Inputs

Introduction

The total number of user inputs is equal to 13.

Among these inputs, 4 are standard inputs and 9 are advanced inputs.

Standard inputs

D-axis operational inductance order

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

This choice depends not only on the presence or absence of dampers in the rotor pole shoes 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 “2nd” order.

Q-axis operational inductance order

The Q-axis operational inductance order (Q-axis operational inductance order) can be either “Zero”, “1st” order or “2nd” order.

This choice depends not only on the presence or absence of dampers in the rotor pole shoes but also on the results obtained with the selected model order. When the selected model order 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, a higher order is needed. The “Zero” order model is available for the Q-axis because for a machine without dampers the frequency response tends to be quasi-constant.

By default, this input is set to “2nd” order.

Reference frequency

To compute machine reactances, an electrical frequency f0 must be provided to define the electrical pulsation ω0, in which ω0 = 2·π·f0.

By default, this input is set to 50 Hz, providing an electrical pulsation of 314.159.. radians per second.

Reference impedance

o compute machine reactances in the per-unit system, a reference impedance Zb must be provided to normalize the reactances values by dividing the calculated ones by Zb.

By default, this input is set to 1 Ω.

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 field current If, the stator current I and the control angle Ψ.

Then, the magnetic permeability mapping of a motor is done at the selected working point (If, I, Ψ). Even though the working-point If-I- Ψ-N will be used in this process, the rotor speed N only impacts post-processing computations but has no impact on the permeability distribution, reason why it is not required as input for the SSFR test.

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 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 the wound field synchronous machine.

Working point characteristics

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 field current If, the stator current I and the control angle Ψ.

Hence, these three data must be defined:

WP- Field current density (Working point – Current density in Field conductors) or WP- Field current (Working point – Field current)
WP- Current density, rms (Working point – Current density in conductors, rms value) or WP- Line current, rms (Working point – Line current, rms value)
WP- Control angle (Working point – Control angle)

Note: Currently, if the designed machine has either stator slots or rotor salient poles skewed, the “Working point” mode for the “Linear permeability distribution” is not available.

SSFR voltage, rms

The rms value of the SSFR voltage “SSFR voltage, rms” (Voltage between two terminals during SSFR test, rms value) must be provided.

This value allows 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 V.

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 (U) applied.

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



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

Skew model – Number of layers

When the stator slots or the rotor salient poles are skewed, the number of layers used in 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).

Rotor initial position

The computations are performed by considering the relative angular position between the rotor and stator.

This relative angular position corresponds to the angular distance between the direct axis of the rotor north pole and the axis of the stator phase 1 (reference phase).

The value of the rotor D-axis location, which is automatically defined for each saliency part.

Note: For the SSFR test, the rotor initial position corresponds to the position in which the Q-axis characteristics will be measured, following the SSFR test standard if referring to the winding connection as described in the scheme above. The D-axis characteristics will always be measured in the following rotor position (in degrees):

With p = number of pole pairs of the machine.

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 Flux® software, is described as:

Mesh Point = (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].

Giving 0.05 produces a very high mesh density and giving 2 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 of huge numerical memory and increases the computation time considerably.