 5-minute intervals, deciding whether to draw power from the battery or panels and when to store it in the water heaters. This program was the first project of its kind in France.[32]​.

Les Anglais, Haiti

A wirelessly managed microgrid is installed in rural Les Anglais, Haiti. The system consists of a three-tier architecture:

Non-technical loss represents a significant challenge when providing reliable electrical service in developing countries, where it often represents 11-15% of total generating capacity.[33]​ An extensive data-driven simulation on seventy-two days of wireless meter data from a 430-home microgrid deployed in Les Anglais investigated how to distinguish it from total energy losses, aiding in the detection of energy theft.[34]​.

Mpeketoni, Kenya

The Mpeketoni Electricity Project is a community-based diesel power microgrid system, which was established in rural Kenya near Mpeketoni. Due to the installation of these microgrids, Mpeketoni has experienced tremendous growth in its infrastructure. This growth includes an increase in productivity per worker, in values ​​of 100% to 200%, and an increase in the level of income from 20 to 70% depending on the product.

Stone Edge Farm Winery

A micro-turbine consists of a series of components:

All this enabled for PV in Sonoma, California.[35]​.

Schneider Electric, Barcelona

Iberdrola has installed a microgrid at the Schneider Electric plant in Barcelona, ​​with 990 solar panels, 5 electric vehicle charging points and a battery system, with a storage capacity of 216 kWh. Schneider Electric has also managed to convert the plant located in Molins de Rei into a Zero CO2 factory. [36][37]​.