Investigation of doubly-fed induction generator drives behaviour at synchronous operating point in wind turbines

State-of-the-art doubly-fed induction generator drives avoid operation at synchronous speed. Engineers point out stability problems and unequal heating of semiconductors and windings as the main reasons. The latter problem is consequence of unequal losses distribution in the semiconductors and rotor windings. This work investigates the thermal behaviour of the inverter switches at this singular point with the help of semiconductor loss and thermal models described along the text. Simulation results of the junction temperatures under different operating conditions are presented and analysed. These results should help on the dimensioning of the semiconductors and possible strategies to avoid the unequal heating are pointed out.