Microgrid Research Advances Blackout Response

Researchers from the College of Engineering at the University of Wisconsin-Madison (UW-Madison) have designed a system to avoid blackouts, like the one that shut down the northeastern United States last summer. The system allows a small network of local generators to reliably disconnect from the rest of the power supply, enabling locations where electricity is critical to stay in operation.

Madison, Wisconsin – December 23, 2003 [SolarAccess.com] As most buildings receive their electrical power from transmission lines branching off a main power grid with energy coming from a large network, any disruption could cause a cascade of powerlessness in cities near and far. The disruption responsible for the August 2003 blackout stretched 157,000 miles. According to Robert Lasseter, UW-Madison Professor Emeritus of Electrical and Computer Engineering, because the new technology developed at UW-Madison receives its power locally, it can “leap frog” transmission lines, avoiding any failures within those lines. 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 photovoltaics (PV). 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. “The critical loads in a microgrid can ride through any event,” Lasseter said. “That means they can stay alive when the grid fails. The ability to ‘island’ generators and electrical loads together has the potential to provide higher local power reliability than that provided by the distribution system as a whole.” However, Lasseter said that providing this reliability requires more than separating the microgrid from the main power system, as drops in voltage, even from generators in a small network, can lead to fluctuations in power that shut down equipment or recalibrate machinery. According to Lasseter, these are the types of costly problems that businesses want to avoid during a blackout. In order to dodge these fluctuations, the Lasseter said that he 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. According to Lasseter, besides sidestepping possible power outages, the microgrid system is more energy efficient. Although all generators (whether part of a utility plant or small building) produce more waste heat than electricity, smaller generators, such as those in Lasseter’s microgrid network, can easily be placed in areas that need to be heated. Lasseter said that this placement of the generators and the waste heat they produce 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. According to Lasseter, the project would simulate the possible use of a microgrid at a small factory.

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