Electronic Design
Smart-Grid Renewable Energy Needs Intelligent Substations

Smart-Grid Renewable Energy Needs Intelligent Substations

Intelligent substations play a significant role in the integration of renewable energy into the smart grid.

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Ellen Blinka, Marketing Manager, Texas Instruments

Smart meters have grabbed a lot of the limelight when it comes to the smart grid. But, let’s face it, next-generation intelligence in substations is the fulcrum for bringing more renewable energy into the electrical distribution network. Smart meters delivered intelligence to the grid’s end points, but increasing intelligence in substations via smarter intelligent electronic devices (IEDs) will enable regional supervisory control and data acquisition (SCADA) systems to more effectively manage power supply and demand in grid segments that contain renewable energy sources.

Arnon Friedmann, Business Manager, Texas Instruments

There’s no denying that renewable energy sources like solar and wind present a greater control challenge for maintaining a reliable, dependable electrical supply system. The very nature of renewable energy sources is quite different from the traditional power generation plants that have formed the grid’s foundation for the last century and more. Unlike the massive power-generation plants fired by fossil fuels, which by necessity are few in number and located relatively far from communities, renewable energy can be sourced from a plant as small as several solar panels on a home or a few wind turbines on the side of a hill behind a new subdivision.

In addition, the traditional power grid can be characterized as many demand points with a relatively few supply points. On the other hand, a smart grid with significant renewable energy will have many demand points while also starting to tilt toward a greater number of smaller energy sources that are closer in proximity to end consumers. In fact, micro-grids—smaller quasi-independent grids within the larger electrical distribution system—are already being deployed and have demonstrated their worth. Many experts expect that the implementation of micro-grids to increase because their scale is well-suited to the scale of most renewable energy sources.

Dealing with Unpredictability

Renewables are intermittent, though. While traditional power sources are dispatchable and can ramp up production to meet demand during peak hours, renewables can be unpredictable and can’t be controlled by operators. The home with the solar panels could be selling power into the grid one sunny day and buying it the next after the clouds roll in. Large-scale wind farms and solar plants are just as reliant on the whims of nature.

The lack of predictability from renewable sources and the larger number of producers are both difficult to handle within the traditional grid, which has unidirectional communication flowing from a centralized hub. Information about the level of demand and the production level from multiple points of supply needs to be communicated to the central supply-and-demand management system, and then back out to the power sources and other grid resources that manage power delivery.

In cases of high demand, dispatchable power sources will need to be told to ramp up. In cases where demand is low or renewable generation is high, dispatchable power sources could ramp down, or renewable sources could be instructed to store their excess produced energy for a high-demand situation. Grid resources, such as IEDs in substations, will need to be told how to manage all of this power routing.

It’s clear that the smart grid will need to seamlessly blend these divergent power sources—traditional power-generation plants and renewable sources—in a way where they will complement and optimize each other’s strengths while minimizing their weaknesses. Doing so will certainly make the smart grid of tomorrow a much more complex place, introducing new control challenges that can be overcome by a more intelligent infrastructure, particularly at the substation level. As such, it will require a large increase in computing power.  

Greater computing power and intelligence could be implemented in a few different places, including at the central level, the regional SCADA system that manages supply and demand, or at a more distributed level (distribution and transmission substations). While adding intelligence at the central level may intuitively make more sense at first, it will require that more and more data be communicated from the distributed points back to the central level as production and demand points invade the grid.

Move It to the Substation

However, if instead more intelligence is placed in the substations, this data can be analyzed before being transmitted so that more useful information—and smaller amounts of it—can be passed back to the central level for regional management. Pushing more analysis and intelligence to the edges of the system, the substation IEDs, enables the substations to supply regional SCADA systems with smarter, more useful data that will facilitate more complex decision making and control.  This places less of a burden on the infrastructure of the overall grid, preventing communications networks from needing to scale up as quickly.

Substation intelligence will require more sophisticated algorithms and real-time, two-way communications in the substation IEDs. These substation IEDs will provide a critical link in the entire system, interfacing on the one hand with energy sources—small and large, renewable and traditional—and on the other interfacing with the many and varied types of energy consumers. Optimizing this fluid, many-to-many relationship will be tricky.

For one thing, power won’t be the only thing traversing the grid. In fact, it already isn’t. Today, data and information flow just as freely as power over the smart grid. Also, the flow of power and data is no longer restricted to one direction, from generating plants to users. Now, power and data travel in both directions: from power sources to end users and from end users back into the grid.

Initiating much of the data flow across the grid are a myriad of sensors and monitors that are watching processes transpire, gathering data and reporting it upward from users to substation IEDs in many cases. In addition, substation IEDs receive and respond to data communicated downward from the energy sources and higher levels of the grid’s multilevel control system, such as the regional SCADA system. All such data must be analyzed immediately by the de-centralized substation IEDs so that intelligent supply-and-demand decisions can be reached and actions taken without human intervention.

The IEDs in substations must be able to process powerful control algorithms, because the smart grid of the future will be a very fluid, always changing place. Renewable energy sources will be constantly coming online and going offline in response to changing weather conditions—and everyone is well aware of the weather’s unpredictability. This means that traditional power plants will dynamically increase or decrease the power they generate to fill in the gaps created when renewables go offline, or to accommodate a surplus of energy when those same renewables come back online. Of course, user demand for power is just as fickle, constantly shifting from hour to hour over the course of every day.

This is why it’s important to integrate renewable energy into the smart grid.

