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A48E_EETimes_2_37x10_87_A19.qxd 3/31/15 12:09 Rare earth magnets still optimum choice, says motor design expert By Graham Prophet Transformers P& Inductors romoting a workshop to be held at the forthcoming CWIEME Berlin event, by SURFACE MOUNT (and thru-hole) Size Does matter! Low Profile From .18” Height 1.2 Grams Weight Reliability: MIL PRF27/MIL PRF21308 Manufacturing Approved DSCC Quality: AS9100C Qualified Facility US Manufactured Military and Commercial Aircraft Supplier for over 45 Years For all your TRANSFORMER & INDUCTOR requirements • Audio • Pulse • DC-DC • MultiPlex • Power & EMI See Pico’s full Catalog immediately at www.picoelect ronic s.com PICOElectronics, Inc. 143 Sparks Ave. Pelham, N.Y. 10803-1837 Pico Representatives Germany ELBV/Electronische Bauelemente Vertrieb E-mail: info@elbv.de Phone: 0049 89 4602852 Fax: 0049 89 46205442 England Ginsbury Electronics Ltd. E-mail: rbennett@ginsbury.co.uk Phone: 0044 1634 298900 Fax: 0044 1634 290904 Motorsolver president and IEEE life fellow Jim Hendershot, the organisers have released a preview of some of his findings regarding current industry practice in the selection of traction motors. At the conference, Hendershot will explore the pros and cons of hybrid and electric vehicle motor designs, encompassing performance, manufacturing methods and cost. Amid concerns over the price, supply and hazardous extraction of rare earth metals used in permanent magnet motors, many members of the motor manufacturing community, especially those in the automotive sector, are carrying out extensive research into eliminating or reducing their use. Visitors to the 2015 CWIEME Berlin exhibition will have heard about several initiatives in this area, such as the EU-funded MotorBrain project and work of the Karlsruhe Institute of Technologys Helmholz Center for hybrid and electric vehicles, in the seminar programme. Practically speaking, however, rare earth permanent magnets still remain the number one choice in hybrid and electric vehicle motors, according to leading design expert Jim Hendershot running the workshop at the exhibition. Mr. Hendershot, based in Kentucky, USA, has over 40 years experience in the design of permanent magnet and brushless switch-reluctant motors for computer disc drives, servo systems, traction drives, and hybrid vehicles, as well as micro-turbine and diesel generators. He has co-authored two of the leading design books on permanent magnet motors and generator design and has worked for some of the worlds most influential manufacturers, including General Motors. There are several types of electric motors for engineers to choose from for hybrid and electric vehicle traction drives: induction (or asynchronous), permanent magnet synchronous, switched-reluctance synchronous or reluctant synchronous. A couple of large front-end loaders earth-moving machines use switched-reluctance wheel motors and some large dump trucks and bulldozers use AC induction motors for traction, as well as newer forklift trucks. But all major hybrid electric vehicles currently in production use rare earth permanent magnet synchronous traction motors, he says. When BMW were beta testing their new i3 model, they ran them around for a few years with induction motors in them. But when it came to high volume production, they changed it to a permanent magnet motor. Similarly, it has been reported that Toyota is investigating motors with no magnets, such as AC induction, but so far there is no clear indication that Toyota will switch over to AC induction motors now that magnet prices have subsided somewhat, he adds. The principle reason for popularity of the permanent magnet machine is that all other machine types without magnets require more mass and are less efficient. These are very important features for transportation vehicles, aircraft and ships. The maximum performance of any machine type is based upon the magnetic and electrical properties of the machine materials and all machine types tend to utilise the same electrical steel grades and copper conductors. Machines without magnets must be magnetised by supply current from their power source, whereas permanent magnet machines require zero magnetising current so their efficiency is always higher than machines such as AC induction and reluctance machines with no magnets. AC Induction machines have rotor slip losses, rotor Ohmic losses and they are limited to four pole designs, compared to permanent magnet synchronous machines that utilise higher pole numbers, making them smaller. Even with the best materials in the world an AC induction motor will still be less efficient as it requires power from the batteries to magnetise the magnetic circuit, he says. www.electronics-eetimes.com Electronic Engineering Times Europe May 2015 43


EETE MAY 2015
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