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With NSF CAREER Award, Dominic Gross will improve renewable energy grid integration

Written By: Jason Daley

Renewable energy is ramping up in a big way, with solar and wind power grabbing a larger and larger share of the electricity market each year. That is great news for efforts to decarbonize the energy and transportation sectors, but it’s not great news for the U.S. electricity grid, which isn’t ready to integrate all those gigawatts of green energy just yet.

Dominic Gross

That’s why Dominic Gross, an assistant professor of electrical and computer engineering at the University of Wisconsin-Madison, is working behind the scenes to develop new frameworks and paradigms for control of renewables and grid-connected power electronics to help make the transition to green energy as seamless as possible.

Through a five-year, $500,000 National Science Foundation CAREER Award, Gross will investigate a flexible universal modeling, control and analysis framework for power electronics and renewable generation that will ensure and enhance grid stability as renewable energy increases its market share.

Currently, legacy power-generating sources like coal plants are very reliable and ensure stability of today’s power system through their feedback controls and inherent physical properties like rotational inertia. Most renewable energy sources, like rooftop solar, do not provide grid support and are a bit more erratic, injecting fluctuating power into the grid. While legacy power generation sources can absorb these fluctuations and correct for the resulting frequency and voltage variations, at a certain point, replacing legacy power generation with too many of these so-called grid-following resources could destabilize the grid, leading to outages and other issues.

The solution is to interface renewables through grid-forming power-electronic converters that autonomously regulate the grid frequency and voltage at the point of connection of distributed energy resources, like wind farms and rooftop solar. Gross is part of major multi-institutional group called the Universal Interoperability for Grid-Forming Inverters that is developing the framework for these new devices.

But Gross believes a more sophisticated type of power converter control could do even more to stabilize the grid. That’s what he hopes to develop in his CAREER Award project.

In the current paradigm, grid-forming converters are mostly an all-or-nothing proposition; with sufficient sunshine or a large enough battery, the converters provide comprehensive grid stabilizing services. When it’s cloudy or with insufficient energy storage, however, the converters sit idle. In his new paradigm, Gross wants to design converter controls that aren’t so black and white, but have the flexibility to help stabilize and monitor the grid to the best of their current ability.

“The main problem is that the controls we have today can only do the two extremes. They don’t support the entire spectrum of functions,” says Gross. “In this new paradigm, if there is no sunshine or a little sunshine, at least your rooftop photovoltaic will still provide some grid services. And all of this will happen automatically.”

The other issue the flexible paradigm overcomes is the mix of power generation sources and controls that are likely to be part of the grid in the future. “If you look at the future power grid, it will be mixing all different kinds of power generation, energy storage and power transmission —high-voltage DC transmission, wind power and photovoltaics,” he says. “They all use slightly different versions of the same controls, but the slight differences are enough that you worry about the complexity of the system. You have millions of devices that are running slightly different flavors of four basic control designs. It becomes hard to understand and put all these things together so it works.”

Gross’s paradigm, however, will be able to constantly monitor the grid and help smooth over those differences. “One of the hopes is that we can deploy the same control and all of these technologies will work together,” he says.

Gross believes that grid-forming converters will likely be part of renewable energy installations in five to 10 years, and he hopes that his new flexible paradigm will soon follow suit. Speed is key when it comes to implementation of these converters; if too many grid-following renewable systems go online before the new converter controls are deployed, it will limit the future flexibility of the system, since those grid-following renewables rely on system properties maintained by legacy power generating technologies.

In the education element of Gross’s CAREER award, he hopes to address some of those issues as well. He plans to work with the NSF-funded technical educator teaching center at Madison College to develop a program to familiarize educators with the need for grid-forming converters.

“These things are happening on a timescale of five to 10 years and then moving into practice,” Gross says. “We need to get a head start on educating technicians and the workforce on these technologies.”