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Old 12-07-2016, 12:56 PM   #2911 (permalink)
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Originally Posted by arber333 View Post
Finally someone figured cruise control for this inverter! Which is what V/Hz is yes?
I guess it would work. That's not really why I was wanting it though. The throttle is a torque signal to the controller. So fixing the throttle signal does not *REALLY* work for cruise control. You need a PID around the present speed. The throttle on a gas engine is actually a torque signal as well ... so cruise control should work similar for gas or electric.

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Well sort off... I suggest the primary use of V/Hz would be to implement cruise control. You have PID regulation working. You frame it for V/Hz to move found one chosen frequency, fixed by a button switch (on dash) and PID would try to follow this frequency - speed control! Throttle would still be effective upwards from chosen speed, so you could tap the button with throttle and set a higher speed or just tap button with throttle loose and car would deccelerate some. To break the link would require pulse on brake switch line
I think all of this works with the throttle/torque signal as well. No need to switch to the less efficient V/Hz output.

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, you have this wired yes?
I have not seen a Brake switch into the controller as yet. It's the lower part of the wig-wag throttle .. so far .. in my testing at least and what I have seen of Paul's Leaf motor cart.

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Limp home mode could effect itself automaticaly if encoder signal would be lost. That way you could have some control if sensor was out. It happened to me with my controller. I use optical RPM sensor for arduino (a glorified mouse sensor) and it caught moisture and corrosion. I replaced it with better protected one but it stays a weak link im my car. My 5c...
The switch between a Torque input and a speed input is going to give you a sudden change, I think. If you are cruising at highway speed, going down a small incline for example, you could have your throttle close to 1/3. If the encoder quit, your speed would drop to 1/3 of your maximum speed, which could be a rapid deceleration.

Or you could be accelerating gently from a traffic light, lose the encoder, and now your car wants to keep accelerating to 3/4 speed instead.

I'm kinda worried about the transition. Right now, if you lose the encoder, the motor decelerates rapidly to maybe 1/10 of the speed you were going ... not a perfect solution if you are on a freeway!

If we can come up with a way to do something reasonable and the speed changes gradually then you have time to get to the side of the road, or use your brakes, or let off the throttle. That's sort of what I'm looking for. The car would definitely handle differently in V/Hz than it does in Field Oriented Control. Acceleration and deceleration would be less aggressive and less efficient. But the car should still be drive-able.

I wonder if the throttle input for V/Hz could be interpreted as amps? That is close to a torque setpoint, and there should be no big change when switching from Field Oriented control to V/Hz and back again ....

I need to do some reading ... Google to the rescue!

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Old 12-08-2016, 03:56 PM   #2912 (permalink)
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Originally Posted by thingstodo View Post
If we can come up with a way to do something reasonable and the speed changes gradually then you have time to get to the side of the road, or use your brakes, or let off the throttle. That's sort of what I'm looking for. The car would definitely handle differently in V/Hz than it does in Field Oriented Control. Acceleration and deceleration would be less aggressive and less efficient. But the car should still be drive-able.

I wonder if the throttle input for V/Hz could be interpreted as amps? That is close to a torque setpoint, and there should be no big change when switching from Field Oriented control to V/Hz and back again ....

I need to do some reading ... Google to the rescue!
A summary of what I've read, mixed with a bit of my own experience:
- The amps for an AC motor don't really go much below 25%, even if it is spinning slowly and unloaded, unless you are moving to regenerative braking from motoring.
- So the amps go from 25% to about 115% for the throttle signal, but it depends almost totally on the acceleration/deceleration
- Keeping the amps at 75% the car speeds up slowly (relatively) compared to keeping the amps at 100%. The controller needs to increase the output voltage as the frequency rises to keep the amps at 100%. At some point you run out of voltage and it can no longer maintain 100% current.
- Using Paul's wig-wag style throttle arrangement, and the amps as a setpoint from the throttle, there is a deadband from 25% down to -25% where the motor is not exactly coasting but is not really motoring or regen braking. Perhaps that works OK as a control philosophy?

Switching to using the throttle as a current command when the encoder signal goes away sounds interesting to me. I think Klaus (is that his name?) does a similar thing with the controller that Damien Maguire is using. I think Klaus refers to it as slip control instead of field oriented control. And it uses encoder feeedback .. so maybe I'm off base there?

