AC 3-phase motor control

[Ethienne]

Hello Everyone,

To begin, you must know that I have little background in electronics. I became very interested in electronics and micro controllers only a few mouths ago.

I intend to build my own brushless outrunner motor, that I will ultimately use as a in-wheel motor for an RC car ( long term project in mind) mainly as a learning experience. I understand the basic electromagnetism principles behind the functioning of a AC motor but not more.

I know that in order to control the speed of my motor, I will need to convert DC in some kinda approximation of three sin waves shifted by 120 degrees using transistors switched by a micro controller that sends out pulse width modulation to these transistors.

What I need to be illuminated about is what exactly am I trying to achieve when i want to, say, accelerate from 1000RPM to 1200RPM? Also, how do I figure out what voltage I must supply for a given speed and how do I manage to get this voltage? I understand that the speed of rotation is related to the frequency of the sine wave and the amount of poles in the motor.

More specifically, my motor would have 14 permanent magnet in the outer rotor and 12 coils on the stator.

So to reiterate, I would like to understand how I would go about programming my micro controller if I want my motor to go from 1000RPM to 1200RPM? What am I trying to achieve at an electromagnetic level and what electronic component do i need in my circuits to acheive this?

Thank you very much for taking the time to help me.

P.S ( I understand Calculus and ODEs if this is required in the explanation???...)

 

[(*steve*)]

I think it might be useful to get a small motor and work out your control logic for that first. That way, if you decide to build your own motor, you won't be dealing with too many unknowns at once.

A spindle motor from an old dead disk drive is a likely source of the right sort of motor. You might also be able to salvage some of the drive components too (e.g. the mosfets used for switching.

 

[Ethienne]

Thanks for your reply,

Ya you're right, its better not to start to big. In fact I have a "Hawking HK2822-14 1200KV RC Outrunner Brushless Motor" on the way from eBay that I intended to mess around with to begin.

Also, I just ordered 6 "IRFZ44 Transistor MOSFET N-Channel" rated 49A 55V...I figured that's probably what i would need.

If anyone knows allot about vector control of AC motors and DC to 3 phase inverters and would be willing to tell me what components i would need to build a motor control for the above stated motor, that would be awesome!.

also If any one as any knowledge related to the questions in my original post i'd like to have a more theoretical explanation of what we are trying to achieve at an electromagnetic level while acceleration.

** apparently this type of motor is also called a brushless DC motor...even though the current alternates...? anyhow, just thought id clarify**

 

[woodchips]

Wow! Why not start with something achievable? Vector control is pretty complicated, why not just start with a simple brushed DC motor driven by pulse width modulation? Can then get the concept working much more easily, then go to brushless as stage 2.

If you want to play with vector control get a small single to three phase induction motor variable speed control. Lethal voltages of course, but easy to play with.

Bob

 

[Ethienne]

Hey woodchips. For the brushed motor, I already build a PWM control using an Arduino and a pot.

Hmm, I mean honestly I dont mind the chalenge but i guess your right. Would you, by any chance, know where or as part of what, I could find a small single to three phase induction motor? also ( as i said i dont know much about that) but, would it be the same motor control principle for an induction motor as one with magnets...?

I mean, If I may ask, have you ever build a 3 phase brushless AC (DC?) motor control. If so, where did you obtain your knowledge? I dont mind reading something. I just dont know where to get started -_-