Anatomy of a Micro-Grid

The main components of a micro-grid include:

• Distributed Energy Resources (DER) for energy generation and storage

• Electrical Infrastructure to allow power to flow between the DER’s

•  Point of Interconnection (POI) to the utility grid for use as another system resource 

•  Switch for dual-mode operation to transition between islanding and grid-connected modes by disconnecting and reconnecting to the grid at any time 

•  Communication infrastructure to allow data to flow through the system 

•  Control systems for managing the microgrid as a single entity to maximize benefits according to the users’ needs

 

Distributed Energy Resources (DERs) 

The ability of microgrids to essentially mix and match different DERs is one of its key advantages. Renewable energy sources including solar PV arrays, fuel cells, wind turbines, biomass, batteries, geothermal energy, and others can be included in these assets. This also applies to currently in use traditional backup generators, such as those powered by natural gas or diesel.

 

Another kind of DER that is essential for sophisticated, contemporary microgrids is energy storage. In Workshop 4, various battery kinds are thoroughly reviewed.

 

The intermittent nature of renewable energy sources is mitigated and the microgrid can continue to function during grid outages thanks to the stored power in a battery energy storage system (BESS). Any extra energy produced at times of strong solar radiation for contemporary microgrids employing decentralized control and optimization systems

 

Electrical Infrastructure 

Microgrids require power conversion and conditioning devices, such as transformers and voltage regulators, in order to convert DC electricity into AC. To fulfill the demands of the microgrid and connected loads, the device converts and modifies electrical energy, ensuring system compatibility and appropriate voltage, frequency, and power quality.

 

Relays, switches, and circuit breakers are examples of electrical protection equipment that ensure the microgrid operates safely and dependably.  Fault-finding and fault-isolating devices additionally support flow control and power stability.

 

Point of Interconnection (POI) 

The point of interaction (POI) of a microgrid is what allows it to exchange and communicate electricity with the larger power grid. Microgrids operating in grid-connected mode require grid-connection devices, such as synchronization devices or grid-tie inverters, in order to facilitate bidirectional power flow and communication with the main grid.  

 

Switch for Dual-Mode Operation 

Grid-connected microgrids with a dual-mode operating switch may easily switch between grid-connected and islanding modes. A modern microgrid's ability to operate in islanded mode is one of its main features. This feature enhances resilience and reliability, especially in the event of grid failures, as the micro-grid has the ability to disconnect and continue providing electricity to support essential functions.

 

Communication Infrastructure 

Micro-grids depend on communication infrastructure to provide commands, data sharing, and component coordination. This infrastructure can be controlled remotely via a cloud-based service or on-site with certain controllers.

 

Control Systems 

The micro-grid's control system is its fundamental component. Sophisticated control and monitoring systems are necessary for micro-grids in order to supervise the intricate functioning of all parts and collect data in real time on energy generation, consumption, storage capacities, and grid conditions.

Ensuring efficient and dependable energy generation, distribution, and consumption is the control system's goal. In order to achieve these goals, the control system needs to be able to adjust to shifting circumstances and make the most of energy storage, grid interactions, and integration of renewable energy sources.

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Types of Micro-Grids

Legacy Microgrids

A solitary distributed energy resource (DER) and local load controlled by a centralized control system can constitute the most basic kind of microgrid. A diesel backup generator or solar panels are examples of local energy sources that can be used as DERs. 

 

Larger outages prevent this kind of micro-grid from disconnecting from the grid and may limit its use to emergencies. Alternatively, it might have a tiny PLC-equipped solar PV system that is always grid-connected and unable to isolate itself to produce electricity during blackouts. 

 

The modern micro-grid has access to ancillary services, resilience, and cost reductions that neither of these solutions can match. A more sophisticated conventional micro-grid would make use of several DERs. The most popular layout combines solar with storage in a hybrid system.

 

Modern Microgrids

Microgrid controls have evolved from centralized to distributed and decentralized systems in response to the microgrids' increased reliance on renewable resources and increased access to ancillary energy markets.
A decentralized control system with software and algorithms in devices implanted in each component is used by a modern microgrid.

Participation in ancillary services like as demand response, peak shaving, and pricing structures are made possible by this design, which completely optimizes the micro-grid for increased income generation options.

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All things considered, a microgrid's size, complexity, operational objectives, and regulatory environment all play a role in choosing the best control system. Unlike older micro-grids that use a PLC method, modern micro-grids offer the convenience of easily updating the logic and rules controlling the components.  As a result, contemporary micro-grids can be adjusted to better suit the goals of the company and adapt to shifts in the market that affect site economics.

