I understand how a 3-phase inverter works (with 6 IGBTs or Mosfets). However I'm a bit puzzled when using it as an active rectifier. For reference, here's an example of the circuit I'm talking about. https://plex.infineon.com/plexim/fullbridge_inv_3ph.html

I also know that IGBT can only conduct in one direction as they are like a bipolar transistor. That's why they add a parallel diode. Therefore, for a bidirectional inverter/rectifier using IGBTs :

Am I correct in presuming that in inverter mode, the diodes never conduct (if the load has a PF of 1)?

Am I correct in presuming that in rectifier mode, the diodes will conduct to charge the DC-link capacitor?

Edit : Added clarification that I want to clarify how current is conducted when suing IGBTs


1 Answer 1


In a perfect world, the diodes would never conduct. A mosfet channel can hapilly pass current in either direction and diodes have much worse volt drop than mosfet channels do. So ideally you want the mosfets to be turned on whenever current is flowing through them in either direction.

In the real world we can't turn mosfets on and of instantly and we don't want to create a current flow path between the two DC rails. So there will likely be a dead time when neither mosfet is turned on and current is forced through the body diodes.

  • \$\begingroup\$ Ok, what about IGBTs? \$\endgroup\$
    – Ben
    Commented Mar 20, 2020 at 12:22
  • \$\begingroup\$ An IGBT has a minimum forward voltage drop of about 700 mV, same as a silicon junction diode, so they cannot be used as an active rectifier to achieve better efficiency than ordinary rectifiers. BJTs, however, can have a Vce(on) of less than 100 mV, so they could be used to advantage, but they need considerable base drive current to achieve saturation. \$\endgroup\$
    – PStechPaul
    Commented Nov 26, 2022 at 6:10

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