Research On The Integrated Magnetic-field-modulated Brushless Compound-structure Machine For Hybrid Electric Vehicles

The electrical continuously variable transmission(ECVT),which is the core technology of the world’s first mass-produced hybrid electric vehicle,i.e.Toyota Prius,has been an international research hotspot.The ECVT used in Toyota Prius is a mechanical scheme which is based on planetary gears.Hence,it has the problems of vibration,noise,abrasion and regular maintenance.Therefore,many schola rs proposed the ECVT schemes which were based on component-structure machines.These schemes do not require planetary gears,so the above-mentioned mechanical problems can be avoided.However,the early component-structure machines require slip rings to feed the windings,causing the problems such as the decrease of reliability of the machine.The integrated magnetic-field-modulated brushless compound-structure machine(IMFM-BCSM)studied in this subject is a new type of brushless multi-port machine,which solves the special problems caused by brushes and slip rings in the early component-structure machines.At the same time,it also has the advantage of compact structure,and is expected to be used in hybrid electric vehicles and other applications which require decoupling control of the input shaft and the output shaft.The main research work of this paper includes the following aspects:Firstly,the working principle and working mode of the IMFM-BCSM are studied.The air-gap magnetic field expression of the IMFM-BCSM is derived.The magnetic field distributions at the inner and outer air gaps of different topology schemes are compared and studied.After comprehensive consideration,the internal modulation rotor scheme is determined as the subsequent researc h scheme.The speed and torque operation characteristics of the IMFM-BCSM are analyzed by graphical method,which shows that the IMFM-BCSM can realize the speed and torque decoupling of its two output shafts.Combined with the multi-port characteristics of the IMFM-BCSM,the power flows of the IMFM-BCSM in different working modes are studied,and a multi-mode unified analysis method under the application background of hybrid electric vehicles is proposed,which lays the foundation for subsequent machine design and efficiency analysis.Secondly,the generation mechanisms of electromagnetic torque,cogging torque and unbalanced magnetic force of the IMFM-BCSM are studied.The electromagnetic torque expression of the IMFM-BCSM is deduced by virtual work method,and the effects of pole pair combination,size of magnetic blocks and permanent magnets(PMs)on electromagnetic torque are also discussed.The expression of cogging torque of the IMFM-BCSM is deduced also by virtual work method.The generation mechanism of cogging torque of the IMFM-BCSM is revealed from the perspective of interaction of modulated magnetic fields.The effects of pole pair combination and shape of magnetic blocks on cogging torque are studied.The expression of unbalanced magnetic force of the IMFM-BCSM is deduced based on Maxwell formula,and the vector characteristics of unbalanced magnetic force under different pole-pair combinations are studied.The research provides a theoretical basis for improving the torque density and reducing the cogging torque and unbalanced magnetic force.Thirdly,the design methods of modulation winding and torque winding of the IMFM-BCSM are studied.Aiming at the problems of mutual coupling of two sets of windings,serious back electromagnetic force(EMF)wav eform distortion of windings and salient pole effect of modulation rotor in the IMFM-BCSM,three basic principles which should be met in the design process of the two sets of windings of the IMFM-BCSM are proposed.The design method of the two sets of windings under the constraints of the three basic principles is studied.On this basis,the corresponding winding evaluation system is established,and the best pole-slot matching scheme suitable for the IMFM-BCSM is obtained.In order to further reduce the back EMF harmonics in torque winding,a quasi-sinusoidal concentrated winding arrangement method is proposed.The effects of quasi-sinusoidal concentrated winding arrangement and traditional fractional-slot concentrated winding arrangement on machine performances are compared and analyzed,and the validity of the proposed low harmonic winding arrangement method is verified.Next,the harmonic loss of the IMFM-BCSM and corresponding suppression methods are studied.In view of the complex harmonic components of the air-gap magnetic field of the IMFM-BCSM,the alternating frequencies of modulated magnetic fields in stator,PM rotor and modulation rotor,respectively,are deduced.The time-varying characteristics of harmonic magnetic fields in each part of the machine are analyzed.The variation laws of stator core loss,PM eddy current loss and modulation rotor core loss are studied.A variable reluctance magnetic circuit model of IMFM-BCSM is established,and the influence mechanism of PM rotor structure on PM eddy current loss is revealed.The effects of different PM rotor structures on machine performances are compared and analyzed.The research shows that the tangentially-magnetized PM rotor scheme has significant advantages in improving output torque and reducing PM loss.Finally,an IMFM-BCSM prototype is developed.An experimental test bench is built and the experimental research is carried out.First,the reinforcement methods of different PM rotor structures are discussed,and the available scheme of PM rotor is determined finally.In order to verify the correctness of theoretical analysis in the previous chapters,the electrical parameters,no-load back EMF,speed and torque characteristics and efficiency of the IMFM-BCSM prototype are comprehensively tested and analyzed.In addition,the simulation test of the IMFM-BCSM prototype is carried out under hybrid conditions.The results show that the IMFM-BCSM can realize the independent control of speed and torque of the input shaft and the output shaft,and meet the needs of complex working conditions of hybrid electric vehicles.The experimental results provide an experimental basis for the further improvement and engineering application of the IMFM-BCSM.