Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

[Cyruscosmo]

Hey Paul

Yes it would be difficult to test a regen with no flywheel to store a bit of momentum. I could set you up with a flywheel if ya want one. I have a few double row pulleys off obsolete equipment that would make a great flywheel for ya. If you are interested let me know what the shaft size is on that motor and I will send ya a split taper bushing and an iron pulley. You would have to bolt the motor to something like the workbench to keep it from flipping over during hard testing.

You know in some vehicles the brake pedal moves a bit before it even starts applying the brakes. The reason being is that movement is used to turn on the brake light "before" you start to slow down. That space could be used for regen without having to tap the hydraulic side of the brakes.

So you do have it set up for separate inputs for throttle and regen, yes?

Cyruscosmo

[MPaulHolmes]

actually, I didn't even know there was such a thing as a variable pressure switch when I sent the board in. we will have to "blue wire" to an unused pin on the microcontroller. it will need a resistor and cap for a filter, but that would be easy to add. Just one more change for the next revision.

I would love a flywheel. on the back side the post sticks out about 1.1 inches, and is a diameter of 1.125". on tje front is a diameter of 1 inch, and has a key of 0.315". the front is unfortunately where the encoder is too. there is about 1.1" of available post on the front. I should have had the encoder put on the back. but I had the front turned down so an encoder would fit, and didnt even know there was a back until later when it was too late.

[thingstodo]

Originally Posted by MPaulHolmes

At the moment, I'm using a hall effect throttle, where the middle 15% is "zero", and clockwise rotoates the motor one way, and counter clockwise rotates it the other way. It regens whenever you turn the throttle the opposite way that it wants to turn.

Awesome!

In real life I think we'll use a variable pressure switch on the brake or something. Then, if you press the brake, it regens, and you slow down.

The EVTV guys do something like that. The pressure transducer is 0 - 5V for 0 - 250 psi. But you can also do regen with the accelerator pedal. It gets involved quickly from there. The Generalized Electric Vehicle Control Unit is open source, and their proven method can be reviewed and parts of it used here.

Once it reaches the max regen that you program, if you push harder, then the regular old brake kicks in. That's the idea at least.

That matches the GEVCU pretty well.

I have no way of testing it at the moment. I guess I could rig a brake pedal or something.

Do you have an extra analog input on the PIC available to implement it?

It's just that my motor has no "whatever that's called" when it's really heavy, and hard to slow down.

?Inertia?

I cranked the regen up to 10 amps this morning, and the motor post went from about 1500RPM to 0RPM in about 0.01 second, like it hit a brick wall. Not exactly what we are shooting for in real life.

You might be able to couple the motor to a load, like a generator or a saw mandrel, that would add to your inertia. Might not be worth the effort though. You likely would not see the regen currents for long.

[freebeard]

Originally Posted by Cyruscosmo

So you do have it set up for separate inputs for throttle and regen, yes?

If I had a vote it would be for that, at least as an option.

The reason is I have a proper lever between the seats for the parking/emergency brake, not the footpedal/hand release. Even now I tend to drive with my left hand at 6 o'clock on the wheel and my right hand on the brake lever.

It seems that putting it in the foot brake would be hard to modulate. The hand brake has 11-12 clicks when it's slack, 7 clicks when it's 'properly' adjusted and it takes 2-3 to engage. So there's room to engage, and then disengage if it's not a good idea to have regen on while parked.

I'm not sure how an electrical part would be added onto the existing lever.

[Astro]

I think this was talked about earlier in the thread (or maybe it was the DC thread?) but i think both options would be good.
Adjustable regen on the throttle and a separate regen input.

I am aiming to make my EV as intuitive as possible for somebody familiar with driving a regular car.
So having a small amount of regen on the throttle would duplicate the engine braking effect you get on a regular car when you lift the throttle. It really is surprising how much i rely on that effect in traffic. I would find it disconcerting to lift my foot off the accelerator and have the car continue rolling at the same speed. It would also mean much more swapping my foot between throttle and brake in traffic.
Yes, i would get used to it and adapt but it would be nice to keep it consistent with what a regular car does.

Then for more regen i will be doing what Paul mentioned and putting a pressure sensor on the brake line which will give a variable voltage depending on brake pedal travel. Hopefully it will be possible to set this up so that the regen kicks in very early on in the brake pedal travel and increases to near maximum regen just as the normal brake pads start to bite the disks/drums,
So most braking would be via regen but any serious/aggressive braking would cause the normal brake pads to do their stuff.

