Motor-CAD modeling of uneven copper loss
distribution in multiphase machines
Description
These notes give brief introduction to the modelling of a fault tolerant multiphase machine in
Motor-CAD. This is for the case where there are redundant windings that are not energised
and the redundant phases are in different slots to the energised phases.
Motor-CAD models a single slot of a machine. For a multiphase machine if the losses of the
machine are the same in each slot then the normal Motor-CAD model can be used.
However where the copper loss distribution is not even in all slots then the Motor-CAD
uneven copper loss distribution model must be used.
The Motor-CAD uneven distribution of copper losses model assumes that the phases are
distributed throughout the machine with each phase in a separate slot, the redundant
phases being in different slots to the energised windings.
Machine Geometry
The standard machine geometry is used in this tutorial as shown below.
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Winding Design
The winding definition in the slot being modelled should be entered in the winding editor as
shown below. In this case the slot has a total of 350 conductors in the slot. The total number
of conductors in the slot should also include any non energised conductors, this is to ensure
the correct amount of copper in the slot. Note: The Motor-CAD model assumes that the
conductors for each phase are evenly distributed throughout the slot.
Uneven copper loss distribution
Cooling options, losses and other machine details should now be entered into the model. In
this machine there are 2 x 3 phase windings with only 1 of the 2 sets of windings energized.
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This is added to the model as shown below.
.
Steady State Analysis
The steady state results are calculated by selecting the schematic tab as shown below. The
copper losses and winding temperatures are highlighted below.
The active and end winding copper losses, the power removed from the stator back iron and
the winding temperatures can be seen in the steady state schematic. To compensate for the
increased copper losses in the slot (due to the uneven distribution) the power is removed
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from the stator back iron.
The uneven copper loss distribution results can be compared with the steady state results
for the same model without the uneven copper loss distribution as shown below.
The comparison of the results between even and the uneven distribution of copper losses
can be seen in the table below. The average winding temperature for the energised windings
has been increased by approx 9 degC due to the uneven distribution of losses.
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Active section
copper losses
(W)
End winding
copper losses
(W)
Stator back
iron losses
(W)
Average Winding
Temperature
(degC)
Winding Hot Spot
Temperature
(degC)
Even distribution
copper loss model
69.8
50.2
30
113.0
114.9
Uneven
distribution copper
loss model
139.5
100.4
-90
121.9
125.7
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Simple Transient Analysis
A simple transient analysis of this machine can be run. The analysis is set up as shown
below.
Selecting the Transient Graph tab will automatically run the transient analysis and produce
the temperature graph shown below:
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The stator copper losses and the stator back iron power (losses + compensation) can be
viewed. The compensation power removed from the stator back iron varies with time to take
account of the storage capacitance effects in the system.
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Duty Cycle Analysis
Transient analysis of this machine can also be made. The duty cycle is set up as shown
below. Note it is not possible to use the Motor-CAD stall calculation when using the uneven
copper loss distribution so all speeds in the transient must be > 0.
Selecting the Transient Graph tab will automatically run the transient analysis and produce
the temperature graph shown below:
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The variation in losses and the stator back iron compensation power can also be viewed as
shown below.
Conclusion
This example has shown how the steady state and transient performance of a machine with
unbalanced copper losses can be modelled in Motor-CAD.
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