2009 Hot Weather High RPMs?
#21
06-23-2009, 04:15 PM
Re: 2009 Hot Weather High RPMs?
It was 100 degrees today but I was able to work from home so I haven't had the FEH out to play with this any more.
-- Rick
#22
06-23-2009, 05:25 PM
Re: 2009 Hot Weather High RPMs?
Anyhow I agree that the stated behavior is totally normal. The ICE must produce more power to run the AC.
#23
06-23-2009, 05:50 PM
Re: 2009 Hot Weather High RPMs?
Desert Dog:
You don't understand how synchronous machines work, sorry. Don't be so ready to tell someone he's wrong. So I guess when I was teaching at Georgia Tech I didn't know what I was talking about? I understand perfectly well how synchronous machines work; I suspect much better than you based on what you've posted.
In a synchronous machine (as both the traction motor & generator are, they're electrically equivalent but differently sized) there are two ways to increase power: rotation rate (eg rpm) and excitation to the rotor (eg magnetic field strength). Since these are synchronous machines with permanent magnet rotors the excitation is necessarily constant.
My statement about increasing rpm assumed that the road speed was being held constant by the controller. Your citing of the equation is incorrectly used. No, it is not. Constant road speed equals constant traction motor RPM. If you are driving in EV on a flat road and encounter an incline, maintaining constant speed means more power from the traction motor at the same RPM. This means more current, not more RPM. If what you are saying was correct, regen power could not be controlled at all. Obviously it can be.
I happen to think this is normal if unusual operation. If I see this in mine I'll just note it.
You don't understand how synchronous machines work, sorry. Don't be so ready to tell someone he's wrong. So I guess when I was teaching at Georgia Tech I didn't know what I was talking about? I understand perfectly well how synchronous machines work; I suspect much better than you based on what you've posted.
In a synchronous machine (as both the traction motor & generator are, they're electrically equivalent but differently sized) there are two ways to increase power: rotation rate (eg rpm) and excitation to the rotor (eg magnetic field strength). Since these are synchronous machines with permanent magnet rotors the excitation is necessarily constant.
My statement about increasing rpm assumed that the road speed was being held constant by the controller. Your citing of the equation is incorrectly used. No, it is not. Constant road speed equals constant traction motor RPM. If you are driving in EV on a flat road and encounter an incline, maintaining constant speed means more power from the traction motor at the same RPM. This means more current, not more RPM. If what you are saying was correct, regen power could not be controlled at all. Obviously it can be.
I happen to think this is normal if unusual operation. If I see this in mine I'll just note it.
#24
06-23-2009, 08:03 PM
Re: 2009 Hot Weather High RPMs?
It is now obvious that you bum doped your students.
You don't make a synchronous machine go faster with more current. Its the AC frequency that changes rpm, period, excamation point professor.
If you wish to go another level and talk about power transfer in synchronous machines and lag angles and such we can do that, but its beyond the scope of this posting.
When I spoke of increasing rpms I was speaking of how the ICE increases power to the generator. Remember that when the controller calls for more power to maintain speed it raises ICE rpms with the traction motor held constant this then means that the generator rpms go up and produce more power by raising the rpm of the generator. The contoller then regulates the power split device, a planetary gear set to keep speed constant.
Of course with a larger load and larger current into the traction motor the lag angle gets bigger since we can't regulate the rotor field. That's how synchronous machines increase power at constant speed.
And that's precisely why the generator must increase rpm. With a constant rotor field strength there's no way to increase power output of the generator unless its rpm goes up. Since it is clear that the ICE rpms go up and the traction motor rpm stays constant when climbing that hill, where did you think the extra rpms went to?
So if the ICE speeds up where does the extra energy go and how does it get there? I believe it shows up in higher generator rpms which means more power. This power is then conditioned and sent on to the traction motor.
There's a reason there is a separate cooling circuit for the power conditioning gear. When such power is called for the conditioning circuitry generates some real heat. (Of course it's a different temp range than the ICE... smile.)
