Power grids are changing in dramatic ways with the rise of distributed energy resources (DER), storage options, demand management and all sorts of new technology. But existing centralized power generation, transmission and distribution infrastructure was designed over 100 years ago under vastly different economic, market and environmental conditions. Bolting on today’s state-of-the-art technology to yesterday’s grid infrastructure is a challenging process that is made easier with sophisticated technology like intelligent inverters.
Inverters have been used by the solar power industry for decades to convert DC electricity generated by solar installations into AC power, but they lack bi-directional capability needed to both take power from the grid and feed power back into it (Solar is only uni-directional). Intelligent inverters – like the ones being used at the University of St. Thomas Renewable Energy Facility in Minnesota – are playing a leading role in grid modernization by packing multiple technologies into a single package.
Under existing standards, if the grid has a problem renewable energy sources must shut down. “This is problematic because you have spent a lot of money on your solar arrays, your wind turbines, fuel cells, etc. and by code if the thing you are connected to has a problem, you must shut down even if you don’t need to [because the renewable energy assets are performing properly],” explained Minnesota’s University of St. Thomas Professor Dr. Greg Mowry.
However, with intelligent inverters you have the ability to run a self-sustaining microgrid. “One of the things an intelligent inverter helps you to do if the grid has trouble, is disconnect from the grid and run in island mode,” said Mowry. The inverter has the intelligence to maintain voltage and frequency and handle load requirements so when the grid comes back an intelligent inverter can easily synchronize and reconnect to the grid. “So, one of the things an intelligent inverter brings is the ability to continue supplying load independent of the state of the grid,” he said. In other words, instead of just shutting down all renewable energy resources during a time of grid instability, these inverters provide another option.
These particular intelligent inverters — supplied by Rhombus Energy Solutions, Inc. — are also critical to Professor Mowry’s microgrid research because he wants the ability to support and interact with the grid when it’s functioning, but if the grid has trouble he wants to be able to continue operating his microgrid.
Another powerful attribute of this technology is the ability to have several intelligent inverters interconnected with the grid that can communicate with each other to act as an intelligent autonomous system with or without the grid. Meaning they can essentially take over the utility’s job under certain conditions explained Rhombus Energy’s CTO & Director Joseph Gottlieb. “In the event of a power failure, these devices can continue to supply power even in the absence of the grid and later reconnect to the grid when available,” he said. For example, if there is a power outage at the University of St. Thomas, the section of the campus connected to Professor Mowry’s microgrid will be able to continue running without grid-supplied power. This capability is often referred to as resilience.
The capabilities that intelligent inverters provide represent another case of technology outpacing regulations and standards. Sophisticated inverters, like the ones Professor Mowry is using, have the technical ability to do much more than standards currently permit. As such, Mowry’s research focuses a lot on how inverters interact with the grid.
When you have various things connected to the grid it would be nice to have them function like other generation facilities. For example, DERs should be able to supply to the grid, “ride through” grid-based power failures and help manage power flow on the grid. “They can be active participants in grid operations, but today that is not the situation,” said Mowry.
The ways in which intelligent inverters communicate with the grid — known as Protocols — is actively being researched by Professor Mowry and his team. How do they “work with the grid”? One exciting thread of this research involves working with the local utility Excel Energy to safely connect to the grid when the University’s microgrid is in island mode. The University of St. Thomas and Excel Energy will work on this next year, Mowry said.
The devil is in the details regarding what can be accomplished, as with any research and development activity, which is why the university’s microgrid serves as an ideal platform for a partnership between a corporation and an educational institution, Mowry explained. Rhombus Energy has a strong team that focuses on developing products, so if Professor Mowry’s research proves something is technically achievable, Rhombus has the capability to commercialize it and bring it to market. “The partnership enables future things to occur where the research can be realized in a practical manner that, down the road, does something useful,” said Mowry.
Intelligent inverter technology has made a major leap forward by combining multiple capabilities into a single, powerful package. A major challenge in the past has been the need to buy multiple components, like a smart inverter plus a software suite to communicate with other devices and run upper-level control algorithms that help control microgrids or perform demand response functions. The Rhombus Energy inverters that Professor Mowry works with can do all of these things in single package.
These systems must have the ability to take on two critical functions. One is to supply power when no grid is present and the other is to support grid stability and provide cost-saving functions to allow quicker return on investment. The extension of these attributes to multiple interacting intelligent inverters on a microgrid (i.e. distributed control intelligence) is a next step in the evolution of smart inverters for controlling microgrids. These are truly exciting times in that the present generation of intelligent inverters give us impressive options now, with even more capability to follow in the very near future; capabilities which are unprecedented in the history of power.
