Litz Wire Modeling in Altair Flux

Litz wire are multristrand conductors that are used for their reduced skin effect and proximity effect losses in high frequency.

                                                  

Figure 1 - Litz Wire representation (Source image : MWS Wire)

Litz Wire can be used in Flux since their particular losses are modeled using the "Detailed description" option in the coil conductor region definition as seen in the next picture.

Figure 2 - Coil Loss Model Description in Flux

This allows you to create an equivalent coil conductor region with particular properties of the Litz Wire. This feature saves you a lot of pre-processing time as you only need to create one face region instead of drawing all the coils. The same time saving is applied to the electric circuit creation.

Precision : In the figure 3a, every coil conductor are put in serie. Even though Litz wire are normally in parallel, this is done to accord the model to the hypothesis that Litz wires strands are twisted so closely that they all are traveled by the same current.

Figure 3 - First Analysis Simple Model - Coil Conductors vs homogenized area with detailed loss model

Magnetic parameters can then be computed on both of these projects to test the equivalent region. For example, magnetic flux density isovalues and magnetic field isolines can be plot :

                       

Figure 4 - Magnetic flux density isovalue and magnetic field isolines comparison between both models

Figure 5 - Magnetic flux density isovalue and magnetic field isolines comparison between both models - Zoom on coil region

Homogenized Model Application Case : IPM Motor Winding

This homogenized face region is now applied on an IPM Motor winding. The two following models, generated with FluxMotor, will be compared in this section to show the robustness of this region :

Figure 6 - IPM Motor models with a) modeling of all coil conductors b) Homogenized face regions with detailed description of loss model

This models present the same geometry except that in the first one, all the coil conductors of the circuit are represented whereas on the second one, the winding are modeled as a homogenized region. A clear advantage of the homogenized region is its set up easiness. You have only one face region per slot to create and only one current source and define it as in the Figure 2's box. This saves up a lot of time when you prepare your project.

Figure 7 - Winding definition : a) Slot filling with coil conductors b) Electric circuit of the model with coil conductors c) Electric circuit of the model with homogenized regions

Precision : In the figure 7b, every strand has its own current source. This is done to accord the model to the hypothesis that Litz wires strands are twisted so closely that they all are traveled by the same current.

Both model are solved with a time-dependent scenario. This is where the homogenized region is interesting as using it reduces computation time by a factor 10 approximately for our 13*18 coils per slot model. Results post-processed in Flux can be found on the following figures :

Figure 8 - Torque comparison over time

Figure 9 - Magnetic Flux Density on a path in the middle of the airgap comparison

Figure 10 - Joule Losses comparison over time

As you can see on figures 8 and 9, the homogenized region gives very good results on the torque and magnetic flux density along a path. It also gives good results on the Losses computation using a sensor (less than 8% difference on the mean value).

This face region can be used on many different application case (other motor topologies, transformers, ...) in magneto-harmonic or transient magnetics. It is recommanded to use it as it will highly reduce your pre-processing and computation time without affecting too much the precision.

This feature is already live in the 2022.1 Version of Altair Flux.