Tuning the small drive unit with charts

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Re: Tuning the small drive unit with charts

Post by johu »

no worries, we are still talking about the DC current limiter which only steps into action at high rpm and full throttle. So no oscillation in day by day driving. The only issue with the current limiter is that it is a pure P-controller and its input signal (the calculated DC current) is not low pass filtered. So any oscillation on the calculated DC current will cause over-limiting of torque. Whacking a simple IIR filter in there solves it as demonstrated in the FOC variant
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Re: Tuning the small drive unit with charts

Post by coleasterling »

catphish wrote: Wed Aug 17, 2022 10:28 pm I can't easily generate an XY scatter plot, but here's a plot with RPM x 10, battery current, and motor current.

This is using my conservative recommended settings (run22-full.json) at full throttle with a load of a 1100kg vehicle.
Thanks! That would seem to indicate that the torque knee is somewhere around 7500rpm on 300V?
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Re: Tuning the small drive unit with charts

Post by catphish »

coleasterling wrote: Mon Aug 22, 2022 3:57 pm Thanks! That would seem to indicate that the torque knee is somewhere around 7500rpm on 300V?
The RPM of the torque knee is directly defined by the value of fweak. In my case fweak is set to 250, so maximum voltage reached at 250Hz, which is is exactly 7500RPM.

Setting a lower value of fweak will cause full voltage to be applied at a lower speed, giving more torque earlier in the rev range, at the cost of more current draw from the battery.
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Re: Tuning the small drive unit with charts

Post by catphish »

johu wrote: Mon Aug 22, 2022 7:59 am PID doesn't magically stop oscillation ;) What is implemented is the P-part of PID. What is lacking is some low pass filtering to dampen oscillation
This is actually a slightly unusual PID because it works in reverse. In a normal PID, the P value would attempt to *reach* a specified value (for example cruise control trying to reach 60mph), but this current limiter is the opposite, its goal is to keep the current away from the specified value.

Essentially what we have here is more like an "audio compressor", the higher we get towards the limit, the more we reduce the input.

Unfortunately, just like a PID, it oscillates. As Johannes says, just limiting the amount that this process is allowed to influence the throttle in each cycle will likely be sufficient to smooth it out, and it sounds like this is already proven.

I personally prefer open loop control. In theory, with the correct V/Hz curve, you could achieve all this with no current feedback at all, but it's definitely worth having the limits for safety, and smoothing it would be a nice improvement.
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Re: Tuning the small drive unit with charts

Post by arber333 »

Heh
What J means is he only implemented P - roportional part of PID banana curve :).
Whatever function he added later because of us made inverter into what it is now.
I remember the V/hz sine code at start when i wanted to drive 75Vac motor with 320V battery. And i could, only very slowly... but it could be done!
Now i remember you did thy some hiperbolic function which would predict throttle response, i think that code went out with 4.75 or similar...
Mazda is still alive so i can offer to test some changes to the sine just because i can...
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Re: Tuning the small drive unit with charts

Post by catphish »

I have some new data. I decided to stop worrying quite so much about the 450A battery current limit, and instead allow 500A. A modest increase, but the results were extremely interesting. Once again, I did a pair of tests, one at slip=3.5 and one at slip=3.0. Once again the test at slip=3.0 gave higher performance with less power consumption and less heat generated, so here's that result in detail:

fslipmax=3.0
boost=3800
fweak=230
AC current: 520A to 380A
DC current: 0A to 475A then falling to 375A
0-60: 5.3 seconds
Battery voltage: 300V (50% SoC)
run2.png
This is a big gain for a fairly small increase in power, but what's more interesting here is that there is considerable scope to improve this while remaining within the 500A limit. Firstly, since DC current never actually reached 500A, we can afford to bring fweak even lower, making that DC current knee higher and sooner.

Another key factor here is that 60 mph (marked by the circle on the graph) now lies well above the fweak knee which means we can get more torque between 50-60mph by using fslipconstmax and fconst, both paramater that I hadn't yet had to touch.

