A lot of disagreement exists about what constitutes a microgrid. But there are two things people generally agree on. First, a microgrid can island or isolate itself from the central grid. Second, they are governed by a microgrid controller that acts as a management brain and distinguishes the system from being just a “dumb” amalgamation of power generators at a site.
It’s that brain — and related equipment — that Schweitzer Engineering Laboratories (SEL) provides. Like most brains, it is complicated.
In an interview Bob Morris, SEL’s chief engineering services officer, offered insight into the microgrid controller, what it does, why it’s important and what people often misunderstand about the technology.
Morris is particularly well-suited to offer this insight, given that he has 23 years of experience at SEL, a company that has been providing microgrids for industrial sites even before they were called microgrids.
“They were just called islands before microgrid became a popular term. We’ve been working on those for 15 years or so,” Morris said.
A controller’s software does many things, such as managing the microgrid’s resources to achieve the owner’s goals, which might be maximize electric reliability, harness best energy pricing, integrate renewables or reduce emissions. Whatever they are programmed to do, and whatever they are called, controllers address an underlying challenge of physics faced by a microgrid: a lack of inertia.
The inertia problem
In contrast, the U.S. electric grid has plenty of inertia in the form of a mass of large spinning generators that take care of imbalances. As Morris explained, should electricity consumers (load) suddenly demand more power than the system is producing at any given moment, these spinning generators can quickly make up the difference and keep supply meeting demand.
“If load increases beyond the present generation, they pull some energy from those spinning masses. The governors from those generators will add more fuel to the prime mover and eventually the generators will start putting out power. It is that inertia in the generators that rides through those small disturbances,” he said.
A microgrid, however, is different. There is not a lot of inertia in its generation system. If there is a power outage on the central grid, and the microgrid islands and begins relying solely on its own generators to serve its customers, it does not have the many spinning generators of the central grid to fall back upon.
That’s where the microgrid controller comes into play.
“The challenge with microgrids is that there is not a lot of inertia in the generation system, so the dynamics are much faster — they are not as forgiving as the electric grid,” he said. “To keep them stable, you need a control system that will respond very rapidly, one that has been preprogrammed.”
Imagine a university with a microgrid. A storm comes through and creates a cascading outage on the central grid. To protect itself from the outage, the university’s microgrid islands and directs its on-site combined heat and power (CHP) system to provide electricity for the campus. Perhaps the CHP plant is not sized to serve the entire campus. So to keep the system in balance, the controller begins to shed load – reducing electric flow to parts of the campus where power is not crucial. Perhaps it restricts power to the pool pump or lights in the lecture hall.
In doing this, the controller must act quickly, balancing supply and demand in milliseconds.
Microgrid controllers not all created equal
One problem, says Morris, is that not all microgrid controllers are created equal. For example, SEL often finds itself working with customers that have old-school microgrids that do not automatically island and then reconnect to the grid. They are not fast – operating in the 10 to 20 milliseconds of new advanced microgrids – nor are they cybersecure.
In other cases, municipalities or small islands have systems with no inertia that may be a mix of diesel generators, solar, wind, battery storage or flywheels. “They have a difficult time keeping the lights on,” he said. SEL brings in high speed controls that can shed loads fast, dispatch signals and control voltage and inverters. “We’re able to take this collection of different sources and make them all work together.”
SEL focuses on educating customers about what microgrid can — and cannot do.
“One of the perceptions is that there is an off-the-shelf microgrid controller that will work for everybody,” Morris said. “That’s not the case. Every single one of these microgrids are different and the dynamics are different. You need to model it.”
Microgrid controllers continue to be improved on several fronts. Efforts are underway to bring standards by the Institute of Electrical and Electronics Engineers, more commonly called IEEE. Research facilities such as MIT’s Lincoln Laboratory and the National Renewable Energy Laboratory are further advancing the technology. (See related story.)
Work is also underway to bring greater sophistication to integrating renewables within microgrids — as well as using microgrids to balance the central grid when solar panels or wind farms suddenly stop producing power.
For SEL it is all a continuum of 15 years of work.
“Our objective is to serve customers and give them safe reliable power 24/7. We’re dedicated to do that and to integrate new and important renewable resources. It’s a challenge we are up to,” Morris said.
For more information about SEL, please visit
Interested in microgrid controllers? Learn more at Microgrid 2018 in Chicago, May 7-9.