Performance optimization of low-speed induction generators for direct drive wind turbines

The paper discusses the optimization of low speed induction generators, directly coupled to the shaft of the turbines in variable-speed wind power generation systems. These low speed induction generators have a big number of poles and, as a consequence, low performance and big stator outer diameter. Because of the variable speed, a power electronic converter has to be used to deliver the produced energy to the grid. By using such a converter, the number of poles can be reduced and the rated generator frequency also decreased to an arbitrary nominal frequency. Both number of poles and rated frequency will be determined within reasonable limits as part of an optimization problem. The objective-function of this optimization is to maximize the product between efficiency and power factor without any geometrical or economical restrictions. Maximum values of this product provide high generator efficiency and lowest generator current and, in consequence, the lowest cost of the converter. The aim of the paper is to emphasize that the low speed induction generators with power electronic converters represent a realistic and useful solution for direct drive wind power application.