You don't make a synchronous machine go faster with more current. Its the AC frequency that changes rpm, period, excamation point professor.
If you wish to go another level and talk about power transfer in synchronous machines and lag angles and such we can do that, but its beyond the scope of this posting.
When I spoke of increasing rpms I was speaking of how the ICE increases power to the generator. Remember that when the controller calls for more power to maintain speed it raises ICE rpms with the traction motor held constant this then means that the generator rpms go up and produce more power by raising the rpm of the generator. The contoller then regulates the power split device, a planetary gear set to keep speed constant.
Of course with a larger load and larger current into the traction motor the lag angle gets bigger since we can't regulate the rotor field. That's how synchronous machines increase power at constant speed.
And that's precisely why the generator must increase rpm. With a constant rotor field strength there's no way to increase power output of the generator unless its rpm goes up. Since it is clear that the ICE rpms go up and the traction motor rpm stays constant when climbing that hill, where did you think the extra rpms went to?
So if the ICE speeds up where does the extra energy go and how does it get there? I believe it shows up in higher generator rpms which means more power. This power is then conditioned and sent on to the traction motor.
There's a reason there is a separate cooling circuit for the power conditioning gear. When such power is called for the conditioning circuitry generates some real heat. (Of course it's a different temp range than the ICE... smile.)
#25
06-23-2009, 08:19 PM
Re: 2009 Hot Weather High RPMs?
It is now obvious that you bum doped your students.
You don't make a synchronous machine go faster with more current. Its the AC frequency that changes rpm, period, excamation point professor.
If you wish to go another level and talk about power transfer in synchronous machines and lag angles and such we can do that, but its beyond the scope of this posting.
When I spoke of increasing rpms I was speaking of how the ICE increases power to the generator. Remember that when the controller calls for more power to maintain speed it raises ICE rpms with the traction motor held constant this then means that the generator rpms go up and produce more power by raising the rpm of the generator. The contoller then regulates the power split device, a planetary gear set to keep speed constant.
Of course with a larger load and larger current into the traction motor the lag angle gets bigger since we can't regulate the rotor field. That's how synchronous machines increase power at constant speed.
And that's precisely why the generator must increase rpm. With a constant rotor field strength there's no way to increase power output of the generator unless its rpm goes up. Since it is clear that the ICE rpms go up and the traction motor rpm stays constant when climbing that hill, where did you think the extra rpms went to?
So if the ICE speeds up where does the extra energy go and how does it get there? I believe it shows up in higher generator rpms which means more power. This power is then conditioned and sent on to the traction motor.
There's a reason there is a separate cooling circuit for the power conditioning gear. When such power is called for the conditioning circuitry generates some real heat. (Of course it's a different temp range than the ICE... smile.)
You don't make a synchronous machine go faster with more current. Its the AC frequency that changes rpm, period, excamation point professor.
If you wish to go another level and talk about power transfer in synchronous machines and lag angles and such we can do that, but its beyond the scope of this posting.
When I spoke of increasing rpms I was speaking of how the ICE increases power to the generator. Remember that when the controller calls for more power to maintain speed it raises ICE rpms with the traction motor held constant this then means that the generator rpms go up and produce more power by raising the rpm of the generator. The contoller then regulates the power split device, a planetary gear set to keep speed constant.
Of course with a larger load and larger current into the traction motor the lag angle gets bigger since we can't regulate the rotor field. That's how synchronous machines increase power at constant speed.
And that's precisely why the generator must increase rpm. With a constant rotor field strength there's no way to increase power output of the generator unless its rpm goes up. Since it is clear that the ICE rpms go up and the traction motor rpm stays constant when climbing that hill, where did you think the extra rpms went to?
So if the ICE speeds up where does the extra energy go and how does it get there? I believe it shows up in higher generator rpms which means more power. This power is then conditioned and sent on to the traction motor.
