Researchers from the College of Engineering have designed a system where a small network of local generators can reliably disconnect from the rest of the power supply, enabling locations where electricity is critical to stay in operation.

Most buildings receive their electrical power from transmission lines branching off a main power grid. With energy coming from a large network -- the one responsible for the August 2003 blackout stretched 157,000 miles -- any disruption could cause a cascade of powerlessness in cities near and far.

Because the new technology developed at UW-Madison receives its power locally, it can "leap frog" transmission lines, avoiding any failures within those lines, says lead inventor Robert Lasseter, professor emeritus of electrical and computer engineering.

The UW-Madison technology consists of a microgrid, a small network of several power generators located at a single site. These generators, integrated into the main energy distribution system, encompass a wide range of power sources, including micro-turbines, gas internal combustion engines, fuel cells and photovoltaic, which generates voltage from light exposure.

When problems occur within the transmission lines, the generators and their loads (the devices each one powers) can separate from the main distribution system to isolate particular areas -- hospital rooms or factory floor, for example -- from the disturbance.

Explains Lasseter: "The critical loads in a microgrid can ride through any event. That means they can stay alive when the grid fails." The ability to "island" generators and electrical loads together, he adds, has the potential to provide higher local power reliability than that provided by the distribution system as a whole.

But providing this reliability requires more than separating the microgrid from the main power system, says Lasseter. Drops in voltage, even from generators in a small network, can lead to fluctuations in power that shut down equipment or recalibrate machinery. These are the types of costly problems that businesses want to avoid during a blackout, Lasseter adds.

To dodge these fluctuations, the Wisconsin engineer and his graduate student, Paolo Piagi, have fit the generators in the migrogrid with voltage source inverters -- a power electronic device that allows each generator to regulate voltage, thereby regulating electric current and the energy it produces.

Besides sidestepping possible power outages, the microgrid system is more energy efficient. All generators -- whether part of a utility plant or small building -- produce more waste heat than electricity.

However, smaller generators, such as those in Lasseter's microgrid network, can easily be placed in areas that need to be heated, says the Wisconsin engineer. This placement of the generators and the waste heat they produce, he adds, can bump up the amount of usable energy to nearly 90 percent, and can do so without the use of complex heat distribution systems, such as steam and chilled water pipes.

Lasseter and his UW-Madison colleagues are discussing a project to build a working microgrid with the California Department of Energy and the national laboratories of Sandia, Oak Ridge and Lawrence Livermore. The project would simulate the possible use of a microgrid at a small factory.

The microgrid design is patented by the Wisconsin Alumni Research Foundation, a non-profit organization that patents and licenses intellectual property for the university.

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