PM magnet 3 phase vs squirrel cage - advantages

leitmotif · Sep 7, 2005

Have not given up on quest for 3 phase drive on electric vehicle.
Have another thread "electric vehicle"

Have a vendor for the controller suggesting using permanent magnet brushless 3 phase. Please assume I know nothing about these (which is close to the truth).

I looked at the motor mfr he suggested
http://www.powertecmotors.com/pactorq.html#ptcat

It appears to be an option but I still need to do some studying.

I would like the feedback from that use these and find out the real world results and experience.

The first question I have is
What will they do for me in this application?
What advantage will it have over a regular 3 phase squirrel cage?

I intend to electrify a small pickup, retain transmisssion and rest of drive train. Motor RPM at 60 mph in 3rd gear is slightly more than 3600. If I design for mostly 60 mph will need 30 HP if I design for say 35 to 45 more like 20 HP (due to windage)

Thanks for help

Dan Bentler

kamenges · Sep 7, 2005

I don't know that a brushless motor will really gain you much in this case. I guess it should be a little more efficient as you get the rotor field 'for free'. You don't have to use power from the drive to create the rotor field as the rotor has permanent magents on it. Also, for a given horsepower the brushless motor should be lighter, which may or may not matter to you.

Now for the downside. There may be some servo drives out there that can commutate the motor without a sensor. However, most can't. So you will need to have a sensor of some type on the motor. Since you probably aren't worried too much about torque ripple you could probably go as simple as Hall Effect sensors and commutate like that. If you do that there are some relatively inexpensive brushless amplifiers you could use. If you want to commutate more accurately you will ned a resolver or an encoder, which costs more money.
The big downside is going to be the cost. I'm guessing here but a 30HP brushless motor will probably cost you $4000 or more new.

We used a Powertec Pactorq motor on a rotary cutoff knife. I am very impressed with what they can do. We used a 75HP dripproof blower ventelated motor at 3600 RPM in an E213TCZ frame. That's 75HP continuous. In a frame size equivalent to a 10-15HP 3-phase AC motor. So you get some pretty good power density. But again, that was blower cooled. You go without the blower and you cut the HP at least in half, probably more.

I just don't think it's worth it for you to go brushless as the price will be pretty nasty.
Keith

Leadfoot · Sep 7, 2005

The powertec brushless system is DY NO MITE. It has tremendous speed and torque regualting capabilities. The were initall touted as being brushless DC. The inverter section and motor windings look like 3 phase motors. The output only turns on 2 transistors at one time while VFD's do 3.

I have seen many WER TEC and POWER TEC drives over the years. The WER is the same Man that was WER industrial that became EMERSON industrial that is now Control Techniques. After he was bought out by emerson, he was not supposed to compete. When the time was over, he released the WER TEC drives, got sued and changed to POWERTEC.

The motors, cables and drives are a system. The encoder on the motors are part of the commutating system. They are 2 to 3 times the cost of closed loop vector.

The drives and motors usually have to be changed as a pair if a failure occurs. What broke, the drive or the motor encoder? I have seen drives changed and the motor trashed the new drive.

I would stick to closed loop vector if you want precision. If you can live with 0.3% regulation use open loop/sensorless vector. You pocket book will be much happier.

The initiall cost and cost to repair is the only real drawback not the actual equipment.

JesperMP · Sep 8, 2005

The encoder on the motors are part of the commutating system.

It sounds like the Powertec drive+motor combination is a specialised system to achieve better performance than regular drive and moto combinations. Therefore it is also more expensive.

A regular AC motor with permanent magnets runs syncronised with the magnetic field generated by the supply voltage.

A regular AC motor with squirrel cage cannot do this, so there will always be a "slip". A VFD can counter the slip to achieve almost zero drop in speed.

But do you need all this ? Maybe your pickup will run happily at a slightly lower speed than 3600 RPM.
Do you need very tight speed or position control ?

Rod · Sep 8, 2005

Dan,
The best brushless 'DC' motors I have worked with were from Kollmorgen.

Yes they are zero maintenaince and are PM motors that use a 3 phase drive. I have more experience with the GE Fanuc or Gettys motors which also have a PM, and are brush type motors. Those I can find used. As long as the magnets haven't been degaussed by major overloads and there is still some mica left on the rotor then....

What we've done in the past is 'shake-n-bake'. pull the rotor, clean with Simple Green, flush, cut the mica and stick in in the oven at 150 overnight. Or leave in the Texas sun for 2 hours. Swap out bearings or flush with a mix of ATF and Slick50.

I've used Fuji, Yaskawa, Gettys, Mitsu and other drives.
Almost all use either an encoder or resolver feedback for velocity and position (Think of lathes and mills spindle motors)

It is confusing to have a motor/drive hookup called a DC system when they a 3 phase AC input that is inverted to DC, chopped up and sent from the drives as a pseudo sine wave at about 4KHz.

