Study On Starting Performance Of A Novel Brushless Doubly-fed Machine Based On Composite Coil Structure

Wound brushless doubly fed machine is a new type of AC machine,which can realize asynchronous start,asynchronous operation,synchronous operation and doubly fed operation.Brushless doubly fed machine,like induction motor,has the advantages of simple structure and strong durability.At the same time,brushless doubly-fed machine eliminates the brush and sliding ring structure,which makes the motor run more safely and reliably.When brushless doubly-fed machine is used as generator,it has good characteristics of variable-speed constant-frequency and constant-voltage power generation,which is widely used in wind power generation,hydro-power generation and marine shaft-belt power generation and so on.When brushless doubly fed machine is used as motor,it has good speed regulation performance and can be easily adjusted.Section control winding frequency to complete the speed control.Rotor structure is an important factor to determine the performance of brushless doubly-fed machine.Compared with the special cage type and magnetoresistive rotor structure,the winding rotor structure has the advantages of high conductor utilization,low harmonic content and flexible connection mode.However,the starting performance of the wound brushless doubly-fed machine limits its industrial application.The purpose of this paper is to make use of the advantages of flexible wiring of winding rotor and adopt compound coil structure to design rotor winding,and take the brushless doubly-fed machine as the research object.As a result,the starting performance of brushless doubly-fed motor is improved.In this way,the industrial application of wound brushless doubly-fed motor can be expanded,so that this kind of machine can better complete the task of speed regulation and promote the process of practicality.The research contents of this paper mainly include the following aspects:Firstly,the research work on the development of brushless doubly-fed machine made by many scholars at home and abroad is reviewed.On the basis of it,the basic principle of brushless doubly-fed machine is summarized,and a variety of operation modes of brushless doubly-fed machine are introduced when it is used as generator and motor respectively.The basic requirements of AC winding design,stator winding design requirements and rotor winding design requirements are introduced.Secondly,by analyzing the starting mode of series resistance and the formula of winding conversion,it is found that the rotor resistance can be changed by changing the number of effective turns in each phase of rotor winding.Through the analysis,we can realize the starting process and effect similar to the string resistance starting by proper design: during starting,the effective turn number per phase of rotor winding is reduced,and the value of rotor resistance reduction is increased,which is equivalent to the external series resistance of rotor winding,which is similar to the external series resistance of rotor winding,which is equivalent to the external series resistance of rotor winding.The starting performance is improved;Under the condition of operation,the effective turns of each phase of the rotor winding are restored to the normal value,and the motor is in normal operation to complete the task of regulating speed.In this way,the motor can be operated efficiently.After that,the structure of the compound coil is introduced.Through the analysis,it is found that the compound coil structure can meet the requirements of effective turns per phase of rotor windings under different operating conditions,and there are prerequisites: different polar logarithms need to be designed under different operating conditions.In addition,the design schemes of two sets of stator windings and rotor windings of the prototype are introduced according to the results of theoretical analysis.Among them,two sets of stator windings are designed by variable pole method,the function of stator windings is similar to that of "switch" to switch the running state of the prototype,and the rotor windings are designed with compound coil structure.Through the slot conductor EMF star diagram to determine whether the design scheme to meet the requirements.Finally,a 4/8 prototype is designed.The design data and parameters of the prototype are given,and the stator structure of the prototype is introduced.Secondly,in order to verify the correctness of the compound coil theory and the effect on the start-up performance,three simulation models have been established and compared.By comparing the simulation structure of the conventional coil model with the simulation result of the prototype model,the correctness of the compound coil theory and whether it can improve the start-up performance can be verified intuitively by comparing the simulation results of the conventional coil model with that of the prototype model.In addition,the starting performance of the double hexapole starting mode of the prototype model is compared with that of the asynchronous starting mode of the prototype.Finally,the prototype is carried out.In order to verify whether the simulation results of the starting performance of the prototype are consistent with the test results of the prototype,the simulation results are tested.Through the comparison and analysis of simulation and test results,it is shown that the prototype designed in this paper has excellent starting performance and can replace the conventional asynchronous starting mode of brushless doubly-fed motor.At the same time,it also lays a solid foundation for the application and further research of this kind of motor.