Research On Counter-Rotating Dual Rotors Permanent-Magnet Machine

Counter-rotating Dual Rotors Permanent-magnet Machine (CDRPM) hascharacteristics of single electrical port input and dual mechanical ports output, which canbe applied to anti-rotation propeller propulsion system of underwater vehicle, since it cansubstantially simplify system structure, decrease volume, reduce mass and cost, moreover,improve reliability without brush and slip-ring. Study on CDRPM is still at an elementarystage at home and abroad due to lack of analysis theory and design method about this kindof machine. The systemic research works are done from the starting of the basicelectromagnetic relationship under the supports by National Natural Science Foundation ofChina and Program for Liaoning Excellent Talents in University.Firstly, in comparison with conventional machine, CDRPM is a new structure. Thebasic electromagnetic relationship and principle of electromechanical energy conversionabout CDRPM are proposed; in view of two counter-rotating main magnetic fieldsgenerated by dual rotors, a unified equivalent magnetic circuit is established. According tothe magnetic field lines can not cross and the minimum reluctance path principle, thecalculation model of interpolar leakage fluxes of semi-closed slot large airgap surfacepermanent magnet machine is established and its validity is verified through the finiteelement method (FEM).Secondly, the idea and principle of electromagnetic design are provided in order tomeet power angle characteristic corresponding to uniform or similar between Inner RotorPermanent-magnet Machine Unit (IRPMU) and Outer Rotor Permanent-magnet MachineUnit (ORPMU). Two-dimensional finite element model is established by FEM. Magneticfield under no load, rated load and overload is presented, respectively. The study of impactof permanent magnet segmenting on the air-gap magnetic field is done. Magnetic fielddistributions of the stator core, inductance, electromotive force (EMF) and torque are analyzed. The torque ripple of the inner and outer permanent magnet attraction andrepulsion between the rotors is reduced by introducing magnetic barrier ring.Thirdly, in view of stator fastener is the part of the magnetic circuit, influence analysisof the stator fasteners is completed both mechanical and electromagnetic aspects. Inmechanical aspects, the stator fasteners material selection, end caps combining and thestator forces are considered. In electromagnetic aspects, the magnetic field distribution,EMF and torque are analyzed when the stator fastener is magnetic carbon steel ornon-magnetic stainless steel, and effects of the inner and outer rotor relative initial positionis also analyzed.Fourth, based on fourier transform and the method of separating variables, ananalytical solution for computation the no-load magnetic field in the CDRPM is presented.The analytical solution is based on two-dimensional analysis in polar coordinates andaccounts for the influence of any pole and slot combinations, radial/parallel magnetization.In order to accurately calculate the magnetic field and cogging torque, the boundaryconditions is used to consider the stator slotting effect. The magnetic field change of notchregion is acquired by rotor rotation, while cogging torque and EMF of CDRPM areestimated.Fifth, a unified to the same d-q coordinate system by coordinate transformation andthe same current constraints between IRPMU and ORPMU, then, the mathematic model ofmachine with single electric port and dual mechanical ports is established. the influence onoperation characteristic of CDRPM because of the no-load EMFs induced by magnets oninner and outer rotors is analyzed. CAD software package about electromagnetic designand operating characteristics program of CDRPM is achieved by MATLAB.Finally, based on theoretical research above, new mechanical structure scheme isproposed to guaranteed concentricity of inner rotor-stator-outer rotor and stable operation.An 11kW 6-poles prototype of CDRPM is manufactured, and carried out experimentsresearch. Correctness and feasibility of theoretical analysis and design method are partlyverified through the comparison of experiment result and simulation, foundation of theoryand technology is laid on further research on this kind of machine.