Simulation Setup

Now that the new electrical machine geometry is defined, one must define the simulation project. It can be created by copying/pasting the reference project file default_project.m and renaming it for instance as tuto_SCIM_01_test.m or with the GUI.

In the script, the simulation input parameters are organized in different chapters. To navigate through the different chapters of the simulation project, one can use the Matlab Editor function "Go To". Some of the input parameters might refer to other machine topologies (e.g. squirrel cage induction machines), these parameters should then be simply ignored.

The name file of the electrical machine to be simulated is here given by :

Input.Simu.machine_name = 'machine_SCIM_A';

In the GUI, you can set the machine by clicking on "Select Machine".

GUI main window buttons
GUI main window buttons

Workflow/Operational parameters

In the Workflow group of the GUI, one can define the main purpose of the simulation (Input, Output, multi-simulation). In our case, we want a sinusoidal voltage driven simulation with "Load Extrapolation Algorithm". It is a single speed simulation that is used to extrapolate the variable speed NVH behaviour of the machine.

The single speed simulation is defined in the Workflow group / Simulation tab :

  • The single-speed sinusoidal simulation is run at 1200 rpm (60 Hz) by specifying Input.Simu.N0 = 60*60/3
  • The phase to phase voltage is imposed at 300V with Input.Simu.U0 = 300/sqrt(3)
  • The no-load operation is fixed by specifying Input.Simu.slip = 0
    Workflow group (Simulation tab)
    Workflow group (Simulation tab)

    In the scripts, the sinusoidal voltage is selected with:

  • As the working point is here imposed by U0, N0 and the slip values, on should have Input.Simu.type_extsupply = 0
  • The sinusoidal operation is activated by Input.Simu.type_gensupply = 0 The fields of “current driven” and “frequency driven” simulation are of no interest as the voltage is here imposed, and the frequency is calculated based on the speed and slip values.

By selecting "Voltage (sinusoidal)" as Input and "Acoustics" as Output in the GUI the 4 models of MANATEE will be run.

MANATEE NVH simulation workflow
MANATEE NVH simulation workflow

Then the variable speed mode based on Load Extrapolation is set in the workflow group/Variable tab:

Workflow group (Variable speed tab)
Workflow group (Variable speed tab)

The corresponding script syntax is:

Input.Simu.type_varspeed =1;


The field weakening operation is active above the supply frequency defined in:

Input.Simu.freq_mains= 140;

This way, the voltage will linearly increase with the speed during the load extrapolation algorithm to obtain a constant phase current below freq_mains ; above this frequency, the voltage is constant and the field drops in a parabolic way, so does the phase current. All the PWM parameters are here ignored as this first simulation is under sinusoidal voltage.
All other fields can be ignored.

Electrical model

The electrical model calculating the equivalent circuit and the excitation currents should be activated putting Input.Simu.is_electrical= 1 (in the GUI this was already set in the Workflow Input/Output)

Electromagnetic model

The electromagnetic module calculating the airgap flux density distribution should be activated putting Input.Simu.is_electromagnetics = 1
For this first simulation, the electromagnetic that is chosen is an electromagnetic model based on magnetomotive force (current linkage) / permeance decomposition with Input.Simu.type_Bmodel = 0

All the other parameters should be kept as default. In particular :

  • The skew model is ignored in this first simualtion with Input.Simu.type_skew = 0
  • The saturation coefficient is calculated with Input.Simu.type_satcoeff = 2

This saturation model modifies the average airgap reluctance, and thereof the magnetizing inductance, but it does not account for harmonic effects on the flux density waveform; it only changes the fundamental current value.

Saturation harmonic effects are first ignored using Input.Simu.type_satmodel = 0
As it is a no-load simulation, the effect of rotor field can also be ignored with Input.Simu.is_mmfr = 0

The fundamental equivalent circuit is used with Input.Simu.is_fundSPEC = 1
If necessary one can impose the fundamental equivalent circuit values by using Input.Simu.is_forceSPEC = 1
In the latter case, the values of equivalent circuit specified in the machine data file are used by MANATEE (e.g. Input.Electrical.R10s = 0.0366)

The iron loss model is the Bertotti model where the coefficients are determined from magnetic sheet supplier data with Input.Simu.type_ironloss = 3 The supplier magnetic losses values should be specified as a .txt file in MaterialData folder with the material data name followed by W (for instance M400-50AW.txt in this example). The first line of the file is the vector of frequencies, and the table values are the losses given in W/kg. Alternatively, one can enforce the Bertotti model coefficients defined in the machine data file (e.g. In-put.Magnetics.KilHs)with Input.Simu.type_ironloss = 2

Fault simulation

The fault simulation (short circuits, broken bars, eccentricities etc) inputs should be ignored in this simulation.