For the next fun, the goal will to have DC current rise to 500A (probably at around 220Hz, and then stay there until at least 60mph before starting to fall off again.
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Re: Tuning the small drive unit with charts

Post by catphish »

Part 2... Building on the above, made the changes to fslipconstmax and fconst. They have the expected impact on the graph, with current being sustained above fweak rather than falling off, but the performance gain from this is surprisingly negligable.
fslipmax=3.0
fslipconstmax=4.0
fconst=300
boost=3800
fweak=230
0-60: 5.13 seconds
Battery voltage: 315V (75% SoC)

It's good to see that the battery voltage has little to no effect on current, so the udcnom works exactly as it should.
run4.png
On a related note, I have reduced fslipmin to 1.5 as I suspect this will improve efficiency of low speed driving, though this is hard to prove.
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Re: Tuning the small drive unit with charts

Post by Peter »

Hi Charlie. Getting closer to the 4 second 0-60 :-)
As you have udcnom set at 300. Would be interesting to see what boost and fweak values become as voltage sags under hard acceleration.
I did try lowering fslipmin to 1.0, that made the motor very lumpy ! Thought I had blown a phase !!
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Re: Tuning the small drive unit with charts

Post by catphish »

I would say I'm probably done with this now. I suspect I'm now pushing this about as hard as Tesla OEM now. My acceleration is the same as the Model S 60D (which has two SDUs and twice the weight), so that seems like a reasonable place to declare success. The current is consistent and no derating is needed.

More torque off the line can be added by pushing the boost higher (Peter has tested up to 6000), but I won't be trying that for now.

The full configuration is attached along with the current chart and log.
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Re: Tuning the small drive unit with charts

Post by johu »

Nice, I will look through it and make it the new default
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Re: Tuning the small drive unit with charts

Post by Peter »

Hi Charlie. I wonder if reducing throtramprpm to maybe 4000 would improve 0-60 a little without straining driveshafts at the start.
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Re: Tuning the small drive unit with charts

Post by catphish »

johu wrote: Fri Sep 02, 2022 7:11 pm Nice, I will look through it and make it the new default
Thanks! Looking at the various recommendations available, we seem to have several published variations:
The openinverter.org current default: 360V at 220Hz, 6Hz slip (1.63V/Hz)
My recommendation: 300V at 230Hz, 3Hz slip (1.30V/Hz)
Damien's recommendation: 360V at 320Hz, 3.5Hz slip (1.13V/Hz)
Seb's recommendation: 300V at 220Hz, 4Hz slip (1.36V/Hz)

I think it's fair to say there's a variety here! In terms of V/Hz I think my suggestion sits right in the middle of the range and would almost definitely be a more sensible default. I can't explain why my slip recommendation is so much lower than others, but in all my tests it appeared to produce more torque per amp than higher values.

I would be confident in my proposed config being the new default, though it would be nice if at least one other person tested them! You might need to publish a new firmware to accept the renamed parameters.

Sources:
https://openinverter.org/parameters/view.html?id=15
https://github.com/damienmaguire/Tesla- ... s_SDU.json
https://github.com/Zero-ev-conversion-l ... arams.json
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Re: Tuning the small drive unit with charts

Post by catphish »

Peter wrote: Fri Sep 02, 2022 7:29 pm Hi Charlie. I wonder if reducing throtramprpm to maybe 4000 would improve 0-60 a little without straining driveshafts at the start.
throtramp determines how quickly the throttle is allowed to go from 0% to 100%, and throtramprpm disables this ramping above a certain speed to give instant throttle response instead.

During a 0-60 run, this ramping up to 100% throttle happens in the first quarter-second of the run (ie below 500rpm), so unless you lower throtramprpm dramatically (ie below 500) it's unlikely to have an impact. In my case, I think 200ms of throttle ramp (ie throtramp=5) is a sensible way to protect my hardware, and it should at at most 100ms to the acceleration time.
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Re: Tuning the small drive unit with charts

Post by catphish »

Following on from deadsled using these parameters and hitting an overcurrent fault, I wondered if I was running boost too high, and the potential peak current was simply being masked by my slower throttle ramp.

I did a new test run today using a somewhat lower value of boost (boost=3200) and more aggressive throttle response (throtramp=10). The result was quite pleasing.
lowboost.png
The unnecessary current spike at the start is flattened off, and the car is more responsive overall. I am not using a higher value of fslipconstmax because I'm more interested in ecomony than top speed.

