Improving the Thermal Performance of Rotor-Side Converter of Doubly Fed Induction Generator Wind Turbine While Operating Around Synchronous Speed

Due to variation in wind velocity, fractional power electronic converter-based variable speed doubly fed induction generator (DFIG) often operates at the low-slip region (near the synchronous speed). The low-slip operation can cause an increased temperature fluctuation in the semiconductor junctions of the rotor side converter which, if uncontrolled, can lead to reduced reliability over time. This article discusses the effects of the low slip operation on the semiconductor junction temperature and the converter power loss. Although decreasing switching frequency can be an obvious solution to this thermal stress problem, a low switching frequency can produce harmonics and torsional vibration. Therefore, this article proposes a switching control technique to deal with the tradeoff between the pulsewidth modulation harmonics and the semiconductor junction temperature. This article also proposes a current derating technique based on the reactive support sharing strategy to reduce the thermal stress on the rotor side converter. Furthermore, the article presents a coordinated switching control scheme with rotor current derating to effectively reduce the conductor thermal stress without compromising the DFIG performance and reliability. The effectiveness of the proposed methods is validated both through simulation and experimental study.