Design Of Low Speed Permanent Magnet Generator Direct Driven By Wind Turbine

Nowadays, more attention has been paid to the wind power generation due since the wind energy is a "green" and cheap renewable energy source. The tendency of modern wind power technology is brushless and gearless without gearbox between the turbine and generator. The low speed permanent magnet (PM) generator direct driven by wind turbine is a typical one to meet the above requirements. Due to the simple structure and high reliability, small and medium size, the low speed PM wind generators which can be either grid connected or stand alone to provide AC power to the users, are particularly suitable for upstate and mountainous area, and have wide application prospect.At present, the domestic study on low speed PM generator is still in a stage of beginning, and there is no ripe design method for low speed PM generator. Taking 50kW low speed PM wind generator as an example, the design method is studied in this thesis.Firstly, the design features of low speed PM generator are analyzed. The rotating speed of the generator direct driven by a wind turbine is slow due to the large size of blades. The low speed machine usually has a short and fat structure in order to use effectively the rotating speed of the rotor, as contrasted with the long and thin structure of the high speed machine. The direct driven PM wind generator usually has a large number of poles in order to obtain the required frequency. However, the number of slots can not be too large due to the stator size limitation. Therefore, special combination of pole number with slot number should be taken in order to get the better voltage waveform and minimize the cogging torque.Secondly, the preliminary design scheme can be carried out by using the equivalent magnetic circuit method based on the technical requirement. The basic structure, dimension of PM and core as well winding parameters etc. can be determined in order to build up the model for magnetic field analysis.Thirdly, the electromagnetic performances of the PM generator can be simulated based on the finite element analysis. The magnetic field distribution, waveforms of voltage and current aswell as instantaneous torque for different rotor positions can be calculated using the iteration method of load current based on combined circuit with field analysis. The best design scheme can be obtained based on the comparative analysis of different schemes.Finally, considering the effect of large armature reaction on the magnetic flux of PM, a Halbach Array of combining radial with tangential magnetization magnets is proposed to increase the flux density in the air gap and decrease the flux density in the rotor core, and enhance the power density and reduce the size and weight of the low speed PM generator.