Permanent Magnet Synchronous Motor Setting Analysis Based on Altair Flux Software

Permanent magnet synchronous motors have a wide range of application scenarios in traditional industries. Under normal working conditions, the rotation axis and geometric axis of the permanent magnet synchronous motor rotor should be the same as the stator axis. However, due to some process or installation problems, the motor may be in an eccentric motion condition. At the same time, with the rapid development of electric vehicles in recent years, permanent magnet synchronous motors are widely used in electric vehicles. Due to the large unsprung mass, they are subjected to severe body loads and road excitations for a long time, causing bearing wear and shaft bending in the motor, resulting in misalignment of the stator and rotor and uneven air gap distribution. This situation is called motor eccentricity.

Rotor eccentricity faults can be divided into static eccentricity faults and dynamic eccentricity faults. The main reason for static eccentricity is that the stator and rotor are not centered, and the reason for dynamic eccentricity is the bending of the shaft or bearing damage. Static eccentricity fault is a common fault in motors. Static eccentricity is equivalent to the rotor rotation center shifting in a certain direction from the stator center, causing the rotor to be eccentric relative to the stator in this direction, and the air gap between the stator and rotor changes. This air gap eccentricity is fixed at a certain position, and it does not change position as the rotor rotates. Dynamic eccentricity fault is also a common fault type in motors. Dynamic eccentricity is equivalent to the rotor center shifting in a certain direction from the stator center, but the rotor rotation center is not offset. This air gap eccentricity rotates as the rotor rotates.

When the motor is eccentric, the air gap magnetic field is asymmetric and the classical algorithm based on the equivalent circuit is no longer applicable. Therefore, a finite element model of the motor is established, and the change characteristics of the air gap magnetic field and torque curve under different fault types are given based on the calculation results of the transient magnetic field.

This article will take a permanent magnet synchronous motor model as an example to describe in detail the setting analysis of the static and dynamic eccentricity of the rotor of the permanent magnet synchronous motor based on Altair Flux software, and further evaluate the problems caused by the eccentricity problem. All analysis operations in this article are based on Flux & FluxMotor2022 version.

1 Classification of motor rotor eccentricity

The motor rotor eccentricity problem can be generally divided into three types: static eccentricity, dynamic eccentricity and mixed eccentricity. Among them, the static eccentricity problem can be described as a certain offset between the rotor geometric center and the motor stator model center, and the rotor's rotation center overlaps with its geometric center; for dynamic eccentricity, the geometric center also has a certain offset, but the rotor's rotation center overlaps with the stator's geometric center; the mixed eccentricity problem is the superposition of the first two problems, that is, the rotor has its own rotation axis rotation, and the rotor also revolves around the stator's geometric center.

Static eccentricity

Dynamic eccentricity

Mixed eccentricity

2 Rapidly Generate a Finite Element Analysis Model of a Permanent Magnet Synchronous Motor

FluxMotor can be used to quickly build a 2D magnetic field finite element analysis model of a permanent magnet synchronous motor, and directly convert it to generate a Flux2D model script file (*.py). Then, running the py script file through Flux2D can obtain a finite element model file containing the permanent magnet synchronous motor model, mesh, and physical settings. For steps on how to quickly build a motor model through FluxMotor, please refer to the relevant documents on FluxMotor component generation.

2.1 Rapidly build a permanent magnet synchronous motor model in FluxMotor

This article takes an 8-pole 48-slot internal three-phase permanent magnet synchronous inner rotor motor as an example, and its basic topological parameters are:

The rotor uses the part template imi_VBlock_01A that comes with the FluxMotor software. The detailed parameter settings are shown in the figure below:

The stator uses the part template os_Free_03A provided by FluxMotor software. The stator slot structure dimension parameters are shown in the figure below:

The stator winding adopts three-phase star connection, with a pitch of 5, single-layer winding method, 2 parallel branches, and 13 turns of a single coil. The relevant parameter settings in FluxMotor are shown in the figure below:

The model magnetic steel and stator and rotor materials in the example use the material model provided by the software. The magnetic steel uses NdFeB_1230_1400, and the stator and rotor silicon steel sheets use M330_35A.

