The consultant has gone now.
I am just wondering about this situation of "Pump suddenly running dry".
I mean,are you in agreement that because we have the SPEEDSET pinof the ML4425 tied directly to the VREF pin of the ML4425, that the bridge IGBTs will be commutated at just one fixed frequency, (in our case 400Hz, which gives the 8000rpm in the 3 ph BLDC motor)
Can't you use a Hall sensor instead of a sense resistor?
...sorry no, a hall sensor has a good FAST bandwidth, but is still not fast enough to resolve the same as using a current sense resistor directly into the PWM comparator of the ML4425. And in any case, even if we used a hall sensor, it wouldn't take away the wiring inductance.
We could however, use a hall sensor as the current sensor for our buckboost converter...maybe that's what you meant?
As regards the question about whether we should stop the pump when it has run dry.....yes that would be nice, but we will settle for simply reducing the current to the motor so that it keeps spinning at 8000rpm...which is harmless, as long as the current does get reduced to that (presumably small) level which allows the motor to spin at 8000rpm.
....yes , we'd like for the pump to stop when it runs dry, but that means having all sorts of external extra bells and whistles like flow sensors etc etc...and we don't want that...after all, we are only watering tulip fields via our irrigation system.