Design And Analysis Of The Novel Hybrid Excitation Synchronous Machine

The electrification of transportation has entered a stage of high-speed development,which puts forward higher requirements on the lightweight,safety,and efficiency of machine systems.The traditional permanent magnet machine has the advantages of high efficiency and high power density,but the magnetic flux is difficult to adjust with the difficulties of flux weakening and magnet demagnetization.The electric excitation synchronous machine is simple to control.The air gap magnetic field can be adjusted by controlling the excitation current to achieve the purpose of speed regulation,but the power density and efficiency are low.The hybrid excitation synchronous machines exhibit relatively good electromagnetic performance and good flux weakening control capability for speed regulation by combining the advantages of permanent magnet machines and electric excitation synchronous machines.However,in the design of traditional hybrid excitation synchronous machines,the permanent magnets are symmetrically placed in the center of the salient pole of the rotor,so that the maximum values of the excitation torque and reluctance torque of the machine are superimposed at different current phase angles,and the torque components cannot be fully utilizedTherefore,through the sufficient analysis of the structural characteristics and torque characteristics of the traditional electric excitation synchronous machine and the traditional hybrid excitation synchronous machine,this thesis proposes a novel hybrid excitation synchronous machine with an asymmetric rotor structure.It exhibits the advantages of not only improving the electromagnetic torque but also reducing the torque ripple,by allowing the maximum values of the excitation torque and reluctance torque to meet at the same current phase angle.The detailed research work are as follows(1)In order to highlight the advantages of the novel hybrid excitation synchronous machine,this thesis adopts the quantitative comparison method.Based on the design of the traditional electric excitation synchronous machine,the traditional hybrid excitation machine and the novel hybrid excitation machine are designed.Through the finite element method,the torque characteristics of the three machine models are analyzed,and the design principle to improve the electromagnetic torque by increasing the utilization of torque components of the machine model is verified.By comparing and analyzing the no-load back EMF,electromagnetic torque,and torque ripple of the three machine models,it is proved that the novel machine has higher RMS value of back EMF,higher electromagnetic torque and lower torque ripple than the other two traditional machines.(2)Taking the size of the machine and the amount of permanent magnets as the constraints,the novel hybrid excitation synchronous machines with five slot-pole combinations are analyzed for the purpose of improving the electromagnetic torque,reducing the back-EMF harmonics and torque ripple.Based on the result of multi-objective optimization,the model with 8 poles and 36 slots is determined as the optimal candidate.In terms of rotor topology optimization,the position and size of permanent magnets are further optimized by keeping the same amount of permanent magnets.When the salient pole of the machine is 34 degrees and the permanent magnets are completely offset,the torque components are fully utilized with the maximum electromagnetic torque,while the back-EMF harmonics and torque ripple are reduced.Compared with the model before optimization,the total electromagnetic torque of the machine is increased by 12.22%,and the superposition of excitation torque and reluctance torque is consistent with the target torque characteristics.(3)The magnetic flux density distributions of the novel hybrid excitation synchronous machine at the no-load,rated load,high-speed field weakening condition,and overload are analyzed,which shows that the novel hybrid excitation synchronous machine can meet the design requirements under different working conditions.The air gap magnetic fields of the novel hybrid excitation synchronous machine can be adjusted flexibly,in this thesis,the strategy of flux weakening control by changing the excitation current is studied,and the torque and torque ripple during the field weakening control area are analyzed.The iron loss and copper loss of the proposed machine under no-load and rated load conditions are analyzed,and the demagnetization analysis of the permanent magnets is also carried out.It is shown that the permanent magnets of the novel hybrid excitation synchronous machine has excellent durability to avoid irreversible demagnetization within two times of the rated currents(4)The electromagnetic vibration of the novel hybrid excitation synchronous machine is analyzed.The radial electromagnetic force expressions under no-load and load conditions are deduced,and the components of the electromagnetic force wave with the production cause are depicted.With aid of the finite element method,the radial electromagnetic forces at the no-load,rated load,and light load at medium and high speeds are analyzed,and the time harmonic frequency order and space harmonic order of the radial electromagnetic force after the two-dimensional Fourier decomposition under the rated operating condition are obtained.The modal analysis of the machine stator is performed,and the natural frequency of the machine at different orders is obtained.Finally,the electromagnetic vibration characteristics of the machine are obtained by combining the radial electromagnetic force and modal analysis.