Research On Interior Permanent Magnet Synchronous Machines For EV Applications

Interior permanent magnet(IPM)machine is the most popular for Hybrid electric vehicle(HEV)and electric vehicle(EV)applications because of its predominant performance,such as high power density,high efficiency,low magnet current loss,and wide constant-power speed range.Because of the high saturation in the bridges of the IPM machines,there are many harmonics in the air-gap flux density distribution,they are mainly determined by the rotor geometry.At lower speeds,the torque ripple caused by these harmonics is significant.It leads to the rise of vibration and acoustic noise.In high-speed operation,the harmonics produce fluctuation in the flux density on the stator core.It increases the iron losses and results in the significant reduction of the efficiency.The typical single-layered rotor topology for electric vehicle applications is V shape IPM machines,(i.e.,the Toyota 2004 Prius,2007 Camry,2010 Prius,and 2014 Accord).The multi-layered IPM machines are more and more attractive in the EV applications.The typical two-layered rotor topology for electric vehicle applications is ? shape IPM machines,(i.e.,the 2008 Lexus LS600 H,and 2012 Leaf).The other typical two-layered IPM machines are 2017 Prius,and 2016 BMW i3.This dissertation choose three typical IPM machines for the research,including the typical V shape,? shape,and three-layered shape.The typical three-layered shape has a complicated rotor structure.In particular,the lengths of the magnets are not the same,resulting in the manufacturing complexity.An interior permanent magnet(IPM)machine with ?+U shape rotor topology is proposed to reduce the parameters of PM lengths and manufacturability.To reduce the THD of air-gap density,the pole-arc to pole-pitch ratios of magnets are optimized for minimizing the THD of air-gap flux density.The results show that with the increase of PM layers,the THD of air-gap flux density is decreased,so the ?+U shape has the lowest THD of air-gap flux density.For electric vehicle applications,the IPM machines are required to operate at high speed,the bridges,rib and magnets should be carefully designed to satisfy the mechanical stress,and the results show they are reasonable.The torque density,torque angle curve,and torque ripple under maximum torque per ampere(MTPA)control at different current densities are investigated.The results show,the ? shape has the highest torque density.With the increase of PM layers,the proportion of reluctance torque is increased,and the ?+U shape can achieve 60% under over load condition.The torque ripple of ?+U shape is the lowest due to the lowest THD.To improve the flux-weakening(FW)capability of IPM machines,the characteristic current is investigated,and the rotor structure is optimized.The results show,reduce the magnet volume can reduce the magnet flux linkage,add the rib or increase the rib width can increase the d-axis inductance.Therefore,reduce the characteristic current can improve the constant power speed range(CPSR).The relationship of flux-weakening capability and saliency ratio is weak,the flux-weakening capability is determined by the characteristic current.The widest field-weakening performance is obtained when the characteristic current smaller or equals to the rated current.With the increase of speed,the iron loss is increasing result the decrease of the efficiency.The flux-density waveform and its harmonics on stator core and rotor core,core loss density,harmonics core losses,segregation of hysteresis and eddy-current losses are investigated for the V shape,? shape,and ?+U shape.The results show,the main iron loss is located at the stator teeth which are generated by rotor magnet harmonics.The iron loss of ?+U shape is decreased by a greater amount than that of the V shape and ? shape machines due to the harmonic component of the magnetic flux was substantially reduced by increasing the magnet layers.The magnet eddy-current losses of the V shape,? shape,and ?+U shape are investigated in this dissertation.There have two methods can reduce the magnet eddy-current loss.The results show,with the increase of PM layer,the magnet eddy-current loss is increased due to the block effect of the armature-reaction flux is more seriously.For the two-layered IPM machine,increasing the PM depth of first layer and the distance of PM layers which can provide more soft iron space for the armature-reaction flux,therefore,the magnet eddy-current losses are reduced.The PM segmentation can be effectively reduce the magnet eddy-current loss because the eddy-current paths are divided into smaller loops,increasing the effective resistance.The efficiency contour maps of the V shape,? shape,and ?+U shape are investigated.Under the FWC at high-speeds,the efficiency of ?+U shape IPM machine is higher than V shape and ? shape machines,because the iron loss of the ?+U shape machine is the lowest.Finally,the prototype ?+U shape IPM machine is fabricated,the rated power is 48 kW,and the experiments are presented to verify the results of FEAs.