Induction Motor Design with Quick Mode
I will introduce an example of three-phase induction motor design using JMAG-Express. The geometry and desired specification of the initial design proposal are shown below (Fig.2, Table 1). I will introduce an evaluation to fulfill an output of 0.5 (kW) at rated speed.
Fig. 2 Geometry of initial design proposal
Table 1 Desired specifications
|Number of poles
Characteristics evaluation of intial design proposal
Create a motor geometry using quick mode. Freely selecting and modifying combinations of rotors and stators from the template is easy in quick mode (Fig.3). Desired geometries are easily created just by modifying the dimension parameters. For this case, we have selected a rectangular model for the rotor and a constant angle of gear tip model for the stator, and by changing the dimension parameter, we were able to create a model close to the geometry of the initial design proposal (Fig.4). Results based on the specifications of the initial design proposal such as the material and winding are displayed (Fig. 5). It can be confirmed that the requirements has not been met as the rated speed has only achieved approximately 0.5 (kW).
Fig. 3 Selecting geometry type
Fig. 4 Intial design proposal created in JMAG-Express
Fig. 5 Characteristics results calculated in quick mode
Performance optimization with changes in bar depth
We have evaluated whether or not motor performances can be improved by changing the bar depth of the rotor. Since the quick mode is equipped with a parametric analysis function, we used the function in deciding the depth of the ideal rotor. By selecting the variable you wish to change from the JMAG-Express data sheet, a dialog to set the parametric range will appear (Fig.6). Specify the range and the number of divisions and the parametric analysis will run when you click on the evaluation button. Once the parametric analysis is over, all case results will be displayed in one graph and easy comparison is possible (Fig, 7). Showing / hiding the graph can also be switched in the checkbox so it is easy to narrow down for examination.We will show the calculation results and bar geometry of a case where we have set the depth to 5mm like in the initial design proposal and another with 10mm (Fig.8, Fig.9).The bar depth is set at 10 mm where it is most efficient and the output meets the requirement. By changing it to 10mm, it can be confirmed that the secondary resistance decreases and the number of rotations at maximum torque has increased. Also, the output has also fulfilled the rated output of 0.5 (kW). Increasing the depth of the bar changes the cost and the mechanical strength, so confirmation in such point of view is required separately.
Fig. 6 Parametric range settings screen
Fig. 7 Parametric analysis results (bar depth 5mm-12mm)
Fig. 8 Parametric analysis results (bar depth 5mm - 10mm)
Fig. 9 Bar geometry of rotor (top: 5mm deep, bottom: 10mm deep)
Characteristics optimization with change in winding
By making effective use of the coil space, I have evaluated whether or not the characteristics can be further improved. Regularly, coil space and lamination factor must be calculated from dimensions and wire diameter on your own. However, with quick mode, lamination factor is automatically calculated from wire diameter and insulation information (Fig.10). Resistance, which changes depending on the winding type such as the coil pitch and number of layers, is also calculated automatically.
To keep the lamination factor below 40%, change the wire diameter and turns to find the ideal combination. Calculation can be done repeatedly as calculation time takes only a second. This time, there is some room left for lamination factor, so we have increased the winding from 48 to 50 turns, wire diameter from 1.1mm to 1.2mm (Fig.11). Increasing the number of turns will increase the total resistance, but by making the wire diameter larger, the resistance per unit length and total resistance has decreased, we have been able to consequently increase the efficiency. The output rises a little with the increase in turns but the rated speed hardly changes.
Fig. 10 Winding setting screen
Fig. 11 Calculation results after winding evaluation