Reducing switching noise in MOSFET inverter

[mike buba]

Hi, I am trying to reduce switching noise in the MOSFET three-phase inverter.

The reason is that a high noise causes the TI control card serial emulator to reset. I am losing the serial communication connection between the local PC and the control card at higher power. TI engineers advised me to try to use more robust emulators ($$). Before doing that, is there a way to reduce switching noise?

I have already reduced gate resistance (Rgon and Rgoff) by 1/3. The noise reduced, but not significantly. I can try to reduce it even more, but I read this can lead to increased switching losses.

Another option is to add/modify RC snubber. There is already an RC snubber on the board, with an option to add another RC snubber across the lower switch. Should I add RC snubber across the lower switch? I have seen online pictures with only snubber across DC+/- or across each switch in a leg, but my configuration only has an option across the lower leg and/or across DC+/-.


Noise is shown in oscillograms below (different time division: 10 ms, 500 us and 20 us, respectively). I don't see much of a ringing, just a spike at 8 kHz. Also, the inverter switching frequency is 4 kHz, but the noise is at 8 kHz?! Not sure why is that.
Ch1 is Rx signal
Ch2 is Tx signal

 

[Easy peasy]

Glad to hear its working, you might want a 45V 1A schottky and series 22E resistor across the 80 ohm Ron resistors to give quicker turn off ( anode pointing away from gate ) this should not give too much extra turn off voltage stress. The 3.3uF caps right by each totem pole are key.

Hopefully that Traco power DC/DC converter is not adding to the noise too much ?

The 100k-ohm resistors shown should probably read 5W, not 50 ?

Look forward to seeing full output load waveforms of the totem poles - zoomed in to see the max transition speeds ...

--- Updated Aug 30, 2022 ---

p.p.s you need to link the mid point of the electro's with the mid point of the 100k R's ... else volt balancing is not achieved on the electro's - without balancing R's, leakage currents ad zener effect of electro's will be the only things limiting any volt imbalance ( eventually a very loud noise and telescoping internals ... )

 

[mike buba]

Look forward to seeing full output load waveforms of the totem poles - zoomed in to see the max transition speeds ...

Voltages for 650 Vdc DC link with differential probe x500 (Ch1) across

• Phase leg midpoint and DC+; Fig. 1: Full pulse, Fig 2. Turn-on, Fig. 3: Turn-off

• Phase leg midpoint and DC-; Fig. 1: Full pulse, Fig 2. Turn-on, Fig. 3: Turn-off

 

[Easy peasy]

They don't look too bad - quite a few points in the operating cycle are always going to be hard switched, as an inverter is essentially a buck converter ...