Structural mechanics model

The radial force calculation is activated with Input.Simu.is_forcerad=1
The effect of tangential force is ignored with Input.Simu.is_forcetan=0

Tangential force space harmonics can generate radial deflections of the stator yoke and thereof acoustic noise, but the permeance / mmf model that is used here in that simulation case cannot calculate the tangential airgap field distribution which is necessary for the evaluation of tangential forces. However, the contribution of the tangential field to the radial Maxwell stress can be neglected in squirrel cage induction machines.

The maximum number of circumferential spatial orders is here set to Input.Simu.Nmax_fft_orders_circ = 9, meaning that the spatial orders 0, 1, 2 … until 8 are taken into account by the structural simulation. Depending on the yoke stiffness and slot numbers, one may have to include up to 20 spatial orders (example of a large multi-pole synchronous generator) to correctly model main vibration waves. To include the largest vibration wave with a spatial frequency of the pole pair number, this parameter should be at least 2p+1 as a rule of thumb; a warning message is given if it is not the case. The number of longitudinal spatial orders is here limited to Input.Simu.Nmax_fft_orders_long = 2.

The 2D analytical model for the calculation of natural frequencies is chosen with Input.Simu.type_natfreq = 0
A constant damping is applied to all structural modes using Input.Simu.type_damping = 0
The value of this constant damping is in the machine data file. The circumferential modes of electrical machine usually lie between 0.8% and 2.5%, here a 2% value is set with Input.Simu.ksi_damp

Alternatively, one can enforce its own experimental values using is_force_natfreq = 1. In that case the structural modes frequency and damping which are used are the ones defined in the machine data file Input.Mechanics.ExpDamp, Input.Mechanics.ExpFreq, Input.Mechanics.ExpModes. The default damping value is replaced by the experimental ones for the specified modes.

The boundary conditions are set to free-free (Input.Simu.type_mechBC = 0). The calculated natural frequencies may differ significantly from the experimental ones in case the lamination package is welded with stiffening bars, or shrink fit in a frame. If necessary some fitting coefficients can be provided with Input.Simu.Knat_freq_user and activated using Input.Simu.is_tune_natfreq = 1
Note that the error on the natural frequencies is less important for variable speed applications.

The FEA structural model parameters are here ignored as an analytical calculation is run.

Acoustic model

The acoustic noise calculation should be activated using Input.Simu.is_acoustics = 1
The sound pressure level calculation is based on a microphone position, here defined at 1 m away from the frame with Input.Simu.type_micro_distance = 0

MANATEE allows to calculate the acoustic noise at variable speed from a single-speed calculation, assuming that the magnitude of magnetic forces change with speed with a predefined law. This Load Extrapolation Algorithm is equivalent to a speed by speed simulation (Input.Simu.type_varspeed = 1) under constant slip, sinusoidal operation, where the current is held constant until field weakening speed, and is then reduced as inversely proportional to the speed for induction machines.

To allow the calculation of the variable speed noise spectrum (“sonogram” or “sonagram”) based on load extrapolation one should put Input.Simu.type_varspeed = 1.

This special calculation algorithm allows the full sonogram to be calculated within a few seconds, giving the maximum noise and vibration levels experienced at variable speed.

Thermal model

The thermal model here only consists in specifying the average stator and rotor winding temperatures. These values will affect in particular the effective resistance of the equivalent circuit, and therefore the current values.

Numerical parameters

An important input variable is the maximum frequency Input.Simu.freq_max_spec = 6400 to be taken into account during vibroacoustic calculations. It should be chosen depending on the highest “dangerous” natural frequency observed in the machine, and the highest significant magnetic excitation frequency (e.g. twice the switching frequency for PWM operation, and 4 times the slot passing frequency for sinusoidal operation). Small power machines will have high frequency modes, thus requiring high time sampling frequency. A warning message is output when these conditions are not fulfilled.
The max frequency to be taken in current spectra Input.Simu.max_curr_freq = 10000 is not important here for sinusoidal operation.

One should be sure that the numerical discretization is high enough, taking at least Input.Simu.Na_tot = 2^11 and Input.Simu.Nt_tot = 2^11. The text output of MANATEE gives an indication of the discretization quality. Powers of 2 slightly speed up the FFT calculations.

The number of revolution is by default 1. One can lower this value if a time symmetry is found in the force spectrum, or increase this value to lower spectral leakage. In our case the no-load operation does not cause any spectral leakage so Input.Simu.Nrev = 1 is kept.
The number of speed steps used in the sinusoidal sonogram is defined with Input.Simu.Nspeeds_sona = 200

Other parameters

In order to have as many comments as possible during this first simulation, it is recommended to leave Input.Simu.is_com = 1 and Input.Simu.is_warning = 1
As some graphical post-processing will be done after the simulation it is also recommended to automatically initialize the plotting structure by setting Input.Simu.is_init_plot = 1
The automatic saving of results can be activated but the .mat file can takes 5 to 10s to be generated and saved, so here one lets Input.Simu.type_save = 0

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