VFD setup help

yes, but the torque is also calculated from the power and speed. And if the power decreases, you have to change something else to get the same torque. I don't think it's possible with the same motor and VFD. A performance diagram of the motor should explain that. I don't think that a 900w motor with the same design has the same torque as a 1.5kw motor.

.....

a 1.5kw 60000rpm motor has 0.24nm torque.
at 36000rpm that motor STILL has 0.24nm torque and puts out 900w.
at 18000rpm that motor STILL has 0.24nm torque and puts out 450w.

220v x 5 amps = 1.5kw (345vdc bus minus losses)
135v x 5 amps= 900w. the motor is still drawing 5 amps here. it is drawing over 1000w, but only OUTPUTTING 400-500.

There is nothing to add here. that is the EXPERCTED behavior. but it's not doing that. Clearly when you alter the base voltage on this delta drive it is not simply reducing the speed, it is doing something else, similar to how cutting the bus voltage on a BLDC motor will cut the available torque, where the normal way you reduce speed is to alter the duty cycle, keeping the peak bus voltage.

I am not an ac motor expert so I do not know the "why". It may be literally the same thing as the DC motor.

The correct way to set this up may well be to keep it at 220v for 599hz, but then set the voltage for 598hz to 135v... but I'm done messing with it. Don't care anymore.

lenze is going to make me a custom drive I hope and i can move on with my life.