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ADC noise alternatives for 3-phase current measurement

Question asked by pantelis on Apr 17, 2015
Latest reply on Apr 22, 2015 by baird.hal.001
Hello again!

I would like to make a question about an issue I have with the measurements of three currents!

Specifically I have a 3-phase converter and I would like to measure its currents as fast and accurate as possible, however there are some noise issues with the one ADC ( I use STM32F407).

Therefore I have thought some alternatives, which are the following:

1. 3 externals ADCs with the 3 SPIs and DMA
2. 1 external ADC with 3 inputs and send the data sequentially using SPI and then DMA
3. 1 internal ADC using 3 of its channels and then DMA
4. 2 internal ADCs and 1 external ADC (with SPI) and DMA
5. 3 internals ADCs and somehow try to filter the incoming noise of the one ADC

Could you please advise me on which one you would pick and why?

My comments on each one of the above alternatives are:

1. Probably the most symmetrical solution (Power consumption, in terms of efficiency, is not an issue for the application)

2. Slower solution with the 3 currents samples in different time moments (It would be much better though if the ADC could sample the three currents simultaneously and then send them through the SPI sequentially. I don't know if such an ADC exists, since most of them have one internal capacitor and a MUX, but I will have a look at it).

3. I think it's exactly the same as the above one, but avoids the SPI part, which makes it preferrable.

4. It will have assymetries because of the differnt ADCs and also because of the delay, due to the SPI.

5. I don't think it is something that will ever work. :D

Thank you very much in advance and excuse me for the long post!