Study On Rotor Loss Calculation And Loss Reducing Measures Of 2DoF Direct Drive Induction Motor

Two-degree-of-freedom motors can produce rotary,linear and helical motions.Due to the traditional mechanical conversion and transmission devices are omitted,this kind of motor has the advantages of high spatial integration,high control accuracy,low maintenance,and low cost.The motors are widely applied in the industrial fields of robot,CNC machine tool,and automobile production lines.The two-degree-of-freedom direct drive induction motor(2DoFDDIM)researched in this paper,which consists of two arcshaped stators and a shared solid rotor,has the advantages of simple structure and high mechanical strength.The solid rotor is coated with a copper layer to improve the torque.However,it causes large rotor copper loss and serious temperature rise.In this paper,the rotor copper loss of 2DoFDDIM is analyzed and calculated,and the motor is optimized to reduce the rotor copper loss and improve efficiency.The research contents of this paper are as follows:1.A novel nonlinear analytical method considering the saturation of the rotor core is proposed to solve the fundamental magnetic field.The novel method divides the time period into segments.The magnetic field distribution at any time is obtained using Maxwell equations.The eddy-current losses in copper layer and rotor core caused by the fundamental magnetic field are calculated.The surface eddy-current losses in copper layer and rotor core caused by harmonics are calculated using 2D analytical method.The copper loss is determined by the sum of eddy-current and surface eddy-current losses.Coefficients are utilized to consider eddy,saturation,and end-region effects when calculating the rotor core copper loss.The novel method is verified using 3D FEM,and results show the proposed method has higher accuracy than the original method.The errors of the rotor core and copper layer copper losses are less than "7%" and "8%",respectively.2.Change the parameters of the outer rotor to reduce the rotor copper loss and improve the motor efficiency.The advantage of using analytical method to calculate the rotor copper loss is that the main parameters affecting the loss can be found out easily.It can be seen from the calculation process of 2DoFDDIM rotor copper loss that the electromagnetic characteristics of the outer rotor are the important factors affecting the rotor copper loss.In this paper,the conductivity and permeability of the out rotor are selected as variables.Firstly,remain other parameters unchanged.Different materials(copper,Cu-Fe alloy containing 16% copper,and Cu-Fe alloy containing 20% copper)are used for the outer rotor.The corresponding 2D finite element models are established.The simulation results of the characteristics are compared to study the influence of the electromagnetic parameters of the outer rotor.To obtain the best performances,different materials are adopted with changed thickness of the outer rotor.Finally,the motor models are established to obtain the parameters.Then the best combination of material and thickness is determined.3.A novel mover,which is slotted along the axial and circumferential directions on a smooth solid mover surface and the copper is cast in the slots(SWCCM)is applied to the 2DoFDDIM.The corresponding equivalent circuit model(ECM)and parameters are studied.When the coupling effect is ignored,it can be analyzed from the perspective of a single-degree-of-freedom motor.Firstly,the rotary part of 2DoFDDIM is selected as the research object.The magnetic field and eddy current distributions are analyzed.The SWCCM is equivalent to a cage rotor according to the distribution characteristics of eddy current and magnetic field,and the ECM of the rotary part is established.The structure modification coefficient is proposed to consider the influence of arc-shaped stator.To consider the influence of rotor core saturation effect on excitation reactance,the additional air gap is adopted to modify the expression of excitation reactance.The characteristics of the rotary part can be calculated by the equivalent circuit model.The analysis process of the linear part is the same as that of the rotary part.The ECM of the linear part is established to obtain the characteristics.Comparing the characteristics obtained by ECM and finite element method,the results shows that the errors are less than 8.2%.The accuracy of the modified ECM and parameters calculation can be verified.To study the influence of alloy on the motor with SWCCM,copper in slots is changed to Cu-Fe alloy containing 16% copper and Cu-Fe alloy containing 20% copper.The comparison of the simulation results obtained by 3D finite element model shows that the motor performances are weakened.Thus,Cu-Fe alloy is not suitable for slotted solid rotor motor.