Guru
Joined: 13/10/2014
Location: AustraliaPosts: 1860
| Posted: 06:37am 07 May 2025 |
A VERY quick Look at Induced buzz:
Bench test Inverter:
1: No Load
2: Hall current sensor on the cable between choke and Toroid.
3: Variable supply
4: Current limit 1A
5: Dynamite on the power board in the form of a 10,000uf big screw terminal cap.
6: Controller in test mode.
I can't induce a buzz below 35v, likely too far away from saturation for the small amount of flux shift I'm generating.
Current waveform is normal as the power is very slowly increased (less than soft start ramp up time)
Inverter idling, I force a small sudden jump in DC volts, buzz begins and stays there, assume DC voltage step is moving the flux to the beginning of saturation.
A: Small current spike has appeared coinciding with AC zero crossing. (start of saturation)
B: DC spike height of the buzz varies with the loudness of buzz. DUH!
Force a slight drop in inverter DC and the buzz dies away.
OR
Put a 1uf across the AC output and the spark does the same thing, it stops the buzz.
However the 1uf splat cannot induce a buzz.
NOTE: When I hit controller AC over-voltage set-point, the inverter ramps down, once below the over voltage, the controller ramps up again, at handover to PID, the Inverter can induce a buzz.
The handover that does this causes a jump in the low current Bench supply, which is what induces the buzz in the first place, so in this test setup it's a case of the Chicken or the Egg for the soft ramp handover buzz.
I may revisit this tomorrow when I'm back in the workshop.
Normal power-on with soft-start is fine at handover, but I want to test this some more to see if I can catch it out.
.