Scott Drive 100kW AC motor & controller - DIY Electric Car Forums
Go Back  

DIY Electric Car Forums > EV Conversions and Builds > Electric Motors

Register Blogs FAQ Members List Social Groups Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Display Modes
  #1  
Old 05-27-2012, 10:15 PM
njloof njloof is offline
Senior Member
 
Join Date: Nov 2011
Posts: 273
njloof is on a distinguished road
Default Scott Drive 100kW AC motor & controller

Quote:
Originally Posted by efan
this controller+motor seem to be a new development, and I dont know of anyone who has used it..but it may be worth checking them out.

http://shop.greenstage.co.nz/product...-motor-package
Anybody actually seen or used this (new?) AC motor/controller combo? I see the Greenstage guys have a good history here, but this seems to be a first for them, and beats out the current HPEVS Curtis/AC50 combo by a good margin.

Thanks to efan for pointing this out!
Reply With Quote
  #2  
Old 05-28-2012, 03:17 AM
Elegancec Elegancec is offline
Member
 
Join Date: May 2012
Posts: 68
Elegancec is on a distinguished road
Default Re: Scott Drive 100kW AC motor & controller

Hello, Im also very interested into this new drive. From the data it would be my favourite, @njloof, thank you for posting in my thread (http://www.diyelectriccar.com/forums...s-74449p2.html) this great news!
Reply With Quote
  #3  
Old 05-28-2012, 08:07 AM
njloof njloof is offline
Senior Member
 
Join Date: Nov 2011
Posts: 273
njloof is on a distinguished road
Default Re: Scott Drive 100kW AC motor & controller

Quote:
Originally Posted by Elegancec View Post
Hello, Im also very interested into this new drive. From the data it would be my favourite, @njloof, thank you for posting in my thread (http://www.diyelectriccar.com/forums...s-74449p2.html) this great news!
I can't take credit for @efan posting this... But thanks anyway
Reply With Quote
  #4  
Old 05-28-2012, 04:53 AM
Tesseract's Avatar
Tesseract Tesseract is offline
Senior Member
 
Join Date: Sep 2008
Location: Tampa, FL USA
Posts: 2,991
Tesseract has a spectacular aura aboutTesseract has a spectacular aura aboutTesseract has a spectacular aura about
Default Re: Scott Drive 100kW AC motor & controller

Quote:
Originally Posted by njloof View Post
...I see the Greenstage guys have a good history here, but this seems to be a first for them, and beats out the current HPEVS Curtis/AC50 combo by a good margin....
Hmm... interesting find. Always good to know what the potential competition is up to.

Note that this system uses a *trapezoidal* BLDC motor, not a sinusoidal type like, e.g., the Remy HVH250 motor. Without getting too wonky, the switching pattern needed for trapezoidal BLDC makes it impossible to use any type of field-oriented control algorithm - only 6-step "V/f" is allowed. This means poor low speed torque, and high levels of torque ripple, noise and vibration at all speeds. Here is a good overview of the two different types of BLDC motor.

As a result of these severe shortcomings, trapezoidal BLDC is really only suitable for small fans and servos, not traction applications.
__________________
Chief Electron Herder for Evnetics, LLC.

Into EV's? Check out ChargedEVs Magazine
Reply With Quote
  #5  
Old 05-28-2012, 06:19 AM
MalcolmB's Avatar
MalcolmB MalcolmB is offline
Senior Member
 
Join Date: Jun 2008
Location: Newcastle upon Tyne, UK
Posts: 553
MalcolmB is on a distinguished road
Default Re: Scott Drive 100kW AC motor & controller

Great link Tesseract!

The only trapezoidally controlled brushless motors I've had experience with are little ebike hub motors. I guess the torque ripple explains why they growl so much under load? But I still don't grasp why they produce poor torque at low rpm, though I know from reading reports on Endless Sphere that this is a big limitation.

According to that link: "Sinusoidal commutation results in smoothness of control that is generally unachievable with trapezoidal commutation. However, while it is very effective at low motor speeds, it tends to fall apart at high motor speeds."
Can you put a rough figure on the upper rpm limit for sinusoidal control, or does that depend on the motor design as well?

Malcolm
__________________
Mini conversion:
http://www.diyelectriccar.com/forums...ad.php?t=52461
Reply With Quote
  #6  
Old 05-28-2012, 07:34 AM
Tesseract's Avatar
Tesseract Tesseract is offline
Senior Member
 
Join Date: Sep 2008
Location: Tampa, FL USA
Posts: 2,991
Tesseract has a spectacular aura aboutTesseract has a spectacular aura aboutTesseract has a spectacular aura about
Default Re: Scott Drive 100kW AC motor & controller

Quote:
Originally Posted by MalcolmB View Post
Great link Tesseract!
Yeah, I thought so to when I read it. I've got all kinds of very expensive books on this stuff and none of them come close to explaining the basic difference in the two types of BLDC stator construction as well as that document.

