Design And Analysis Of Brushless Doubly-fed Generator Based On Permanent Magnet Field Modulation

In the current human society,Seeking new renewable clean energy,reducing dependence on traditional fossil energy and realizing the third energy conversion have become the urgent needs.Wind power generation technology has become one of the most widely used and mature new energy generation technologies due to its abundant reserves and easy to be captured,utilized and converted into electric energy.With the improvement of wind power absorption and the reduction of wind abandonment rate in the past two years,wind power generation will develop faster.As a device converting wind energy into electric energy,the performance of wind power generator directly restrict the efficiency,capacity and power quality of wind power generation system.With the increase of the capacity of wind turbines,higher requirements are put forward for the performance of wind power generator.A new brushless doubly-fed generator based on permanent magnet field modulation is presented in this dissertation.It inherits the advantages of doubly-fed induction generator and permanent magnet synchronous generator,such as high power density,few gearbox series,without carbon brush and slip ring,high reliability,part-size power converter,and low cost,etc.It has great application potential in high-efficiency and high-power wind power generation systems.The key points of this dissertation are as follows:Firstly,the mechanism of magnetic field modulation in different structures is analyzed.By introducing the magnetic field modulation theory,the working principles of emerging new machines are effectively expounded,which enriches and improves the traditional motor theory,and provides a theoretical basis for the design and optimization of new machines.A new doubly-fed brushless generator based on permanent magnet field modulation is proposed by combining the permanent magnetic gear with the brushless doubly-fed generator,which realizes the permanent magnetization of the brushless doubly-fed generator.The working principle and electromagnetic characteristics of the new generator are analyzed.The phenomenon is found that the nolad EMF of power winding and control winding are three-phase asymmetrical.A thorough study of the phenomenon reveals that the root cause is the radial asymmetry of three-phase magnetic circuit.And the solution is proposed,which realizes three-phase symmetry of power winding and control winding.The influence of the size of the field modulation ring on the performance of the generator is analyzed.The design optimization method of the generator is proposed.A prototype is designed and manufactured.The electromagnetic characteristics of the prototype are simulated and tested.The test results agree with the simulation results.Two improved schemes of generator topology are proposed,which can effectively improve the utilization ratio of permanent magnet and further improve the power density of the doubly-fed brushless generator based on permanent magnet field modulation.The mathematical model of the generation system is established.The control strategy of the generator is proposed.The simulation results verify the correctness of the control strategy.Finally,the experimental platform of the prototype is built.The off-grid power generation experiment is carried out and the generator realizes the variable speed and constant frequency operation.