Research On Starting Of Brushless Doubly Fed Motor Based On Rotor's Compound Coil Structure

Brushless doubly-fed machine is a new type of AC motor which developed on the basis of cascade induction motor.It is essentially a kind of asynchronous motor.Because of its wide application prospects in the field of variable frequency speed regulation,wind power generation,ship shaft belt power generation,it is of great significance to conduct in-depth research on it.The structure of the brushless doubly-fed induction motor is different from the general induction motor,and the slip ring and brush have been canceled,there are two sets of windings in the stator,and the air gap magnetic field is modulated by a special structure of rotor.The literature has shown that the rotor structure of brushless doubly-fed machine is the key factor affecting its performance.By force of contrast several main design schemes,such as the cage,magnetoresistance and winding type of the rotor winding(mixed structure of rotor's application is not widespread,so no detailed introduction is made here),it is knowable that the wound rotor winding has the advantages of a more flexible arrangement,and through reasonable design of rotor,can get two high fundamental winding coefficient sand weaken the other useless harmonic etc,it has good harmonic control performance and high efficiency.However,the starting performance of winding type brushless doubly-fed motor is largely influenced by rotor winding's equivalent impedance,and few people have studied it,in order to meet the need of heavy load,frequent starting of the motor,in this paper the structure of stator and rotor windings of the winding type brushless doubly-fed has been given in-depth discussion.Firstly,based on summarizing the development history of brushless doubly-fed machine and the research status at home and abroad,the research significance and existing defects of wound brushless doubly-fed machine are given.Secondly,by introducing the working principle and various operation modes of the winding brushless doubly-fed machine,the theoretical basis of brushless doubly-fed machine for variable speed constant frequency constant voltage drive,wind power generation and ship traction power generation is given and the design scheme of the stator and rotor winding is compared and analyzed.For the further analysis of the factors affecting the brushless doubly-fed motor electromagnetic torque and speed,using the existing theory for reference,the static coordinate system and d-q axis mathematical model of the brushless doubly-fed machine and the steady state equivalent circuit in the motor running mode are derived which gets ready for the next derivation of the starting principle of brushless doubly-fed motor with compound coil structure.Finally,the structure and working principle of the composite coil and the design ideas and principles are described in detail.On the basis of theoretical deduction,the stator with 54 slots,rotor with 36 slots,2/4 pairs pole,stator with 36 slots,rotor with 24 slots,2/4 pairs pole,these two pole start winding connection examples are given respectively,and their harmonic analysis is carried out.A prototype of stator 36 slots,rotor 24 slots,2/4 poles variable polarity starting brushless doubly-fed motor prototype is designed,and its performance under different starting modes is simulated by finite element method.The correctness of theoretical analysis and simulation is verified by taking experimental measures to the prototype.The study on the starting performance of the brushless doubly fed machine in this paper is of certain guiding significance for the design of brushless doubly fed machine.