In Induction Generator Double Fed(DFIG), stator connect Dyn when wind speed (speed of prime mover) is high; stator connect Star when wind speed (speed of prime mover) is low. This reduce flux level and magnetizing losses. Why?

When wind speed low, P1 low, stator connect Star so that U1 low, so keep I1 = const, flux is const
(If stator connect Dyn, U1 will high but I1 low, flux is low too and not enough to magnetize iron)


When wind speed high, P1 high, stator connect Dyn so that U1 high, so keep I1 = const, flux is const (If stator connect Star, U1 low but I1 will high, flux will very high, machine will too hot and magnetizing losses will increase)

Is it wrong if I think so?

Hello thanhdd

Sorry about the delayed reply!

A double fed induction generator has the stator connected to the supply, and the rotor fed from the output of an inverter such that the resultant rotating magnetic field in the stator from the excitation is in synch with the supply.
If the rotor was stationary, the frequency applied to the rotor is equal to the supply frequency. At half speed, the frequency is equal to half the line frequency etc.
The voltage generated by the DFIG is proportional to the speed of rotation of the rotor and the flux in the rotor. At low speeds, the maximu flux is limited by the iron characteristics which results in reducing output voltage as the speed is reduced.
In teurn, this limits the usefoul operating range of the machine.
By switching the stator to star, there is effectively an increase in output voltage of rt 3 for the same speed and flux density so the useful operating range is extended.

Hoep this answers your question.

Best regards,
Mark.