Talk:Brushless DC electric motor

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Brushless DC electric motor don't exist !! there is allway a electronic module to convert DC to AC for Brushless engines .. I think you have to change the Electric motor article ! and make a link to an article whitch explaim how the electronic module witch convert DC to AC .. ? --Xulin 16:40, 6 Aug 2004 (UTC)

The commutator in a brushed DC motor also converts the current to AC, but it's still called a DC motor, bacuse it operates on DC current.
--GalFisk 09:47, 14 May 2005 (UTC)
I will address this. Kipperoo 03:42, 5 January 2007 (UTC)

A "Brush" implies, or rather denotes a method of commutation involving intermittent electrical contact through touching, moving parts which necessarily introduce friction, and conductive waste. The existence of an electronic component (almost a computer really) to 'control' a brushless motor, does not in my opinion exclude such a motor from the class that might be called 'brushless'. Perhapse the original comment was made with the intent to dispute the idea that a DC motor has yet been created without the use of a "commutator", which is really a name for the "electronic module to convert DC to AC" which was mentioned in the first comment.

Contents

[edit] High power motors

"High power BLDC motors are found in electric vehicles" Why arn't hey used on railed vehicles? Is its becuase asynchronous motor are preffered there due to absence of permenant magnets?Myrtone (the strict Australian wikipedian)

I think you've got it. A traction motor leads an awful life, getting hot, dirty, overloaded, mechanically shocked, and often flooded and/or poorly maintained. The AC induction motor is just about the simplest, most-rugged design in existence so it suits the application very well. By comparison, given the fact that either an induction motor or a BLDC motor would have sophisticated high-powered drive electronics, I'm not sure there'd be any advantage to using the BLDC over the induction motor.
Atlant 12:49, 12 March 2006 (UTC)

[edit] Theory of Operation

There should be a section on the theory of operation. —The preceding unsigned comment was added by Kfrance (talk • contribs) .

[edit] Is it a synchronous motor or a BLDC?

Why are *AC* syncronous motors classified under BL*DC*? Glueball 17:53, 13 August 2006 (UTC)

You've actually asked a very-pertinent question and I've been gearing-up to start a similar discussion. It turns out that there's a huge revolution under way in the design of fractional to low-horsepower AC motors. The induction motor as we know it is rapidly becoming passé for many of its classical applications including home appliances and HVAC. Instead, extremely sophisticated motors which we might call BLDCs are taking over. Only BLDC isn't the best term because they run on single- or polyphase AC input power. These motors typically contain a number of subsystems:
  • A power-factor-correcting rectifier stage
  • Bulk power storage in capacitors
  • A motion engine that uses digital signal processing to track the rotation of the rotor, often using back EMF rather than any discrete sensors. It then synthesizes the required drive waveforms.
  • A power-stage using IGBTs or FREDFETs that inverts the bulk-DC into three-phase AC
  • An internal- or external-permanent magnet rotor
These motors are used because they provide several advantages over the classical induction motor that they replace:
  • Lowered power consumption
  • Simple variable-speed operation (which reduces the power consumption farther)
  • Often, the possibility of direct-drive (rather than using belts or gears.
In the near future, we're going to have to decide on a wholly-new taxonomy for classifying all these new motors.
Atlant 13:16, 14 August 2006 (UTC)
This would be a very good idea (ie, new taxonomy), because the classification of brushless motors as synchronous, stepper, reluctance, etc - although correct, is missing the point with respect to practical brushless DC motors. It is true that induction motors are brushless ( I mean, try to find the brush -- or look at the definition of induction). But in practical engineering a brushless DC motor is one that has the same characterictics as a DC shunt wound motor ( ie nearly linear rpm to voltage -- linear torque to current), all done without brushes AND driven by a DC supply, even a battery.
The two basic types of brushless DC motors are electronically generated sinusodial armature drive and square wave armature drive ( and in this case the armature is stationary, ie in the frame and ONLY the average current is sinusodial (ie the coil inductance integrates the voltage pulses), the acutal instantaneous voltage is in the form of pulses). Since the power supply is DC transistor switching is necessary( ie an inverter and at high power ( ie amplifier) using PWM - pulse width modulation) to generate the waveforms. You could effective argue that these are continous stepper motors ( ie one multi-revolution step). This might help some, but confuse others.
Electric motors are a fascinating and wonderful mix of the physics of electromagnetics and mechanics. Sensorless PMDC motors are even more fascinating ( ie rotor position is sensed my BEMF as opposed to a powered Hall effect or optical sensing device). The electronic commutation/switching/sequencing is done by a microprocessor/DSP and an attendant program.
Where do we go from here? Electron pond 22:00, 22 August 2006 (UTC)
I totally agree about making a new taxonomy for the motors Alant brought up. There is a world of difference between the subfractional motor that powers a hard drive and the 2HP motor found in a furnace air handler. The latter has a couple other notable features beyond what Alant's list, including programmable runtime functions, lowered noise creation and heat generation, the ability to maintain torque or RPM despite restrictions (to a point), and the new ones even have full-on serial communication abilities.
Here's my suggestion — in the HVACR industry, there are a couple million of these installed, usually called ECM (short for electronically-commutated motor). ECM seems like a good name to me since most people who hear it specifically envision the exact motor you folks are discussing here, multiple motor manufacturers call their version of this motor an ECM, and third-party researchers refer to the motors as ECM.
  • I have also heard researchers call these motors BLDC, "Permanent Magnet (PM)", or some combination of the two. To me, that doesn't seem like a very clear difference.
  • Sometimes are called "variable-speed (VS)" since they are usually used in VS applications, but this gets confusing too because you can make an induction motor run at variable speeds and you can also run a BLDC at only one speed. Jeremy RBC 19:52, 1 September 2006 (UTC)
  • Hmm, classifying taxonomy is a good idea, but watch out for the hair. The 5-gram motor+controller on the RC plane image is pretty much the same as the 100-pound permanent-magnet brushless motors that would be used in a full size vehicle, except cars would use sensors instead of back-EMF... That controller is capable of measuring and governing speed, torque, efficiency... Kipperoo 06:10, 30 December 2006 (UTC)

