About BLDC

Hi!!
I'm interestig in control of BLDC motor. I have one of this motor,their trade is GLOBE MOTOR and it is in automotive application, Electric
Power Steering of Fiat Stilo has one.
This motor has 11 pin, 3 are big (is possible are power supply), other 8 are small. 2 of this are controling one relay that short circuit the 3 big pin. Is possible stop this type of motor when you short circuit??
I would like have the datasheet and pin out of this motor.
Thank you and sorry for muy english.
Best regards.
Igor
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Igor wrote:

Your English is plenty good enough. Brushless DC motors commonly have Hall-effect sensors built in to control the commutation; the smaller contacts probably connect to them. I agree that the larger contacts probably connect to the coils, but I can't guess about how they are wired internally. A delta connection is difficult to drive. Is the frame used as a common? An ohmmeter might tell.
Shorting the coils together applies a braking torque proportion to rotation speed. It won't hold the motor, but it will slow it.
Jerry
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Thanks for your help. I move de rotor with the help of drill and I measure the larger contacts and they have voltage. When I probe to measure with ohmmeter, it dont measure anything, I don't know why.
Best Regards.
Igor
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Igor wrote:

Many ohmmeters aren't sensitive enough to distinguish fractional ohms from a short circuit. Do you measure zero ohms? That would indicate a low-resistance winding, what I would expect.
Globe has been around for a long time. You can probably get a data sheet at http://www.globe-motors.com/fullline.html if you have the motor's part number.
Jerry
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Thanks for all !!!
This motor is in EPS (Electric Power Steering) of FIAT STILO,and I would like have its datasheet (winding connection,Ke,Km, Power,J, R, L,...) because I would like simulate in Simulink. I would like to control with a Data Acquisition Target (Advantech) and 3 phase bridge with mosfet (International Rectifier F1404L) I would like very much model this type of motor. Have you any idea?
Best Regards!!
Igor
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Igor wrote:
> Thanks for all !!! > > This motor is in EPS (Electric Power Steering) of FIAT STILO,and I > would like have its datasheet (winding connection,Ke,Km, Power,J, R, > L,...) because I would like simulate in Simulink. > I would like to control with a Data Acquisition Target (Advantech) and > 3 phase bridge with mosfet (International Rectifier F1404L) > I would like very much model this type of motor. Have you any idea?
Ask Globe Motor if they can identify the motor you have. I gave you the URL of their catalog, but they make specials. Most specials are simply winding variations on their standard frames, so inertias will have the catalog values. You may need an accurate measurement of winding resistance so they can help you identify the part.
If you find a picture of the motor in the catalog, you can infer winding variations by comparing the torque constant you measure with the published value.
Jerry
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Thanks again!!
If you see in Global Motor web (http://www.globe-motors.com/electricpowerassiststeer.html ) you can see the EPS and the motor. I think that this type of motor isnt in the catalog.
Do you know some web with information about modelling and control this type of motor??
Kind Regards!!!
Igor
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Igor wrote:

