Date: 17/04/2015

Motor selection for your EV car/drone design, material economics matters

Over the decades of scientific research, the miniaturization and increase in the power efficiencies of electronics devices is an important area achieved by the electronic industry.

Advanced semiconductor technology could pack billions of transistors in a thumbnail sized today's chips compared to a thumbnail size transistor in late 50s. Tiny BAW and SAW filters replace bulky traditional LC filters. The bulky powerline Transformers used to step down AC voltage to lower level for converting it into DC power for electronics systems are now made quite small due to switching power supply design. And even in the batteries-area, there is some amount of miniaturisation happening. The most widely used electrical machine 'electrical motor' is also miniaturised and made power efficient, and also light in weight, so that it can be even used in solar powered aeroplanes and drones as propellers.

All these achievements is done through innovation in material-science research and the processing of those materiperals. In some cases such as Silicon in ICs, the material used is abundant and nothing much to worry. But in many other cases the material is short in supply and has a lot of economical impact, if the device made using a less-abundant material is produced in very large volumes.

Some of the important materials which are short in supply and expected to be used in larger scale are rare-earth materials such as neodymium, dysprosium used in manufacturing of permanent magnets in motors.

High-efficiency motors are required in electric vehicles, solar powered aeroplanes and drones. Due to the environmental and economic benefits of electric power driven vehicles both on road, water and air, the demand for electric driven vehicles expected to grow faster in the coming years which will result in huge demand for high-efficiency motors. If these motors are made using rare earth materials which are short in supply, the price of such materials are going to shoot up and also the motors and finally the electric driven vehicles.

So if you are into the area of high efficiency motor design or use of such motor in your application such as electric car design, there are two events to learn about material related economic impact on your motor design and selection.

1. At the CWIEME workshop going to be held on 5-7 of May 2015 at Berlin, Germany, Jim Hendershot, Motorsolver president and IEEE life fellow will talk on pros and cons of hybrid and electric vehicle motor designs, encompassing performance, manufacturing methods and cost.

Jim Hendershot commented “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 use switched-reluctance wheel motors and some large dump trucks and dozers 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” .

“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.

Permanent magnet based motors occupy less space and doesn't need any current for magnetisation, this makes them suitable 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 utilize the same electrical steel grades and copper conductors. Machines without magnets must be magnetized by supply current from their power source, whereas permanent magnet machines require zero magnetizing current so their efficiency is always higher than machines like 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 utilize 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 magnetize the magnetic circuit,” says Jim.

2. If you're in India, you don't need to be disappointed for not able to attend the above said far-away event. Indian Institute of Technology (IIT), Bombay has arranged a talk on the same subject by another good expert of the subject Prof. Alexander H. King, Director of Critical Materials Institute, Ames Laboratory, US Department of Energy, Iowa, USA. The talk is titled as "Critical Materials for Energy Systems"

The abstract for the talk reads "In 2010, the prices of neodymium, dysprosium and several other rare earth elements ballooned to levels never seen before, and the attention of the world was drawn to the issue of critical materials – substances for which there are fragile supply chains and no easy substitutes. The Speaker in his lecture will review the underlying causes of materials criticality; describe the impacts of supply disruptions, assess the current state of play; and describe the strategies that can be used to mitigate supply chain problems."

The talk is scheduled on 27 April 2015 - 4:00pm at Lecture Hall No. 21, 2nd Floor, Victor Menezes Convention Centre (VMCC) IIT Bombay, Powai.

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Author: Srinivasa Reddy N
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