Hello, I try to use a Vesc to inject little power (a few tens of watts would be okay) from a 24Vdc solar system (approx 30Vdc fully charged) to a 400Vac 3 phase grid.
I use 3 toroid transformers to get 15Vrms between phases from the 400Vrms grid, I can see in Vesc tool nice 3 phase BEMF with 3000ERPM (=50Hz grid), just like a running motor.
In FOC mode, the VESC shows 88% duty to keep track of the grid. I set a 2Amps motor current and expected to inject around 30Watts (don't know if it is per phase or total).
But the duty rises to 95% (max), and curiously the motor amps is always around -3.5Amps. I tried braking, reversing.. no success.
Probably I need to dig more into the FOC R and L settings. I used R=0.4Ohms (approximate of deltaU / deltaI when applying a load on one phase). No idea how to set the inductance, I played directly on the flux linkage, but could not find suitable values. I just see it impacts the phase in the BEMF sample window. Too low or too high values yield some bad noise and no more current...
I suspect the phase calculation is not correct in the VESC, hence it would require more duty (or input voltage) to be able to push some power into the grid. On contrary, it seems to be charging from the grid.
Could anyone help in determining the proper R, L and flux linkage for this application ? Thks ! Pierre
"In FOC mode, the VESC shows 88% duty to keep track of the grid." when does duty rises to 95% (max),?
toroid type is important. should be a low frequency type.
regenerated voltage should be greater than the nominal voltage in order to push it up.
using a lcr meter is better for measureing l & r.
The duty rises to 95% when I set 2Amps and start the motor in Vesc Tool. Same withe breaking the motor or setting other motor currents, even negative.
Yes I use 3 low frequency toroid transformers (30VA each) in a start/delta config to get 15Vrms betwwen two "motor" phase. I tried different FOC frequencies, there is some audible noise, and the 3 transformers heat up to 35C quite rapidly. From a 3 phase power measurement on the 400Vac, there is no power injected to the grid. Just a little bit of power flowing from one phase to another due to some voltage unbalance. When starting the motor on VESC tool, some power flows out of the grid, the VESC shows the battery is charging, but the battery (28Vdc) voltage decreases somewhat (maybe this explains why the duty has to increase)
Even if my 400Vac grid has relatively high impedance (around 1R between phase and neutral), pushing a little power to it will barely affect its voltage.
Using a L meter between 2 phases secondary transformer yields either 47mH at 2.3kHz or 5mH at 67kHz. So I guess the "real H" is in between ?
I made some progress using lower motor flux linkage (0.001mW). Now I can push power to the grid. I am still a bit surprised that the duty has to rise quite a lot (approx +10%) in order to start injecting current instead drawing from the grid to my dc battery.
The toroid voltage ratio 230/15Vac is a bit low for my application, the current I can inject is limited by the max duty of 95% (by the way, is it safe and how can I go over the 95% limit in VescTool ?)
Maybe, delta connection on primary winding could be used.
maybe it means that lowering motor flux linkage could yield increase on voltage.
I think using delta on primary side means 400/15V transformers instead 230/15. This is more difficult to source and possibly slightly less efficient. I cannot really see how motor flux linkage is used by the Vesc pwm control. I suspect it affects the phase observer.
Does anyone know if the phase (as displayed in the sampled data bemf screen) should be 0 when the voltage of the motor phase1 reaches its maximum ? I'd like to tweak the parameters to control the phase of the current I inject..
I try to increase the output power, so I replaced the 3 transformers by more powerful ones (so less resistance / more inductance). I have more problems to set the parameters. I realized that the motor flux linkage simply reflects the "motor" bemf at a certain speed. So it should be straightforward to get it from the BEMF sampled data, where I get 7.5Vrms (21.2Vpeakpeak) at 3000Erpm. Does anyone know the formula to calculate the flux linkage from these numbers ? (the result is probably near 32mWb - but it needs to be accurate, other wise, upon startup, the inrush current is high and causes a fault. I only managed to get it to work by adding series power resistors before the transformers, but this causes a lot of power losses obviously..