How much current is too much for an SDU?

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catphish
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How much current is too much for an SDU?

Post by catphish »

As some people will know, I recently developed a current control algorithm for induction motors, and have been testing this on my Tesla SDU. In general, I usually configure this at 700A peak (500A AC RMS) current, which is perfect for my car, but I can't help but wonder how far the inverter can really be pushed!

It's my understanding that the SDU overcurrent cutoff can be configured up to 1200A peak (850A RMS). So my question is how much current can the SDU really take? Are we likely to damage it by pushing it too far? Has anyone tested this to its limits?

My suspicion is that with the 17.6kHz PWM we'll probably run into thermal limits pretty quickly, but I'm curious if anyone else has given it 100%
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Re: How much current is too much for an SDU?

Post by johu »

Just some background on the choice of 17.6 kHz. Back in the days we got a report of guys having blown 4 SDU inverters. We scoped the current at 8.8 kHz, it had nasty spikes on it and we figured the motor must be very low inductance and not liking the low frequency.
This was never "scientifically" proven though. Thing is, revisiting it could be painful ...
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Re: How much current is too much for an SDU?

Post by catphish »

johu wrote: Sat Feb 04, 2023 10:55 pm Just some background on the choice of 17.6 kHz. Back in the days we got a report of guys having blown 4 SDU inverters. We scoped the current at 8.8 kHz, it had nasty spikes on it and we figured the motor must be very low inductance and not liking the low frequency.
This was never "scientifically" proven though. Thing is, revisiting it could be painful ...
Thanks, I realise I asked this question previously. I did look through Damien's videos at the time, but I don't think he recorded the scope traces, which is a shame as I'd love to see what the real current waveforms look like.

Since I have no way to verify this myself as long as my SDU is in my car, I'm just sticking with the 17.6kHz as recommended.

I was just rewatching some videos. Thanks as always to Damien for doing the hard work. This video suggests that he was running the SDU at 900A+ peak.

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Re: How much current is too much for an SDU?

Post by catphish »

It occurs to me that this drive unit is advertized as having a capacity of 220kW. That equates to 600A at 360V. In my experience, at 100% voltage, RMS phase current is roughly equal to DC current.

It seems reasonable therefore that we should be able to run the phases at 600A RMS (850A peak) without issue. I suspect there will definitely be thermal limitations at such current levels though.

Would love to know if anyone's pushed this to further though :twisted:
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