At this point, the basic model of the permanent magnet synchronous motor in FluxMotor has been established. You can click TEST to quickly evaluate the motor's related performance. This article will not go into detail. Since the eccentricity problem is a type of fault problem, the rotation position of the rotor needs to be edited and modified, so the model generated by FluxMotor needs to be transferred to Flux2D first.

2.2 FluxMotor motor model output to Flux2D

Click EXPORT>FLUX2D, select I-φ-N in Transient, set the relevant working condition calculation parameters (which will be modified in the subsequent Flux analysis), select the directory to save the Flux2D script file, and click the Export model button.

The *.py files are generated in the target folder.

Click the Flux Supervisor management interface, select 2D, select "Python scripts" in the left column, and locate the working directory to the *.py script file generated above. Click to select the script file, click the Run the selected script button to generate the permanent magnet synchronous motor Flux2D finite element analysis model and save it.

3 Eccentricity Condition and Calculation of Permanent Magnet Synchronous Motor (PMSM)

3.1 Setting of static eccentricity condition of motor finite element model

Opening the above Flux2D model will result in a model under normal working point conditions. For the static eccentricity problem, the above motor model needs to be edited for motor eccentricity settings, which includes two parts. The first part is the eccentricity problem of the rotor geometry model, and the second part is the rotational physics settings.

First, delete the grid, and then translate the rotor geometry model of the motor. For the .py parametric permanent magnet synchronous motor model exported from FluxMotor, the geometric points on the rotor model are mainly defined based on the two coordinate systems _IM_CART and _IM_POLAR, where the former is a rectangular coordinate system and the latter is a polar coordinate system. To offset the permanent magnet synchronous motor, you only need to edit these two coordinate systems. In this article, the DX and DY offsets of the two coordinate systems are defined for the static eccentricity problem.

The first step is to uniformly change the relative coordinate system of the slip boundary arc and points of the existing parameterized permanent magnet synchronous motor from _OS_CART to _IM_CART.

Right-click Geometry > Geometric tools > Transformation > _AG_AIRGAPROT and change the coordinate system from _OS_CART to _IM_CART.

Click Geometry > Geometric tools > Geometricparameter > New, create DX and DY variables.

Hold down Ctrl, select Geometric parameter > Coordinate system > _IM_POLAR and _IM_CART, right-click edit array.

After the operation, the geometric horizontal coordinate of the entire rotor shifted by 0.25mm.

Here we need to pay attention to the maximum values ​​of the offsets DX and DY and note that geometric interference problems may occur.

Finally, modify the mechanical settings and physical properties of the static eccentricity. First, edit it through Physics > Mechanical set > Rotor and change the rotation center to _IM_CART.

After completing this step, the static eccentricity working condition setting of the permanent magnet synchronous motor is completed.

3.2 Static eccentricity working condition setting

Create a scenario calculation, Solver > Solving scenario > New, select at least one scenario calculation, and select offset DX and DY in Control of parameters for offset parametric calculation. Activate the "Parametric distribution" option to use the Flux parametric distributed computing function to speed up the multi-parameter scanning analysis process.

3.3 Data Post-Processing

After the calculation is completed, obtain the rotor static eccentricity electromagnetic torque curve in Generaldata > Post processing > Curve > 3D curve (2 I/O parameter) on the left.

To analyze the electromagnetic force of the static eccentric tooth, click Parameter/Quantity > Sensor> New to create the electromagnetic force calculation of the nearest and farthest stator teeth after offset. General data > Post processing> Curve > 2D curve (2 I/O parameter) to obtain the electromagnetic force curves at both ends.

3.4 Setting of the dynamic eccentricity condition of the motor finite element model

Regarding the setting of dynamic eccentricity, this article will discuss two ways to achieve the setting: