| The permanent-magnet linear oscillating actuator is a kind of single-phase linear machines which operate at a linear reciprocating motion by applying alternating current.It is characterized by compact structure and high power efficiency,and is widely applied in applications such as linear compressors.At present,neodymium iron boron having large coercivity and residual flux density has been used in linear oscillating actuators.However,compared with the soft magnetic materials and the copper wires,the cost of neodymium iron boron is high,accounting for about 90% of the total material cost of the actuators.Therefore,it has become an important research to improve the magnet utilization of the permanent-magnet linear oscillating motor for further low-cost industrialization promotion.Based on this,this thesis focuses on improving the structure of permanent magnet with restriction on the motor volume,the manufacturing cost,and the permanent magnet materials,aiming to make a forward step for wider low-cost applications.The main contents of this thesis are as follows:On the basis of magnetic field distribution of the traditional Halbach permanent magnet array moving-magnet-iron linear oscillating actuators,one of the reasons which cause a low magnet utilization is that the air-gap flux density at the end of the actuators is pretty small due to the large end air-gap reluctance.Considering this reason,this thesis proposes Halbach permanent magnet array with end ferromagnetic material.This novel structure with combination of magnets and ferromagnetic materials will greatly improve the end air-gap flux density although the mover mass increases to some extent.Analytical results show that the magnet utilization,the electromagnetic thrust force,and the power efficiency of the improved structure are all enhanced.The dynamic oscillating performance of the improved actuators does not decrease with the increase of the mover mass,but makes the actuators have better oscillating performance under the same current excitation.Besides,the traditional surface-mounted permanent magnet(SPM)and interior permanent magnet(IPM)structures are analyzed,and results show that IPM features a larger flux per pole but a higher leakage flux of magnet,whereas SPM structure is on the contrary.Therefore,a semi-IPM structure is proposed in this thesis to improve the magnet utilization of actuators,which considers the flux per pole and the magnet leakage flux simultaneously by designing the thickness of pole pieces.The proposed structure is characterized by much higher magnet utilization but a little decrease in electromagnetic force as compared with the popular Halbach permanent magnet array structure.Therefore,for some low-cost linear oscillating occasions with low thrust output requirements,the linear oscillating actuators with the semi-IPM structure will have significant advantages.The permanent magnet structures proposed in this thesis are all analyzed theoretically and tested by static test platform.Results show that the two proposed structures can greatly improve the magnet utilization of linear oscillating actuators with a certain mover structure,and can provide an optional design scheme of permanent magnet structures for further industrialization and popularization of linear oscillating actuators. |
