Electromagnetic Design And Analysis Of 3MW Direct-Drive Dual-Stator Brushless Doubly-Fed Wind Power Generator

Offshore wind energy has the advantages of good stability,high wind speed,easy to predict and so on,but it has high demand on the reliability of wind power generation system because of the special climate environment of the sea.Therefore,it is of great significance to develop a large-scale wind power generator which is easy to maintain,high power density,low speed direct drive and high reliability for offshore wind power technology.The brushless doubly-fed machine has the advantages of high pole number,brushless and reliable,small converter power,and can realize the operation of variable speed constant frequency wind power generation,especially suitable for offshore wind power generation system.In view of the problem which the inner cavity of the rotor could not be fully utilized resulting in the low power density because of the large diameter-length ratio of the direct drive wind generator.A dual-stator brushless doubly-fed wind power generator(DSBDFG)which using the back-to-back rotor magnetic barrier module(BTB-RMBM)is introduced to solve this problem in this paper.However,the operation mechanism of this kind of machine is very complex,and electromagnetic design theory is not mature.Moreover,the structure of dual-stator and direct-drive increases the design difficulty.So the feasibility of electromagnetic design method is investigated,the key dimensions are initialized,and the generator performance are calculated.Aiming at these problems,this paper carried out the following contents:First,the structure,mechanism of magnetic field modulation and energy flow of DSBDFG are introduced.The circuit schematic diagram of different connected mode,equivalent circuit diagram and power flow diagram of DSBDFG are obtained.Second,the method of determining the key dimensions is carried out.The relationship between key electromagnetic parameters and power split ratio is revealed.The harmonic distortion rate of EMF in power windings(PW)and air-gap flux density harmonics under the different pole pair combination are calculated.The key dimensions of DSBDFG is initialized based on the rated parameters,and the calculation example of the electromagnetic design is derived.In addition,the finite element simulation model of DSBDFG is established by Ansys Maxwell.Finite element analysis is carried out to deduce the no load characteristics,rated load characteristics and variable speed constant frequency generation characteristics.At the same time,the core loss,copper loss and additional loss of the machine under the rated load are analyzed and calculated,thus the efficiency of the machine is obtained.Finally,according to the design principle of DSBDFG,the electromagnetic calculation program is wrote up including key dimensions calculated,winding parameters calculated,magnetic circuit parameters calculated,material dosage calculated and so on.The GUI function of Matlab is used to establish the parameters visualization interface which provides a friendly man-machine interaction environment.Last but not the least,the advantages and disadvantages are analyzed after comparing the different types of direct-drive wind power generator.