Tool/software:
We have designed a 3 phase Inverter board with Totem pole PFC stage at front end based of this reference design (Only PFC section is referred) TIDA-010062 . This is for a HVAC Heat pump application.
High level specs of the Inverter :
Input voltage : 187Vac-253Vac, 57-63Hz
PFC output voltage : 390Vdc
Rated output power : 2.5KW
During one of our heating performance test @187Vac,60Hz , Input power ~1000watts, We have 2 different failure modes
Failure mode-1:
Tested with power source with Harmonics:
This power source (187Vac) is derived of the Variac which is powered by 460Vac, 3ph grid.
PFC works fine at powerup but after 20-30min, suddenly PFC shuts down due to Input Over current TTPLPFC_overCurrentProtection(). Overcurrent protection is set to 30A in the FW. Steady state current during this test <10A peak.
Tested with good power source:
This power source (187Vac) is derived of the Variac which is powered by 208Vac, 60Hz Light commercial/residential power.
PFC works without any interruption for the entire duration of the test 2Hrs. All the Test conditions. Test setup is same except the power source is changed.
Below is the Input voltage and current waveforms for both the sources. Observe harmonics in the input voltage with bad source.
Failure mode-2:
Tested with power source with Harmonics:
Test started at 230Vac, 60Hz and ran for almost 2Hrs without any fault then the voltage is reduced to 187Vac. After running for 10-15min at 187Vac, Board is damaged and the Failure analysis revealed that low side Bridge FET damaged and the fuses on the board opened.
Below is the FA for reference. I suspect that the root cause was a false zero cross detection that mis switched the Low Side Bridge FET when Input voltage is in -Ve half cycle might be due to spike/distortion at zero crossing.
Did anyone faced this issue and if yes, how did it get resolved ? How to make the PFC design robust to withstand input voltage harmonics ?
