Effects of Voltage Unbalance and System Harmonics on the Performance of Doubly Fed Induction Wind Generators

Renewable energy harvesting is of prime interest in lieu of the increasing demand for energy and high price of fossil fuels, albeit the diminishing resources of petroleum and natural gas have given a renewed attention to the topic. Wind energy is, by far, the most accessible and efficient form of renewable energy given the state of technology in other renewable resources, i.e., solar, fuel cells, etc. Over the past decade, there have been significant advances in capturing wind energy using doubly fed induction generators (DFIGs). The versatility of the DFIG in providing a controllable flow of active and reactive power to the system, as well as its inherent low cost and minimum-size power electronic converters, has been the driving force in superior adequacy of this family of generators. However, as it has been noted in the literature, voltage unbalance and system harmonics can deteriorate the performance of DFIGs by introducing unwanted torque harmonics and inaccuracy in the generation of commanded active/reactive power. This paper will address this phenomenon from an electromagnetic and system analysis point of view. Simulation results are given to validate the claims.