Code: Select all

boost = 3200
fweak = 230
fslipmin=1.5
fslipmax = 3.0
fslipconstmax = 3.0
throtramp = 10
0-60 = 5.4 seconds
Full config attached again for reference.

I would also like to draw attention to the value tripmode=1. It has been proven now beyond any doubt that using other tripmodes has the potential to cause immediate and irreparable damage to small drive units in the case of an overcurrent event.

It's entirely possible that this boost is *still* too high, so more tests may be needed, but clearly 3200 is an improvement on 3800 without substantial loss of performance.
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Re: Tuning the small drive unit with charts

Post by StefSonic7EV »

Super interesting thread plenty of interesting observations. I was starting a similar discussion some time ago, so good to see some new facts coming in.

I finally took my car to the dyno, so hopefully the finding I share will contribute to further understanding of the SDU parameters setup.
I personally think this engine has superb potential, it is light, still well prices and I’m getting 180-190kW which suit my applications.

My setup:
- SDU, Quaife diff, running on reverse gear, v6 Board
- 17 modules from Ioniq 5 2022, 102s2p. According to hyndai numbers from Ioniq5, cell voltage of 3,48V is on 14% SoC and 4,15V on 97% SoC
- I charge the pack up to 430V (catalogue limit of SDU inverter, so I read) which gives me about 4,21V per cell
- NB, I once charged to 440V and inverter still worked fine
- After 2 years of testing, I settled on these parameters for road and track:
Boost: 2200, Fweak: 230, fslipmax: 2.7, fslipconstmax: 5.9, idcmax: 500

What I want to achieve:
- Understand the parameters and understand why I don’t get to 220kW for the racetrack 
- Improve power beyond field weakening point
- Flatten out the power curve and limit it to have the same amount of power to the wheels down to 30-40% of SoC. It is not very rewarding when you see the power dropping 0.1s every second or two compared to the previous lap:

- Better the 0-100km/h from the current 3.9s


The dyno
It is not a wheelhub dyno so the first disappoint was that despite my super soft slicks it could cope with the strong electric motor toque up to the power level of 170bhp. The torque readout itself was weird, ~100Nm. We had no idea why, I was first electric car ever on this dyno.
I limited the power by reducing the fweak, hard. On test runs it had to be only 500 at the start, then we improved a few things (0 camber and tighter belts).
image.png
image.png

That will be the baseline for the other graphs:
Run_14: Boost: 2500, Fweak: 350, fslipmax: 2.7, fslipconstmax: 5.9, idcmax: 700, thrtramp 10
image.png
Graph from the BMS for this run:
image.png
325 * 390 V = 170bhp
That would mean the losses (inverter, motor, powertrain) are on the 6.5% level, which in ICE numbers, it is crazy low!


Run_16: Boost: 2500, Fweak: 350, fslipmax: 3, fslipconstmax: 5.9, idcmax: 700, thrtramp 10
image.png
Run_17: Boost: 2500, Fweak: 350, fslipmax: 2.7, fslipconstmax: 5.9, idcmax: 250, thrtramp 10
image.png
Run_18: Boost: 2500, Fweak: 350, fslipmax: 2.7, fslipconstmax: 5.9, idcmax: 250, thrtramp 30
image.png
Run_20: Boost: 2500, Fweak: 350, fslipmax: 2.7, fslipconstmax: 4, idcmax: 250, thrtramp 10
image.png
Run_21: Boost: 2500, Fweak: 350, fslipmax: 2.7, fslipconstmax: 8, idcmax: 250, thrtramp 10
image.png
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Re: Tuning the small drive unit with charts

Post by catphish »

StefSonic7EV wrote: Thu Oct 06, 2022 8:53 pm Super interesting thread plenty of interesting observations. I was starting a similar discussion some time ago, so good to see some new facts coming in.
Thank you for posting all this. I will go through it in more detail, but I have one immediate question. What is your value of udcnom? That will have quite a few implications for the interpretation of the data.

