Research On Less-magnets-type Hybrid Excitation Brushless Synchronous Generator

Permanent magnet motors have the advantages of small size,high power density,flexible structure,etc.With the economic development,the application range of permanent magnet motors is becoming wider and wider.Since permanent magnet motors generally use expensive high-performance NdFeB materials as the source of magnetic potential,the consequent-pole permanent magnet motor with less permanent magnets is an effective way to reduce the cost of the motor.The consequent-pole permanent magnet motor adopted a structure in which the PM pole and the iron pole were alternately arranged so some permanent magnetic materials can be replaced by ferromagnetic materials,the magnetism of iron poles are formed by the magnetization of adjacent permanent magnets,which effectively reduces the amount of rare earth permanent magnet materials in the motor.In addition,the permanent magnet motor also has the defect that it is difficult to adjust the air gap magnetic field.Therefore,a hybrid excitation motor based on the motor body design came into being.Hybrid excitation motors usually include permanent magnets and electric excitation as sources of magnetic potential,which can fully combine the advantages of high efficiency of permanent magnet motors and the flexible tuning of electric excitation motors,and the structural design is changeable.However,many hybrid excitation schemes still have problems such as the magnetic resistance in the series connection structure is too large,the existence of brush and slip ring reduce the reliability of motors,complex structure,or insufficient utilization of motor materials.In order to reduce the cost of the motor and improve the magnetic regulation performance of the motor while ensuring the reliability of the motor,a topology of a less-magnets-type hybrid excitation brushless synchronous generator was proposed in this paper.The motor has consequent-pole rotor structure,which effectively reduces the amount of permanent magnets.And the structure of brushless electric excitation method based on induce excitation is simple,so reliability of the motor is greatly improved.The electromagnetism and permanent magnetism are in parallel structure,which makes the motor have good magnetic regulation performance.The main research of this article are as follows:(1)Structural design and magnetic tuning analysis of the less-magnets-type hybrid excitation brushless synchronous generator.The basic topology of the motor is determined in the first place,and the theory of the motor's magnetization is introduced based on the structural characteristics of the motor.After that the cogging torque of the consequent-pole motor and the relationship between the input current and output current during the induction excitation are analyzed.On this basis,the specific parameters of the structure size and material of each part of the motor are determined initially,and the winding design is completed.(2)The equivalent magnetic circuit model of the less-magnets-type hybrid excitation brushless synchronous generator.Based on the determination of the motor solution area,the magnetic flux path and the calculation process,the equivalent magnetic circuit models of only the permanent magnet excitation and the hybrid excitation are established,and the specific calculation methods of each magnetic circuit element are described.After solving the model some important parameters such as the approximate electromagnetic field distribution of the motor,the magnetic flux in air-gap per pole,and the change in magnetic flux in each phase are obtained.The rationality of the design of the motor is verified initially.(3)The finite element model of the less-magnets-type hybrid excitation brushless synchronous generator.Based on the finite element theory and boundary condition,the corresponding finite element model is established in the software according to the structure,material and winding parameters of the motor design and the external circuit settings are completed.Firstly,the no-load magnetic field of the motor is analyzed through simulation.Because of the special structure of the hybrid excitation motor,an unequal air gap is designed between the PM poles and iron poles of the motor.This design can reducing the magnetic field density of stator teeth effectively while ensuring the motor's magnetic regulation performance and output voltage.Then the no-load characteristics,load characteristics,and regulation characteristics of the motor are analyzed,and the superiority of the less-magnets-type hybrid excitation brushless synchronous generator in terms of output efficiency and tuning performance is demonstrated compared to induction-excited and permanent magnet motors of the same specifications.(4)The prototype test platform and the corresponding test work.After preparation work the no-load characteristics,load characteristics,and regulation characteristics of the prototype are analyzed.The comparison between the test results and simulation results proves the rationality of the less-magnets-type hybrid excitation brushless synchronous generator proposed in this paper.