Electronics > Projects, Designs, and Technical Stuff
100+kW Motor Controller
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Yansi:
Nothing personal, of course if you thought it was! Just ranting around, as I was involved in formula student for some years and last years changes in rules were downright under-thought.  One of them is to forbid any PLDs as devices handling safety related things.
ejeffrey:
The problem with putting safety interlocks or other features on an fpga is that it is too easy for them to be accidentally removed during synthesis.  It isn't really a problem in a production / product environment but can be a danger in a development environment like a student project
marcos_:

--- Quote from: ejeffrey on May 05, 2019, 09:05:09 pm ---The problem with putting safety interlocks or other features on an fpga is that it is too easy for them to be accidentally removed during synthesis.  It isn't really a problem in a production / product environment but can be a danger in a development environment like a student project

--- End quote ---
+1. No one wants to be responsible of a student injury, especially if its avoidable with a simple rule.
Yansi:
Synthesis will not remove anything, there is a post synthesis simulation of the design and real HW tests after anyway. So this comment is I think pointless.

I would not like to go into details in this thread,  but it is not only about "real safety",  but also repression of custom built HW, which in direct manner is a violation of it being an engineering competition. What they want you is to just slap together bought off-the-shelf parts, which is what most of the teams do anyway, so why be bothered with others, sigh.

To stay on topic, with the motor controllers: if I remember right what I have been told, you are required to FUSE every output of a custom built motor controller, unless there is a HW based over-current protection. So good luck designing a custom HW for I2t protection circuit, or good luck with finding space and cooling air to install for example 12 fuses for a quad motor controller.  (Of course, off the shelf motor controller does not require the fuses).

So where's the safety in this one? If a team can spin four motors using custom built HW and SW, they likely know ho to code a I2t integrator.  The protection can also be set wrong both on the off-the-shelf one and on the custom built one. So fusing is just solving half the problem and forcing some to be disadvantaged.

slloyd:
on subject of fault protection, Axiom controller has multiple levels of protection when it comes to current monitoring. for current there is slow moving average, I2t so to speak to watch for overload conditions and throttle back power. it takes feedback from heatsink temperature measurement as well. user configurable. this is in the works.   what is already coded and ready for use is software has a threshold for phase current which will limit power or trip depending on the threshold and then hardware protection for fault current which does not rely on software, it just shuts down the gating. threshold for hardware protection is rather high because its meant to protect against short-circuits, not overloads, here i'm talking about phase current out to the motor. 

there's actually a 4th protection which is for short-circuit where two adjacent IGBTs turn ON at the same time for some reason and the DC link cap shorts to ground.  this is fire inducing failure so we have a detect and shut-down in less than 10us and that's over the wide temperature range too.  we've tested this a lot.. just shorting the output together during operation.  starting up into a dead short.  over and over.  devices survive, no fire. also, we take into consideration when you have a shoot-through and the desat circuit kicks in to shut down the drive in <10us, there is .. after the immediate shut-down .. a very large voltage spike simply because of the very high current being suddenly extinguished and the parasitic inductance in the copper bussing that stored energy during the extreme amps.  the voltage spike after is something designers might forget about; thankfully Axiom didn't. 

actually, there's a 5th level of protection too now that i'm thinking about it.  Axiom monitors for circulating currents and adjusts the operation to compensate and take more action if needed.

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