My immediate thought here is that you're not pulling nearly as much current as you might. I tuned for a peak current of 500A, but you are only pulling 325A. I guess that was for the benefit of the dyno, so as for the question of whether you can get 220kW, you probably can, but you didn't test that.
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Re: Tuning the small drive unit with charts

Post by Romale »

catphish wrote: Thu Oct 06, 2022 9:13 pm What is your value of udcnom? That will have quite a few implications for the interpretation of the data.
I may have a stupid question (I am not strong in sine firmware), if the inverter does not receive information about the battery voltage, will it work? or is it necessary for him to know how many volts are there now?
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Re: Tuning the small drive unit with charts

Post by catphish »

Romale wrote: Fri Oct 07, 2022 12:49 am I may have a stupid question (I am not strong in sine firmware), if the inverter does not receive information about the battery voltage, will it work? or is it necessary for him to know how many volts are there now?
In theory, no, the inverter does not need to know the battery voltage.

However some features do require it:
* Contactor control (at least so precharge safely)
* udcmon (to automatically compensate for changes in voltage)
* overvoltage and undervoltage shuddown

However, I think it would be unwise for any inverter not to have a voltage sensor.
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Re: Tuning the small drive unit with charts

Post by StefSonic7EV »

udcnom is 360 for me, I did not care about this parameter too much. Engine operates on a voltage from 430 to 370 V.

One of the biggest findings from the dyno for me is that powertrain losses are low 6.5% when calculating the engine power from the electrical power.

So on the full charge (I'm assuming the inverter's efficiency is much higher at peak voltage) I was getting 180kW of electric power drawn out of the battery.

Which parameters might limit me in getting to to 220kW?

I will be testing it on the road tomorrow and will post the results immediately. :)


catphish wrote: Thu Oct 06, 2022 9:13 pm Thank you for posting all this. I will go through it in more detail, but I have one immediate question. What is your value of udcnom? That will have quite a few implications for the interpretation of the data.

My immediate thought here is that you're not pulling nearly as much current as you might. I tuned for a peak current of 500A, but you are only pulling 325A. I guess that was for the benefit of the dyno, so as for the question of whether you can get 220kW, you probably can, but you didn't test that.
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Re: Tuning the small drive unit with charts

Post by RiPower »

Hello Catphish,
I have an SDU on the front of my car and an LDU on the rear. It's a Chevrolet pickup. I tested your parameters for the SDU on my car today and I think they work very well. As a maximum current, the controller takes about 500A from the batteries.
That's the point I don't like yet, with which parameter can I increase the current a little more without changing or destroying everything, do you have an idea? You've gained a lot of experience.
Also, I'm not entirely satisfied with the LDU either. I'll describe this problem here and hope that someone can help me:
Here are the parameters with which I have been driving the LDU since January and which unfortunately always have an overcurrent:
boost": 1850,
"fweak": 258,
"fweakstrt": 400,
"fconst": 450,
"udcnom": 327,
"fslipmin": 0.96,
"fslipmax": 1.5,
"fslipconstmax": 9,
Today I switched to this, I spoke to Johannes Hübner and asked how I can lower the overcurrent, he told me to increase fweak, I did this up to the value when the overcurrent no longer came. Unfortunately, the LDU has been totally weak in the lower speed range since then and only generates little torque. I kept trying and got these values, but the drive is still totally sluggish up to 80 km/h and from around 80 km/h it really kicks off with a jolt. However, tmphsmax comes up again and again, here are the values:
"boost": 1850,
"fweak": 330,
"fweakstrt": 400,
"fconst": 450,
"udcnom": 327,
"fslipmin": 1.5,
"fslipmax": 2.59,
"fslipconstmax": 9,
Does anyone have any ideas how I can continue here?
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Re: Tuning the small drive unit with charts

Post by catphish »

RiPower wrote: Mon Oct 17, 2022 5:56 pm with which parameter can I increase the current a little more without changing or destroying everything
To increase the DC current and peak power, you reduce fweak. If you are using my recommended value of fweak=230 and you want more power, reduce this number is increments of 5 (fweak=225, 220, 215, etc).

Each time you reduce it you will get a higher peak power, and you will get it at slightly lower RPM sooner. My suggested value of fweak=230 will give you 150kW at 6900RPM. A value of 220 will give peak power at 6600RPM, and that peak will be a stronger.

You will need to monitor the current and decide how much you are comfortable with.

You should set the value of idcmax to about 150A more than your target current, so if you are aiming for 600A, set idcmax to 750. This will provide some degree of safety and temporarily cut your throttle (it starts to act 100A below its stated value).


