Welcome to this Ansys innovation course.
In this video we will learn how to define
a nonlinear BH curve in Ansys Maxwell and
key points to remember while defining this.
Before jumping on to Maxwell, let's see
why and when we need to define a BH curve.
Electrical steels forms the core of
all electrical machine applications
including rotating machines,
linear machines, solenoid valves
and transformers.
The electrical steels used in most of
these applications are subjected to alternating
magnetic fields and are required
to reverse their magnetization directions quickly
with low energy loss while doing so.
These materials are called soft magnetic
materials and they have a narrow BH loop.
As you can see, the BH curve is nonlinear
and it starts saturating beyond the knee point
indicating further magnetic induction
in the material is limited.
For the accurate consideration of
material behavior at various magnetic induction
points, it is necessary to define the BH curve of
respective material in Maxwell material definition.
In this video we will be discussing only about
the Initial BH curve definition
for soft magnetic materials in Maxwell.
So, lets get started.
For this IPM machine
that you are seeing on the screen,
if you want to assign a material to the stator
one way is to right click on the stator definition
on the history tree window > edit > properties.
In the properties window, under material section
select edit. A material library window pops up.
Maxwell has an extensive library of
material properties. However,
if you want to define your own material
properties, that you received from manufacturer,
then select add material
or you can clone any existing material.
Let's choose add material.
Under relative permeability, select
type as nonlinear, then you will see
a BH curve button
available under value.
Click on the BH curve button.
This pop-up window allows you to enter the
B and H data.
By default, normal BH curve is selected.
You can choose intrinsic, if you have the
data or if you want to convert the existing data
to intrinsic. For an existing curve,
validation checks are performed on the
coordinate list when you attempt to change the type.
If the data is not valid, an error message will be
displayed and the type of B will not be changed.
If data is valid, a query dialog box displays
asking if the coordinates should be converted.
Pressing no can be used when you specified
the BH coordinates and then realize
you have not selected the desired type.
Here you can start entering the data manually
or you can import the data from a ".bh" or
".tab" format.
You can simply rename a text file to
".tab" format and it will accept the data.
Before you enter the data or import the data,
check the units of B & H values set
on this window.
You can change the units for both H & B
using the bottom right drop-down menus.
If required, you can append more rows
or delete rows using these buttons
below the table.
As you start entering the data or
when you import the data an interpolated curve
in green is automatically created,
curve from the data point is shown in red.
To view these two graphs separately
you can right click on the plot window, go to
view > visibility and select the curve
you want to view. By default,
the BH data entered is
applicable to all the temperatures,
which is generally the case with the steels.
When you want to enter the temperature
dependent data, you can select
edit temperature dependency
and select temperature dependent.
And add, at least two temperature values
for which you want to add the BH data.
Now you can select the temperature from the
dropdown menu and follow the same procedure
to input the BH data for the temperature.
Note that, if temperature dependent BH curves
are used, the selected units are applied
to all the temperature dependent curves.
Now that you have seen
how to input the BH data,
let us look at some of the key points to be
considered while defining the nonlinear BH curve.
The first data points for B and H
must be 0.
The value of B must increase along the curve.
For an Intrinsic BH curve, the slope of the
curve cannot be less than 0.
For a Normal BH curve, the slope of the
curve cannot be less than that of vacuum
anywhere along the curve.
The data points representing the BH curve
should have enough points for accurate
representation of the curve. 20 or more points
should be specified with increased
concentration on the "knee" of the curve.
Since BH operating points in the FEA solution
may extend beyond the input BH data set,
the BH data set is extrapolated in Maxwell.
The slope of the last two user-defined data
points is used to extrapolate the BH curve,
and thus should be as close to µ0 as possible.
The slope can be described as
Relative Incremental Permeability and can be
calculated using this formula with units of
Tesla and A/m for B and H respectively.
This value should be as close to 1 as possible
to best represent saturated behavior.
If the slope of the last 2 points is more than
twice the permeability of free space,
a warning message is issued during the solution
cautioning about possible non-physical solution.
Once you enter the BH data,
click OK below the table.
On this window under material name,
you can give an appropriate name
for this material.
Let's name it as Stator steel for now
and click ok.
You can see the stator has been moved
under the material stator steel.
By following these guidelines, you will be able
to successfully define the nonlinear
BH curve in Maxwell.
Thank you for watching this video.
For more information on Ansys Maxwell
or any of our simulation tools,
visit our Ansys learning channel
ansys.com/courses.