Optimal direct-drive permanent magnet wind generator systems for different rated wind speeds

The objective of this paper is to investigate possible ranges of rated wind speeds and rated power levels to have the better performance of the annual energy output per cost (AEOPC) for an individual direct-drive wind energy conversion system. Based on a given rated wind speed, the turbine blade sizing and rotor speed can be determined by using the maximal wind energy capture characteristics, the calculation of annual energy output (AEO) of wind turbines are also described. Based on a given wind turbine, a three-phase radial-flux PM synchronous generator (PMSG) with a back-to-back power converter is optimized for the minimal generator system cost. The analytical design models and optimization are developed and demonstrated by a rated power 500 kW PMSG. The optimal results of direct-drive PM wind generator systems with various combinations of different rated wind speeds and different rated power levels of wind turbines are obtained and compared, including the AEO and AEOPC at the high, medium and low wind speed sites, respectively. By comparison with the AEOPC of the optimized PM generators, the appropriate design ranges with the more cost-effective performance are analyzed and discussed for the direct-drive PM wind generator systems.