Does this re-interpreting -the-throttle-signal-and-switching-to-V/Hz-control -with-amps sound like something that we should pursue? Comments?

Besides the math and tracking the rotor position/angle ... Field Oriented Control appears to allow for the voltage to adjust auto-magically as required to get the commanded torque. Where the V/Hz has a specific voltage programmed as an equation for each output frequency. If you want the current to rise, you increase the output frequency with your PID loop. Depending on the motor load, you could be applying 'TOO MUCH' voltage and wasting some power as motor heat .. or you could be applying 'TOO LITTLE' voltage and not getting the current (and the torque) that you want.

I'm getting excited about seeing the difference in the control schemes, and trying to determine how much farther you can go, or how much faster you can accelerate, with Field Oriented Control ... or specifically the encoder signal .. compared to essentially open loop control at V/Hz.

My my ... I do get long winded!
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Old 12-08-2016, 05:41 PM   #2913 (permalink)
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Quote:
Originally Posted by thingstodo View Post
A summary of what I've read, mixed with a bit of my own experience:
- The amps for an AC motor don't really go much below 25%, even if it is spinning slowly and unloaded, unless you are moving to regenerative braking from motoring.
- So the amps go from 25% to about 115% for the throttle signal, but it depends almost totally on the acceleration/deceleration
- Keeping the amps at 75% the car speeds up slowly (relatively) compared to keeping the amps at 100%. The controller needs to increase the output voltage as the frequency rises to keep the amps at 100%. At some point you run out of voltage and it can no longer maintain 100% current.
- Using Paul's wig-wag style throttle arrangement, and the amps as a setpoint from the throttle, there is a deadband from 25% down to -25% where the motor is not exactly coasting but is not really motoring or regen braking. Perhaps that works OK as a control philosophy?

Switching to using the throttle as a current command when the encoder signal goes away sounds interesting to me. I think Klaus (is that his name?) does a similar thing with the controller that Damien Maguire is using. I think Klaus refers to it as slip control instead of field oriented control. And it uses encoder feeedback .. so maybe I'm off base there?

My my ... I do get long winded!
Well in short, yes i use Johannes inverter in my car, and it is excellent. It uses a sort of V/Hz to spin motor first couple of turns and then switches to slip mode with optical encoder. It uses PI regulator. Even for cruise control it uses PI with time supression. I drive every day. Only one bad thing about it, it is made for ACIM only. I spun my Leaf motor unloaded with it but reverse EMI were so bad my DCDC shorted!

I dont want to use wig-wag throttle since i want to drive a car not a ship or submarine. I really need reverse switch in software.

A
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Old 12-08-2016, 06:05 PM   #2914 (permalink)
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The encoder signal breaking is pretty catastrophic. So maybe if that happens, the controller could go into a coast mode where all IGBTs go off. Then whether it's permanent magnet or induction, it would just be like you lost power in a normal car, and are coasting. Maybe then you could assume the motor is about the same RPM as it was before "broken encoder" happened. Then you could set the frequency/voltage to match what the frequency was before, and officially be in V/Hz mode for the purpose of limping home. Or if it's a Leaf sort of motor, just coast to a halt with all igbts off. One reason I like the Leaf resolver is it's very reliable and is largely immune to noise/dirt. It would have to be a cut wire to cause a problem.

The newest board has a variable brake input. Just like a throttle. I'm not sure how useful it is. Tesla, for example, uses normal brakes, and has the throttle in a wig wag, with programmable max regen, but just stops the regen once the car has stopped. I don't know if everybody does that or what. Arber, do you have reverse from the transmission? I wonder how standard it would be for people driving a car with no reverse except for a button on their dashboard.
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Old 12-08-2016, 07:56 PM   #2915 (permalink)
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I am sorry i havent got the meaning of wig wag throttle. I meant it as a boat throttle where one moves throttle back and eventually gets a backward movement. Not a good throttle in a car.
But what you use now is good. I can compare to BMW I3 and my car. Yes i have first 30% regen then throttle region with seamless transition. Thingstodo was right about ACIM coasting at 25% power. You just dont see it often since you need quite some torque keeping 1t beast at speed.

For a brake signal i would rather use a switch. In my experience variable braking is better controlled by throttle pedal, brake switch could then be programed to give a little less force than fully released throttle to avoid jerky stops from a right turn where you use brake to stop.
And with brake SW you could disable cruise control or have a hill hold function for 1s etc...

