motor control - beginning

[omatza]

Posted on December 06, 2005 at 14:19

motor control - beginning

[omatza]

Posted on May 17, 2011 at 10:19

Hello All

I have BLDC starter kit, with the st7fmc2. I started to read some AN regarding control the motor. one applicaition note pointed to another, until I finally found AN1130 (http://www.st.com/stonline/products/literature/an/7209.pdf) I don't know about electricity, and I wanted to understand little bit about the motor operaiton. I understood that there are 6 steps, cause the motor has 3 windings. Am I right ? What is the T1, T2, .. in page 7 (pigure 3.6) in this AN ? What is the pairs of poles ? Tanio - if you find some material to Luter, I am sure lot of people will also love to read it, so maybe you can put it in this forum. Thanks a lot Oren

[luter]

Posted on May 17, 2011 at 10:19

Hi.

I will share with you my experience. I am only beginer as well. I deal with motors since half of year and at most cases all information i get from st ap. notes. If you will read carefully you will get answers on most of your questions. Also try ap notes from another motor equipment producers. Good luck

[omatza]

Posted on May 17, 2011 at 10:19

Thanks Luter

I am reading AN as we speak :) What about answers to my 3 questions bellow ? (I read AN for all kind of chips, and those 3 questions pop up AFTER I read it :( ) Thanks Oren

[luter]

Posted on May 17, 2011 at 10:19I understood that there are 6 steps, cause the motor has 3 windings. Am I right ? >> Yes, you 'r. Number of steps depends on number of windings, but could be also 12, 24 ... (I have implemented 12 steps, 24 -- may be in the future) What is the T1, T2, .. in page 7 (pigure 3.6) in this AN ? >> I just can suggest you AN2009. There you will find deeper explanation. What is the pairs of poles ? >> I think u've got a good explanation from tanio in post about electrical freq. Additionally i can suggest u to check folder ''Tutorial'' at ST7MC-KIT/BLDC Starter kit Software Suite. (http://mcu.st.com/mcdfiles/1131027818.exe) . There you will find nice Flash explanations what the motors are.

[gaetano]

Posted on May 17, 2011 at 10:19

Hello Omatza,

I would be glad to help you giving all the answers to your questions. But, the motor theory is too wide and that would take a lot of time: at the end, what you are asking is written in each AN or technical literature about motor control (including all the ANs written by ST people involved with the ST7FMC MCU). Please, try to follow the advise given to you by Luter; I know that you will take more time to read all the technical literature on the subject, but, alternatively, your knowledge at the end of this learning period will be complete and allow you to save time in designing your final applications. Regarding the sharing of documents, it is not legal to provide books via internet for copyright issues and about other technical literatures in internet you can find whatever you want :-] Now, some answers: ----------------------------------------------------------- I understood that there are 6 steps, cause the motor has 3 windings. Am I right ? ----------------------------------------------------------- No, the number of steps could be higher (for instance, there are 12 steps driving modes). In case, the step numbers can be considered as a multiple of the number of phases, depending on your commutations strategy. More steps you have, more close to a sinusoidal is your current waveform, that is, the ideal case. ----------------------------------------------------------- What is the T1, T2, .. in page 7 (pigure 3.6) in this AN ? ----------------------------------------------------------- Simply... the name of the power switches in the inverter bridge. -------------------------------- What is the pairs of poles ? -------------------------------- Generally in the rotor, you can have a magnet generating a magnetic flux constitued by two poles: a SOUTH pole and a NORTH pole. That's called a 'pair pole'. But the rotor can have more magnets that produce more than one pair poles (2,3,4,...). The magnetic flux generated by the current flowing in the stator windings, react with that magnetic flux generated by the magnets by creating torque and hence rotation.... (to be continued!) Best regards, Tanio

[omatza]

Posted on May 17, 2011 at 10:19

Hello All and Thanks a lot for Tanio !!!

I didn't know about the ''Tutorial'' of ST7MC-KIT/BLDC Starter kit, and about AN2009. What I read so far was AN1905 (long ago), AN1130, AN1321. Reading the material Luter recomended really taught me a lot. What I wonder now is: when to choose voltage mode and when current ? I mean I know that voltage mode control the speed, and current mode control the torque. But what is the torque ? I thought that the speed of the motor is what metter. (In my application the motor should push air, out of a turbine.) Also AN2009 is very good, but for sensorless motor. I use sensor motor, so any idea what is the best AN to read ? (am I right that in sensor mode only Z event is needed ?) To all of the guys that helpped, thanks a lot for your answers. BTW - Tanio, if I am asking to much, just tell me. (and I wil love to get a name of a book or something, that doesn't assume I am electrical engineer ;) Thanks Oren

[luter]

Posted on May 17, 2011 at 10:19

Hi.

Torque is one of the basics of physics. Books describe it perfectly. As far as you have st7mc2 read this datasheet (http://www.st.com/stonline/books/pdf/docs/9721.pdf), especially 9.6 section. Don't worry if u will not understand. I have read 10 times to get an idea what is happening. Be quiet and patient.

[gaetano]

Posted on May 17, 2011 at 10:19

Let's suppose you have to buy a car and when you test it by the dealer you are able to reach roughly 100Km/h driving in plain. Maybe, you are satisfied by this performance. :)

As soon as you decide to go in the mountain, you are not able to reach more than 40Km/h for moderate uphill. :( Will you buy that car? This happens as your car engine has not enough TORQUE. ;) In other words, the torque in rotational motion is the correspondent of strength (or force) for translation motion. Then the power is: P = F * v in translation (force per velocity) and P = C * w in roational (torque per angular velocity). Moreover, related to the motor: try to block with your hands or even a tool the shaft of a motor during rotation: you will not be able to stop it if the motor torque is higher than the one you are applying, and that is not related with the rotor speed. The examples discussed above can be applied whatever you want in the physiscs field. Answering to your question: In some motor applications, it is preferable to control or regulate the motor torque capability at a given speed: in this case you choose the current mode (as the current is related to the torque). In some other applications, you cannot have enough information about the torque needs in particular working conditions (at the motor startup for instance): in these cases you fix the voltage level, letting the motor to absorb whatever current he needs to start. The same applies when you don't know a priori how the resistive torque is delivered by your load (not predictable loads). For fans, the torque curve is well known and normally you have to control the motor speed for producing air flux: voltage mode is the preferred way to drive the motor. I hope I helped you. Regards, Gaetano