Greener Energy Pastures

The consuming public’s interest in and demand for clean “green” energy certainly will not abate any time soon. For those utilities transforming their transmission and distribution grids into the smart grid of the future, the question becomes how to best integrate renewable energy into tomorrow’s much more intelligent transmission network. A likely place to start would be substations, because they will be critical to interfacing renewable energy sources with the larger smart grid.

Intelligent IEDs handle controls, analytics, and reliable industrial communications to efficiently integrate renewable sources into the power grid. (Click for larger image.)

Although much of the substation equipment currently deployed features some sort of IED that interfaces the equipment to the substation’s control systems (see the figure), the integration of renewable energy sources into the smart grid will bring about fundamental changes to the nature of the grid. As a result, a new level of intelligence will be needed to support more sophisticated control algorithms as well as the fast real-time communications that maintain reliability and redundancy without compromising reaction times.

Essentially, renewable energy sources will create a more distributed, decentralized network of smaller power-generation plants. Certainly large fossil-fueled plants will always have a role in the grid, but they will be surrounded by small wind and solar farms, as well as other sources of renewable energy that will be located much closer to the segment of the grid to which they provide power. This close proximity to the load has advantages insofar as it reduces the power lost in long-distance transmission, but it also adds another layer of complexity to the grid. Greater complexity further challenges the smart grid’s control systems, which is where the substation IED will play a critical role.

Bidirectional Communications

Before the entire grid began to move toward greater inherent intelligence, the dominant mode of communications for the grid’s control systems was one-way and hierarchical, from central control operations to regional centers and eventually filtering down to IEDs within substations. Some control data did flow back upstream from substation IEDs to regional control centers, but this was limited.

Now, with the smart grid and renewable energy, the IEDs in substations will be communicating with and monitoring demand and small sources of renewable energy, and sending data used for controls up to regional systems. All of this data must be processed at the IED level, quickly analyzed with sophisticated analytics, and responded to with real-time communications in both directions, upstream to higher levels in the regional SCADA system and downstream to grid equipment and renewable energy sources. 

These bidirectional communications must be done in real-time, because the IED will be responding to and controlling real-time events, such as sudden overvoltage or overcurrent situations. If the correct level of intelligence isn’t present, or if the data processing takes too long, consequences could be large. For instance, a sudden surge in demand may cause a circuit breaker in a substation to shut off a portion of the grid and black out an area.

As demand increases and supply becomes more complex with the addition of multiple, small renewable sources, the margin for error shrinks on the complex task of balancing supply and demand. When timing is so critical, older and slower communications protocols like RS-232 or RS-485 won’t suffice. Newer industrial Ethernet standards, such as IEC61850, have guidelines to ensure the real-time requirements are met. They also feature standardized ways of describing events on the grid and their associated timing.

Ethernet-Based Grids Look to IEC61850

IEC61850 is rapidly becoming the standard for Ethernet-based grid communications around the world. It provides standard variables for describing measurements taken (sampled values, or SV), substation events (Generic Object Oriented Substation Events, or GOOSE), and control commands (called Manufacturing Message Specifications, or MMS). Each has its own priority and recommended timing. These features, and the standardization used on equipment from multiple manufacturers, facilitate control coordination among substations to guard against the cascading effects of power outages and brownouts.

Moreover, communications failures could lead to events like blackouts or damage to equipment, and thus cannot be tolerated in such a real-time regional and national control system. Fortunately, the IEC61850 real-time Ethernet standard can be layered with redundancy protocols like High-Availability Seamless Redundancy (HSR) or Parallel Redundancy Protocol (PRP). These communications layers ensure that messages arrive at every node of a ring (in the case of HSR) or mesh (in the case of PRP) network, even in the event of damage to just one connection between nodes.

These protocols take advantage of IEEE1588 timestamping and PTP clocking, which marks packets with precise timing information. The timestamp information can be utilized for various tasks, such as determining when and where grid events have taken place, synchronizing events, and ordering packets so that information is processed in the correct order. Since thousands of measurements and events can occur per second per IED, synchronization and message redundancy are keys to keeping the grid operating properly and without error.

In addition to redundancy protocols ensuring that messages are passed to each node on a network, substation IEDs must have redundant physical communications resources. These include multiple Ethernet physical interfaces and, in certain critical cases, multiple real-time communications processing engines to overcome any potential failures and ensure critical messages are received or sent within tens-of-microseconds time windows.

Conclusion

When one envisions the smart grid of the future, what emerges is the notion of an environment that’s constantly changing, always reacting to new information, and instantaneously analyzing and taking action on its own. Such a power grid argues for agile and adaptable systems throughout, but especially in substation IEDs that will be critical for managing the task of providing renewable energy to consumers due to the unpredictable nature of that energy’s availability.

Highly programmable systems will better provide the basis for this malleable mesh of resources. Upgrading legacy hardcoded control systems based on technologies such as ASICs or FPGAs to a new version of a protocol standard would likely involve expensive and extensive hardware swaps. But with extended programmability, substation IEDs could have updates and upgrades to the latest versions of IEC61850 or HSR done remotely through a new firmware or software load.

This capability becomes important in our current environment, where renewable resources and increasing supply are quickly changing the needs of the grid. As grid requirements change, the protocol standards are updated to ensure needs are met and the grid remains reliable. Improvements and extensions to IEC62439, which covers HSR and PRP, and to IEC61850 are likely in the future to expand use cases. Programmability also allows for algorithms on IEDs to be updated as needed to deal with more complex events in more efficient ways.

Certainly, the role of renewable sources of energy in the smart grid will only increase with the passing of time. The controls-processing abilities, agility, programmability, and real-time communications capability of substation IEDs must be able to keep up with the changes taking place in the grid itself.

TAGS: Energy Power
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