Analysis And Optimization Of Five-phase Permanent Magnet Machine With Harmonics Injection

Motor is the significant part of more-electric aircraft electrical propulsion system,its power density has important influence on the weight of more-electric aircraft.For the high-speed motors,the reducing mechanism is required,while the efficiency and reliability of the whole system will be compromised.For the direct drive motors,the speed of the motor is limited by the aircraft rotor speed.Therefore,it is necessary to increase the torque density of the motor in order to improve its power density.For multi-phase machines,the third harmonic current is commonly injected into the fundamental one to improve the torque density of the motor.The injected third harmonic current will interact with the third harmonic back-EMF and provide extra torque improvement.Firstly,in this thesis,the fractional slot concentrated winding(FSCW)five-phase permanent magnet(PM)machine is employed to study the influence of the third harmonic current injection on the output torque.When the third harmonic current is injected under the same amplitude constraint,the motor's output torque can improve remarkably,and the copper loss increases as well.The efficiency of the motor will decrease.When the third harmonic current is injected under the same rms value,the output torque will not improve.In order to increase the output torque of the five-phase machines contributed by the third harmonic component,the unequal tooth structure is employed in this thesis,which will increase the third harmonic winding factor.By optimizing the combination of the wider teeth width and narrow teeth width,the optimal fundamental and third harmonic winding factors can be obtained.Besides,sinusoidal PM shape with harmonics injected and PM segmentation technique are investigated in this thesis to increase the third harmonic airgap flux density in the machine.The optimal injection ratio of the harmonics into the sinusoidal PM shape is analytically derived.The harmonics higher than third harmonic are considered in this thesis and studied to improve output torque.For PM segmentation structure,by optimizing the number of the PM segments,the optimal third harmonic airgap flux density can be achieved.Finally,the unequal tooth and PM segmentation technique are employed at the same time in the FSCW PM machine and the electromagnetic performance for all the machines including back-EMF,average torque,etc.are compared.Due to the improvement of the third harmonic winding factor and airgap flux density,the FSCW five phase PM machine with unequal teeth and PM segmentation can provide more torque improvement with the third harmonic current injection.Lastly,the machines with proposed structures are prototyped and experiments of the proposed motors are carried out.Back-EMF,cogging torque and static torque are measured to validate the correctness of theoretical analysis.The curve of the variation of the output torque with the injection ratio is drawing in this thesis.All the experimental results are analyzed and agree well with the related calculated and FE analysis results.