Research Of Permanent Magnet Synchronous Generator With Conical Rotor For Wind Power Application

As permanent magnet synchronous generator (PMSG) has advantages of simplestructure, high reliability and high efficiency for wind power generation, permanentmagnet generator has a dominant position in small and medium sized wind powergeneration applications. However, the inherent cogging torque of PMSG hasdisadvantageous influence on low speed and starting perfomance of wind turbine, and itis difficult to adjust the excitation of PMSG. All these key tequnonlogy problemsaffecting practical application of PMSG need to be further studied. In this paper,permanent magnet synchronous generator with conical rotor for wind power applicationwas proposed, in which the conical rotor could move in axial direction and the air gaplength would be changed to adjust air gap magnetic field, thus the reduction of coggingtorque and regulation of output characteristics could be accomplished effectively. Thestructure feature, mathematics model, calculation method for magnetic field,performance parameters and these influence factors were discussed to provide afoundation for the design and application of permanent magnet wind generator withconical rotor.The rotor of conical shape which could move in axial direction is the structuredifferentia between PMSG with conical rotor and the nomal PMSG. In this paper, theglobal structure and operation mechanism of PMSG with conical were proposed firstly.The movement of conical PM rotor in axial direction was elaborated, and the action ofmechanical actuator which is installed in the back end of generator was analyzed.Thechoice of rotor structure and arrangement of permanent magnet was also illuminated. Theequivalent magnetic network model and mathematical model of permanent magnetsynchronous generator with conical rotor were set up, and the calculation of permeabilityof the equilalent magnetic network was investigated. The feature of parameters of themathematical model, such as inductaces and magnetic flux linkage of permanent magnet,was also discussed.Then, the appropriateness of segmental2dimensional finite element method and thethree dimensional finite element method for the magnetic field analysis of PMSG withcoanical rotor were contrast studied. In this paper, the flux distribution of permanentmagnet synchronous generator with conical rotor was studied for two types of permanentmagnet, ie. trapezoidal shape and parallelogram shape. And the influence of the structuralparameters of the generator such as the conical angle, the rotor axial displacement onthe no load magnetic flux leakage coefficient was analyzed. Then the externalcharacteristic of the generator with different axial displacement of rotor was experimental studied, which was compared to the external characteristic of nomal PMSG withcylindrical rotor in the meaning of a near electric machine constant. The analysis resultswere verified by experiment.For the d and q axis inductance parameters affected the operating characteristics ofthe generator directly, the d and q axis inductance parameters of permanent magnetsynchronous generator with conical rotor were researched through calculation andexperiment subsequently in this paper. Firstly, the d and q axisinductance parameters and their influence factor for permanent magnet synchronousgenerator with conical rotor were analyzed qualitatively, and then the influence of theair gap length, the conical angle, the axial displacement of rotor and the magnet shape ond and q axis inductance was analyzed quantitatively base on flux linkage calculationmethod. Using voltage integral method, the d and q axis inductances with different axialdisplacements of rotor were tested under the sinusoidal voltage excitation of theprototype without regard to the coupling effect between the d and q axis magneticcircuits. Taking into account the coupling effect between the d and q axis magneticcircuits, when the rotor is at different axial locations, the d axis (q axis) inductances weremeasured with q axis (d axis) current under square wave voltage excitation with DCoffset. It is shown that the test results deviation was slightly larger under the square wavevoltage excitation because of the rotor vibration, but the calculated and tested valuesunder sinusoidal voltage excitation agreed well.For the specific feature of PMSG with conical rotor that the air gap magnetica fieldwill be changed along with the movement of rotor in axial direction, the cogging torque,the electromagnetical torque and the axial magnetic force on the conical rotor werestudied lastly in this paper. Integrated with phrototype of permanent magnet synchronousgenerator with conical rotor, the relationship between torque as well as axial magneticforce, and conical angle, the axial displacement of rotor, the d and q axis current wasanalyzed, and the coggong torque and electrical torque for the prototype of permanentmagnet synchronous generator with conical rotor were measured to verify the calculationresults.