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Electromagnetic torque analysis of a DFIG for wind turbines

Electromagnetic torque of doubly fed induction generator (DFIG) is a consequence of the rotor and stator supply. The stator voltage has a fixed amount and frequency. The rotor voltage of the DFIG as a part of a wind turbine has a variable amount and frequency. The aim of this paper is an investigation of the torque-speed characteristics of the DFIG depending on the amount of the stator and rotor voltage space vectors and angle δ between them. A mathematical model of DFIG for steady-state modes in a known double-axis dq reference frame concerned with stator voltage vector has been made. Expressions concerning DFIG power from both the rotor and the stator side have been derived. Expressions regarding torque values have been obtained from the generator active power and mechanical rotational speed. Torque consists of asynchronous and synchronous torque components, whereas DFIG has been observed as a hybrid between asynchronous and synchronous machine. The asynchronous torque and the synchronous torque depend on the amount of the stator and rotor voltage space vectors. The synchronous torque depends on the angle between stator and rotor space vectors δ , while asynchronous component do not depend on the angle δ .

DFIG; electromagnetic torque; wind turbine; renewable energy

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