How a Virginia Tech researcher plans to use smart inverters to change the grid

grid probe smart inverters

The U.S. power grid, after faithfully delivering electricity to our neighborhoods for generations, is facing significant changes to how it operates — thanks to solar installations, wind farms, new energy storage systems and electric vehicles. As utilities meet the challenges of incorporating distributed energy sources on the low- and medium-voltage grids, however, they are hindered by incomplete knowledge.

“Limited instrumentation and their sheer size has kept a full picture of distribution grids out of focus,” said Vassilis Kekatos, an assistant professor in the Bradley Department of Electrical and Computer Engineering.

Kekatos and his team hit upon a novel technique called grid probing to generate the information needed about what is often called the world’s largest machine. Their pioneering process engages smart inverters — devices that convert the direct current output of renewable sources into the alternating current used by consumers — outside their intended function.

For this effort, Kekatos, who specializes in power systems and smart grids, was awarded the National Science Foundation Faculty Early Career Development Award.


The state of the grid

Today’s residential electricity networks are sprawling configurations and reconfigurations of decades-old infrastructure strung through a patchwork of smart updates. A utility company may own 3,000 feeders, each of which transfers power from substations to thousands of nodes. Half of those nodes may be outfitted with smart meters, but those are only sampled hourly.

To accomplish any meaningful grid-wide optimization, we need to know the power consumed or generated at every node, the line and transformer parameters, and the grid layout — all in real time, said Kekatos.
“Utility companies do not have information this detailed,” he said. “But we must acquire it to bring about the smart grids of the future.”

Grid probing explained

Kekatos plans to close the information gap with an original and potentially transformative solution he calls grid probing.

“Grid probing casts smart inverters in a second role,” explained Kekatos. “This is in addition to their standard conversion and control functionality.”

Smart inverters are found in solar panels, energy storage devices, and electric vehicles and come with unprecedented capabilities in sensing, actuation, and communication. Kekatos wants to use them for learning tasks as well. He plans to direct smart inverters to inject a short burst of power through the grid, eliciting additional grid readings at the inverter meter. By comparing “probed” voltage responses with baseline voltages, he expects to discover non-metered loads and unknown network parameters.

The power injections will be minimally invasive, causing no harm, but could yield significant information for understanding the nonlinear behavior of power grids.

Kekatos and his team will combine data from the grid probing with data from existing smart metering and grid sensing. Coupling power system modeling with data analytics, they plan to map the connectivity and line parameters of the distribution networks.

Outreach and education

All CAREER awards have an educational component and Kekatos has designed an integrated approach. Undergraduate students are actively involved in this research via grid visualization and cross-validation tasks. The students will also work with graduate students in testing and cross-validating grid learning schemes.
Kekatos has designed a new graduate-level course on power distribution systems with emphasis on multi-phase analysis, optimization, and learning.

— Solar Builder magazine

NREL asks: What’s the state of EV infrastructure in the U.S.?

EV charging stations

A new study from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) quantifies how much charging infrastructure would be needed in the United States to support various market growth scenarios for plug-in electric vehicles (PEVs).

Sales of PEVs—which include plug-in hybrid electric vehicles (PHEVs) and all-electric vehicles (EVs)—have surged recently. Most PEV charging occurs at home, but widespread PEV adoption would require the development of a national network of non-residential charging stations. Strategically installing these stations early would maximize their economic viability while enabling efficient network growth as the PEV market matures.

“The potential number, capacity, and location of charging stations needed to enable broad PEV adoption over the coming decades hinge on a variety of variables,” said Eric Wood, lead author of the National Plug-In Electric Vehicle Infrastructure Analysis. “NREL’s analysis shows what effective co-evolution of the PEV fleet and charging infrastructure might look like under a range of scenarios.”

NREL analyzed PEV charging requirements within urban and rural communities and along interstate corridors. For each type of area considered, NREL examined the station coverage needed by early-market PEVs and the station capacity required to satisfy potentially high future demand for electric charging.

The results suggest…

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…that a few hundred corridor fast-charging stations could enable long-distance EV travel between U.S. cities. Although many of these early-market stations could be underutilized at first, NREL’s analysis of driving patterns and vehicle characteristics suggests how corridors could be prioritized and station spacing set to enhance station utility and economics.

Compared to interstate corridors, urban and rural communities are expected to have significantly larger charging infrastructure needs. About 8,000 fast-charging stations would be needed to provide a minimum level of urban and rural coverage nationwide. In a PEV market with 15 million vehicles, the total number of non-residential charging outlets or “plugs” needed to meet urban and rural demand ranges from around 100,000 to more than 1.2 million. Understanding what drives this large range in capacity is critical. For example, whether consumers prefer long-range or short-range PEVs has a larger effect on plug needs than does the total number of PEVs on the road. The relative success of PHEVs versus EVs also has a major impact, as does the number of PHEVs that charge away from home.

“This study shows how important it is to understand consumer preferences and driving behaviors when planning charging networks,” said Chris Gearhart, director of NREL’s Transportation and Hydrogen Systems Center.
This work was funded by the Vehicle Technologies Office in the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy.

— Solar Builder magazine

Transparent utility data key factor in grid modernization, says new SEIA paper

SEIA grid modernization

Earlier this week we noted that SEPA was looking for opinions concerning the evolving role of utilities in this increasingly distributed generation world. Right on cue, the Solar Energy Industries Association (SEIA) released the second paper in a series on grid modernization that tackles the need for improved distribution planning and operations.

In Improving Distribution System Planning to Incorporate Distributed Energy Resources, SEIA reviews the current utility distribution planning process and highlights how two leading states, California and New York, are attempting to modernize their systems to leverage the vast capabilities of distributed energy resources.

“Grid modernization is a complex topic and through this series we’re hoping to show how every American using electricity today can benefit from smart, proactive planning,” said Sean Gallagher, SEIA’s vice president of state affairs. “When done correctly, grid modernization can create new opportunities for energy sources like solar, leading to economic benefits for both utility customers and the grid.”

The white paper explores how data transparency is critical to modernizing and improving system planning. The paper also examines the progress of states that are at the forefront of this issue. Here’s a taste:

Through power flow modeling, utilities use data about the equipment on- and configuration of- their distribution system to determine where upgrades are needed for their distribution systems due to load. The same underlying distribution grid data and power flow modeling can be used to identify how much additional distributed generation (or load, such as electric vehicle fast charging) can be interconnected to the utilities’ distribution system. Transparency of these limitations both through hosting capacity maps, and the data underlying these maps, can help reduce interconnection costs and uncertainty for distributed energy resource developers.

Head here to read the full report.

— Solar Builder magazine