There's a reason there is a separate cooling circuit for the power conditioning gear. When such power is called for the conditioning circuitry generates some real heat. (Of course it's a different temp range than the ICE... smile.)
Last edited by MMooney; 06-23-2009 at 08:20 PM. Reason: Didn't finish.
#26
06-23-2009, 08:34 PM
Ridiculously Active Enthusiast
Join Date: Sep 2006
Location: Beautiful Pacific NW
Posts: 1,678
Re: 2009 Hot Weather High RPMs?
Desert Dog:
You don't understand how synchronous machines work, sorry. Don't be so ready to tell someone he's wrong.
In a synchronous machine (as both the traction motor & generator are, they're electrically equivalent but differently sized) there are two ways to increase power: rotation rate (eg rpm) and excitation to the rotor (eg magnetic field strength).
Since these are synchronous machines with permanent magnet rotors the excitation is necessarily constant.
Yes, the rotor's excitation field will be constant, but the stator fields' voltage and current can be varied "at will". I would guess that at lower electric motor speeds the supply is based moreso on current flow levels then voltage. But my point is that these AC motors can have varibale torque as function of stator field modulation, even stationary.
My statement about increasing rpm assumed that the road speed was being held constant by the controller. Your citing of the equation is incorrectly used.
I happen to think this is normal if unusual operation. If I see this in mine I'll just note it.
You don't understand how synchronous machines work, sorry. Don't be so ready to tell someone he's wrong.
In a synchronous machine (as both the traction motor & generator are, they're electrically equivalent but differently sized) there are two ways to increase power: rotation rate (eg rpm) and excitation to the rotor (eg magnetic field strength).
Since these are synchronous machines with permanent magnet rotors the excitation is necessarily constant.
Yes, the rotor's excitation field will be constant, but the stator fields' voltage and current can be varied "at will". I would guess that at lower electric motor speeds the supply is based moreso on current flow levels then voltage. But my point is that these AC motors can have varibale torque as function of stator field modulation, even stationary.
My statement about increasing rpm assumed that the road speed was being held constant by the controller. Your citing of the equation is incorrectly used.
I happen to think this is normal if unusual operation. If I see this in mine I'll just note it.
#27
06-23-2009, 10:55 PM
Hybrid and Ethanol Expert
Join Date: Mar 2005
Location: All over the Central U.S.
Posts: 3,616
Re: 2009 Hot Weather High RPMs?
( not true in some Honda Hybrids )
It is a 3 part transmission with fixed gear ratios that are ALWAYS in mesh.
You can only change the RPM ratios.
Assume the wheel speed is constant, then the traction motor speed is constant.
Then if you speed up the engine, the generator speed will change in an inverse proportion. ( you can think of it "slowing down" but it could be speeding up in the negative )
I made a neat graph to show some of this relationship...
Gotta go find it....
Yes, AC frequency = speed.
More current = more torque, which is felt as more "power".
I work with industrial motors in the 480 to 4160 volt range.
They are 5 HP to 1000 HP.
They are all constant voltage, but they are variable frequency.
The current just does what it needs to, to keep the machines rolling at the speed set point.
#28
06-24-2009, 12:53 AM
Re: 2009 Hot Weather High RPMs?
It is now obvious that you bum doped your students.
You don't make a synchronous machine go faster with more current.
I NEVER said this anywhere! Where the heck did you get that from??
Its the AC frequency that changes rpm, period, exclamation point professor. DUH!
If you wish to go another level and talk about power transfer in synchronous machines and lag angles and such we can do that, but its beyond the scope of this posting. We need to discuss FOC and PWM controllers, that is more to the point.
When I spoke of increasing rpms I was speaking of how the ICE increases power to the generator. Remember that when the controller calls for more power to maintain speed it raises ICE rpms with the traction motor held constant this then means that the generator rpms go up and produce more power by raising the rpm of the generator. NO, NO, NO! The equation I gave describes the planetary gear set for all conditions. The ICE RPM going from 1400 to 2000 reduces the generator speed to near zero! What don't you understand about this? It's all in the shop manuals! The contoller then regulates the power split device, a planetary gear set to keep speed constant.
