A method for operating a doubly-fed machine by determining its rotational speed (nact), forming a rotational speed reference (nref), measuring network voltage and current, and calculating network active power (Pact) and reactive power (Q act). Thereafter, calculating shaft torque (T) based on active
A method for operating a doubly-fed machine by determining its rotational speed (nact), forming a rotational speed reference (nref), measuring network voltage and current, and calculating network active power (Pact) and reactive power (Q act). Thereafter, calculating shaft torque (T) based on active power (Pact) and rotating speed (nact), forming a frequency reference (Fref) for the inverter based on machine rotating speed (nact), rotating speed reference (nref), shaft torque (T), and the known pole pair number and network frequency, forming a reactive power reference (Qref) for the machine. Forming an Ir compensation reference (IRref) for the inverter on the basis of the reactive reference (Qref) and the reactive power (Q act), and controlling the inverter to produce rotor voltage based on frequency reference (Fref) and the IR compensation reference
대표청구항▼
The invention claimed is: 1. 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 (nact)
The invention claimed is: 1. 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 (nact) of the machine, forming a rotational speed reference (nref) for the machine, measuring network voltage, measuring network current, and calculating network active power (Pact) and network reactive power (Qact) from the network voltage and current, calculating a shaft torque (T) of the machine on the basis of the active power (Pact) and the rotating speed-(nact), forming a frequency reference (Fref) for the inverter with a control circuit on the basis of the determined machine rotating speed (nact), rotating speed reference (nref) and shaft torque (T), a pole pair number of the machine and a network frequency, forming a reactive power reference (Qref) for the machine, forming an Ir compensation reference (IRref) for the inverter with the control circuit on the basis of the reactive reference (Qref) and the reactive power (Qact), and controlling the inverter to produce voltage for the rotor of the machine on the basis of the formed frequency reference (Fref) and the IR compensation reference (IRref). 2. A method as claimed in claim 1, wherein the calculation of the machine shaft torque comprises a step of dividing the active power (Pact) by the rotational speed (nact) to obtain the torque (T). 3. A method as claimed in claim 1, wherein the creation of the frequency reference (fref) comprises the steps of; subtracting the machine rotational speed (nact) from the rotational speed reference (nref) to obtain a speed difference (en), feeding the speed difference (en) to a speed controller to obtain a torque reference (Tref), subtracting the machine shaft torque (T) from the torque reference (Tref) to obtain a torque difference (et), feeding the torque difference (et) to a torque controller to obtain a torque frequency (fT), multiplying the machine rotating speed (nact) and the pole pair number (p) to obtain an electrical frequency (fact) of the machine, subtracting the electrical frequency (fact) of the machine from the network frequency (fnetwork) to obtain a basic frequency (fbasic) and summing the basic frequency (fbasic) and the torque frequency (FT) to obtain a frequency reference (fref). 4. A method as claimed in claim 1, wherein the formation of the Ir compensation reference comprises the steps of: subtracting the reactive power reference (Qref) from the network reactive power (Qact) to obtain a reactive power difference (eq), feeding the reactive power difference (eq) to a reactive power controller to obtain an Ir compensation reference (Ir comp). 5. A method as claimed in claim 4, wherein the Ir compensation reference is used for controlling the reactive power of the machine. 6. A method as claimed in claim 3, wherein the speed controller is a PI controller. 7. A method as claimed in claim 3, wherein the torque controller is a P controller. 8. A method as claimed in claim 4, wherein the reactive power controller is a PI controller.
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