Wind power technology has been developed much during recent years. The real cost of energy from wind turbines is falling dramatically. The rotor of a wind turbine rotates typically at a speed of 20- 100 rpm. In conventional wind power plants the generator is coupled to the turbine via a gear so that the generator can rotate at a speed of 1000 or 1500 rpm. However, the gearbox has the disadvantages which are an additional weight, a noise, a regular maintenance and additional losses. In a directly driven low-speed wind generator, no gears are needed and the above mentioned disadvantages can be avoided Most of the low-speed wind turbine generators presented is a surface-mounted permanent magnet synchronous generator (SPMSG). These have the advantages of high efficiency and reliability since there is no need of external excitation and conductor losses are removed from the rotor.
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