Photo by Rebecca Gustaf, Sandia National Laboratory.
Sandia National Laboratories electrical engineers Rachid Darbali-Zamora, front, and Lee Raskin test out an algorithm on a hardware-in-the-loop set-up at the Distributed Energy Technologies Laboratory.

Coding Better Microgrids

June 13, 2024
In the pursuit of a self-healing grid, scientists, engineers and utilities work together on tying grid assets together in more efficient ways.

Like the words alchemy, alkali, alcohol and algebra, the word algorithm has its roots in the Islamic Golden Age and the work of Muhammad ibn Musa al-Khwarizmi, an astronomer, geographer and mathematician who is known as the father of algebra — a word that means “completion” or “rejoining” in Arabic. Algorithm is thought to be the Latinization of al-Khwarizmi’s name.

Throughout history, algorithms were used to encrypt and decode secret messages, as well as to predict the movement of bodies in space. It wasn’t until the 19th century and Ada Lovelace and Charles Babbage’s proto computers and Alan Turing’s 20th century computers that algorithms took on a form we are more familiar with, thereby making the great leaps in computer science we have seen in our lifetimes possible.

For the power grid, computer scientists are devising ever more sophisticated algorithms. The National Renewable Energy Laboratory developed algorithms to process signals from distributed generation sources like rooftop solar and wind turbines so their generation can be more predictable for grid operators. Researchers at Princeton’s Department of Electrical Engineering wrote algorithms to protect against botnet-style cyberattacks on the power grid from high-wattage, internet-enabled devices. There are further applications in load demand prediction, fault detection, power grid monitoring, outage restoration and, broadly, helping grid operators distill the ocean of data pouring in from the meters, sensors and other smart devices now being deployed across service territories.

There are also a host of applications for microgrids. A platform developed by Irvine, California-based Veritone employed decades of pricing, demand and solar power resource data to figure out the right size energy storage batteries to use for solar power systems in Texas’ ERCOT grid.

As a part of one of the Department of Energy’s Earthshot research programs for clean energy R&D, NREL and several National Laboratories are developing new algorithms to study long-term wind resource availability the hopes of lowering the levelized cost of electricity for floating offshore wind power projects. Another Earthshot NREL is participating in is studying the problem of long-term degradation in thermal energy storage materials, which is a barrier to their use in long-duration energy storage projects.

R&D on what algorithms can do for microgrids — and therefore energy resilience and decarbonization — has matured to the point where it is leaving the laboratory and being put into use by utilities.

Writing New Libraries

At Sandia National Laboratory, located inside Kirtland Air Force Base in Albuquerque, New Mexico, researchers study more advanced algorithms for an array of purposes and industries. Alongside scientists from New Mexico State University, they create libraries of algorithms they hope could one day lead to a self-healing power grid.

Michael Ropp, the project lead, told T&D World this could mean for getting power restored automatically to critical locations such as government buildings, hospitals or grocery stores before utilities or grid operators could conduct damage reports or deploy workers for repairs.

“The technology set we’re working with here is primarily intended to improve resilience during severe events, at the distribution-system level. This technology is designed to automate the process of enabling the power system to self-assemble into a configuration that powers as many customers as possible, using whatever sources are available, over whatever paths are still intact, after the power system has suffered a major insult,” Ropp said via email.

These black sky technologies could be useful even under blue sky conditions, leading to greater efficiencies under any conditions.

“Basically, we are looking at two types of system element: Line relays, which sectionalize and reconfigure the system, and load relays, which control local loads. Our technology set aims to allow these elements to discern what’s going on with the power system using only the voltages and currents they measure themselves, without relying on data being sent over a high-speed, ‘real-time’ communications channel that a) is cost-prohibitive in many cases and b) often becomes unreliable under the types of contingencies we’re talking about here,” he said.

When grid operators are forced to use only local measurements, this creates certain technical challenges, he said. Self-healing using only these data is necessarily slower than self-healing with two-way, real-time communication. On the other hand, the reliance on local measurement is leading to self-healing systems that can be highly effective at making power grids more resilient and reliable at a modest cost.

A particular area of interest is microgrids. The technology developed at Sandia is meant to work with microgrids with distributed inverter-level resources at the distribution level that are operating in their off-grid mode.

“Let’s say that we have a microgrid of this type operating off-grid. A fault occurs in which we have a circuit shorted to ground somewhere. The technology we’ve developed allows the system first to isolate and locate the fault, then bring the rest of the system back online,” he said.

For power engineers, the techniques used will probably sound familiar — concepts like undervoltage and underfrequency load shedding, undervoltage-supervised overcurrent and segmented black start.

Researchers strove intentionally to set systems up so they can be used with only existing, widely used equipment without the need to install new hardware platforms or expensive communications networks. Such systems can become unreliable in black sky conditions, and may introduce vulnerability to cyber attacks.

“If isolating the fault caused us to lose one of our generators, so that now we can’t carry as much load as we could before, we have a means for making the loads aware of this, so that we connect only the amount of load that the sources can handle,” he said.

Avoiding the Microgrid Loop

Because of the way electric distribution systems are designed in North America, system designers need to avoid forming closed loops when designing microgrids.

