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Winding Layouts, Analysis and Short Pitching of a Brushless DC motor

Motors and generators with MotorSolve

One of the most important aspects of motor design is to choose the correct winding layout. For a given pole-slot combination and winding type, MotorSolve automatically computes and gives the designer the option of choosing from a selection of balanced (i.e. all phases with same back emf and out of phase by 120 degrees) layout possibilities (assuming 3 phase windings). For each of these layouts the back emf, back emf harmonics and winding factors are also readily available for analysis. In this page, each of these capabilities is demonstrated and a simple application and a number of examples are shown.

Winding Layouts, Analysis and Short Pitching

METHODS and RESULTS

AUTOMATICALLY GENERATING the WINDING LAYOUT OPTIONS

In MotorSolve, the user simply enters the input parameters such as the pole, slot numbers and the best values of the coil span, phase offsets and the winding layout options are automatically generated. For example, consider a 4-pole 24-slot BLDC motor. For this pole-slot combination, MotorSolve generates the set of coil span, phase offsets and balanced winding layout options shown on the right.

The drop down window lists a number of balanced winding layout options. On each row, the slot numbers and the current directions (negative for into the plane) are indicated for phase A coils. It also shows the winding and current directions (as an animation) of the first of the suggested possible layouts on the main view area including its winding factor, angular spread and the conductor area. It is possible to change and inspect each of these winding options with just a click.

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MODIFYING the WINDING PARAMETERS

From this window, the user can simply change any of the parameters such as the phase offsets, number of layers etc. and a new set of winding layout options are immediately generated. For example, change the coil span from 6 to 4 and the new winding options are shown to the left.

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HARMONIC CHARTS

A simple application of the winding layout options and the use of harmonic charts is presented now. Consider an 18 slot 4 pole surface mounted motor and coil span set to 4 slots. MotorSolve reports a number of winding layout options each of which has a large third harmonic.

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EXAMPLE of SHORT PITCHING

Now change the coil span from 4 to 2 and consider the winding factor harmonics as shown on the left. It is clear that the third harmonic was eliminated. This is an example of short pitching and it demonstrates how easily such modifications can be done in MotorSolve and the results analyzed during the early stages of motor design.

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BLDC SLOT/POLE RATIO EXAMPLES

Presented below are a number of various BLDC slot/pole ratio and the corresponding back emf, harmonics and winding factors that are generated in MotorSolve by simply changing the appropriate parameters with just a click. It should be noted that the back emf, harmonic indices and winding factors shown below are analytic approximations and more accurate results using finite element analysis can also be generated quite easily using MotorSolve.

EXAMPLE 1: 6/8 at 45 degrees

Slots6
Poles8
Phases3
Pole arc45 degrees
Offset2
Coil span1

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EXAMPLE 2: 6/8 at 30 degrees

Slots6
Poles8
Phases3
Pole arc30 degrees
Offset2
Coil span1

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EXAMPLE 3: 9/8 at 45 degrees

Slots9
Poles8
Phases3
Pole arc45 degrees
Offset3
Coil span1

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EXAMPLE 4: 9/8 at 30 degrees

Slots9
Poles8
Phases3
Pole arc30 degrees
Offset3
Coil span1

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EXAMPLE 5: 12/10 at 36 degrees

Slots12
Poles10
Phases3
Pole arc36 degrees
Offset8
Coil span1

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EXAMPLE 6: 12/10 at 24 degrees

Slots12
Poles10
Phases3
Pole arc24 degrees
Offset8
Coil span1

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EXAMPLE 7: 18/8 at 45 degrees

Slots18
Poles8
Phases3
Pole arc45 degrees
Offset6
Coil span2

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EXAMPLE 8: 18/8 at 30 degrees

Slots18
Poles8
Phases3
Pole arc30 degrees
Offset6
Coil span2

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