I defer to the more knowledgeable peoplle on this forum.

Have fun
Rod

leitmotif · Sep 8, 2005

Thank you all for the field knowledge.
I do not need many capabilities of a PM 3 phase motor including
rapid reversal, precise positioning etc. These features are definitely needed on precise machinery I know, but I surely don't need them to make a truck go down the road or stop. The only two things it could do for me is
1. precise RPM matching of the transmission gears when shifting without a clutch (I know I can do this on trucks - if the motor does not slow too fast it should be no problem).
2. The encoder (is it?) could be used for speed signal for tach and speeedometer. Since I am keepint the transmission that is already installed.

Sounds like the expense does not justify. Back to the squirrel cage - which I am finding out is not gonna be easy to do with my requirement of 120VDC battery volt.

I think we can close this out I have my answer.

Again thank you all for the help
Dan Bentler

rsdoran · Sep 8, 2005

I have limited access these days so my comments will be short therefore may not offer enough information.

First and foremost I would not eliminate DC motor(s), more on that later.

The one thing that caught my attention is the fact that you plan to use the existing drivetrain components...ie transmission etc. You may want to study details applicable to those components...example the old Ford C6 tranny needed 60HP just to operate...technically this "HP" did not transfer to the rear axle. I doubt your system is that inefficient but it will require X amount of HP just to operate the tranny....in other words there will be energy used that is not transfered to the wheels.

The other issue will be RPM and torque combined at the tranny input to develop the required output...newer systems operate at higher rpm's than older systems so that may be a detail that has to be considered.

leitmotif · Sep 8, 2005

rsdoran said:
I have limited access these days so my comments will be short therefore may not offer enough information.

First and foremost I would not eliminate DC motor(s), more on that later.

The one thing that caught my attention is the fact that you plan to use the existing drivetrain components...ie transmission etc. You may want to study details applicable to those components...example the old Ford C6 tranny needed 60HP just to operate...technically this "HP" did not transfer to the rear axle. I doubt your system is that inefficient but it will require X amount of HP just to operate the tranny....in other words there will be energy used that is not transfered to the wheels.

The other issue will be RPM and torque combined at the tranny input to develop the required output...newer systems operate at higher rpm's than older systems so that may be a detail that has to be considered.

Ron
You have returned - welcome back.
The ford C 6 - remember the number
BUT was it a slush box or gear box?

Everything I have read so far says to retain the stock drive train (in this case transmission is 5 fwd speed manual)

Some also state efficiency on these gear boxes is 90% - I am bit skeptical on that number, but ??

With motor at 3600 RPM
low gear up to 20 mph
2nd to about 45
3rd to 60

Will definitly need low gear for climbng Seattle hills.

Let me make if very plain I know DC has been the standby forever - it works very well - drove Seattle buses with series 600VDC motor for eons. Used on rail we had 150 HP DC as reserve on submarine. I KNOW DC is good.
However industry, railroads, forklifts are switching to AC drive. Ford had AC drive on their electric pickup - worked great
- as an aside I know of two that are out of operation because of deplected batterries and there are no replacements allowed to go to non "Ford technicians" (I think that is the term used by the vendor)

I wanted to see if I could find the 3 phase motor and controller that could do it AND keep battery voltage around 120. I do not think I am going to for the next several years.

If I go to 312 VDC I could do it but I shiver at that high a DC voltage not so much for me (I am ex submarine battery electrician 250 VDC) but for equipment cost (higher dieelectric strenth, arcing on contacts, parts availability, etc etc) and i have to keep others in mind also firemen at wreck etc etc.

Dan Bentler

Leadfoot · Sep 8, 2005

250 VDC and most anybody's 200 volt series inverter would power a 230 VAC motor just fine. Are there motors available in 110 volt 3 phase at 40 to 60 HP?

Something to consider, if you have a 3600 rpm motor, thru 5 speeds would work. I think an automatic would be much smoother. The converter could absorbe the rpm changes better than the stick could.

You would need to program for a rapid decel when clutched and allow for longer decel for braking while in gear.

I seem to remember the old mail truck that was electrified used direct drive or minimal gearing.

The C6 trannies used bands. The FMX was a slush box.

leitmotif · Sep 8, 2005

Leadfoot said:
250 VDC and most anybody's 200 volt series inverter would power a 230 VAC motor just fine.

REPLY That thinking is what gave me the idea of using a forklift drive. I think the forklift drive is great - in Hyster case I CANNOT get the software so that whole idea is pretty much "on shelf" for two years.

