In permanent magnet electric motor designs, the magnetization patterns of the magnets will have significant impacts on the performance of the motors (power density, torque ripple, efficiency, etc.).
This blog demonstrates how to assign three different magnetization patterns (Parallel, Radial and Halbach) to permanent magnet motors in ANSYS MotorCAD and the results are compared.
The motor used here has 18 slots and 12 poles.
Once MotorCAD is launched, go to the Calculation tab. The setting for the Magnetization is located at the left bottom corner.
Magnetization Pattern #1: Parallel
The magnetization direction is parallel to the center line of each magnet segment.
Magnetization Pattern #2: Radial
The magnetization direction is always in the radial direction with the same magnitude.
Magnetization Pattern #3: Halbach
There are 5 Halbach types that the users can choose.
- Continuous Ring Array (default)
There are 3 magnet segments for each pole. Each segment is parallel magnetized. By default, each magnet pole has a magnetic arc of 180 electric degree (ED) and the center segment has an arc of 120 ED. Users can change the arc of the center magnet as needed. The # of magnet segments must be 3 in this case.
- Sinusoidal Array
If the users want to change the number of magnet segments per pole, they can select the second type: Sinusoidal Array. In this case, the magnet segments can be 2 or more. Below is one example of 8 segments per pole.
- Ideal Pattern
The ideal pattern is a continuous sinusoidal variation of the radial component of the remanent magnetic field, such that at the boundary of two poles the radial component is zero and the tangential component is at a maximum. The Halbach array is assumed to be a perfect sinusoidal pattern (infinite # of segments per pole). This represents the best case in theory (in reality, it will not be perfectly sinusoidal). The # of magnet segments must be 1 in this case.
- Radial Pattern
The radial Halbach magnetization always has a radial direction, but the amplitude of the field drops to zero at the boundaries of a pole and has a maximum at the center.
- Customer
It is possible to define your own function for the magnetization pattern. For example, combining two radial magnetization definitions:
It should be noted that with a custom magnetization function a full machine is always modelled, since the magnetization function may not be symmetric. Flux density of a customized Halbach pattern:
Note: The magnetization direction is always determined by the "Magnetization" setting and not from the magnet shape (parallel or radial).
The impacts from different magnetization patterns on the flux density and torque are shown below:
The video below walks through these steps in detail, and the model shown is available in the downloadable resources.
Downloadable Resources: Magnetization Patterns for PMSM
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