New Motor Drive 2

[jjohnson]

We are finalizing design of a motor drive (small 2" x 4" x 0.5", 43-pin package) for 3-phase brushless DC motors. It will control 30amp per phase at a max bus voltage of 80volts. It will control speed and direction, features soft-start and over-current protection, tachometer output. Are we missing anything? Is there some particular parameter that would make this a winner? Thanks.

 

[jbartos]

Suggestions:
1. A communication port
2. C-form auxiliary relay contact, dry or solid state related to power on / off

 

[rhatcher]

jbartos, good answer with respect to suggesting desirable features for a drive. However, I would suggest that no matter how many features jjohnson added that there is probably not much of a market for drives to control "3-phase brushless DC motors".......

 

[jbartos]

Suggestion: There are some permanent magnet motors coming that do not have some problems squirrel-cage induction motors have, e.g. cracking cages, high inrush currents, speed-torque curve forms, complexity, etc. They may be called 3-phase DC brushless motors by some.

 

[rhatcher]

Not by me......I have two problems with this.

- brushless DC motor?
- 3-phase DC motor?

Obviously, the combination of the two seems even more unlikely. However, I am not an expert so if you can offer a web link with more info on '3-phase DC brushless motors' I would appreciate it.

 

[driveguy]

rhatcher,




Brushless DC Motors

"Despite their superior qualities, brushless motors still run second to brush types in motion-control applications. Brushless systems are usually preferred, however, where their benefits outweigh their higher price. And they cost less than brush types in some applications when energy, maintenance, and downtime costs are included in the comparison between the two approaches.

Amplifier costs for both systems have dropped in recent years, moreover, and are forecast to drop further. Thus, the cost differential between the two approaches is an increasingly smaller percentage of total system cost. The situation has brought a large number of competitors into the market, helping to reduce prices for brushless systems. A result is that brushless motor sales have risen rapidly in the last few years. And sales of brushless motors continue to increase.

Conventional brushless motors come in a variety of configurations. The most widely used look much like brush-type motors. But brushless motors have a wound stator that surrounds a permanent-magnet rotor, an inverse arrangement from that for brush motors. And stator windings are commutated electronically rather than through a conventional commutator and brushes.

Brushless motors generally contain a three-phase winding, although some operate four phase. Brushless motors powering small fans and other constant-speed equipment are often two phase.

Power for brushless motors generally is a trapezoidal ac wave form, but some of the motors operate with sine waves. Trapezoidal-powered motors develop about 10% more torque than those on sine-wave power. Sinusoidal-powered motors, however, exhibit less torque ripple and operate smoother at low speed. Thus, sinusoidal-powered motors are often used for machining, grinding, coating, and other operations calling for fine surface finishes.

Because they have no commutator, brushless motors are more efficient, need less maintenance, and can operate at higher speeds than conventional dc motors. High efficiency and small size are especially important for military, aircraft, and automotive applications, and for portable instruments and communications equipment.

The cost of both brush-type and brushless motors likely will rise because of increasing costs for iron, steel, copper, aluminum, and magnets. The increases will be partly offset by use of neodymium-iron-boron magnets. The magnets are often more powerful than samarium-cobalt magnets and promise to be much less expensive.

Amplifiers for brushless motors are more complex than brush types and generally call for two additional solid-state power switches. These switches account for most of the cost differential between the two types. But switch cost continues to drop, in part because of increased use of MOSFET and insulated-gate type switches. Costs also are dropping for ICs used in commutation, feedback interpretation, and PWM circuits. The lower costs reduce but do not eliminate the price differential between amplifiers for the two types of systems."


Because of the low bus voltage this would realistically be limited to the automotive industry. For line operated applications the Bus voltages would need to be in the 120 to 370 VDC range

 

[rhatcher]

driveguy, thank you very much for the information. I gave you a star for your informative post. I guess this proves what I have always believed (and loved) about our field...one can never know it all.

Obviously you have now fueled my curiosity (you know what they say about curiosity and cats?...if I was a cat I would have used my nine lives long ago...). I am interested in knowing more about this motor type. If you can refer me to a web site (manufacturer of motors and/or controllers) with more info then I can pursue my interests without troubling you further. If not, would you please take the time to answer the following questions?

- is this motor otherwise known as a permanent magnet synchronous motor? If so, disregard the rest of my questions as I am familiar with this type (although not by the name '3-phase DC brushless motor')

If not, then:

- arrangement of the windings on the stator. Are the windings arranged in salient poles like those of a standard (brush type) DC motor or are they arranged to form non-salient poles like those of an AC motor. If they are non-salient, are they concentric or lap wound?

- exact nature of the voltages applied to the windings. Is the voltage DC or AC? The above post implies an AC voltage, but the motor is named as a DC.

- related to previous question: number of phases. Are there actually 2, 3, or 4 different circuits each receiving a voltage that is out of phase with the others (for example true 3 phase AC as in an induction motor)?

- method of speed control. Is the speed controlled by voltage amplitude, frequency (in the case of AC), or perhaps both (VV/VF)?

Again, thank you for the information and thanks in advance for any further help on this topic.

 

[nbucska]

hi temperature shot-down <nbucska@pcperipherals.com>

 

[don01]

hi guys
yep i'm back
rhatcher can only echo your sentiments (meow)
please mr drive guy fill us in
I have only heard the name dc brushless motor with 2,3,4 phases
and I'm very interested too

Regards
Don

 

[still]

Hi I'm olso interested in this subject.
And my question is:
HOW TO CONTROL DC BRUSHLESS MOTOR IN A HIGH SPEED(10000 RPM)
I NOW THAT I CANT USE PWM.


Thank you for the information and thanks in advance for any further help.

 

[jbartos]

Suggestions: Visit

http://www.thomasregister.com

and type Controls: Brushless DC Motor under Product / Service which will return 6 companies to contact
Also, type Motors: Brushless DC which will return 190 companies to contact for more info
There are also good books at

http://www.amazon.com

Design of Brushless Permanent-Magnet (Monographs in Electrical and Electronic Engineering, 37) -- by J. R. Hendershot, T. J. E. Miller; Hardcover Our Price: $150.00
Industrial Brushless Servomotors -- by Peter Moreton; Hardcover, Our Price: $56.95
Brushless Servomotors : Fundamentals and Applications (Monographs in Electrical and
Electronic Engineering, Vol 23) by Yasuhiko Dote, Sakan Kinoshita (Editor)
Brushless Dc Motors : Electronic Commutation and Controls by Thomas J. Sokira
or

http://www.barnesnoble.com

in addition to Technical Library resources