I am working on a higher power vesc for about 200A. I have probed all my phases and gate voltages and everything looks good.
With no motor connected this is what the phases look like at 50% duty cycle
Once I connect a motor if I try to start it, it starts for a fraction of a second, with maybe 1-4 commutation steps before the abs over current fault occurs
For the initial commutations it looks reasonable. Until it stops.
This shows what happens on the phases when the abs over current fault happens
A closer look at the end, this looks like it rapidly increases the duty cycle or switching speed for some reason, until it is almost 100%, which would explain the huge spike in current shown in VESC tool.
What I don't understand is why it is doing this? The BEMF screen shows me a decent set of traces and I have checked that the current readings are correct too.
This is what is shown in VESC tool, my understanding is that since the current shunts are measuring the current it has to be passing through the motor. Which means this is not a shoot through problem. (I also have the deadtime on the pwm output set to the maximum)
Any help would be greatly appreciated, I have been looking at this for the last few days and haven't made any progress.
The main things on this board are,
- 6x Mosfets per phase - FDBL86361_F085
- 1x Gate driver per phase - UCC27211DDAR
- 18x 4u7 ceramic caps on other side of board from fets (Can increase to 10u if needed)
- 2x 1000uF electrolytic caps very close
- 3x phase shunts (configured to only use two at the moment)
Motor is a Turnigy Rotomax 1.2 (https://hobbyking.com/en_us/turnigy-rotomax-1-20-brushless-outrunner-mot...)
which has 27mOhm resistance.
Some pics so you can see how it is laid out.