Inputs

Standard inputs ––––--

Operational inductance order

The operational inductance order (Operational inductance order) can be either “1st” order or “2nd” order.

This choice depends on the squirrel cage topology but also on the results obtained with the 1st order model. When the first order model doesn’t allow getting good fitting between computation results from Finite Elements computations of the operational inductance and those got with the resulting analytical model, the 2nd order is needed.

By default, this input is set to “1st order”.

Model evaluation

The “Model evaluation” of the resulting equivalent scheme (Model evaluation of SSFR model by a direct starting test) is possible by performing a direct starting of the motor.

The starting is operated with a start winding connection.

When the “Model evaluation” is “Yes”, quantities like speed, electromagnetic torque and stator current are computed, and displayed based on the calculated model.

By default, this input is set to “No”.

Op. Line-Line voltage, h1 rms

The rms value of the Line-Line voltage supplying the machine: “Op. Line-Line voltage, h1 rms” (Line-Line voltage, first harmonic rms value) must be provided to compute the starting of the motor.

Notes:

The number of parallel paths is automatically considered in the results.
The starting is always operated by considering a start winding connection.

Op. power supply freq.

The value of the power supply frequency of the machine: “Op. power supply freq.” (Operating power supply frequency to evaluate the SSFR model) must be provided.

The power supply frequency is the electrical frequency applied at the terminals of the machine.

Add. moment of inertia

An additional moment of inertia: “Add. moment of inertia” (Additional moment of inertia) can be added for considering an additional moment of inertia of a load on the shaft line for instance.

By default, this input is equal to 0 N.m.

Max. evaluation duration

The Max. evaluation duration (Maximum evaluation duration) allows us to limit the computation time needed to evaluate the starting of the motor.

However, an internal process detects automatically when the motor reaches the steady state after the transient starting phase.

When the time required for reaching the steady state is lower than the maximum evaluation duration, the computation ends automatically. When the steady state is established instead of computing the maximum evaluation duration it ends automatically.

By default, this input is equal to 1 second.

Advanced inputs ––––--

Linear permeability distribution

Two methods allow defining the permeability in the magnetic circuit of the machine; either the magnetic permeability is constant in the stator, rotor and shaft or the magnetic permeability is linked to the magnetic state of the machine when running at a working point.

When the “Linear permeability distribution” mode is “Constant”, the relative magnetic permeability must be defined for the stator, the rotor, and the shaft.

When the “Linear permeability distribution” mode is “Working point” the characteristics of the working point must be defined with the Line-Line voltage U, the power supply frequency f and the speed N.

Then, the magnetic permeability mapping of a motor is done at the selected working point (U, f, N).

The resulting map of permeability is then applied to the model while performing the frequency analysis. This is what we call the frozen permeability method.

Stator permeability

This input allows to set the value of the magnetic permeabilities for the stator. To meet the requirements of the test assumptions, the computations with Finite Elements are operated by considering linear ferromagnetic materials.

The relative permeability of the stator “Stator permeability” (stator magnetic relative permeability) is by default set to Auto. In this auto mode, the applied stator relative permeability is computed by an internal process (see illustration in below section) in case of a nonlinear magnetic material since the SSFR test is based on the principle that magnetic materials need to be linear.

In case of a linear magnetic material, the stator permeability is the one defined in the material properties (no internal computation is necessary).

The user can enter his own stator permeability by using the toggle button added for this purpose.

This value allows to perform the SSFR test.

Rotor permeability

This input allows to set the value of the magnetic permeabilities for the rotor. To meet the requirements of the test assumptions, the computations with Finite Elements are operated by considering linear ferromagnetic materials

The relative permeability of the rotor “Rotor permeability” (rotor magnetic relative permeability) is defined as the stator permeability by two modes. An auto mode and a user mode. By default, it is set to Auto.

This value allows to perform the SSFR test.

Shaft permeability

This input allows us to set the value of the magnetic permeabilities for the shaft. To meet the requirements of the test assumptions, the computations with Finite Elements are operated by considering linear ferromagnetic materials.

The relative permeability of the shaft “Shaft permeability” (shaft magnetic relative permeability) is defined as the stator and rotor permeabilities in case of the existence of a shaft. By default, the relative permeability of the shaft is set to Auto.

