# Mechanical stress analysis based on finite element

2022-07-24
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Mechanical stress analysis based on finite element

generally, IPM motors have two commonly used rotor structures, I-type and V-type. These two types of LPM rotors limit the magnitude of magnetic flux leakage through the saturation of the magnetic isolation bridge. The PDS System (formerly known as percudyn system) (Fig. 4) achieves the purpose of magnetic isolation in a different way from the above systems. In the V-type IPM, in order to reduce the force on the magnetic isolation bridge, we reduce the pole shoe deformation through actual production, and generally use the auxiliary magnetic isolation bridge (magnetic isolation bridge 2)

the force on the rotor of the two LPM motors. During the force analysis of the rotor, the following three forces are generally considered, namely, centrifugal force, stator and rotor electromagnetic force and rotor attraction. The centrifugal force and the stator and rotor electromagnetic force have the same direction, both of which are radially outward, while the attraction between the permanent magnet and the rotor core is radially inward at the boundary of the permanent magnet with higher vertical accuracy. This paper will analyze the influence of the above three forces on the rotor stress and deformation

1 finite element analysis model

finite element analysis is an effective analysis method for the analysis of excellent comprehensive performance of IPM motor. The electromagnetic finite element method can obtain the saturation condition and electromagnetic performance of the rotor magnetic isolation bridge and pole shoes, while the structural finite element method can analyze the deformation of the magnetic isolation bridge. Based on the characteristics of weak coupling between structural field and electromagnetic field in strength analysis, the analysis process is as follows: firstly, the finite element node and element model of the motor are constructed, then the electromagnetic force and electromagnetic performance of the electromagnetic model are calculated, and finally the results of the electromagnetic model analysis are taken as the boundary conditions of the structural field in the structural analysis, and the corresponding stress calculation and structural analysis are carried out

according to the analysis of the electromagnetic model, according to the symmetry of the motor, the 6-pole motor only needs to analyze the L/3 motor model. The distribution of electromagnetic force is different when the relative positions of stator and rotor are different. By changing the relative position of the stator and rotor, the electromagnetic distribution at different rotating positions can be obtained

the electromagnetic finite element analysis mainly obtains two results: one is the distribution of the rotor electromagnetic force as the boundary condition of the structural field; the other is the electromagnetic performance of the motor, including its back EMF and magnetic leakage. The stress distribution of the rotor and the deformation of the pole shoe are mainly considered in the structural finite element analysis

2 analysis of rotor stress and deformation results

because the contact between the magnetic steel and the rotor is not ideal, the magnetic permeability of the gap, glue and other substances in the middle is much lower than that of silicon steel., Therefore, the radial electromagnetic force will be perpendicular to the outer surface of the rotor, and the amplitude of the force at different positions will change (as shown in Figure L). The attraction between the rotor punching plate and the permanent magnet is also basically perpendicular to the contact surface. In fact, as the only force with different directions among the above three forces, the internal attraction of the rotor will reduce the centrifugal force. In this paper, three cases of finite element analysis will be carried out

(1) independent rotation in this state, the magnetic effect in the stator and rotor is not considered, the rotor rotates alone in the air, and only the centrifugal force acting on the rotor is considered

(2) under no-load condition, the rotor rotates in the stator without current. Compared with case L, the electromagnetic force generated by the permanent magnet needs to be considered additionally

(3) load condition in this state, the current is applied in the stator winding, and the rotor rotates in the stator. Compared with case 2, the electromagnetic force between stator and rotor shall be considered more. The only difference between the latter two cases is whether there is current in the stator. The change trend of the three cases is consistent. This is because the centrifugal force is proportional to the square of the rotating speed, so the centrifugal force of the rotor will increase with the increase of the rotating speed, while the attraction between the permanent magnet and the rotor only plays a role in relieving the centrifugal stress, which makes the stress and deformation of the "no-load" case smaller than that of the "independent rotor", and the stress and deformation of the "load" case will increase slightly, This is mainly caused by the electromagnetic force generated by the armature reaction in the same direction as the centrifugal force

when the rotating speed changes, the proportion of mechanical stress and rotor deformation caused by centrifugal force and electromagnetic force is shown in Figure 3. When the rotating speed reaches 10000 R/min, 70% of the mechanical stress and rotor deformation effects are provided by centrifugal stress. In contrast, the effect of electromagnetic force is much lower

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