New GUI and user guide for coil modeling

Introduction

In order to simplify the creation and to clarify the underlying models of Coil conductor regions in Flux, the GUI (i.e., the dialog box) of this type of region has been renewed. This new GUI merges two "legacy" regions, namely:

the Coil conductor region and
the Coil conductor region with losses (available only in AC Steady State Magnetic application)

into a new region that keeps the name Coil conductor region. In other words, the type with losses is now included in the more general Coil conductor region.

The backward compatibility of all legacy Flux projects and of all related Python commands is ensured. However, a few types of wire belonging to the coil conductor region with losses that were redundant were not converted to the new Coil conductor region. These are no longer available for creating new regions, but they are still usable (even for new computations) in read-only mode by users loading legacy projects. In case the user needs to modify the definition of such a region, he or she is encouraged to move forward to the new scheme, which is intended to be more friendly and simple. All details on these changes are presented below. Several messages and warnings are also displayed by Flux to support the user in this transition.

The following topics are covered in this release note article:

Presentation of the new GUI;
Backward compatibilities;
New enhanced section of Flux user guide on coils and windings.

Note: Also in this release, the geometrical constraints on the shapes of coil conductor regions in Flux 3D have been deleted, due to a new method for evaluating the current density in their volumes. For more details, consult Improved coil conductor regions in 3D with relaxed geometrical constraints

Presentation of the new GUI

The new GUI for the coil conductor region includes now two tabs ensuring the input of all the parameters leading to a fully described coil. The content of these two tabs is detailed in the following paragraphs.

The first tab labeled as "Basic Definition" allows the user to describe the essential parameters of the coil conductor region, such as the orientation of the current, the associated circuit component and the number of turns. It also contains settings related to the management of the symmetries and the periodicities, as shown in Figure 1(a). If the user fills only the fields of this tab, Flux will simulate an ideal coil without losses and any loss-related quantity on the region will not be available for post-processing.

The second tab named "Coil Loss Models" allows the user to complete the definition for the coil conductor region with additional parameters, so that Flux will include a model for the Joule losses computations. Once the material is filled, the user has the choice between two descriptions of the winding geometry:

Simplified description (neglects proximity and skin effects)
Detailed description (considers proximity and skin effects), available only in AC Steady State Magnetic application

The simplified description shown in Figure 1(b) allows the computation of the Joule losses in the region without taking into account the proximity and skin effects, that may be important at higher frequencies. This simplified definition only asks for the fill factor coefficient of the coil.

On the other hand, the detailed description presented in Figure 1(c) considers the proximity and the skin effects in the Joule losses computation through special homogenization techniques. Consequently, to set up this model, Flux asks for a full description of the coil wires, i.e., it requires more geometric parameters. Several possibilities (or unit cell templates) exist in this case, as described in Table 1 below:

Table 1. Unit cell templates available in Flux
Type	Required parameters
Rectangular section wire	Horizontal dimension of the wire; Vertical dimension of the wire; Ratio between the horizontal and vertical gaps between strands; Number of strands in parallel. Orientation & units
Circular section wire: diameter	Wire diameter; Number of strands in parallel. Orientation & units
Circular section wire: fill factor	Fill factor Number of strands in parallel. Orientation & units

Figure 1. The new Coil conductor region GUI: (a) the basic definition tab, (b) the coil loss models tab set to simplified description for the winding geometry and (c) the coil loss models tab set to detailed description for the winding geometry.

Backward compatibility

According to the previous section, the definition of a Coil conductor region in the dialog box is now split in two parts: the electrical definition of the coil is done in a first tab called Basic Definition (Figure 1(a)), while the definition of a Joule losses model (requiring the coil material and the coil fill factor) is now performed in the Coil loss models tab by selecting the Simplified description (Figure 1(b)).

For legacy regions created with older versions of the software, Flux 2021.1 ensures backward compatibility. The fields in the dialog box are automatically updated while opening a project created with a previous version and the old Python commands are still valid in user scripts and macros based upon them.

When opening an old Flux project containing a legacy Coil conductor region, three cases are possible depending on the set of optional parameters that were defined:

The legacy Coil conductor region does not have neither the material nor the fill factor defined: in this case, only the Basic Definition tab will be automatically filled in the new GUI.
The legacy Coil conductor region has a material or the fill factor value: in this case, only the tab Basic Definition will be automatically filled in the new GUI. In fact, both parameters are mandatory for the simplified description and Flux can't perform an automatic conversion without one of them.
The legacy Coil conductor region has the material and the fill factor defined: in this case, both tabs Basic Definition and Coil loss models with simplified geometrical description will be automatically filled in the new GUI.

The legacy region called Coil conductor region with losses corresponding now to the Coil conductor region with losses and detailed description (Figure 1(c)) provided several possibilities regarding the strand definition, namely:

Rectangular section: dimensions and gaps
Circular section: diameter and gap
Circular section: fill factor and number of strands
Circular section: diameter and number of strands

Even in this case, all the backward compatibilities for Python commands and for Flux projects are ensured, with the following specificities:

Rectangular section: dimensions and gaps: this model is now in read-only mode; the region remains valid even for new computations: the number of turns (which was not a mandatory parameter) is automatically evaluated during solving. An automatic conversion to the corresponding region in the new GUI Rectangular section wire was not feasible due to redundant parameters in the legacy way of definition: this region now asks for one quantity (the ratio between horizontal and vertical gaps) instead of two quantities (the value of the horizontal and the vertical gaps).
Circular section: diameter and gap: this model is now in read-only mode; the region remains valid even for new computations: the number of turns (which was not a mandatory parameter) is automatically evaluated during solving, but there is no corresponding region in the new GUI since this legacy way of definition was redundant with the option Circular section: diameter and number of strands.
Circular section: fill factor and number of strands: this feature remains fully available in the new GUI: its corresponding template is the Circular section wire: fill factor and the legacy projects are automatically converted. In this region, the number of strands asked in the previous version is now computed by multiplying the number of turns and the number of strands in parallel.
Circular section: diameter and number of strands: this feature remains fully available in the new GUI: its corresponding region is the Circular section wire: diameter and the legacy projects are automatically converted. In this region, the number of strands asked in the previous version is now computed by multiplying the number of turns and the number of strands in parallel.

Note: To move from an old definition to a new one, the region must be deleted and recreated.

New enhanced section of Flux user guide on coils and windings

A new documentation branch describing the creation and usage of coil entities is now available in the user guide. Since coils are frequently present in Flux projects, these new chapters aim to discuss their representation from a user-oriented point of view.

This section discusses the new GUI presented in the previous paragraphs of this release note. Moreover, it goes further beyond describing other region types (solid conductor region) and entities (non-meshed coil magnetic sources) allowing the representation of windings in Flux projects.

This new documentation is composed of the following topics:

a general overview;
several topics describing all possible regions (coil conductor and solid conductor regions) allowing the modeling of windings, including examples of application.
a topic discussing non-meshed coil entities;
a chapter on the use of symmetries and periodicities with coils;
a summary of the availability of the different coil models in Flux applications;
bibliographical references.

This documentation node is accessible in the Flux user guide through the following path: Flux > Construction of a Flux project > Coils and winding and/or by typing Coils and windings in the dedicated search engine of the Flux user guide.

Figure 2. Samples of the new documentation on coils available in the user guide