Modeling Of The Doubly-fed Induction Generator Based Wind Turbines And Investigation Of Their Voltage Fault Ride Through Technologies

With the emergence of the energy crisis and environmental issues, the development of renewable energy technologies has become a hot topic and caught the attention worldwide. The wind power, thanks to its mature technology development and low cost, has become the most widely used renewable energy technology in the world. But as the wind farm and wind turbine capacities keep increasing, there are higher requirements to the wind turbines for the safe operation and dispatch of the power grid. To meet the needs, the codes for wind farms to be connected to the grid have been enforced. As the doubly-fed induction generator(DFIG) based wind turbines are currently the most widely used wind generator, the special topology makes them quite susceptible to the power faults. So how to improve their grid fault tolerance is very worthy of further discussion and study.In this work, comprehensive study for DFIG has been completed. The mathematical modeling and analysis of a DFIG system has been studied,including the wind rotor, the power train, the generator and the converters.The corresponding vector control strategy has also been deduced. Then the internal model control has been used to define the parameters of the controller. A simulation model has been established in the PSCAD /EMTDC and the operational principles have been verified. The transient behavior of the DFIG in the case of grid faults has been analyzed and the mathematical expressions of the rotor voltages and currents under the grid symmetrical and asymmetrical faults have been derived, and the corresponding grid fault ride through control strategy was verified in the simulation models. Furthermore, this work has proposed a method to improve the grid fault tolerance of the DFIG by using the super-capacitor,where the topology of the system, super-capacitor value calculation and the control strategies have been illustrated. And the proposed approach has been validated in the simulation model.