SO use an industrial drive ?? Hmmm if I can keep battery voltage at 200 or less, throw out the AC to DC converter and tie battery directly to VFD's DC bus -- you bet that was option # 2. Now I think that 208 3 phase cuts off at 10 to 15 HP and then shifts to 460. However will need to rsearch this a little deeper.
The other thing I don't like is according to SIEMENS training web site the DC bus voltage is 1.35 that of incoming line -
SO at 208 that works out to 280VDC. That is a little high - higher yet than the battery and DC distribution / motors we had on submarine - not the end of the world though.

Are there motors available in 110 volt 3 phase at 40 to 60 HP?
REPLY While this would be perfect, I believe the single phase 120 volt inverters stop at about 2 HP. Even at 20 HP it would take a custom wound motor given the larger size of the conductor windings.

Something to consider, if you have a 3600 rpm motor, thru 5 speeds would work. I think an automatic would be much smoother. The converter could absorbe the rpm changes better than the stick could. The C6 trannies used bands. The FMX was a slush box.[/

REPLY SO the C 6 was still basically an automatic ?? That explains the higher power consumption.
I agree an automatic would be smoother. However IF you know how to shift without clutch (and I do -- learned 5 main 3 speed strait cut brownie) then smoooth is not a problem on the shift.

You would need to program for a rapid decel when clutched and allow for longer decel for braking while in gear.
REPLY not sure I follow here. Braking would be regen - oughta work great on Seattle hills. Would only shift to get next higher / lower "range" that keeps motor at 75% speed or more (mostly to ensure motor cooling)

I seem to remember the old mail truck that was electrified used direct drive or minimal gearing.
REPLY Remember it too. I believe the project was done in California. I interpreted the project as very successful. Mail service routes especially those in town would be perfect for electric.

Let there be NO doubt in anyones mind I am NOT opposed to DC.
I want to try AC first. It is my final fallback position.

I am OPEN to all suggestions.

All parts donations grateully accepted - I am unemployed. Will take free engineering also - the bit I do (however erroneous) keeps my mind busy - idle mind and the devil and all that stuff.

Dan Bentler

rdrast · Sep 9, 2005

Just a note, I've been following the discussion, but being quiet...

My car, the one in my avatar, uses a nominal 201 volt, 21 KW battery stack, which is fed through a DC/DC doubler to provide up to 500VDC to a 3 phase inverter drive. The drive powers what is about a 67 HP AC Permenant magnet motor.

On electric only, the performance and acceleratino is excellent, but hard accels can suck the battery stack dry in no time.

leitmotif · Sep 9, 2005

rdrast said:
Just a note, I've been following the discussion, but being quiet...

My car, the one in my avatar, uses a nominal 201 volt, 21 KW battery stack, which is fed through a DC/DC doubler to provide up to 500VDC to a 3 phase inverter drive. The drive powers what is about a 67 HP AC Permenant magnet motor.

On electric only, the performance and acceleratino is excellent, but hard accels can suck the battery stack dry in no time.

REPLY
Well I am all ears. I take it the car is a hybrid.
Tell me more.
ESPECIALLY about that DC / DC doubler.
That had crossed my mind - was not sure if it could be done (easily). That would solve most if not all problems and let me get the bus voltage up to that of a 460 inverter. In theory now I could use off shelf inverter and motor.

Thanks for the help
Dan Bentler

rdrast · Sep 9, 2005

I haven't taken it apart (yet), but I'm assuming that the converter is a fairly simple high-frequency chopper driving a pulse transformer; similar to a normal switching supply. One nice thing about the switch-mode DC/DC doubler is that it's very efficient, and lightweight, especially as the frequencies increase. I can't actually hear it in operation, which might indicate that the switch frequency is above the audible range; then again, it's only operating when the AC motor is energized, and I am always in the passenger cab when the things in motion

A switch-mode DC/DC converter like that could probably be built fairly simply around a switch power supply controller IC, some beefy MOSFETS, and perhaps a relatively small toroidal transformer. That into a rectifier stack and very little filtering, and you've got a regulated high voltage DC supply.

On my car, the Toyota Prius, it's mounted with the inverter section, and the entire inverter/doubler arrangement is liquid cooled (seperate cooling system from the engine cooling system).

leitmotif · Sep 9, 2005

Uh oh I hope I have not stimulated your curiosity.

If it ain't broke don't tinker with it.
DO NOT take that apart on my account.

How long have you had the car?
What do you think of this electric drive stuff?
Thanks for info.

Dan Bentler

Rod · Sep 9, 2005

My .01 cents again,

Dan,
I like the idea of conecting to the DC bus on the drive.

My crazy idea is to find 10 ferrite toroids and hand wrap them. You could make a voltage tripler or quadrupler. Crankup the freq for effeciency. Run the torroids in parallel and drive them with very effcient Hexfets (check Digikey). They would work like a passbank switcher. Each section would handle it's part of the load (10% in this mental exercise). A common input from the battery stack and a common output to the bus.

The killer is regen.

Rod

PM magnet 3 phase vs squirrel cage - advantages

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