New Alternator Technology Boosts Power In Future Cars By Lisa Eccles Indianapolis has reaped the bless- ing of its designation as Crossroads of America; making it easy for folks to discover all the nation’s 12th largest city has to offer. In fact, more inter- state highways run through this city of nearly one million than any other! While more than five million visitors stop for a day or more each year, Indianapolis residents are eager to share the “Hoo- sier Hospitality” with even more of the country’s multitudes. Convenient ac- cess by air and 12minute cab rides from the airport to downtown make this metrop- olis easy and affordable to navigate. Designed by the architects of Re- searchers at the Massachusetts In- stitute of Technology’s Laboratory for Electromagnetic and Electronic Systems in Cambridge, MA have developed methods to boost the power in upcoming automobiles. Led by David I. Perreault, the sci- entists have found effective ways to move from the standard 14-volt au- tomobile electrical systems to the 42-volt system of the future. A 42-volt electrical system is nec- essary to enable the performance of advanced electrical features. Heated windshields, devices for reducing nox- ious emissions, and advanced suspen- sions will require additional power. As a result, the team has focused on reconfiguring the alternator, or electri- cal generator, to enhance vehicle power. The experimental alternator is based upon mathematical modeling. Its configuration dramatically increases the peak and average power output from aconventional Lundell alternator. The researchers replaced three of the pas- sive elements for directing current, or diodes, in a standard alternator with three active switches. Engineers can then control and optimize energy flow through the vehicle. Additionally, the experimental al- ternator configuration incorporates a simple switched-mode rectifier and a load-matching control technique. While the Lundell alternator model optimizes energy only in the idle mode and the fixed output voltage is not matched to the alternator characteris- tics at other operating points, the MIT alternator attains maximum load- matched power at all speeds. The new system uses field control and a switched-mode rectifier to achieve higher power than conven- tional systems. Higher power output is enabled by using the switched mode rectifier as a second control handle to properly match the constant-voltage load to the alternator. Also, the switched-mode rectifier provides the necessary controlled-voltage transfor- mation to match the constant—volt- age load to the alternator as speed varies. Power output in this configura- tion is a function of the bridge voltage rather than the output voltage. This lets the alternator generate up to its maxi- mum power as speed varies without increasing alternator losses or thermal stress. Thanks to increased efficiency, the new system dissipates less energy in the form of heat. It also burns signifi- cantly less fuel to produce exactly the same amount of power as standard automobiles. The MIT configuration solves the problem of voltage spikes in a 42-volt electrical system, too. While a maximum spike ina 14-volt APRIL, 2001 system is 80 volts, a similar spike in the higher-voltage system can reach 240 volts. This design ensures that the voltage spikes up to no more than 60 volts during such an episode. One additional complication ofa 42-volt electrical system is the inabil- ity to jumpstart the vehicle witha 14- volt vehicle battery. The design, how- ever, uses the energy stored magneti- cally in the alternator during current flow to aid in jumpstarting. The stored energy coupled with controls included in the new system make jumpstarting a 42-volt vehicle with a 14-volt ve- hicle battery possible. For more information concerning the MIT alternator experiment, visit http://web.mit.edu. Reprinted with permission, Electronic Design magazine. Page 1 of 1