Research On New Topologies And Electromagnetic Characteristics Of Doubly Salient Pm Machines

Doubly salient permanent magnet(DSPM)machines have broad application due to their uncomplicated structure,convenient assembly,high reliability,and strong antidemagnetization ability.However,the coil flux linkage of this kind of machine is unipolar,which restricts the torque output ability to a certain extent.In addition,owing to doubly salient structures,the torque ripple is also large,so DSPM machines are difficult to be used in some occasions with critical torque quality requirements.Therefore,this thesis focuses on the torque ripple suppression and torque density improvement method of DSPM machines from three aspects of stator structure,stator/rotor-pole number combination,and winding configuration.For the traditional 12/8 stator/rotor-pole 3-phase DSPM machine,stator core is composed of four modular E-type segments.So the magnetic circuit of the stator middle tooth is different from that of the stator side tooth.In addition,the stator/rotor-pole number combination is 12/8,so the phase coil distribution of each E-type stator core segment is completely uniform,leading to unbalanced 3-phase back-electromotive force(back-EMF).When the current is injected,the machine generates more electromagnetic torque harmonics,causing an increased torque pulsation.In this thesis,the impact of four stator structures on torque ripple is compared and studied.The number of stator teeth on the stator core segments between adjacent PMs is adjusted from 3 to 1(T-type)or 2(Π-type),which can fundamentally solve the problem of magnetic circuit asymmetry,thereby suppressing torque ripple.Additionally,the flux focusing tooth design is introduced to increase the stator slot area and torque density by removing the low flux density area of the stator yoke.The designed stator structure can decrease torque ripple and increase torque density to a certain extent.However,reducing the number of stator teeth between adjacent PMs is bound to increase the amount of PMs,which is easy to cause poor utilization of PMs.Therefore,based on the traditional E-type 3-phase DSPM machine,this thesis proposes a method to reduce the torque ripple only by using the novel 18k/11 k and 18k/13 k stator/rotor-pole number combinations,where k is a positive integer.With the above method,the middle teeth of the traditional E-type stator core segments are evenly distributed to three phases,thus leading to the balanced 3-phase back-EMF.In addition,the even-order harmonics in each phase back-EMF can be eliminated.Eventually,the resultant 3-phase back-EMFs exhibit the balanced and approximately sinusoidal waveforms,so their interaction with 3-phase sinusoidal currents produces less pulsating harmonics.In addition,the newly conceived stator/rotor-pole number combination also effectively reduces the cogging torque,which further inhibits the torque ripple of the machine.To reveal the comprehensive performance of the E-type DSPM with the improved stator/rotor-pole number combination,this thesis compares and studies two DSPM machines with different stator/rotor-pole number combinations and stator structures.One machine has an 18/13 stator/rotor-pole number combination and E-type stator core segments,while the other machine exhibits an 18/17 stator/rotor-pole number combination and T-type stator core segments.The results show that the improved stator/rotor-pole number combination is a better torque ripple suppression method without sacrificing the utilization of PM,and can also obtain smooth torque output.Moreover,the torque ripple of the DSPM machine can be sharply suppressed by the new stator/rotor-pole number combination,but its average torque is also slightly reduced.This further deteriorates the poor torque density characteristics.To this end,this thesis proposes a dual armature winding configuration and applies it to the DSPM machine with the improved stator/rotor-pole number combinations,eventually forming a new type of dual-armature DSPM machine.Since the additional rotor armature winding can also induce back EMF and act with phase current to generate torque,the total torque density is significantly improved.For the aforementioned stator structure,stator/rotor-pole number combination,and winding configuration design,several prototypes are manufactured,and the torque performance test is completed to verify the presented method.