Research On Magnetic Field Characteristic Of Tooth Standing Wave Brushless Doubly-Fed Machine And Its Application

Nowadays,since the poverty of energy resources and the aggravation of ecological problems,developing new types of electrical machine that are suitable for renewable energy power generation and new energy driving,which can realize energy substitution,becomes imminent for our country and even the whole world.As a new type of AC electrical machine with high operation reliability and various operation modes,the structure and operation characteristics of brushless doubly-fed machine(BDFM)make it be fit for frequency controlled adjustable speed driving(ASD)and variable-speed constant frequency(VSCF)power generation including wind power,hydraulic power as well as ship shaft power generation,which is in accord with industrial development trend of energy conservation,environmental protection and high efficiency.In recent years,it becomes more and more popular for the research of structure optimization,magnetic field theory,mathematical model and new control strategy of various types of BDFM.Wound rotor BDFM is chosen as the research object in this thesis,and the following aspects would be introduced and analyzed by theoretical derivation,finiteelement(FE)simulation and prototype experiments:First of all,the emergence and early development of BDFM are reviewed,and according to the type of structure,the research status of all kinds of BDFM are introduced.Meanwhile,the advantages of BDFM are introduced according to its industrial application.Then,wound rotor BDFM would be focused for further study.After brief introduction of the electromagnetic relationship between major physical quantities and both structures of stator and rotor,some basic operational principles are analyzed in detail,including the expression of rotational speed,the law of power transmission and various operation modes,which lays foundation for further research on its air-gap resultant magnetic field.Secondly,by transforming the reference coordinate system and reasonable simplification of analytical expression,characteristic of the air-gap resultant magnetic field in wound rotor BDFM that similar with standing wave is proposed,which is called tooth standing wave characteristic.On account of this conclusion,three following aspects of its application would be studied innovatively.Primarily,the design method of double-sinusoidal rotor winding with unequal pitch and unequal turns is concluded,and a winding analytical method with universal applicability is introduced.Then,in the purpose of eliminating unbalanced magnetic pull inside machine,reasonable selection of pole number combination is deduced.Besides,based on the expression of air-gap resultant magnetic field with tooth standing wave characteristic and notching effect,the frequency law of torque harmonics caused torque ripple is found,and the solution of notching auxiliary slots is proposed too.Thirdly,the mentioned conclusions of theoretical analysis are calculated by FE simulation.Primarily,resultant magnetic field wave of different timing is simulated,and the validity of tooth standing wave characteristic can be proved by periodic variation of flux density amplitude and the existence of antinode and node in the wave.Then,the validity of proposed pole number combination is proved by comparison of the simulation results on radial magnetic pull between BDFMs with different pole number combination.Also,electromagnetic torque wave of simulation is Fourier decomposed to verify the acquired frequency law of torque harmonic.The validity of notching auxiliary slots and optimum approach can be obtained by comparing electromagnetic torque of different notching cases.Finally,the air-gap resultant magnetic field wave of wound rotor BDFM is measured in prototype experiment for the first time by modified rotor and embedding detective coils in rotor slots,which provides further proof for the validity of tooth standing wave characteristic.Meanwhile,the accuracy of proposed pole number combination is verified again by comparison of vibration and noise between 2/4-pole and 4/8-pole wound rotor BDFM,which is measured by vibration meter and sound meter.In the end of the thesis,based on a 5kW wound rotor brushless doubly-fed generator designed in guidance of tooth standing wave characteristic,the power generating performance of which is tested under various load and different rotational rate.