Of course with a larger load and larger current into the traction motor the lag angle gets bigger since we can't regulate the rotor field. That's how synchronous machines increase power at constant speed. Wait a minute - you have been arguing that the only way to increase power was to increase speed - you are now agreeing with me!
And that's precisely why the generator must increase rpm. With a constant rotor field strength there's no way to increase power output of the generator unless its rpm goes up. Since it is clear that the ICE rpms go up and the traction motor rpm stays constant when climbing that hill, where did you think the extra rpms went to? Bill Winney's law of conservation of RPMs I guess. Go back and read about planetary gearsets and maybe you'll finally get it.
So if the ICE speeds up where does the extra energy go and how does it get there? I believe it shows up in higher generator rpms which means more power. You believe wrong. The extra ICE power is transferred through the sun (generator) to the ring (traction) or it is absorbed by the AC compressor. This power is then conditioned and sent on to the traction motor.
There's a reason there is a separate cooling circuit for the power conditioning gear. When such power is called for the conditioning circuitry generates some real heat. (Of course it's a different temp range than the ICE... smile.)
You don't make a synchronous machine go faster with more current.
I NEVER said this anywhere! Where the heck did you get that from??
Its the AC frequency that changes rpm, period, exclamation point professor. DUH!
If you wish to go another level and talk about power transfer in synchronous machines and lag angles and such we can do that, but its beyond the scope of this posting. We need to discuss FOC and PWM controllers, that is more to the point.
When I spoke of increasing rpms I was speaking of how the ICE increases power to the generator. Remember that when the controller calls for more power to maintain speed it raises ICE rpms with the traction motor held constant this then means that the generator rpms go up and produce more power by raising the rpm of the generator. NO, NO, NO! The equation I gave describes the planetary gear set for all conditions. The ICE RPM going from 1400 to 2000 reduces the generator speed to near zero! What don't you understand about this? It's all in the shop manuals! The contoller then regulates the power split device, a planetary gear set to keep speed constant.
Of course with a larger load and larger current into the traction motor the lag angle gets bigger since we can't regulate the rotor field. That's how synchronous machines increase power at constant speed. Wait a minute - you have been arguing that the only way to increase power was to increase speed - you are now agreeing with me!
And that's precisely why the generator must increase rpm. With a constant rotor field strength there's no way to increase power output of the generator unless its rpm goes up. Since it is clear that the ICE rpms go up and the traction motor rpm stays constant when climbing that hill, where did you think the extra rpms went to? Bill Winney's law of conservation of RPMs I guess. Go back and read about planetary gearsets and maybe you'll finally get it.
So if the ICE speeds up where does the extra energy go and how does it get there? I believe it shows up in higher generator rpms which means more power. You believe wrong. The extra ICE power is transferred through the sun (generator) to the ring (traction) or it is absorbed by the AC compressor. This power is then conditioned and sent on to the traction motor.
There's a reason there is a separate cooling circuit for the power conditioning gear. When such power is called for the conditioning circuitry generates some real heat. (Of course it's a different temp range than the ICE... smile.)
#29
06-24-2009, 08:24 AM
Ridiculously Active Enthusiast
Join Date: Sep 2006
Location: Beautiful Pacific NW
Posts: 1,678
Re: 2009 Hot Weather High RPMs?
It might be more proper, appropriate to think of these electric motors as permanent magnet rotor STEPPER MOTORS wherein the output torque is TOTALLY a function of stator DRIVE current.
#30
06-24-2009, 11:52 AM
Join Date: Apr 2008
Location: Los Angeles
Posts: 895
Re: 2009 Hot Weather High RPMs?
This is effectively what we are seeing in the FEH (actual cutoff temperature may vary by a couple of degrees).
