Patent ID: 7023160

Claim:
A method in connection with a doubly-fed machine, the machine comprising a stator, which is connected to a power network, and a rotor, which is connected to the power network through an inverter, the method comprising the steps of: determining a rotational speed (n act ) of the machine, forming a rotational speed reference (n ref ) for the machine, measuring network voltage, measuring network current, and calculating network active power (P act ) and network reactive power (Q act ) from the network voltage and current, calculating a shaft torque (T) of the machine on the basis of the active power (P act ) and the rotating speed-(n act ), forming a frequency reference (F ref ) for the inverter with a control circuit on the basis of the determined machine rotating speed (n act ), rotating speed reference (n ref ) and shaft torque (T), a pole pair number of the machine and a network frequency, forming a reactive power reference (Q ref ) for the machine, forming an Ir compensation reference (IR ref ) for the inverter with the control circuit on the basis of the reactive reference (Q ref ) and the reactive power (Q act ), and controlling the inverter to produce voltage for the rotor of the machine on the basis of the formed frequency reference (F ref ) and the IR compensation reference (IR ref ).