New generator structure with the doubly fed induction machine for better fault ride through properties

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Due to the expansion of alternative energy the interactions with the grid especially during faults become an important topic. Caused by the growing installed power of wind plants, it is necessary to keep them connected with the grid during faults and support the grid. Attributable to the configuration and the function principle of the known generator structure with the doubly fed induction generator voltage dips cause excessive voltage and current increase at the generator clamps which may destroy the converter and stress the grid. In this project a new generator structure have to be analysed which reduces the impact of grid fault on the doubly fed induction machine. This is achieved by introducing an ac-chopper between grid and generator. With the direct matrix converter connected with the rotor windings the ac-chopper effects minimal hardware effort. The control of this new generator structure is the major part of the applied proposal. With an appropriate control of ac-chopper and matrix converter the stator voltage have to be controlled to the reference value during grid faults and should not be influenced by the grid voltage. Commutation strategies for the ac-chopper are also an outstanding subject which has to be treated in this project. The theoretical work is accompanied by simulative analyses and the construction of a converter prototype. Finally, the theoretical results haveto be approved by measurements at a machine test bench with the new generator structure and the converter prototype.