Motor-CAD winding temperature model verification using Finite Element Analysis

Size: px

Start display at page:

Download "Motor-CAD winding temperature model verification using Finite Element Analysis"

Bruce Davis
5 years ago
Views:

Motor-CAD winding temperature model verification using Finite Element Analysis Description Motor-CAD uses a layered model, where the copper, insulation and impregnation are evenly distributed through

1 Motor-CAD winding temperature model verification using Finite Element Analysis Description Motor-CAD uses a layered model, where the copper, insulation and impregnation are evenly distributed through the slot, to produce the equivalent thermal circuit for the winding. This document gives a brief description of how to check the Motor-CAD winding model using the Flux2D finite element analysis tool. Machine Geometry The standard default machine geometry for a BPM machine is used in this tutorial as shown below. Page 1

2 Winding Model The winding editor view shows the winding layer model used for this machine. The winding layer model shows how the copper, insulation and impregnation is evenly distributed throughout the slot. In this case we will model 50 conductors of 0.8mm diameter wire in the slot. There is also a coil divider of width 1mm down the centre of the slot as set up and shown below. Page 2

3 Page 3

4 The conductors can be viewed in the slot by selecting the Show Conductors option shown below: In the winding editor view the conductors are now shown in the slot: Page 4

5 Losses 250W will be specified as the stator copper losses as shown below. All the other loss values will be taken as the default values for this example. Page 5

6 Other model settings For the rest of the model the default cooling options, materials, interface gaps etc will be used for this example. Page 6

7 Steady State Thermal Results The average (152 degc) and maximum (156 degc) active section winding temperatures are shown in the schematic view below. Page 7

Verification of Motor-CAD Winding Layer Model using a Finite Element model The Flux2D Finite Element tool will be used to verify the Motor-CAD winding model.

8 Verification of Motor-CAD Winding Layer Model using a Finite Element model The Flux2D Finite Element tool will be used to verify the Motor-CAD winding model. As Motor-CAD has a complex 3D model and Flux2D is in 2D then the Motor-CAD model needs to be modified to give an equivalent 2D model. Note: This modified Motor-CAD model is only to be used for the winding calibration using Flux2D. Creating Motor-CAD 2D model This Motor-CAD 2D model is created as follows. Set the pole number equal to the number of slots to allow symmetry to be used and reduce the size of the model. Page 8

9 Set the stator lamination to housing interface gap to 0mm as this is not modeled in the FE model. Page 9

10 Set the EWdgMLT (end winding mean length per turn) to 0 to ensure all losses are in the active section of the machine. Set the Copper diameter to 0.8mm so that there is no insulation on the wire. This helps keep the size of the mesh down. With a small number of conductors it should be possible to include the wire insulation in the FE model. Note: the line region functionality does currently not work in Flux2D for thermal problems. This means that if you have many conductors with a small insulation layer it may produce an overly large mesh that cannot be solved. To get round this it may be necessary to remove the insulation from the Motor-CAD model as shown above. (i.e. set Wire Diameter = Copper Diameter) Page 10

11 You can also adjust the spacing of the conductors in the winding view as shown below. Always check that the required number of conductors have been drawn in the slot by checking the conductors/slot drawn value is equal to the conductors/slot value. Page 11

12 The circuit should be modified to remove the active to end winding resistances and the stator to rotor resistance path as shown below. The modified circuit with the isolated winding node can be seen in the circuit view as shown below. Page 12

13 The steady state Motor-CAD 2D winding model results are shown below. Page 13

py file from the Flux supervisor this runs all the other files and it will produce the model and also solve it in Flux2D version 10.3 and later.

14 Creating Flux2D model You can then export the Motor-CAD 2D winding model to Flux to view the temperatures inside the slot. To do this you select the File Menu->Tools>Flux2D as shown below. This will create several script files myname.py, myname_1.py, myname_2.py. If you run the myname.py file from the Flux supervisor this runs all the other files and it will produce the model and also solve it in Flux2D version 10.3 and later. Select the file to create and then click the Export button as shown below. If you are using a version of Flux 10.3 or later then select yes and the script will be generated that will also solve the model. Page 14

will take approximately 5 minutes to run depending on the number of

15 The script should then be run from the Flux supervisor as shown below. (It is also possible to run the script from inside PreFlux2D) The script will take approximately 5 minutes to run depending on the number of conductors and the speed of your machine. The results are displayed as shown below. Page 15

16 Page 16

17 The temperatures of each of the conductors can be exported to Excel to allow calculation of the average and hotspot winding temperatures. From Flux2D model: Hotspot winding temperature = 159 degc Average winding temperature = 148 degc Page 17

18 Calibrating the Motor-CAD model The Motor-CAD model can be calibrated by changing the value of the impregnation goodness in the active section. This varies the thermal resistance values in the layered model. The calibrated temperatures are shown below. Page 18

19 Conclusions The different winding temperatures predicted are shown in the table below. Flux model Motor-CAD model Calibrated Motor-CAD model Average winding temperature (DegC) Winding hotspot temperature (DegC) It can be seen that Motor-CAD is slightly over predicting the winding temperature for this machine. This gives confidence that the Motor-CAD layered winding model will not under predict the temperature under different operating conditions. The Motor-CAD model can be calibrated to give an accurate average or hotspot temperature. In this example the calibrated model gives a slight over prediction in average winding temperature but gives good agreement with the winding hotspot temperature. Page 19

Electromagnetic and thermal model for Brushless PM motors

22 December 2017 Motor-CAD Software Tutorial: Electromagnetic and thermal model for Brushless PM motors Contents 1. Description... 1 2. Model Definition... 2 3. Machine Geometry... 3 4. Winding Definition...