Research On An Axial-Axial Flux Compound-Structure Permanent-Magnet Synchronous Machine Used For Hybrid Electric Vehicles

With the development of hybrid electric vehicles (HEVs), the hybrid drive system is becoming a research hotspot. The power-split hybrid drive system, which integrates the advantages of the parallel and series hybrid drive systems, has the most development potential. The most successful power-split hybrid technology is a electromechanical power-split device. It employs a planetary gear, a generator and a motor to adjust the torque and speed difference between the engine and the load, providing the function of the continuously variable transmission (CVT). A compound-structure permanent-magnet synchronous machine (CS-PMSM) is the high integration of two electric machines to implement pure electrical power spliting. As a substitute of the planetary gear, generator and motor, the CS-PMSM features compact structure and simple control. One topology of the CS-PMSM, i.e., axial-axial flux compound-structure permanent-magnet synchronous machine (AAF-CS-PMSM) is researched in this thesis.First of all, the magnetic coupling problem caused by the special structure of the AAF-CS-PMSM is investigated based on magnetic circuit and finite-element method (FEM). Law of the magnetic interference caused by the axially magnetized PM magnetomotive force (MMF) and armature MMF is researched, which provides reference for the magnetic decoupling design of the CS-PMSM. Owing to the limited space of disk machine rotor, the influence of the surface-mounted PMs rotor and inset-type PMs rotor on the magnetic coupling is investigated, which provides reference and suggestion to selection of the magnet rotor structure. The Halbach magnetized PMs are proposed to solve the magnetic coupling problem caused by different pole number design of the two machines, which makes the CS-PMSM design more flexible. A 20kW AAF-CS-PMSM is designed based on the proposed method. The magnetic coupling degree of the machine is evaluated by FEM, which validates the proposed design method.Secondly, to analyze the three-dimensional flux characteristic of the axial flux machine, different electromagnetic structures are compared from aspects of magnetic field distribution, electromagnetic performance, material utilization, manufacturing process, especially the utilization of end winding space and material, which provide important reference for the optimal selection of the electromagnetic structure. The axial electromagnetic force is analyzed and calculated by FEM. The influencing factors of the axial electromagnetic force are analyzed and the influence on the axial electromagnetic force is researched; the influences of uneven air gap are discussed, both providing important reference to the machine design.Thirdly, the field weakening method is investigated to meet the requirement of wide speed range of the driving machine used for HEVs. A field-weakening scheme using radially slided PMs is proposed. The rules for the adjustment of electromagnetic performances by radially slided PMs is researched. The field-weakening result is evaluated by FEM. The influence of the force on PMs on the machine performance is discussed. The design method and procedure of this kind of machine is put forward. Another field-weakening scheme by varying air gap is also researched. The influence of the air-gap length on the machine performance is discussed and evaluated. The design principle of the original air-gap length is proposed. The field-weakening characteristic is validated by FEM, which provides a theoretical reference for the AAF-CS-PMSM.Lastly, a prototype AAF-CS-PMSM was design and manufactured, and the experimental test was performed. The tested results validate the proposed design and calculation methods, and further optimization of the prototype machine was suggusted, which provides an important reference for the practical application of the CS-PMSM system used in HEVs.