openinverter forum

I'm trying to figure out what boost parameter mean. https://openinverter.org/wiki/Parameters describes "boost is the digital amplitude of the sine wave at motor startup.". I don't know if that makes sense to others, but to me it tells nothing. So I'm trying to find another way of describing it.

Doing bit of a research I found out that boost increases battery voltage to higher DC voltage before converting it to AC voltage for the motor. In conversion, current goes down and voltage goes up. This can increase the power and efficiency of the motor as you can have the motor working on the voltage that it's designed. And it's not only a parameter for motor startup, like wiki page says but It's constant voltage step-up that happens?

In my setup I have nominal voltage of 266V (72 cell) and using Tesla sport LDU. Parameters around the parameter database and on forums have boost set to somewhere around 1800-2500 with 355V (96 cell) nominal setups. I think with my lower voltage setup, I need to set much higher boost. So I tested now with boost of 3500 and it worked well, but didn't notice much difference how it acted. I previously had it set to 2400.

This leads me to many question, like:

- How to know/find the sweet spot of motor & battery combo?
- What is the optimal boosted DC voltage for my motor and where can I see it?
- How much does it up the voltage if I have for example boost of 2500? Does it matter?
- What happens if I set boost too high. Can the higher DC voltage break inverter or some components?
- How high should I go? 4000? 4500?
- Should I get more power throughout the rpm range?

I'm guessing that simple answer for all of these is that "up the boost so high that you get OVERCURRENT error and back down a bit". But I would like to know if there is mathematical way of calculating this?

mane2 wrote: ↑Sun Sep 08, 2024 11:21 am I'm trying to figure out what boost parameter mean.
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I'm guessing that simple answer for all of these is that "up the boost so high that you get OVERCURRENT error and back down a bit". But I would like to know if there is mathematical way of calculating this?

Boost parameter was meant for ACIM motors at start where you need additional voltage just to overcome winding internal resistance.
So when you try to determine boost you need to observe the starting behaviour of your motor. On flat ground and uphill.
Here is a tuning procedure i wrote a long time ago to help with setting correct ACIM motor parameters: viewtopic.php?t=468
They went into wiki as well
https://openinverter.org/wiki/Parameters

In the case you need boost as help to get a bit more voltage to get sharper motor response in winter you can vary udcnom parameter which will move motor voltage curve somewhat, You need to have strong batteries for that as in case of motor response increase inverter will pull morte current to boost more voltage response in motor core. But that is a different mechanism for ACIM.

I couldnt find any mathematical thing about boost to get it more scientific. I did however notice it is somewhat connected with desat mechanism. If i would run too much boost my desat would quickly tell me to stop . This is why i would burn quite a few unprotected IGBTs in first days of the OI.

I have read that wiki and tuning guide, thanks for that!

However, I'm trying to understand if boost affects the performance and maybe efficiency too. Especially when having lower pack voltage than usual.

eg. having low boost like 1400, motor might jitter when starting to move. When set to 4000 you get no jitter and quicker ramp-up for the power. But is the total power still the same, and efficiency?

I asked about inverters and boost feature from "reliable source" ChatGPT and it told me that upping the voltage would improve power and efficiency, but reading your post and wiki, it seems to only mention about starting from dead stop and overcoming motor winding resistance. Also, seeing that people have backed down with boost setting as they got overcurrent errors when flooring it would hint to the direction that it affects continuously to produced power.

mane2 wrote: ↑Sun Sep 08, 2024 1:14 pm I have read that wiki and tuning guide, thanks for that!

However, I'm trying to understand if boost affects the performance and maybe efficiency too. Especially when having lower pack voltage than usual.

eg. having low boost like 1400, motor might jitter when starting to move. When set to 4000 you get no jitter and quicker ramp-up for the power. But is the total power still the same, and efficiency?

I asked about inverters and boost feature from "reliable source" ChatGPT and it told me that upping the voltage would improve power and efficiency, but reading your post and wiki, it seems to only mention about starting from dead stop and overcoming motor winding resistance. Also, seeing that people have backed down with boost setting as they got overcurrent errors when flooring it would hint to the direction that it affects continuously to produced power.

Like i said boost is used only at slow speed. It helps to overcome first few revolutions only.

Now using/adapting udcnom could up the voltage your motor sees at speed but at the cost of more amps from the battery as this mechanism actually boosts voltage across motor windings. If you have Tesla ACIM you will need some tough battery for that though...
I used this mechanism to lean out my motor as it was wound for 180Vrms and 360V nominal was a bit too much for it. I dropped udcnom to 320V and motor behaved a lot better there.

Here is the graphics



Ideally for a theoretical motor with no winding resistance you would not need it. For a real one you do. It affects mostly startup but changes the slope of the entire voltage @ frequency curve.

It is not related to boost converters. The description is like 15 years old please update it once you get a grasp

Thanks, both! So once the motor reaches it's ideal/rated AC voltage, it won't boost AC voltage any higher. So to answer my question: boost doesn't give you more power. It just takes you rated/ideal voltage faster and also, with help of udcnom, pushes voltage (boosts) even more to cover voltage sag.

How would you feel for changing wiki description for boost, to something like this

Boost helps the motor overcome resistance when starting from a stop. It adjusts how much power the motor gets at startup to help it begin turning. It doesn’t increase the total power of the motor. If the boost is set to 0, the motor won’t get enough power to start moving. At the maximum value of 37813, the motor gets maximum power.