The Future of AC Motor Drives

Stefan,

AC drives have come a long ways since DC drives that were 100% of the industry for many years. Up till around 1988 DC drives were king in the printing and paper industry. Since that time AC Drives have really started to come on line and the performance has improved so much so that they have replaced almost all applications in the paper industry. My last job was with Elco Electric Launch, started in 1893 at the worlds fair in Chicago, we built electric boats up till Oct08 when the economy shut us down. I designed a drop in drive to replace Diesel engines up to 16HP using DC drive/motor, once passed the 16HP Diesel engine, switched over to 144VDC inverted to 220 3Phase AC motor up to 40HP, Beyond 40HP went to 216VDC inverted to 60HP AC motor.

Bottom line is AC is cheap, no moving parts, with the new AC VFD's you can do almost anything you want to do with these motors and if you are looking for energy efficiency. It is the only way to go. AC is here to stay, DC is a dinosaur.

I'd suggest getting in touch with application engineers at some of the companies who have been making industrial drives for decades, such as Reliance and GE.

In industrial settings, the general trend has been toward AC drives when variable speed is required. There are still DC drives in use in many settings, but AC motors are hard to beat for reliability and simplicity.

In the electric vehicle world, AC is taking over, although there are still more DC motors on fork lift trucks, golf carts, neighborhood vehicles, etc. In hybrid and electric road vehicles, AC will probably prevail, although there are some brushless DC motors in use (and these are controlled in a manner similar to an AC motor). In low horspower motors (40-50 and less) brushless DC motors are more efficient, mainly because they rely on permanent magnets for their fields. In very heavy equipment, AC drives are taking over from hydraulics for traction uses.

I'd guess that the controls for AC motors will evolve but remain in principal about as they are today. The efficiency is already very high, so there are not a lot of people saying that they would use variable speed drives if they worked better. Instead I think the market will look for lower cost (and perhaps greater convenience) in what is a fairly mature technology. Increasing emphasis on energy efficiency should increase interest in VFDs.

Stefan,

There are a number of directions an answer can take.

• For ease of implementation, there are so many different schemes of operator interfaces with fault codes, etc. A careful and long look at this topic could yield some approaches much simpler than the cryptic fault codes and convoluted setup sequences so common now.
• For power quality, the odd-numbered harmonics continue to be a serious problem to distribution systems, as the number of electronic devices in use increases. Incremental developments or other work done here may be fruitful.
• For drive durability, the miniaturization of components continues to produce heat stress and resultant failure. It would be nice to see designs that are truly industrially robust.
• For quietness, the drives with no carrier frequency are superior.
• For motor durability, the problems of impedance mismatch at motor terminals and resultant reflected higher-frequency waves have punched through the insulation in the first few turns of many otherwise good motors. As IGBT and later semiconductor switching frequencies get higher, this problem will only increase, but the capability for filtering it out will also improve.
  
• Beyond these, look at the macro-changes in technology and try to figure out what these can imply for how changes will occur in the future. I have taken out a couple very large six-transistor drives and admire the quietness and infinite speed control of wound-rotor motors with variable secondary resistors.

Good studies. JMM

Hello dear Stefan,

please check the following link for further information for new developments on materials and topologies for electric motors: www.hoganas.com/en/products--applications/soft-magnetic-composites/application-examples/

If you need further information, please contact me @ henrique.lopes@hoganas.com

Best regards,

Henrique