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On a three-phase inverter working as a Master Control Unit (MCU) to control a permanent magnet synchronous motor, if we replace the IGBTs with SiC MOSFETs, what could be the possible impact of this change on overall control strategy?

Both devices have different architectures and the most significant difference, in my mind, is the reverse conduction mechanism as in an IGBT either there is forward conduction or body diode conduction during dead-time. However, this reverse conduction of SiC MOSFETs has created some ambiguity for me and at the moment I don't have any clue regarding that. Could anyone here please guide me?

ocrdu
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Alison
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  • Can you define MCU? – Tim Williams Jan 10 '23 at 07:30
  • Master Control Unit – Alison Jan 10 '23 at 08:12
  • Hm, doesn't ring a bell. (Translated?) It sounds like a VFD (variable frequency drive), or motor control/driver in general. Or maybe BLDC, since those are PMSM as well. What do you know about the inverter characteristics currently? Schematic, waveforms, control mechanisms, etc.? – Tim Williams Jan 10 '23 at 10:10
  • its not for VFD. its general motor control strategy to control PMSM motor with three phase PWM based inverter. for now i just want to know theoretically what could be the effect of reverse conduction mechanism of SiC MOSFET on overall control Strategy – Alison Jan 10 '23 at 12:27
  • Well I'd be inclined to say "nothing" but I have absolutely no idea where you're coming from, what motivates the question, or why you'd suspect a difference – Tim Williams Jan 10 '23 at 13:10

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Both MOSFEtS and IGBTs can be used as switching devices in bridges for motor controller switching and PWM. Use of the bridge requires current flow in both directions; when a switching element in the bridge is turned "off," there are periods in the cycle during which reverse current must flow back through the switch. If an IGBT is used, a "freewheeling" diode must be placed across the IGBT to allow the reverse current to occur. Some IGBT's incorporate this diode in the package, but one must always be present for bridge operation. During the freewheeling conduction, there is a diode drop in the current path, so power is dissipated.

MOSFETs intrinsically have a "body" diode; they will conduct in the reverse direction (with a diode drop) when they are "off," even if no other diode is provided. Separate diodes are sometimes used with MOSFETs as well to improve freewheeling switching characteristics or reduce losses. Unlike an IGBT, a MOSFET will conduct in both directions when "on" with no diode drop, and it is possible to use this feature to increase efficiency in some applications, although I have no experience with this in a motor controller.

John Birckhead
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