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How to calculate phase currents of the drive board AD-FMCMOTCON2-EBZ?

Question asked by qxj on Jan 11, 2016
Latest reply on Mar 17, 2016 by ACozma

Hello everyone!


could anybody tell me how can I calculate three phase currents Ia, Ib and Ic, when my drive board is AD-FMCMOTCON2-EBZ?


In the article titled "AD-FMCMOTCON2-EBZ Signal Measurement Chain" (abbr. FMCMOTCON2), there are not any calculation formulas. However, according to the article titled "AD-FMCMOTCON1-EBZ Signal Measurement Chain" (abbr. FMCMOTCON1), some fomulas are introduced. The following one is an example.

calculation formula.png

But I have some questions for calculating phase currents in FMCMOTCON2:


a) The current measurement method used in borad FMCMOTCON2 has the same principle with Case 1 introduced in the article "FMCMOTCON1". The only difference is the resitance value of shunt resistors. In board FMCMOTCON2, 10mO shunt resistors are used.


Figure 1: Current measurement method in FMCMOTCON1 (here please focus on Case 1)


Figure 2: Current measurement method in FMCMOTCON2


Can I directly use this calculation formula described in FMCMOTCON1 to calculate three phase currents in board FMCMOTCON2 by setting the value of the parameter "RS" to 10e-3 instead of 6e-3?

b) The modulator AD7403 is used to sense the differential voltage on the shunt resistor in board FMCMOTCON2. According to the data sheet of AD7403, its output signal is a single-bit data stream and must be digitally filtered by using a sinc3 filter. This is the same for AD7401 used in board FMCMOTCON1. But I can't find any relationship between the formula mentioned before and the sinc3 filter.


Could you explain it for me in detail?

In addition, you can find these two mentioned articles under the following links:

FMCMOTCON1: AD-FMCMOTCON1-EBZ Signal Measurement Chain [Analog Devices Wiki]

FMCMOTCON2: AD-FMCMOTCON2-EBZ Signal Measurement Chain [Analog Devices Wiki]