“The loop we’re talking about is a literal loop — a situation in which we’ve closed certain switches so that we have a closed, continuous circle of wire. If the system is designed to operate with closed loops like this, then that can actually be a good thing that significantly improves reliability,” he said.

Sandia’s research partners developed a way to allow the controller at each switch to determine, using only local measurements, when closing its switch would create a closed loop. The method relies on a statistical comparison of the frequencies seen on either side of the switch to be closed. 

From Theory to Reality

These new algorithm libraries need at-scale testing before getting deployed on any customer-facing power grid. So, researchers are looking for partners to assist with the next step. Sandia has two manufacturers working with them.

“We are presently seeking follow-on funding to do some further technical development, solve some remaining challenges, and expand the applicability of this suite of techniques to more situations,” Ropp said.

Last year, T&D World talked to EPB, the municipal utility for Chattanooga, Tennessee, about a microgrid designed to keep their central city functions operational during a blackout. These included surveillance cameras, radio control centers, a fire station and other critical communications infrastructure used by the city.

Jim Glass, Manager of Smart Grid Operations for EPB, said his utility collects waveform data from some 1200 automated switches with fault-sensing capability to automatically classify power grid events, which helps them address outages, solve equipment problems and test functionality.

The advanced algorithms currently being written provide evidence to help industrial customers optimize their equipment and settings to avoid disruption in voltage drops, Glass said.

“For residential customers, we can address outage frequency and duration more precisely and identify issues that may lead to future outages,” Glass said.

The utility uses an application with Fault Location, Isolation and Service Restoration (FLISR) capability, which springs into action automatically.

“When a fault occurs, the automated switches closest to the fault will sense it and open. It will communicate with the switch downstream and tell it to open. When both switches are open, the fault becomes isolated to a small section of the circuit. Once faults are isolated through this mechanism, the system communicates to normally open switches at the back end of feeders to close, which restores service to the back end of the circuit. The entire process takes just seconds and is entirely automated by the smart grid,” he said.

An Idea Taking Flight

At Kirtland AFB, Sandia scientists worked with Emera Technologies on a microgrid demonstration project intended to show how DC microgrids could work seamlessly with AC electrical systems to provide power. The hybrid DC/AC system was a “grid of grids,” linking several microgrids together for greater safety and efficiency.

The purpose of the project was to demonstrate and deploy a load-serving DC microgrid where every node had co-located generation and storage with interconnection via power electronics, as well as to do this in a modular system that could be easily deployed to microgrids of many different designs, Sandia electrical engineer Jack Flicker said.

“This allows for freedom on how power is delivered to the load. This is essentially changing the power system, where every electron required by the load has to be delivered to that load over wires at every given point of time, to an energy system where we can supply the electronics whenever is convenient,” Flicker said.

Besides the design and construction of the microgrid, there was quite a bit of work done on modeling and determining how big all the assets need to be as well as making sure the system is stable in all sorts of conditions. This included a cyber threat analysis on the communications infrastructure, he said.

Designing New Grids

The project used a few different design concepts, he said, one of which is a DC microgrid. These deliver safety, simplicity and efficiency advantages. Another concept is what Flicker calls the hierarchical microgrid, where different assets can operate independently or cooperatively as needed to increase resiliency and meet load demands. 

“I like the term hierarchical microgrid, but ‘fractal’ is more commonly used,” he said.  “The concept of a hierarchical microgrid is that you have various layers that can either operate independently or in a coordinated sense.”

Finally, another concept under exploration is the idea of modular power electronics blocks at each node which can integrate generation, storage, control, and the grid interface at each node. 

“All of these concepts are demonstrated, but they are not all required. Each piece can be utilized without the others. For example, you can create a hierarchical microgrid with an AC system rather than a DC system and have all the benefits of that,” he said.

Glass said EPB is enhancing its energy mix by expanding the number of microgrids in the area, tying them together and designing them with islanding capacity if it is needed.

“However, they are not designed to automatically island because we use every opportunity available to us for distribution automation technology through the smart grid first,” Glass said. “We will only operate microgrids in island mode when there isn’t an alternate power source.”

Before EPB system operators initiate microgrid operations, they try to fully understand where problems are using locally available information so as not to compound any issues.

“First, we exhaust all available options through automated switches and manual system operator switching to restore as many customers as possible,” he said.

EPB’s microgrid plans focus on remote areas at the end of service lines because of lack of redundancy. In such cases, we will likely install energy storage in these locations to provide reliability for customers.

Technologies that network grid assets more efficiently are of great benefit to the community, he said. EPB’s combination of smart grid and fiber optic networking resulted in 55% fewer outage minutes and saved customers more than $26 million by avoiding spoilage, lost productivity and other power outage impacts.

About the Author

Jeff Postelwait | Senior Editor

Jeff Postelwait is a writer and editor with a background in newspapers and online editing who has been writing about the electric utility industry since 2008. Jeff is senior editor for T&D World magazine and sits on the advisory board of the T&D World Conference and Exhibition. Utility Products, Power Engineering, Powergrid International and Electric Light & Power are some of the other publications in which Jeff's work has been featured. Jeff received his degree in journalism news editing from Oklahoma State University and currently operates out of Oregon.

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