Note: If a shaft is added to a motor, the default value of the shaft permeability is equal to the rotor permeability for an IMSQ IR. For an IMSQ OR, it’s the same as the stator permeability. To have the real shaft permeability, users need to restore default values of the SSFR test. The user can set his own shaft permeability using the toggle button added for this purpose.

Materials magnetic properties

To meet the requirements of the test assumptions, the computations with Finite Elements are operated by considering linear ferromagnetic materials.

The constant value of each material magnetic permeability is computed by considering a mean value in the very first part of the considered B(H) curve.

At a practical point of view, the constant magnetic permeability used in the computation is the average value of initial and the upper bound permeability defined as below illustrated.

Figure 1. Definition of constant magnetic permeability used for computations with Finite Elements software

WP – Line-Line voltage, h1 rms

When the “Linear permeability distribution” mode is “working point, it means that the frequency analysis to compute the operational inductance - L(p) – is based on a working point defined with the Line-Line voltage U, the power supply frequency f, and the speed N.

The working point – Line-Line voltage, first harmonic rms value (WP – Line-Line voltage, h1 rms) must be provided.

WP – power supply frequency

When the “Linear permeability distribution” mode is “working point, it means that the frequency analysis to compute the operational inductance - L(p) – is based on a working point defined with the Line-Line voltage U, the power supply frequency f, and the speed N.

The working point – power supply frequency (WP – power supply frequency) must be provided.

WP – Slip

When the “Linear permeability distribution” mode is “working point, it means that the frequency analysis to compute the operational inductance - L(p) – is based on a working point defined with the Line-Line voltage U, the power supply frequency f, and the speed N.

The working point – slip (WP – Slip) must be provided.

No. comp. / elec. period

To get the quantities like the speed, torque and current versus time, an analytical computation is performed.

The number of computations per electrical period “No. comp. / elec. period” (Number of computations per electrical period) influences the accuracy of results and the computation time.

The default value is equal to 50. The minimum allowed value is 40. This default value provides a good compromise between the accuracy of results and computation time.

SSFR voltage, h1 rms

The rms value of the SSFR voltage “SSFR voltage, h1 rms” (Voltage between two terminals during SSFR test, first harmonic rms value) must be provided. This value allows us to perform the SSFR test.

Note:

The number of parallel paths is automatically considered in the results.
The test is always operated by considering a star winding connection.

By default, this input is equal to 0.2 volt.

The test procedure for performing the SSFR test consists in applying a fixed low voltage source between two terminals of the machine armature winding (Star winding connection) over a range of frequencies. SSFR voltage corresponds to the voltage source magnitude (U) applied.

For additional information please refer to the main principles of computation, section.

Figure 2. SSFR voltage (U) applied between two terminals of the machine armature winding

Skew model – No. of layers

When the rotor magnets or the stator slots are skewed, the number of layers used in Altair Flux Skew environment to model the machine can be modified: “Skew model - No. of layers” (Number of layers for modelling the skewing in Flux Skew environment).

Note: When there is magnet step skew topology, the number of layers is defined at the design level.

Airgap mesh coefficient

The advanced user input “Airgap mesh coefficient” is a coefficient which adjusts the size of mesh elements inside the airgap. When the value of “Airgap mesh coefficient” decreases, the mesh elements get smaller, leading to a higher mesh density inside the airgap, increasing the computation accuracy.

The imposed Mesh Point (size of mesh elements touching points of the geometry), inside the Altair Flux software, is described as:

MeshPoint = (airgap) x (airgap mesh coefficient)

Airgap mesh coefficient is set to 1.5 by default.

The variation range of values for this parameter is [0.05; 2].

0.05 giving a very high mesh density and 2 giving a very coarse mesh density.

CAUTION: Be aware, a very high mesh density does not always mean a better result quality. However, this always leads to a huge number of nodes in the corresponding finite element model. So, it means a need for huge numerical memory and increases the computation time considerably.

The impact of the airgap mesh coefficient on resultant meshing is illustrated bellow:

Figure 3. Airgap mesh coefficient = 0.45 = default value

Figure 6. Airgap mesh coefficient = 0.1 (zoomed view)