Study On Design And Features Of Small-to-Medium Permanent Magnetic Generators Directly Driven By Wind Turbine

In a conventional wind power plant, a generator is coupled to the turbine via a gear-box in order to reduce its sizes. However, the gear-box brings some problems such as producing noise, needing regular maintenance and increasing losses etc. In order to overcome these problems, the direct-driven style is being used nowadays. Permanent magnet generator direct driven (DPMG) by wind-turbine becomes the tendency of wind power development. In our country, the study of DPMG is being at initial step and the small-to-medium wind power plant for stand-alone generation-battery system directly driven by wind turbine is quite fit to remote village, pasture, frontier or coast defensive station due to its operating reliability and low cost. It is profound significance to improve the conditions of these areas.In this study, DPMG will be designed with "fat and short" style, i.e. its diameter is large while its length is small. More turns of winding is needed to produce enough voltage because the DPMG rotates at low speed, but the armature reaction is high at same time. The DPMG has a large number of poles in order to get the necessary frequency of the output voltage. Simple and reliable PM rotor structure is a favorite with small-to-medium DPMG design.The preliminary design and machine parameters are determined by means of the traditional design method of PM machine. The waveforms of voltage, current and electromagnetic torque for different loads can be calculated based on FEM combined with circuit analysis. The effect of different poles and slots on the machine performance is analyzed in detail. Based on the comparison of different design schemes, the final decision can be made, and some design features of small-to-medium DPMG can be deduced. Two prototype DPMGs have been designed and built. The test data verified the correctness of the proposed design method.The DPMG is a kind of synchronous generator with unchangeable excitation. Due to the changeable wind speed, the output frequency and voltage of the DPMG are not constant, and need to be converted into constant through AC-DC-AC converter.