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Capabilities of a Modern Micro-Grid

Monitoring: The microgrid's control system continuously keeps an eye on the condition and functionality of its many components. 

 

Energy Management: The control system makes intelligent judgments regarding resource allocation and usage by assessing real-time data on energy production, consumption, and storage in order to maintain a balance between the microgrid's energy generation and demand. 

 

Load Balancing: By prioritizing important loads during times of peak demand and optimizing power distribution based on load profiles, the control system makes sure that the microgrid's energy supply meets its demand. By doing this, overloads and blackouts are avoided.

Power Quality and Stability: To preserve power quality and stability, the control system sets acceptable limits for voltage, frequency, and power factor. In order to provide dependable electricity delivery, it combines sporadic renewable energy sources with a steady power source and reduces variations. 

Islanding and Grid Interaction: When microgrids detach from the main grid, the control system facilitates the smooth transition between grid-connected and islanded modes. It makes sure that the main grid is properly synchronized and reconnected when necessary, enabling bidirectional power flow and involvement in demand response or energy trading programs. 

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Energy Storage Management: In microgrids with BESS, the control system determines the most economical way to use stored energy based on grid circumstances, demand response signals, and cost considerations. This allows the battery or other storage device to be charged and discharged as efficiently as possible. 

Fault Detection and Self-Healing: When a microgrid experiences problems or anomalies, the control system finds them and takes action. It detects imbalances in load, voltage fluctuations, or equipment breakdowns. Occasionally, the control system sets off automated remedial procedures or sounds an alarm to need human intervention.

 

Communication and Data Exchange: The microgrid's numerous components can communicate and share data more easily thanks to the control system. Between energy sources, storage systems, loads, and control devices, it permits real-time monitoring, control commands, and data sharing. This makes it possible to operate in concert and make wise decisions. 

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Control System Strategies

Centralized Control Systems

A central processing unit is used by centralized control systems to collect data and determine the best course of action for the micro-grid's coordinated operation. Energy management, load balancing, and resource optimization are made possible by their ability to monitor energy production, consumption, and storage across several components. 

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A programmable logic controller (PLC) is a popular type of centralized control system. Because engineers knew them and had used them in previous industrial automation operations, PLCs were used as control systems in the initial micro-grid installations. PLCs were not designed for the complexity and demands of modern micro-grids and auxiliary services, despite the fact that they can provide some degree of control. This technique does not allow for regular updates to operating rules to account for changing external situations. As a result, the PLCs' logic ages and the microgrid's overall performance deviates from the company's objectives.

The centralized controller and PLC "top-down" approach has several drawbacks, such as 

• being restricted to rules-based operations, 

• being more expensive due to substantial integration and re-engineering costs, 

• being riskier due to a single point of vulnerability, 

• having an inflexible architecture that is difficult to scale or adapt, and

• having communication delays and synchronization problems

• Inability to handle intricate regulatory and commercial challenges

 

 

Decentralized Control and Optimization Systems

The decentralized approach uses software and algorithms that are built into each asset to build self-forming systems from the ground up. When applied to this context, the word "decentralized" emphasizes how distinct microgrid subsystems or components are endowed with independent control capabilities and the ability to make decisions in response to local data and objectives.

 

This model's decentralized architecture allows the local controller to maintain decision-making authority for the specific DER while maintaining communication with every other component of the micro-grid.

 

A backup generator could be one of the micro-grid's distributed energy resources (DERs). The generator's decentralized controller could include logic to stop operations in response to equipment or safety precautions. Therefore, even though the generator may receive a signal from the micro-grid controller to start, it is capable of making the decision to stop if there are safety issues.

 

The main difference is in the emphasis on the terms: "decentralized" highlights the distribution of decision-making and control power, while "distributed" emphasizes the general dispersion of control functions throughout the micro-grid.

 

Unlike most centralized control systems (PLCs), a decentralized control system makes it possible to include economic principles into microgrid operations. When energy can be exchanged or swapped between different Distributed Energy Resources (DERs), it may be priced and distributed more efficiently. Cost-effectiveness is encouraged by this market-driven approach.

 

A decentralized control system for micro-grids offers additional benefits compared to a centralized control system, including:

• Minimizes failure risks and promotes self-healing with minimal delay in response to local and system objectives. 

• Access to supplementary markets; 

• Standardized, agnostic ecosystem for asset integration; 

• Scalability through easy expansion as needs change 

• Better handling of communication delays due to the absence of a single point of failure; increased resilience and reliability

• Dynamic, rapid response to local and system objectives