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three shunt resistors method of current measurement

shady mamdouh
Intellectual 575 points
Other Parts Discussed in Thread: UCC28070

please 

i want to ask about the current sensing using 3 shunt resistors placed under the three switches of a 3 phase inverter. How can i calculate the phase currents ?

the phase current only equals the sensed current when the lower switch is ON

i mean what is the relation between the phase current and the sensed current ?

  • 0
    TI__Intellectual 1615 points

    Here is what to do.

       Assume you are holding a inductor load (big assumption), the current behaves as an inductor current, linear up and down

      For the bottom switch current sense resistor, you can sense the current start and ending point, connect the start point to the previous switching cycle ending point, you can get the full phase current, as well as the high side switch current.

      We used this technique called "current synthesis" in UCC28070.

      Have fun with it.