“Hell, there are no rules here — we're trying to accomplish something.” —Thomas Edison
“Using dc probably makes better sense today because of power electronics and alternative energy sources.” —Fred Lee
Edison was probably right: we should use dc distribution systems, says Fred Lee, director of the Center for Power Electronics (CPES) and a University Distinguished Professor. “Using dc probably makes better sense today because of power electronics and alternative energy sources,” he says.
“To run a motor today, you start with power from the ac grid and you first rectify the ac into dc,” he explains. “When you rectify, you need to make a power factor correction to make sure your current works with the voltage, in phase and with a compatible wave shape.” Without this correction, 130 watts that come into the home may only contain 100 that are usable.
“That’s a total waste,” Lee says. “Taking ac, rectifying it to dc, then inverting it into ac again for a variable speed drive … that process is totally unnecessary with dc power and alternative energy sources.”
He cites another example: “Computers all run on low voltage. The first thing we do is convert our ac power to 400 V, then convert it into the 12 or so volts needed by the computer. Every conversion wastes energy. If I work with dc directly, I can save all that wasted energy.”
The ac infrastructure took 100 years to build and would take years to change, he admits. He expains, however, that off-the-grid or power sub-systems may be cost-effective in the near future using dc systems.
A large data center could be converted to a dc sub-system, for example. “Data centers were all built without considering the optimal power system. The internet era erupted so abruptly that they quickly grabbed components off the shelf and set them up,” he says.
Right now, data centers using utility ac install an online uninterruptible power supply to make the data center fault tolerant. They take the ac voltage, convert it to dc, then invert it back to ac. The ac then flows into the servers. Then, each server takes the ac and rectifies it into dc. “You could probably save 20 percent of the electricity by eliminating those conversions. If you add the heat and air conditioning, you can definitely save more than 20 percent,” he says.
“It’s all talk right now; nobody is doing anything commercially,” he adds.
CPES researchers are exploring the concept of dc systems with a new dc distribution testbed being established in Whittemore Hall. Four rooms are being converted into a “living lab” for students, faculty and staff, with a conference room, library/lounge, kitchen, and utility room.