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Amping up microgrid R&D in Minnesota

A new Minnesota university lab-utilizing inverters from Rhombus Energy-is playing an important role in microgrid research and development, including connecting to renewable power and bringing power to less developed countries.

By Tony Kryzanowski

Microgrids are power distribution systems that provide electricity to small geographic areas, and research and development focused on the economics of providing this method of distributed power is still evolving. But there have been significant advances over the past five years toward greater commercialization and implementation.

A new microgrid research lab at the University of St. Thomas in St. Paul-Minneapolis, Minnesota, is hoping to play an important role in further microgrid research and development. Called the Microgrid Research and Testing Center, the university's School of Engineering has received a multi-million dollar grant from the Xcel Energy Renewable Development Fund to establish the center. It came on line at the end of 2018.

Microgrids can support existing conventional powergrids, provide stand-alone emergency power to facilities, and bring power to billions of people around the world who still lack access to any power.

Renewable power sources like solar, wind, diesel generators, and fuel cells represent convenient sources of power for distribution by these microgrids, with some as large as 20 megawatts (MW), but most distribute power in the range of one MW or less.

The University of St. Thomas microgrid lab has been equipped with a variety of renewable power generation tie-ins that includes a solar array, diesel powered genset, fuel cells, and storage batteries designed to produce between 25 kW and 60 kW, for a total of 200 kW of simultaneous power generation. The lab can also accept third-party power generation through its switch gear. This allows companies and researchers to conduct microgrid research from power that they generate. This is a helpful feature since in addition to providing research opportunities at the university, the lab is providing R&D infrastructure to companies and institutions interested in testing and advancing their own renewable and alternative electric power endeavors.

Dr. Greg Mowry, director of the Microgrid Research and Testing Center, emphasizes that the lab is equipped with state-of-the-art hardware, like the new Rhombus Energy multi-port 50-kW smart inverter, that is already designed to meet incoming microgrid infrastructure and tie-in standards. So the lab is providing researchers and industry with a test facility with the capacity to allow them to develop the next generation of microgrid architecture.

"For the central U.S. to the Rockies and to the Appalachians, and maybe even the Oklahoma to Canada region, this is probably one of the few research microgrids of its type in existence over this geographical area that I am aware of," says Mowry.

The University of St. Thomas microgrid lab has been equipped with a variety of renewable power generation tie-ins—including a solar array—designed to produce between 25 kW and 60 kW. 

Microgrids and their application are Mowry's major field of study, with a focus on the economics of developing hardware and distribution systems that make their deployment feasible to the billions on the planet still without access to electricity. He has deployed about a dozen microgrids over the past 15 years. Among the post-graduate students enrolled at the University of St. Thomas School of Engineering, about 90 percent are engaged in engineering related to power generation, distribution, and the humanitarian application of microgrids.

"There's a big picture here," Mowry says. "About four billion people on the planet do not have access to electricity. At the end of the day, the microgrid is probably one of the best ways of providing the advantages that electrical power provides to society, to four billion people."

Mowry says the microgrid lab will be available for research and testing of microgrid applications in support of conventional grid systems located in economically advanced countries. But just as important an area of research is how to design, build, and manage microgrids with economics that make them accessible to these four billion people who still lack access to electricity, he added.

Researchers have made great strides in advancing microgrid economics, Mowry says, with a path having been identified where a microgrid could provide power to an average American home with an investment of under $15,000. This opens the door to making affordable power, at a delivery rate of about 5 kW/hr, accessible to many residences and villages in lesser developed regions worldwide.

He feels that the new microgrid lab at the University of St. Thomas can play a role in helping to make that happen, while improving the lives of nearly half the world's population.

Rhombus Energy provided two UPC-30/60 kW bi-directional inverters to the project. They come equipped with two 30-kW DC input ports and one 60-kW AC output port.

 In addition to providing research opportunities, the University of St. Thomas microgrid lab is providing R&D infrastructure to companies and institutions interested in testing and advancing their own renewable and alternative electric power endeavors.

