Interesting! I'd forgotten about dual wound motors and have never wired one in my puff.The speed change is not quite the same as a star-delta starter, where you limit the startup current by switching between low, then high power configurations.
This is a delta to star-star switch, which changes the speed by changing the number of poles from 4 (slow, 1500 rpm) to 2 (fast, 3000rpm).
My vote would be to configure the motors as per the diagram, and feed the inverter input to ABC, after the contactor. After all, if you can produce c.400V three phase, you can use the machine pretty much as intended. As for speed switching on the fly, you do have the cutter motor as a permanent load so it shouldn’t be a problem.
Wire in a prominent stop switch via the inverter’s control terminals. Set the inverter overload current to something like 20% above the combined maximum of both motors, frequency to 45.7Hz and see how it goes.
Torque remains constant, but power reduces, as power is a function of torque and speed.I'd think it would be better to use switch if you can as from memory motors running at low frequencies on inverters have less torque generally- unless it's a fancy inverter.
A Variator essentially gives a constant power source, as the electric motor spins at it's rated speed. The variator then provides gearing, so as you slow the spindle down, the torque increases, and as you speed the spindle up, the torque decreases, so you potentially always have near rated motor power available.Good to know I was under the misunderstanding the torque dropped. I've got a chipmaster with a dodgy variator and was hoping to take the thing out and drive it directly via a vfd but was concerned about low speed operation. Sounds like it may be ok.