February 22, 2014
Charge Management Device Would Help Keep Plug-in Cars From Crashing The Electric Grid
April Flowers for redOrbit.com - Your Universe Online
In 2013, more than 96,000 plug-in electric cars were bought in the United States. That number only represents a tiny slice of the auto market, but it is up 84 percent from 2012. As of January 2014, the Vermont Energy Investment Corporation reports that there are 679 plug-in automobiles in Vermont alone — a 200 percent growth over 2013.
In terms of oil consumption and air pollution, that is really good news. The bad news? Every electric car has to be plugged in, putting a strain on the nation's aging electrical distribution systems — like transformers and underground cables. This is especially true during hours of peak demand, such as 6pm when everyone is coming home from work.
Some utilities are already wondering, if not worrying, about how to manage all those cars seeking a socket at the same time without crashing the grid or pushing rates through the roof. A team of scientists from the University of Vermont (UVM) has created a novel solution. Their findings will be published in an upcoming issue of the journal IEEE Transactions on Smart Grid.
“The key to our approach is to break up the request for power from each car into multiple small chunks — into packets,” says Jeff Frolik, a professor in the College of Engineering and Mathematical Sciences.
The new approach uses the nation's growing network of “smart meters,” which are a new generation of household electric meters that communicate back-and-forth between a house and the utility. The UVM plan would allow a car to charge for, perhaps, five or ten minutes at a time. The car would then “get back into the line,” Frolik says, to make another request for power. During times of low demand, the car would continue to charge, but during high demand times it would have to wait.
“The vehicle doesn't care. And, most of the time, as long as people get charged by morning, they won’t care either,” says UVM’s Paul Hines, an expert on power systems. “By charging cars in this way, it's really easy to let everybody share the capacity that is available on the grid.”
The new strategy takes a page from radio and internet communication distributions to allow electric utilities to spread out the demand from plug-in cars over the whole day and night. The data submitted from the smart meter prevents the grid from being overloaded. "And the problem of peaks and valleys is becoming more pronounced as we get more intermittent power — wind and solar — in the system,” says Hines. “There is a growing need to smooth out supply and demand.”
The research team has a patent pending on their new invention, which would work simultaneously with the smart meters to protect the car owner's privacy. The invention, a charge management device, could be located at the level of a neighborhood substation, for example, to assess local strain on the grid. It would randomly distribute “charge packets” of power when the demand wasn't too high to those households putting in requests.
“Our solution is decentralized,” says Pooya Rezaei, a doctoral student working with Hines. “The utility doesn't know who is charging.”
The power would be distributed by a computer algorithm called an “automaton.” This automaton is the technical heart of the new approach. It is driven by rising and falling probabilities, which means every car requesting a charge would eventually get a turn. The utility company, however, wouldn't know, or need to know, a person's driving patterns or what house was receiving power when.
Sometimes, though, the need to charge a car immediately arises. “We assumed that drivers can decide to choose between urgent and non-urgent charging modes,” the scientists wrote. If urgent mode is selected, the car would charge regardless of the price of electricity. The car would have the best odds of moving to the front of the waiting line, almost certainly guaranteeing a full charge as soon as possible. Unfortunately, this would be accomplished at full market rates rather than the discount rate that would be used as an incentive for those opting-in to the new approach.
Why is there a need to put plug-in cars on “packetized demand” rather than the other electrical demands in a house? The new generation of plug-in cars, those with Level 2 PEV chargers, are likely to have the biggest power load of any item in a home. “The load provided by an electric vehicle and the load provided by a house are basically equivalent,” says Frolik. “If someone gets an electric vehicle it's like adding another house to that neighborhood.”
In a neighborhood, for example, where every household bought at least one plug-in vehicle the demand would double. The infrastructure—the wires and transformers, however, would remain the same. Some researchers and utilities, concerned about this potential for overload, are exploring systems where the company has centralized control over who can charge when. This scenario, called “omniscient centralized optimization,” could create a perfectly efficient use of the available power—in theory.
Such an approach would also mean that drivers would either have to be willing to provide information about their driving habits, or set schedules for when they will charge their cars. In a nation with a century's worth of idolizing the car as a tool of autonomy, this rubs against the grain.
Other researchers have proposed elaborate online auctions to manage demand. “Some of the other systems are way too complicated,” says Hines, who has extensive experience working with actual power companies. “In a big city, a utility doesn’t want to be managing millions of tiny auctions. Ours is a much simpler system that gets the job done without overloading the grid and gets people what they want the vast majority of the time.”