| The arc motor is a kind of special linear motor which adopts the block stator structure and multiple stator assembly.This kind of motor can be used to directly drive the large scanning equipment such as the astronomical telescope,large antenna,rotating photovoltaic bracket,missile observer,nuclear magnetic resonance machine for continuous or limited rotation without complex intermediate transmission device.Therefore,arc motors have been used in many occasions at home and abroad.The current arc motor is mainly rotor permanent magnet typed,which results in low utilization rate of permanent magnets,complex rotor and poor safety.The use of arc motors in large precision scanning equipment is seriously restricted.Previous study on arc motor focused on reducing torque ripples.The unbalanced radial force caused by stator discontinuity and the problem of temperature rise are ignored.Therefore,previous research can hardly meet the key engineering needs of stable positioning for precision equipment and temperature rise control for imaging scanning system.In view of the existing problems of the rotor permanent magnet typed arc motor and the deficiencies of the existing research on the arc motor,an arc linear flux switching permanent magnet motor using the stator permanent magnet structure and reluctance rotor is proposed in this paper.Key problems of operation mechanism,accurate model,circumferential end effect,torque ripple,unbalanced radial force suppression,structural optimization,accurate calculation of magnetic field and temperature rise,as well as thermal reliability improvement are studied.Firstly,the vector magnetic potential is used as relating item.The analytical magnetic field model of the proposed motor is established by solving the Laplace equation and Poisson equation of the vector magnetic potential.The analytical expressions of air gap flux density,torque,radial force,flux linkage and losses are further deduced.Due to double salient pole effects,the high order harmonic content in air gap flux density is increased.Thus,the magnetic field analytical harmonics are selected based on the improved permeance function.The calculation time is shortened and the practicability of the analytical magnetic field model is enhanced.The accuracy of the analytical model is verified by comparison with the finite element model.It can provide a fast and accurate tool for the analysis of the proposed motor,as well as the coupling calculation with other physical fields.Secondly,the unique circumferential end effect of the arc motor,and the asymmetric problems of the winding inductance and circumferential end leakage reactance are analyzed based on the equivalent stator circuit.The asymmetric parameters are balanced by the methods of auxiliary teeth and interchanged winding,and the constraint of the rotor pole number is given.The harmonic characteristics of the detent force and radial force are analyzed by the permeance function.The inconsistency in harmonic distributions and optimization requirements is revealed.On this basis,a novel stator dislocation structure is proposed,which can restrain the main harmonics of radial force and residual harmonics of detent force.The significance of radial force suppression is discussed through structural stress analysis.A prototype test platform is developed to verify the advantages of the proposed new structure.Then,a three-dimensional thermal network model of the proposed motor is established.The problems of the motor losses,temperature rise and their influences on the permanent magnet performance are studied for in stator excitation typed arc motors.By combining the thermal network and analytical magnetic field model,a bidirectional coupling model of the magnetic and thermal is proposed,which can consider the interaction between the electromagnetic characteristics and temperature rise process.The shortcomings of the previous methods in the magnetic-thermal coupled analysis are made up.Based on the proposed model,the electromagnetic and temperature rise characteristics of the proposed motor are studied under the natural air cooling condition.The iterative methods of the steady and transient temperature rises are given.The changes of the motor electromagnetic process and temperature rise are analyzed under constant current and constant torque conditions,and the coupling relationship between electromagnetic and temperature rise under different conditions is obtained.Finally,a bidirectional waterway structure suitable for the arc stator is designed to improve the thermal reliability of the proposed motor.The stator temperature difference in the circumferential direction can be effectively balanced by this structure.On the basis of the magnetic-thermal bidirectional coupling model,an additional branch of thermal network considering water cooling is added.The calculation verifies that the designed water channel structure can meet the temperature rise limitation of the motor system.The fault-tolerant methods of open fault are studied.The effects of three-phase series connection and dual three-phase parallel connection of multi-stator,as well as open winding and neutral connection structures on fault-tolerant temperature rise are compared.An enhanced structure of fault-tolerant is proposed based on redundant windings.It can effectively restrain the increase of copper loss and temperature rise in fault-tolerant conditions,and is suitable for occasions with strict requirements on fault-tolerant thermal reliability. |
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