Research On Magnetic Field Modulation Permanent Magnet Machines

With the rapid development of emerging industries such as new energy power generation,new energy vehicles and electric ship propulsion,the research trends of permanent magnet machines have turned from initial medium/low power to high power,high torque.Although permanent magnet machines have obvious advantages such as torque density and efficiency compared with traditional machines,as torque demand increases,permanent magnet machines also suffer from increasing material usage,excessive size and weight,etc.In industrial applications,the common solution is to apply a combination machine of high-speed motors and mechanical speed reduction gear-boxes to realize high torque density.However,since adding mechanical gear-boxes will inevitably bring a series of new problems such as friction loss(which will lead to efficiency reduction),vibration and noise increase,reliability reduction,it's not the optimized choice.In order to avoid the problems introduced by the mechanical gear box,two mainstream solutions are proposed:developing novel high torque density direct-drive permanent magnet machines or applying combination machines of high-speed motors and electromagnetic gear boxes.Since both the two methods are able to achieve high torque density while avoiding issues brought by adding mechanical gear-boxes,they have a prospective prospect in applications.The theory and application technology of novel ultra-high torque density permanent magnet machines "magnetic field modulation permanent magnet machines" is selected as research topics in this paper,this paper focus on topology unified theory of Magnetic Field Modulation Permanent Magnet(MFM PM)machine and topology theory and design method of novel MFM PM machines.Through theoretical analysis,finite element algorithm(FEA)and prototype experiment,several innovative achievements have been realized.Firstly,this paper provides a brief overview of a combination machine of high-speed motors and mechanical speed reduction gear-boxes and novel high torque density direct-drive permanent magnet machine topology.Through topology evolution,this paper unifies novel high torque density direct-drive permanent magnet machine topologies such as vernier machines,flux reversal machines,transverse flux machines as a novel machine family which produces the steady torque based on the so-called magnetic field modulation principles.This machine family is named as the MFM PM machine.Meanwhile,this paper also theoretically proves that combination machines of high-speed motors and electromagnetic gear-boxes also share same operational principles.After that,general formulas of air-gap magnetic field density harmonics,back-EMF,torque and power factor of MFM PM machines are developed.Based on the analysis results of air-gap magnetic field density harmonics,by deeply researching on the application of classic winding theory in MFM PM machines,this paper has successfully applied classic winding theory achievements to MFM PM machines and perfected its winding theory and design method.Moreover,in order to further improve the MFM PM machine topology,magnetic field modulation induction motors and magnetic field modulation gearing are concluded.Magnetic field modulation electromagnetic couplings are brought forward and their operation principles are proved through FEA.After discussing the basic theory and common issues of MFM PM machine race,a MFM PM machine with relatively simple mechanical structure is chosen as the research object so the design and application technology of MFM PM machines could been studied in a more specific and detailed level.The torque performance of regular vernier permanent magnet(VPM)machines is analyzed by the analytical expression,FEA and experiments.This paper also presents performance comparison of a regular PM prototype with a commercial PM machine based on the experiment results.According to previous results,a novel VPM machine-consequent pole,toroidal winding VPM machines which has shorter end windings and less permanent magnet usage is proposed.Followed by the analysis of the influences topology structure parameters towards electromagnetic properties,a prototype is designed to verify its operation principles.Another innovation research achievement of this paper is proposing a high power factor,high power density vernier permanent magnet machine-dual-stator spoke-array VPM(DSSA VPM)machine.By analyzing its topology structure and operation principles,this paper explains the reason why this topology is able to achieve high power factor and calculates its electromagnetic performances such as power factor and torque density.Detailed design process is illustrated and necessary design formulas including initial structure parameter choosing formula,main dimensions calculation formula and electromagnetic geometry formula is listed.A 2000Nm large DSSA VPM prototype is designed,built and tested.The operation principle and design procedure for the DSSA VPM topology are verified by the no-and on-load experiment results,and these test results also proves the DSSA VPM machine high-power factor and high-torque density.