Design And Thrust Force Characteristics Investigation Of Linear Permanent Magnet Machines

Gear boxes and ball screws are usually adopted in conventional linear servo to convert the rotary torque generated by rotary machine into linear thrust force,which is harmful for the positioning accuracy,response speed and efficiency.However,linear permanent magnet machine can replace the motion conversion devices and provide linear thrust force directly.So in this paper,two kinds of topologies of linear permanent magnet machine,i.e.linear fluxswitching permanent magnet machine(FSPMLM)and 5-phase modular permanent magnet synchronous machine(MPMLSM)are investigated.Firstly,the structure of FSPMLM is depicted and its operation principle is studied from the motor perspective,namely the principle of generation of the average thrust force,as well as from the generator perspective,namely the principle of generation of back electromotive force.The prototype of FSPMLM is also manufactured and its back electromotive force and detent force in no load condition is studied to verify the effectiveness of finite elements method.To eliminate the thrust ripple of FSPMLM,the auxiliary teeth wrapped with compensation windings are installed on the primary side of FSPMLM,and the method to calculate the compensation current is also proposed.To decouple the compensation windings and phase windings,a compensation module is proposed,and its structure is also described.Then the effectiveness of compensation module and auxiliary teeth with compensation windings are compared with each other.However,the permanent magnets in primary side occupy the place of phase windings in FSPMLM,which causes the decrease of force density of FSPMLM.So MPMLSM is investigated.For the modules of 5-phase MPMLSM,4 different structure(planar C-Core module,planar E-Core module,tubular C-Core module and tubular E-Core module)are selected to be optimized to acquire largest average force.In the process of optimization,the utilization of iron core is focused.After the optimization,the average forces of 4 modules are compared with each other.Consequently,planar C-Core and planar E-Core are selected to be appropriate modules for MPMLSM,because they provide the largest average thrust force.For the 5-phase MPMLSM constructed by planar C-Core(PC-Core MPMLSM)and planar E-Core(PE-Core MPMLSM),this paper analyzes the characteristics of their thrust forces and derive its expressions.The different methods are used to eliminate the special thrust force harmonics.After that,the force density and force ripple of PC-Core MPMLSM and PE-Core MPMLSM are compared with each other.As the result,PE-Core MPMLSM is selected to be the most suitable machine for linear servo.So its mathematical model is established and the mutual inductances between phase windings are studied.Finally,to verify the rationality of PE-Core MPMLSM,a simulation of position control system is established according to the mathematical model.