4 pins connector on a Daikin compressor

[Peter_1]

VRV II has 3 connectilns on its compressor ...U,V, W
The replacement compressor has 4 connections: U, V, W and ...N
N is connected in the starpoint of the compressor
Why do they need an extrenal connection in the starpoint? Heating via pulsating DC current on 1 winding to heat up sump?

[Tayters]

Someone told me it was to help measure compressor rpm, not sure it that's true...
Not sure if it was for heating as only seen belt heaters on them.

[frank]

It is a feedback signal to the electronics to indicate motor position

[R666A]

It is a feedback signal to the electronics to indicate motor position

IPM detects rotor position by reverse Elecro Mooving Forсe created by permanent magnets mooving near "empty" stator coil. Isn't it?