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Tool/software:
Hi team,
I am using ADS8688 in my design. I am designing PMSM FOC but am unable to tune my FOC.
I need to ask if ADS8688 is enough in terms of speed to be used in FOC. I am implementing FOC PMSM
It requires sensing inline current along with shaft angle to compute d and q currents
I am currently using ads8688 at around 8Mhz and it is taking roughly 22us for 3 channels. Then I measure my shaft angle, So which add a phase delay between the shaft angle and phase currents.
Please advise
Regards,
Josel
Hi Josel,
can we get more detail? Perhaps a schematic or block diagram of the proposed setup? The ADS8688 has a fixed 15kHz low pass filter built into the device, which may be causing the tuning issue.
Hi Tom,
Yes I'm aware of that. But the max electrical cycle will of 250Hz at 3500rpm.
If you have fast edges on the input signal, yes, the 15kHz LPF could be an issue. The ADS8688 does not have simultaneous sampling capabilities, so there is no way to sample the signals at the same time. The MAX SCLK on the ADS8688 is 17MHz so running at that speed would put you at sub 10uS to sample three inputs.
Hi Tom,
I think the problem is that I sampled the electrical angle and then measured phase currents. It gives me a delay of ~20us between the angle and currents. Do you think this might be an issue?
Josel,
It could be, usually there are (at least) two phase currents that are simultaneously sampled. Here are a couple of app notes for your reference.
Hi Tom,
I have already read them and had a look at them again.
The first paper doesn't give a detailed guide/explanation of the current inline sense. And I am using inline current sense. But it seems very clear that both currents and angles should be sampled simultaneously.
Regards,
Josel
Hi Tom,
So should I be shifted to a built in adc? or you can name a TI adc that has a sampling option?
Here are some 4 and 8 channel simultaneous sampling options for you to take a look at.