Quote:
Originally Posted by MalcolmB View Post
The only trapezoidally controlled brushless motors I've had experience with are little ebike hub motors. I guess the torque ripple explains why they growl so much under load? But I still don't grasp why they produce poor torque at low rpm, though I know from reading reports on Endless Sphere that this is a big limitation.
Generally speaking, it's because there are only 6 points where the stator windings and rotor magnets are perfectly aligned in the trapezoidal BLDC; at every other rotor angle some of the phase current goes towards uselessly trying to counteract (or add to) the flux of the rotor magnets rather than moving the rotor through space.

Quote:
Originally Posted by MalcolmB View Post
According to that link: "Sinusoidal commutation results in smoothness of control that is generally unachievable with trapezoidal commutation. However, while it is very effective at low motor speeds, it tends to fall apart at high motor speeds."
Can you put a rough figure on the upper rpm limit for sinusoidal control, or does that depend on the motor design as well?...
The higher the rotor RPM the higher the stator frequency and therefore the higher the AC losses in the motor, thus the design of the stator sets a practical upper limit on the RPM, assuming the rotor can handle the centrifugal* force, that is. However, the higher the RPM the faster the processor in the controller needs to be to calculate the switching state needed to create the correct voltage vector for the rotor's actual position. In other words, at a high enough RPM the rotor will move a significant angular distance in the time it takes the processor to calculate the voltage vector. A graceful fallback is to drop the number of voltage vectors until you ultimately end up at 6-step operation.

* - the oldest argument on the interwebz is that centrifugal force doesn't exist, but everyone knows what it means so let's pretend that it does.
__________________
Chief Electron Herder for Evnetics, LLC.

Into EV's? Check out ChargedEVs Magazine

Last edited by Tesseract; 05-28-2012 at 08:56 AM. Reason: forgot *
Reply With Quote
  #7  
Old 05-28-2012, 08:30 AM
njloof njloof is offline
Senior Member
 
Join Date: Nov 2011
Posts: 273
njloof is on a distinguished road
Default Re: Scott Drive 100kW AC motor & controller

Quote:
Originally Posted by Tesseract View Post
Note that this system uses a *trapezoidal* BLDC motor, not a sinusoidal type like, e.g., the Remy HVH250 motor. Without getting too wonky, the switching pattern needed for trapezoidal BLDC makes it impossible to use any type of field-oriented control algorithm - only 6-step "V/f" is allowed. This means poor low speed torque, and high levels of torque ripple, noise and vibration at all speeds.
Great article, and makes sense -- it describes quite well what I see on my brushless e-bike as well

But... why not filter the discrete Hall signal into a sinusoidal curve? Or, if you've got a decent processor available, predict the true position of the rotor? At worst the motor is hooked to a flywheel, and at best to a 1+ ton car; the change in rotational velocity of the rotor should be relatively small during 60 degrees of rotation...
Reply With Quote
  #8  
Old 05-28-2012, 08:39 AM
Tesseract's Avatar
Tesseract Tesseract is offline
Senior Member
 
Join Date: Sep 2008
Location: Tampa, FL USA
Posts: 2,991
Tesseract has a spectacular aura aboutTesseract has a spectacular aura aboutTesseract has a spectacular aura about
Default Re: Scott Drive 100kW AC motor & controller

Quote:
Originally Posted by njloof View Post
...
But... why not filter the discrete Hall signal into a sinusoidal curve?...
Firstly, because the phase angle of a waveform is always shifted when you filter it, but secondly, the poor performance of the trapezoidal BLDC is directly the result of its simpler construction. If you want better performance you need to rewind the stator. No two ways about it. And just to make it extra clear, it doesn't matter if you know exactly where the rotor is, there are still only going to be 6 points equally spaced about the stator where you will get maximum torque for a given RMS phase current.
__________________
Chief Electron Herder for Evnetics, LLC.

Into EV's? Check out ChargedEVs Magazine

Last edited by Tesseract; 05-28-2012 at 08:40 AM. Reason: Added "And just to make it extra clear..."
Reply With Quote
  #9  
Old 05-28-2012, 09:11 AM
njloof njloof is offline
Senior Member
 
Join Date: Nov 2011
Posts: 273
njloof is on a distinguished road
Default Re: Scott Drive 100kW AC motor & controller

Quote:
Originally Posted by Tesseract View Post
And just to make it extra clear, it doesn't matter if you know exactly where the rotor is, there are still only going to be 6 points equally spaced about the stator where you will get maximum torque for a given RMS phase current.
Because you can't excite all three windings independently?
Reply With Quote
  #10  
Old 05-28-2012, 10:51 AM
Elegancec Elegancec is offline
Member
 
Join Date: May 2012
Posts: 68
Elegancec is on a distinguished road
Default Re: Scott Drive 100kW AC motor & controller

So I think its clear, the controller can also only operate with this treapezodial brushless motor and with no other AC motors, because of its simpler design.

The torque curve would be interesting.
Reply With Quote
Reply

Share or Bookmark this

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

 
Support DIY Electric Car
Sponsors

All times are GMT -6. The time now is 09:53 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.

Ad Management by RedTyger