The keys factor in making wind power one of the main power sources to meet the world's growing energy demands is the reliability improvement of wind turbines (WTs). However, the eventuality of fault occurrence on WT components cannot be avoided, especially for doubly-fed induction generator (DFIG) based WTs, which are operating in severe environments. The maintenance need increases due to unexpected faults, which in turn leads to higher operating cost and poor reliability. Extensive investigation into DFIG internal fault detection techniques has been carried out in the last decade. This paper presents a detailed review of these techniques. It discusses the methods that can be used to detect internal electrical faults in a DFIG stator, rotor, or both. A novel sorting technique is presented which takes into consideration different parameters such as fault location, detection technique, and DFIG modelling. The main mathematical representation used to detect these faults is presented to allow an easier and faster understanding of each method. In addition, a comparison is carried out in every section to illustrate the main differences, advantages, and disadvantages of every method and/or model. Some real monitoring systems available in the market are presented. Finally, recommendations for the challenges, future work, and main gaps in the field of internal faults in a DFIG are presented. This review is organized in a tutorial manner, to be an effective guide for future research for enhancing the reliability of DFIG-based WTs.

This study presents novel control design for improving the performance of large-scale wind park (LSWP) based on self-excited induction generator under unbalanced voltage conditions. A dual controller for static synchronous compensator (STATCOM) employing controller by employing positive-and negative-sequence synchronous frames is implemented and analysed in response to severely unbalanced voltage conditions. The test system simulated represents a wind park rated at 100 MW connected to a weak electrical grid. The potential of the dual STATCOM controller is evaluated and analysed for severely unbalanced voltage conditions at the grid interface of LSWP. The dual controller with STATCOM overloading capability is tested and compared with the performance of the positive-sequence controller in response to different types of asymmetrical grid faults at low short-circuit ratios. The simulations performed using PSCAD/EMTDC demonstrate superior performance of dual STATCOM control strategy for improving unbalanced operation, fault ride through capability and transient stability margin in response to severely unbalanced voltage conditions.

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