I have a single speed gearbox for Leaf motor. There is no other provision for reverse than switching phases. I insist on this because it should be easier to do in software than by hw and every commercial inverter has this.
Leaf, I3, C0 and Tesla dont have reverse gear, they simply switch phases and lower available torque so you dont go backwards into wall. That means you have to connect phase cable in correct order so the motor spins the correct way and then say "this is reverse".

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Old 12-08-2016, 08:00 PM   #2916 (permalink)
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That's good to know! I'll make sure I include a reverse button then.
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Old 12-09-2016, 10:47 AM   #2917 (permalink)
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Well in short, yes i use Johannes inverter in my car, and it is excellent.
My apologies to Johannes - I'm not sure why I thought his name was Klaus?
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Old 12-09-2016, 10:52 AM   #2918 (permalink)
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That's good to know! I'll make sure I include a reverse button then.
If you are using a manual gearbox, it is still nice to reduce available torque and max speed when you are in reverse.

Can you make the reverse switch configurable, so that the motor direction can be switched (for a single speed gearbox) or not (if you want to switch to a reverse gear) but the max speed and motor torque are reduced?
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Old 12-09-2016, 11:07 AM   #2919 (permalink)
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The encoder signal breaking is pretty catastrophic.
Sounds like the Leaf has the encoder well protected. The Siemens motor I tested with has the encoder internal to the motor casing so I expect it is a bit more difficult to damage.

My external encoders are really easy to damage. Alignment, vibration, coupling ... my DIY stuff is much less robust!

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So maybe if that happens, the controller could go into a coast mode where all IGBTs go off. Then whether it's permanent magnet or induction, it would just be like you lost power in a normal car, and are coasting.
That sounds pretty good. You may need some extra code to figure out whether the motor has no encoder when it begins to move or perhaps you are on a hill and need a bit more throttle to get the motor to rotate?

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Maybe then you could assume the motor is about the same RPM as it was before "broken encoder" happened. Then you could set the frequency/voltage to match what the frequency was before, and officially be in V/Hz mode for the purpose of limping home.
The switch from Field Oriented Control to V/Hz is sounding like a risk. Coasting to a stop, then starting out in limp mode on V/Hz should be an acceptable solution for as often as this should happen.

I'm not sure what I was thinking .. switching control methods while the motor is still rotating ... !!! .. my normal paranoia seems to have taken a short vacation.

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The newest board has a variable brake input. Just like a throttle. I'm not sure how useful it is. Tesla, for example, uses normal brakes, and has the throttle in a wig wag, with programmable max regen, but just stops the regen once the car has stopped. I don't know if everybody does that or what. Arber, do you have reverse from the transmission? I wonder how standard it would be for people driving a car with no reverse except for a button on their dashboard.
There are a couple of things to watch for with regen. When you are doing regen from the throttle, and then press on the brake, the brake needs to ramp up the regen from that regen point you are already at, not release the regen to 0 and start ramping again. That feels like pressing the brake gives you acceleration ... very disturbing!

And the regen only pumps power back into the batteries to a certain speed. After that you are using battery power to slow down your car and would be better off letting the friction brakes heat up a bit instead. That may be a bit hard to determine by calculations ... perhaps experimentally would be best and just enter the low speed cutoff into the configuration?

That could be tricky, as you have no control on when the friction brakes engage ... how much HIP you need to put into the brake pedal before the friction brakes start helping to slow the car.

Maybe I'm getting carried away again? Heck, we KNOW I'm getting carried away! That's what I do.
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Old 12-09-2016, 03:50 PM   #2920 (permalink)
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Originally Posted by thingstodo View Post
If you are using a manual gearbox, it is still nice to reduce available torque and max speed when you are in reverse.

Can you make the reverse switch configurable, so that the motor direction can be switched (for a single speed gearbox) or not (if you want to switch to a reverse gear) but the max speed and motor torque are reduced?
Yes excellent notion! Currently i use my transmission reverse light to signal inverter i am in reverse and it reduces torque to 30%. If i had 100% for reverse the acceleration backwards would brake my teeth on a steering wheel!

Regarding regen, Johannes uses a ramp configurable from certain Hz to 0 to be sure not to have high slip regen in lo rpm area. That would avoid high regen at stopping, like hitting a brick wall! I tried this with early software, not pleasant at all...


Last edited by arber333; 12-09-2016 at 03:59 PM..
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