Mitigation of harmonics in wind turbine driven variable speed permanent magnet synchronous generators

Permanent magnet synchronous generators (PMSG) have been used more frequently as variable speed systems in wind energy conversion systems (WECS). Variable speed systems have several advantages such as yielding maximum power output while developing low amount of mechanical stress compared to constant speed systems. AC-DC converter such as six-pulse rectifier is used to convert variable voltage and variable frequency from the PMSG to DC voltage, thereby producing DC power. The DC link is converted back to AC at a fixed frequency that is appropriate for electrical utilizations in the grid. However, the use of six pulse rectifiers introduces high intensity of low frequency current harmonic content into the PMSG. The flow of these harmonic current induce further losses to the generator, thereby producing more heat in the generator. This leads to reduction in efficiency in WECS and also decreases the life span of the generator. This paper investigates and analyse the level of harmonic content of two different AC-DC converters operating at various wind speed. Mitigation techniques such as introducing passive filters are implemented and tested to the system. PSIM/spl reg/ simulation package was used in developing generator models, AC-DC converters.