Quantitative Analysis and Rating Considerations of a Doubly Fed Induction Generator for Wind Energy Conversion Systems

This paper presents a quantitative analysis of the advantages of a grid connected doubly fed induction generator (DFIG) for wind energy conversion systems (WECS) over the other available variable speed WECS. The WEC system includes back-to-back connected PWM voltage source converters (VSC) in the rotor circuit of the DFIG. The control strategy implemented is - unity power factor operation of the machine (for loss minimization), efficient active and reactive powers flow control and the maximum power point tracking of the wind turbine. The analysis is made in terms of the active and reactive powers sharing between the machine and the grid, for a range of operation of the machine (sub synchronous speed to super synchronous speed through synchronous speed). Practical data of a 2MW wind turbine is considered and the WEC system including the control algorithm is simulated in MATLAB-SIMULINK. This WEC system is then reconfigured by a DFIG of 1.5MW and a comparison is performed in terms of the losses and efficiency of the WEC system. The advantages of implementing a DFIG in WECS are quantitatively established using the obtained results. Efforts are made to make the study contemporary to all existing literature related to the topologies and control strategies of variable speed WECS.