BLDC rotor and stator poles

[jainabhs]

hi,
There is one thing that I do not understand and nor do I find any direct explanations for it.
Is there any relationship between no of rotor poles and no of stator poles in BLDC motor (or PM Synchronous Motor)? I have read somewhere there doesn't have to be. I can imagine if no of poles are same then each rotor pole would interact with stator pole. But it is difficult for me to imagine if the numbers are unequal.
Can somebody explain or point to any resource...

Thanks in advance.
aj

 

[meBigGuy]

Perhaps this will help
http://www.edn.com/design/sensors/4...Part-I--Construction-and-Operating-Principles

 

[jainabhs]

Thanks meBigGuy for pointing to this page.
Although I have been to this page before, some how when I read it this time, I got slightly better idea what is going on. So it looks like if you have more rotor poles, you have to change the stator winding firing more rapidly than for less no of poles (feedback from hall/bEmf) so that rotor and stator magnetic field vectors have certain angle (I think is 90 degree) maintained between them, which produces the required torque.
But half part of my question is still open, let me rephrase, if we have six stator poles (2 poles per phase for 3phase motor) then we will have one stator magnetic field vector. What is we have more stator poles like 12, 18 will we have more than one mag field vectors to align with rotor's field.

Let me know what you think or have some other resource on this.

 

[meBigGuy]

I'm not very strong in this area.

My assumption would be that you can have any relationship as long as there is proper alignment between the stator and rotor when the stator(s) is/are fired. (I'm thinking like a many legged Y or multiple Y's). I have not researched what is available.

 

[alphy]

Hello aj,

Thank you for your question about the relationship between rotor and stator poles in a BLDC (brushless DC) motor or PM (permanent magnet) synchronous motor. This is a common question and there is a relationship between the two that is important to understand in order to design and operate these types of motors efficiently.

In a BLDC motor, the rotor is the rotating part of the motor and the stator is the stationary part. The rotor contains permanent magnets while the stator contains electromagnets. The number of poles on the rotor and stator refers to the number of magnetic poles present in each component. The magnetic poles are what create the magnetic field that drives the motor's rotation.

In general, the number of stator poles is equal to or a multiple of the number of rotor poles. This is because the stator poles need to be positioned in a way that they can effectively interact with the rotor poles to produce torque and rotation. If the numbers are unequal, it can result in uneven distribution of the magnetic field and lead to inefficiencies in the motor's operation.

However, there are some cases where the number of stator poles can be different from the number of rotor poles. This is typically seen in motors with a large number of poles, where it may not be practical to have an equal number of stator poles. In these cases, the stator poles are arranged in a way that still allows for effective interaction with the rotor poles.

I recommend doing further research on the specific motor design you are interested in to understand the specific relationship between rotor and stator poles. Additionally, consulting with a motor design expert can provide more detailed information on this topic.

I hope this helps clarify the relationship between rotor and stator poles in BLDC and PM synchronous motors. Best of luck with your research.