Do you mean brushless motors in general, or this particular motor?
Have you done a web search on modeling brushless motors?
Here's a rough guess at how you should go about it. Anything I say here should be backed up with measurements and experiments, and probably with reference to a text on electrical machines.
The electromechanical torques on a brushless motor will be due to two things: the cogging torque, which is a function of the geometry of the magnets and iron in the motor, and the motor torque, which is a function of the magnets, iron, windings and current.
The cogging torque is nominally a sine wave with a period equal to 1/(P*N) revolutions, where P is the number of magnetic poles and N is the number of phases (brushless motors are almost always three phase). In reality it's not really sinusoidal and it really has a period of 1 rotation; it's up to you to discover/decide how close your motor is to the ideal.
The motor torque is nominally a product of the torque constant (kt) times the current in one winding times the sine of the angle between that winding and the magnets -- so if you energize one winding you'll see the motor snapping to one position and staying there; driving the motor requires that you keep the leading coil energized in the correct direction so the motor will go the direction you want it to go. Your motor sounds like it's connected in a delta (3 heavy wires), which means that you can't energize just one winding, but running a current through any one pair of terminals should get the same effect.
In reality this motor torque will not be sinusoidal; once again it's up to you to decide/determine how far off it is. In addition iron saturates, so the motor torque won't be quite proportional to current, although this is usually not a big deal unless you need to do some pretty tight simulations, or if you're worried about motor efficiency.
As the motor turns it generates a voltage ("back EMF"). In a perfect motor the relationship between motor voltage vs. speed and torque vs. current are the same; this is a direct consequence of the power balance equation that says that power in = power out, so voltage * current torque * speed. The primary effect of this back EMF is that if you drive your motor with a constant-voltage drive it'll draw lots of current at stall, then as the motor speeds up the back EMF will reduce the voltage available to drive current through the armature so the motor will draw less and less current until finally the torque required to turn the armature equals the torque available and the speed will level out.
At this point I've done two things: I've used up a page of text, and I've only scratched the surface of how the motor works. Once again, you need to get a good book on electric machines and spend some quality time with it. The electric machines book that I use is "Electric Machines - Steady State Theory and Dynamic Performance" by Mulukutla S. Sarma. It's what I use for a reference but it's a bit out of date and not the best for self-study. It's also the only one that I've read so I can't recommend any other.
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Tim Wescott
Wescott Design Services
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Igor wrote:

Then you should ask their customer support people for for the motor's descriptive constants. Assuming that you connect it in in the expected way, the motor's torque, voltage, and speed constants are used pretty much like any other PM DC motor. The cogging will be higher than with a brush servo motor because there are only three poles, but that is a second-order effect.

Circuitry beginning with the Hall effect sensors and ending with the MOSFET H bridges replace physical brushes while performing the same function. It is basically a PM motor. You can control the speed by varying the applied voltage, just as with any PM motor. Since the drive is electronic, you can do that with PWM on the drive transistors. Think of that as a superposition of two controls; one for speed, the other for commutation. During the 'off' time, you want to open-circuit the windings, not short them.
Jerry
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Thanks Tim and Jerry for your answer.
When I have 3 phase bridge, and use PWM, how I control speed of motor?? I Know that in PWM: Voltage=>V=Vn*D and D=t/T (duty cycle) where t=Signal On time and T=period Duty cycle=(Motor Rated Voltage/DC bus voltage)* Speed Reference Are correct this calculus??
How I know if my motor is delta or star??
In this type of motor, can I control torque?? Because I have control the amount of assistence.
I search information and I have the conmutation of this type of motor when you have Hall sensors at 60 degrees.I have the truth table and which phases I have applied voltage.
Thank you for all!!!
Best Regards.
Igor
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Igor wrote:

I don't know what "Speed Reference" stands for, but probably. Do you intend to run the motor open loop? If not, it hardly matters.

Delta is most likely. With three coil leads, star can only be accomplished by using the frame (check with ohmmeter) or by letting the neutral float. The only difference between delta and floating neutral is effective winding impedance. It doesn't matter to you whether the winding impedance you see is caused by connections or wire size.

Torque is proportional to current. The motor torque/speed/voltage relations are essentially the same as a two-wire permanent-magnet carbon-brush motor. Small ones of that type are used in electric toys. You need to understand one of those to accomplish what you want.

That's a good place to start.
Jerry
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Igor wrote:

Normally you switch from one winding to the next depending on the position of the motor, and control the current or voltage to control motor speed, much like a regular DC motor.

Yes.
Yes, the torque is proportional to motor current if you're commutating properly.

You need a web page or book section on "How to control brushless motors". This is a big subject, and you seem to be pretty light on the required information. It's _not_ something that can be easily answered in a few newsgroup postings.
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Tim Wescott
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