Example13 Demagnetization of SPM Motor

General

• The demagnetization of the SPM motor (surface permanent magnet motor) is analyzed.

• Torque, distribution of demagnetization rate, magnetic flux density, iron loss, cogging torque, and induced voltage are solved.

• The analysis is coupled with the external circuit.

• The homogenizing method is applied to simulate the layer structure of the electromagnetic plates of steel for the core.

• Unless specified in the list below, the default conditions are applied.
   

• In this example, a quarter period symmetric model is used for faster calculation.

Analysis Conditions

The Rotating Machinery tab is set as follows.

External circuit is as follows.

3-phase AC of 60Hz and 40A is applied.

The U phase is calculated with a function to [search for power phase at the maximum torque].

As [Conversion of external circuit I/O values] is ON, the resistance value of the FEM coil is set to the phase resistance which is equivalent to a full model instead of a quarter model.

See [External Circuit Conversion] and [Example of External Circuit Conversion Setup] for the details of conversion.

Set the Mesh Tab as follows.

The Transient Analysis tab is set up as follows.

The number of steps is 180, circumferential division angle is 1.0[deg], and rotational quantity per step is 1[mesh]. The rotation up to 180 degrees (=180*1.0*1) is analyzed.

It can be converted to the electric angle of 360[deg] (=180*4/2) (mechanical angle x number of poles). One period of electric angle is analyzed.

• As the input power is specified by current, the coil current is in the steady state from the beginning. The torque is also in the steady state.

• To calculate the iron loss, it is necessary to set the timesteps for one period of electric angle in the steady state, and to define the iron loss characteristic for the material property.

Model

A rotor core and magnet are placed in the center. A stator and coils are placed around them.

The motor has 4 poles and 24 slots.

This is a 2D model analysis.

By utilizing the symmetry, the model is quarter period symmetric.

Rotation period boundary (symmetric) is set.

The full model is as follows.

* Available from the material DB

In order to take the irreversible demagnetization into account, the magnet material setting is modified as below.

The body attribute is set up as follows.

For the core, the homogenizing method is selected to simulate the layered steel plates.

Boundary Condition

Half period symmetric boundary is set.

Results

The below are the results.

The distribution of the demagnetization rate at the rotation angle of 180[deg] is shown below.

The right side of the magneti is demagnetized because of the strong diamagnetism of the coil.

The diagram below shows rotation angle-torque characteristics. It is output to “Torque [N*m]” of the result table.

You can see the torque decreases as the rotation goes on.