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Old 12-01-2016, 12:42 AM   #2902 (permalink)
thingstodo
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Quote:
Originally Posted by johkim View Post
Hello!

I am completely new to the EV community, and have been reading a lot of information on EVs online for the last few days. I have an interest in cars in general, and currently drive a modded VW GTI

Not to bore you with too much of my own story, I was just wondering where I would go to learn more about inverters before coming back to this thread and also Paul's instructables. I am by no means a ME or an EE, just an ordinary guy (my background is in civil engineering!), but I dream of one day making my own EV hotrod.

(the reason why I'm asking about inverters is that AC motors, and batteries are something that I understand to some degree, including BMS, at least enough to read and learn, but inverters are quite a bit harder!)

Sorry if I've posted in the wrong section! I just got stuck here hahaha
I have not seen a primer for three phase AC inverters.

The wikipedia article is OK as far as it goes

https://en.wikipedia.org/wiki/Power_inverter

My poor and disjointed summary:
- The inverter turns on 2 or 3 transistors (IGBTs) in different combinations to get current running through the motor.
- How these pulses are controlled is the magic behind Paul's controller. A bunch of math is used to figure out the angle between where the rotor is and where the voltage applied to the motor should be in order to apply torque.
- How much torque you want is controlled by how hard you push the throttle.
- The controller makes that happen by varying the applied voltage and the phase angle that the voltage is applied at relative to what angle the rotor is at now. That is calculated ... hmm ... at least 8000 times per second but I think it is more like 20,000 times per second.
- The motor position is measured by the encoder (or a resolver that pretends it is an encoder). 64 pulses per rotation is OK. More is better. My testing started out with 1000 pulses per rotation and ended up with 64 pulses per rotation.

Paul has over-current measurements that shut down the controller in the case of a problem .. sort of hard-wired into the enable circuit that drives the transistors. The temperature sensors ... if I remember .. (doubtful) .. I think those are inputs to the controller.

Many plans on the internet have been published by people with limited experience. It is quite easy to burn up IGBT(s) by turning on the positive transistor before the negative transistor finishes turning off. Ask me how I know! These types of mistakes are expensive ... and it is not usually obvious what you did wrong, or what part of your code is responsible ... or if it was a bad solder joint ... or ... you get the idea.

Paul has done a good job of ensuring that these types of things do not happen - traces well separated, ground and power planes used, inductive loop areas minimized - and of shutting things down immediately if .. sh*t happens .. and there is a lot of current somehow going through one or more of the IGBTs.

I can point you to a few videos that begin with the three phase motor and continue on to the inverters, field oriented control, the theory involved, the math, etc. It is not like a video night. Several of the videos I had to watch maybe 10 or 12 times to get through all of the details ... and the info still does not make sense to me when I go through it! I end up going through it a couple of times each time I need to revisit a small chunk of it.

Paul sent me the links. If there is any interest, I can post them
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