This would also mean any failure of the controller would cause the regen part of the brake to stop working but the driver would just naturally press the brake pedal harder and the normal brakes would save the day. This seems the safest way , IMO.

It would also mean the controller wouldn't have to interface with the brake light and worry about when to activate the light. The brake lights would still be activated by the original switch on the brake pedal mechanism.
The slight regen on throttle off wouldn't require the brake light as the engine braking on a regular car doesn't activate the brake lights either.

[cts_casemod]

I find the regen on the throttle quite easy to use. I also find that its more natural to release the throttle and let the car slow down that to place the foot on the brake pedal. Gives a few metets advantage while one switches pedals.

A few thoughts tough:
Regent should be gradually reduced as the vehicle slows down. Too much makes it hard to switch pedals.

A neutral point is good.

If the throttle is used to brake and accelerate, the available resolution goes down. This can make subtle movements a bit rough at low speed. Typically some digital filtering solves the problem. I use a variable that increments by one at low pedal travel and by 5 at full throttle.

[freebeard]

I guess I'm fine with either, really. If the vehicle is motionless with a closed throttle, is regen on? Could the pivot for the pedal be raised so you press with your heel to get regen?

[cts_casemod]

Originally Posted by freebeard

I guess I'm fine with either, really. If the vehicle is motionless with a closed throttle, is regen on? Could the pivot for the pedal be raised so you press with your heel to get regen?

You can let Regen go all the way down to zero, in which case the motor will sometimes draw a bit of power if the deceleration is very slow. This is because the motor is acting as a brake to slow down the vehicle. If deceleration is slow, then the power recovered is less than the power needed to feed the stator and the result is a small power loss.

Advantages:
Allows full control with only one pedal (which is quite nice!)

On the other end you can start reducing Regen as the speed goes below a certain point, which should then allow you to safely switch pedals (say 5MPH).

My system is a hybrid. If I am slowly decelerating it will start to reduce at 7MPH so that I can either use the brake or coast till stop. Useful in stop-go traffic.

If I start to press the brake before this speed ramp, the controller commands regeneration until the car is stopped or I release the brake. If the brake is then reapplied below 7MPH it has no effect, only the mechanical brakes are used.

The Regen itself is a bit more complex that what it would seem at first glance

[MPaulHolmes]

I fixed what seems like the last major problem with just basic hard acceleration and deceleration, and the PI loop staying on track with IqRef and IdRef. What was happening was,

if (distance(Id,Iq) > MAX_RADIUS), then clamp Vd and Vq.

OK, no problem. But then Vd and Vq were much smaller than they should have been for Id and Iq to track IdRef and IqRef. So, Iq (especially) fell further and further away from IqRef, and would oscillate around 0, causing the slip speed to oscillate. This wouldn't force the motor to change directions, but would make it run rough and slower. At first I was dealing with this by limiting IdRef and IqRef as a function of RPM. That would work OK as long as the ramp rate for IdRef and IqRef to make it back to throttle position was slow enough. But what I tried this morning was this:

I was clamping Vd and Vq using a scale factor. So, it was like this:

VdClamped = scale*Vd
VqClamped = scale*Vq

So that dist(VdClamped,VqClamped) <= MAX_RADIUS.

Id is proportional to Vd, and Iq is proportional to Vq, so why not clamp IdRef and IqRef with the same scale factor?! And then let them ramp up quickly to where they wanted to be. Each time Vd and Vq bump into the ceiling, Id and Iq now can still track IdRef and IqRef.

It works REALLY REALLY well. Hard accelerations, hard decelerations, oh ya, no problems whatsoever. Field weakening happens automatically. No messing around with the actual RPM. I think I have a winner winner chicken dinner.

[thingstodo]

Originally Posted by cts_casemod

You can let Regen go all the way down to zero, in which case the motor will sometimes draw a bit of power if the deceleration is very slow. This is because the motor is acting as a brake to slow down the vehicle. If deceleration is slow, then the power recovered is less than the power needed to feed the stator and the result is a small power loss.

Good description!

The Regen itself is a bit more complex that what it would seem at first glance

Between single-pedal driving, the width of the 'coast' throttle range, the max regen on the throttle pedal versus pushing on the brake ... there are a lot of options that people can experiment with.

How one would configure these options, keeping the various variables or setpoints straight in your head ... remains a challenge.

The GEVCU uses a webserver built into the ethernet interface to deal with the settings, showing them on a web page and allowing for graphical representation of the options they support. This is not as complex as you have already programmed, but it's somewhere that is available to review code ... and borrow code that is already running.

The GEVCU is Arduino based, so I don't think that the code will not be verbatim, but the web interface should be close.