| Brushless doubly-fed machine(BDFM)is a new type of AC excitation motor that can be used both as a motor and a generator.It has the advantages of simple structure,strong reliability,adjustable power factor,etc.It can realize synchronous operation,asynchronous start,double-fed operation and other operations the way.Brushless doubly-fed motors have good characteristics of variable-speed constant-frequency constant-voltage power generation when operating as generators,and are frequently used in fields such as wind power,hydraulic power,and marine shaft power generation;as motors,they have precise speed regulation performance and can be used for Frequency conversion energy-saving speed regulation system for loads such as fans and pumps.The rotor plays the role of "pole-number converter" in BDFM operation,and its structural performance determines the power density and efficiency of BDFM.The winding type BDFM is a new type of rotor structure BDFM.Compared with the special cage and reluctance rotor structure BDFM,the biggest advantage of the winding rotor BDFM is that the rotor winding can use a combination of unequal turns and unequal pitch coils.Furthermore,the harmonic content of the rotor winding is effectively controlled,the winding coefficient of the main magnetic field is improved,the motor loss caused by the harmonics is reduced,and the efficiency and power density of the motor are improved.This paper takes the winding BDFM as the research object.The purpose of the research work is: BDFM has problems such as low starting torque,large starting current,and large impact on the power grid and the motor during the starting process,which makes the starting performance of the motor fail to meet industrial requirements.In this paper,the composite coil structure is introduced into the rotor winding of BDFM,and combined with the stator magnetomotive force harmonic theory,a multi-harmonic combined starting method is proposed to improve the starting performance of the motor.Then carry on in-depth theoretical research on this kind of motor,put forward an effective design method of stator-rotor winding,conduct electro-mechanical characteristics analysis and simulation test research,and then promote the practical process of BDFM with multi-harmonic combined starting.The research content of this article mainly includes the following aspects:First,the magnetic field modulation mechanism and working characteristics of BDFM are analyzed,the general fixed rotor structure and some special structures are summarized,and a variety of control strategies are summarized.In addition,the research and application of BDFM in different fields are discussed,and the development direction of related theoretical and technical research is summarized and prospected.On this basis,the basic principles of BDFM with the multi-harmonic combined starting,the structure of the fixed rotor winding and various operating modes are introduced in detail.Secondly,the BDFM fixed rotor slot number and pole pair number matching principle is given,focusing on the design of the stator and rotor windings of BDFM with the multi-harmonic combined starting,and the general principle design methods and connection methods of the stator and rotor windings are proposed.Next,the analysis of the design scheme of the stator rotor winding found that the stator winding designed with a large and small double star structure can generate multiple pole-pair number starting harmonic magnetic fields.The composite coil in the rotor winding is induced by the starting harmonic magnetic field of the stator winding.The resistance value converted from the rotor to the stator side increases when starting,and returns to the normal value during operation.In this way,the starting current is reduced,the starting torque is increased,and the motor can be operated efficiently.Then,starting from the basic theory of electromechanics and AC windings,the magnetomotive force of stator winding and rotor winding is deeply analyzed,and the harmonic analysis of magnetomotive force is given.After that,starting from the basic electromagnetic relationship analysis,combined with the basic equivalent circuit of BDFM,the equivalent circuit of the multi-harmonic combined start BDFM under starting and running conditions is given.Through the equivalent circuit of the BDFM starting and running state of the multi-harmonic combined start,the torque characteristics of the motor at starting and running are analyzed respectively,so as to further study the starting performance and running performance of the BDFM of the multi-harmonic combined starting.Through analysis,it is found that during the entire starting process of BDFM with multi-harmonic start,as the motor speed continues to rise,the mechanical characteristics are harder,the electromagnetic torque decreases slowly,and does not need to pass the maximum torque point.This starting method is suitable for the occasions of belt conveyors such as cement and mines.The conveyor belt used can greatly reduce the thickness and reduce the cost of the system.Finally,based on the YZR132 motor,a 2/4 pole-pairs test prototype was designed.The design data and parameters of the prototype and the fixed rotor structure of the prototype are introduced.Secondly,based on theoretical and simulation studies,the no-load start and load start studies of BDFM with multi-harmonic combined starting were carried out through time-step finite element software.At the same time,the motor was simulated and studied under different operating modes and different turns ratio of the rotor composite coil.Then,test platform was built of BDFM with multi-harmonic combined starting.By comparing and analyzing the test results of different starting methods under different loads,it further explained that BDFM with multi-harmonic combined starting has a maximum starting current and less impact on the power grid,which is better than The asynchronous start of BDFM verified the effectiveness and feasibility of the proposed scheme. |
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