Kent Harmon, Rhombus Energy general manager, says that the company provides power converters, bi-directional inverters, and testing equipment to the renewable power generation and storage industry. What qualifies the inverters supplied to the University of St. Thomas as 'smart' inverters is that they can accept input from two separate types of power production sources, which is one of the inverter's attractive features, along with seamless, bi-directional power flow.

"Each DC input port is independently controlled, or they can be paralleled together to act as one 60-kW input port, if desired," Harmon says, adding that it is possible to create a communication link with the inverters to use them in various operational modes. Essentially, they are designed with the ability to mix and match, with greater control of their functionality, which is particularly important for the University of St. Thomas microgrid lab, given the variety of power generation sources available for research and testing at this location.

Mowry says he appreciates that the inverters are "very intelligent machines architecturally" and well-suited for the type of research that will be conducted at the lab, with two of the areas being studied being development of distributed intelligent energy management systems and advanced inverter design. So the university is able to pursue two avenues of research with one inverter.

One of the inverters is connected to the lab's solar power production system working strictly as a DC to AC inverter, generating about 50 kW of AC power. The second inverter is interfacing with a lead acid battery pack, discharging power from the battery pack into the microgrid. Power also flows in the opposite direction through the inverter, as needed, to recharge the batteries once they have been depleted.

Rhombus Energy provided two UPC-30/60 kW bi-directional inverters to the project. They come equipped with two 30-kW DC input ports and one 60-kW AC output port. 

Harmon says that the Rhombus team is working with Mowry on algorithm inputs aimed at control functions such as peak shaving, load shifting, and frequency regulation.

Thao Attard, director of technical sales at Rhombus, says that it was a unique experience working with Mowry, given his advanced knowledge related to microgrids and the knowledge he shared with the company on his plans for integrating the inverters into the overall design of the microgrid lab. The discussions ultimately determined that the Rhombus inverter would be a good fit.

"Dr. Mowry discussed the various ways that you can become a microgrid, control the inverter, and do the energy management portion of these energy nodes related to such issues as voltage control," she says. "Our inverter has that ability right now to perform those sophisticated functions to become a self-sustaining grid."

The inverter will be UL certified to the IEEE 1547 (2018) requirement as well as the 1741 SA requirement for inverters to tie into conventional grids by the first quarter of 2019.

"The Rhombus company basically designed their inverters with the capability to meet the new standard, so one of the reasons for our partnership with Rhombus and using their inverters in the research microgrid is that their inverters met the new 1547 standard before it was even published," says Mowry. "That's very good hardware to integrate into a brand new research microgrid because it is capable of allowing next generation research against a new standard."

Because of the level of state-of-the-art hardware installed in the lab, including the Rhombus inverters, Mowry says that the university has been designated a 1547 test facility where companies can bring their inverters to the lab, and the lab will be able to certify whether their inverters are compliant with the 1547 standard.

Attard says that Rhombus can offer advanced inverter technology based on what is currently available in today's market.

"The standards have been around for some time, but there have been additions to the standards over time, and we have been adapting to them and, in fact, surpassing them," she says.

Mowry describes Rhombus as an outstanding inverter supplier, based upon his 25 years of experience working in the industry—prior to joining the University of St. Thomas—where he was involved in many procurement endeavors.

"They were responsive, receptive, flexible, and professional," he says.

A major motivator for the University of St. Thomas to establish its microgrid lab was a commitment made by all universities in the United States to become carbon neutral by 2030 under guidance provided by the Obama administration. While there are various pathways that universities can take to achieve that milestone, one way is for these institutions to install their own power systems.

"Microgrids fall into that space, if a university is trying to achieve carbon neutrality through its own renewable and sustainable energy systems," says Mowry. "Since the University of St. Thomas is part of that program to become carbon neutral by 2030, our research microgrid is important to the university in the sense that it allows the university to see what goes on in running a power system, and would they want to generate more of their own energy or decide to pursue some of the other avenues."