Next... if you want more of a kick of torque off the line (at 0RPM), then increase boost. This setting is much harder to accurately make recommendations for. Increasing boost created a larger surge of AC current at 0RPM. You should increase this in increments of about 100 and measure your AC current each time. My value of boost creates a current of about 500A at 0RPM, but you can in theory allow as much as 750A.

If you set it too high, you will first run into the limit defined by "iacmax", which you can increase. If you go much too high, you may hit "ocurlim". If this happens, the inverter will shut down. This shouldn't cause damage, just don't go too crazy with it. I am reluctant to make specific recommendations about this value, but there is definitely some scope to increase it in sensible increments.
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Re: Tuning the small drive unit with charts

Post by catphish »

RiPower wrote: Mon Oct 17, 2022 5:56 pm Also, I'm not entirely satisfied with the LDU either. I'll describe this problem here and hope that someone can help me:
Here are the parameters with which I have been driving the LDU since January and which unfortunately always have an overcurrent:
boost": 1850,
"fweak": 258,
"fweakstrt": 400,
"fconst": 450,
"udcnom": 327,
"fslipmin": 0.96,
"fslipmax": 1.5,
"fslipconstmax": 9,
I don't claim to be an expert on the LDU at all, but here are some parameters I used during some early tuning of one:

Code: Select all

  "boost": 1850,
  "fweak": 258,
  "fweakstrt": 400,
  "fconst": 450,
  "udcnom": 0,
  "fslipmin": 0.87,
  "fslipmax": 3.09,
  "fslipconstmax": 9,
My suspicion is that your fslipmax of 1.5 was too low.

Based on this, my recommendation would be that you start with Johannes's recommendations, and then follow the same procedure as with the SDU, decreasing fweak until you are happy with the compromise between torque and "not blowing things up".
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Re: Tuning the small drive unit with charts

Post by RiPower »

Thank you for your help, I'll take your advice on the SDU and I'm happy to give you feedback.

As for the LDU, by the way it's a sport LDU, I still don't understand your recommendation.
The values from Johannes always caused an overcurrent shutdown for me. When I spoke to him on the phone he told me to increase "fweak" in small increments. I have done this. From 258 I went up to 330 so that the overcurrent error no longer occurs, but unfortunately I have weakened the drive. If I decrease "fweak" again, the overcurrent shutdown comes back. I'm looking for a solution to increase the motor's performance at lower speeds and reduce the performance at high speeds so that I no longer have an overcurrent shutdown.

First of all, thank you for your help and forgive me for working with Google Translate. My English is not good, I have no other choice.
I drive a 1998 Chevi K1500 Silverado with 2 x Tesla Power (SDU + LDU)
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Re: Tuning the small drive unit with charts

Post by Peter »

Hi RiPower. Please list your full parameter set so we can see idcmax, iacmax, etc etc
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Re: Tuning the small drive unit with charts

Post by catphish »

RiPower wrote: Mon Oct 17, 2022 8:32 pm Thank you for your help, I'll take your advice on the SDU and I'm happy to give you feedback.

As for the LDU, by the way it's a sport LDU, I still don't understand your recommendation.
The values from Johannes always caused an overcurrent shutdown for me. When I spoke to him on the phone he told me to increase "fweak" in small increments. I have done this. From 258 I went up to 330 so that the overcurrent error no longer occurs, but unfortunately I have weakened the drive. If I decrease "fweak" again, the overcurrent shutdown comes back. I'm looking for a solution to increase the motor's performance at lower speeds and reduce the performance at high speeds so that I no longer have an overcurrent shutdown.

First of all, thank you for your help and forgive me for working with Google Translate. My English is not good, I have no other choice.
Sorry, perhaps I didn't fully understand the LDU issue, as I saw the change in fslipmax and assumed that was what resolved the overcurrent issue. In any case, I would suggest you make a new thread with your LDU question, ans post he full config, and if possible a chart of the AC and DC current, so we can get an idea of why the overcurrent is getting tripped. I'm not that experienced with the LDU though sadly. I can best suggest starting with the values I posted below, which did not seem to cause overcurrent trips for me. You might want to explain why you changes fslipmax and what impact that had. I would suggest your new value of around 3 is correct.
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