Custom Analytical Design

This section will describe how to model an existing motor based on modifying the default design that Samarium contains. The motor geometry, material information, winding, rated speed, and performance points are assumed to be known. The description includes how to modify the existing default design and set the parameters in Samarium so that the existing motor is accurately modeled.

Please read this page carefully as adequate instructions are provided to enter all parameters so that the outputs can be visualized after modeling and analytical design computations.

Symbol	Value	Description
Nss	9	Number of stator slots
Dso	76 mm	Stator outer diameter
Dsbi	64 mm	Stator back iron diameter
Dsi	41.17 mm	Stator inner diameter
So	3.7 mm	Slot opening at air gap
Tw	9.5 mm	Stator tooth width
Lstk	40 mm	Stator axial length
Skew	0	Skew in terms of number of slots
Ptt	1.5 mm	Tooth tip thickness
Pta	0.3 mm	Tooth tip to tooth angular height
R3	0.5 mm	Radius at tooth tip and tooth
R4	1.0 mm	Radius at tooth and stator back iron
Tlam	0.5 mm	Axial thickness of stator laminations
\|\| So	1	Parallel slot opening geometry or no (1/0)

Symbol	Value	Description
Nrm	6	Number of rotor poles
g	0.5 mm	Air gap radial height per side
Lm	2.5 mm	Magnet radial height in direction of magnetization
Arcm	60 mech. deg.	Magnet pole angle at inner diameter od magnet
Dpm	45 mm	Magnet axial length
Lrbi	0	Length of the rotor back iron for outer rotor motors
Dsh	25 mm	Shaft diameter
Ang	0 mech. deg.	Rotor angle

In the 'General' page of the input property sheets, the motor type is set to 'Motor-Inner rotor, slotted'. The rotor is set to 'Magnet-Ring'. This defines the overall design parameters. The check boxes for 2D, 2D, and Analytical design are switched OFF. Notes can be added and then the file saved.

Next, in the 'Dimensions' page, the above numbers are entered appropriately. After entering all the data, the Apply or OK button can be clicked to generate the line drawing. Inspection of the line drawing should produce a cross section as shown below.

Care must be taken to make sure that the geometry is correct. There must not be any interesting sections or inverted lines which may occur if the input geometry is entered incorrectly or some dimensions are not physically possible. 2 and 3 dimensional model can be generated if no errors are found and visualized.

The previous section defined the motor geometry. In this section the definitions for the steel materials and control data are specified.

In the 'Control' page of the input data sheets, the voltage, current limit, semiconductor parameters, rated and no load speeds, and rotor and stator steels are specified. The method of commutation is also set. The existing motor runs of 24 V at 2500 rpm which is the rated speed.

The magnet material is set in the 'Magnet' page. The existing motor uses a 9.25 MGOe bonded Nd-Fe-B ring which is magnetized radially with 6 poles. The material can be chosen from the magnet database menu. The air gap magnet waveform is modeled by the 'Exponent' method with the Fringing and Exponent coefficients set to 0.4 and 3.0 respectively. If the Analytical design is performed now, the air gap flux density waveform should appear as shown below.

The winding of the existing motor uses a delta connection, 35 turns/coil of 1 strand of 22 AWG wire and 3 coils per phase. The winding pattern is the same as that generated by Samarium. The coil span is just 1 slot. These parameters are entered into the appropriate fields in the 'Winding' page of the input data sheets. While choosing the wire size from the wire data base, the insulation must also be specified. After an analytical design the winding can be displayed as well as inspected in the 'Winding' page or in the output Data window. Graphically, the winding is displayed with the zero back emf positions for Hall effect sensors as shown below.

Once all the parameters have been entered in, analytical design can be performed and all outputs visualized. Graphs show the back emf, cogging torque, rated performance points, currents in the phases and other parameters of interest. The output data sheet can be inspected in the Data window. In the 'Coefficients' page, the mean length of turn coefficient, Kmlt, is set to 0.8 as the winding is around a single tooth. The stator steel stacking factor can be set to 0.95 or an appropriate value. The magnet flux leakage coefficient is set to 0.975 based on design experience with these types of motors. The file is now saved and an analytical design is run. In the 'Analytical Design Properties' (Tool menu), the 'Lm multiplier' is set to 1.0, again based on design experience.

Based on the data entered into the input data property pages, Samarium can now simulate the entire motor. The back emf was computed as 8 V 0-pk/ phase which is in close agreement with measured data. The line resistance was computed as 0.43 W which is also in agreement with measured data. As the motor performance is known, some more adjustments of some coefficients may be required to exactly match the model and motor, for example, in the core loss coefficients.

Several parameters like inductance, flux density in the stator, demagnetization current value, etc. are available in the output data sheets.