3 Phase inverter, shunt resistor waveform

wozniakm19 · ‎2015-10-11

Posted on October 11, 2015 at 16:32

Hi.

I have one question about AN4076 ''Two or three shunt resistor based current sensing circuit design in 3-phase inverters''.

On the page 6, 10 we can see signals on shunt resistor. How it is possible it's bipolar?

I my opinion current (and shunt resistor voltage) shouldn't have values below zero except some noises. Could anyone explain this?

Gigi · ‎2015-10-13

Posted on October 13, 2015 at 16:31

If the motor is flowing from the inverter to the motor and the high side switch is turned ON the current flows from the BUS voltage to the motor.

But when the high side is switched OFF (typically during the dead time and the condution time of LOW side) the current flows from the low side diode from the ground to the motor and this generate a negative voltage drop into the shunt resistor.

Ciao

Gigi