Research On Pole Standing-wave Feature Of Magnetic Potentials In The Air-gap Of Wound Rotor Brushless Doubly-fed Machine

Within the distributed microgrid system such as the the ship generating and the alternative drive system such as the the wind turbine and pump driving system,the purpose of reducing energy cost can be achieved by using brushless doubly fed machine.The brushless doubly fed machine(BDFM)applies a special designed rotor to convert the energy two three-phase magnetic fields with different pole pairs,in order to accomplish the brushless operating.Thus the shape of the magnetic field of BDFM is different from the traditional AC machines.Now the FE method is usually used in the design of the rotor of BDFM and the analysis of the shape of magnetic field,which the research focuses on the static feature of air-gap megnetic field,however the time-varying feature of the field has been less focused.The wound-rotor brushless doubly-fed motor is taken as the object in this paper,the reference frame will set on the rotor side to observe the rotor,and an analytic method will be used to analysis the shape of distribution and the variety of the air gap magnetic field of BDFM in depth,which concluded them as the pole standing wave feature.And then a method of measuring the magnetic field in the motor is proposed by using the measurement coils in the rotor,the feasibility of this method is verified by comparing the measuring data and the theoretical results,thus providing a new thought of machine design and magnetic field analysis of BDFM,and spreading the applications in more industrial situations.The main work contents are shown as follows:1)The relations between the rotation speed of rotor and the magnetic fields which contribute to the air-gap combinative magnetomotive forces is analyzed,it is pointed out that the frequency of these two magnetic fields are equal when they are observed from the rotor side,however the directions of rotation is opposite,which explains the similarities between the magnetic fields and tooth harmonics.According to the fact that the expressions of magnetic fields is observed from the rotor,the the expression of air-gap combinative magnetomotive force of BDFM is conducted,indicating that the magnetic field and the rotor rotate synchronously,however the polarity of the magnetic pole changes along with time.The shape of air-gap magnetic field of BDFM is similar to the shape of standing wave when observed from rotor,and the characteristics are conclued as the pole standing wave feature of air-gap magnetic field of BDFM.2)The distributing feature of air-gap magnetic field of BDFM in perfect and imperfect condition is researched,which is pointed out that the amplitude enveloping line and the phase-angle curve are the two key aspects of describing the air-gap combination MMF,the number of pole pairs and the amplitude ratio of magnetic field are important parameters.The number of pole pairs influences the shape of distribution of combinative MMF,it can also decide the number of extremums and the positions of standing points.The amplitude ratio of MMF can decide the division degree between the practical and the ideal distribution of air-gap combinative MMF.3)According to the expression of air-gap combination MMF of BDFM,the relationship between BDFM and traditional synchronous motor is conducted combining with the distribution of amplitude enveloping line and phase-angle curve.It is pointed out that the BDFM should be involved in synchronous motor from the observation of magnetic pole.Optimize the rotor winding design based on the tooth harmonic theory,and a rotor winding design scheme based on the pole standing wave feature is proposed.Comparing the performance of different rotor structure based on the pole standing wave feature,giving a reliable reference of performance analysis of BDFM,and the conclusions are verified by the simulation and experiments.4)A method of measuring and analyzing the air-gap combination MMF of BDFM based on measurement coils is proposed,also the conclusion of the magnetic field can be detected and measured effectively by measurement coils with particular pitch is proposed.According to the electromagnetic induction principle,some measurement coils are set on the rotor,and the calculation method of the pitch of measurement coils is conducted and concluded,thus the tracking and recording of the variation of magnetic field in the fixed position on the rotor can be achieved.By setting the reference coil,the processing of the recorded data is optimized.By comparing the processing results with the theoretical curves of amplitude enveloping line and angle-phase relations in Chapter 2,the morphological features of air-gap combination MMF is verified by emulations and experiments.