I hope I am not too far off base here. Please be gentle as I am a noob here. I've quoted the segment of the article and bolded the exact text I think needs clarification. While the word "vice" has three common meanings, none of them seem to apply here.

Applications

BLDC motors can potentially be deployed in any field-application currently fulfilled by brushed DC motors. Cost and control complexity prevents BLDC motors from replacing brushed motors in most common areas of use. Nevertheless, BLDC motors have come to dominate many applications: Consumer devices such as computer hard drives, CD/DVD players, and PC cooling fans use BLDC motors almost exclusively. Low speed, low power brushless DC motors are used in direct-drive turntables. High power BLDC motors are found in electric vehicles and some industrial machinery. These motors are essentially AC synchronous motors with permanent magnet rotors.

The Honda Civic hybrid car uses a BLDC motor to supplement the output of the internal combustion engine when the extra power is needed. It is also used to start the engine vice a conventional starter and solenoid method.


[edit] German Wiki Entry

How do you like what I wrote into the german wiki (sorry for the google assited translation):

There are three kinds:

  • With the stepping motor a constant holding current stamps the phases blindly switched. This is used, if the load is well-known and constant or only small achievements b.z.w. Losses arise. It is to be noted that hard switching of the phases leads in connection with the Rotational Inertia and the inertia of the rotor to a resonance, which is absorbed by the absorber cage because of the missing feedback only by the soft iron, b.z.w with the three-phase alternating current synchronous machine.
  • As is the case for the brush-afflicted d.c. machine is constantly measured the phases can as a function of the situation of the rotor are switched, therefore it e.g. by means of hall effect sensors with high-quality industrial engines (e.g. servo actuators).
  • For e.g. the drive of a propeller low is needed torque and it a stepping motor are used at low numbers of revolutions. As soon as the number of revolutions rises thus resonance occur can and the necessary torque at the propeller becomes larger, induces the motor also a measurable voltage to determine the position of the rotor . This variant is called in English “sensorless”.

Arnero 18:43, 27 August 2006 (UTC)

And then there is the possibility to replace the permanent magnets with electro magnets and do all kind of nasty stuff like:

And of course you are free to mix all these. This techniques may still be important for superconducting motors which produce fields strengths wich saturate iron 128.176.151.112 07:45, 28 August 2006 (UTC)

Can someone add an explanation what DURKA is? I can not find anything meaningful in the internet...


All that the above suggested “to do/ can do ” is why permanent magnet brushless DC motors have been developed as a superior replacement for all DC motors that have come before ( with the exception of cost).

Inducing voltage from one winding to another is the classic AC induction motor.

DC wire coiled electromagnetic stator/rotor motors ( ie brushed) are designed so that the mutual inductances are in quaduature ( ie mutual inductance M=0); but this is never perfect, and the imperfections are known as armature reaction, etc

Classic DC motors have the rotor and stator electromagnetic circuits in series or parrallel ( ie shunt wound) or a combination thereof ( ie compond motors)

So you are a very good historian of DC motor technology.

Today the variable voltage controlling the high power stage (ampligier) suppling the field windings for a PMDC motor is digital logic level ( ie 3-5 volt logic circuit/computer), usually using PWM ( ie pulse width modulation where the duty cycle is the percentage/fraction of the bus/supply voltage applied to the coil -- basically a switch DC power supply).

For a shunt wound DC motor rpm is nearly linear with voltage, and even more linear with PMDC. Before we had high voltage semiconductors ( ie transistors) that could switch .5 to 1 kilovolt via PWM, the variable field voltage of the DC motors could be supplied by a companion DC generator! Electron pond 22:17, 5 October 2006 (UTC)

[edit] Comparison with brushed-DC motors

I dont see why one winding can be done by machine and annother must be done by hand. Could you clairfy, or perhaps provide illustrations that compare the interior design of the two? I have seen a brushless motor, but for those who havent it also would be nice to have an illustration that shows how the permanent magnets are on a cup that fits around the coils. Thanks.

  • I tried to address this. It's just about who invented machines suitable to wind for a certain motor and when. There are machine-wound BLDC motors, but it's much less common. Kipperoo 06:10, 30 December 2006 (UTC)

[edit] Trapezoidal BackEMF

BackEMF of a DC brushless motor is NOT trapezoidal; it only looks that way when measured on a single leg of a motor being driven at full power. The period at the "sides" of the trapezoid, called zero-cross, is where back-EMF measurement takes place, and it IS sinusoidal. All other times, the leg is being driven high and low, interfering with the sinusoidal back-EMF. If you were to disconnect the controller and spin the motor, turn its output power down or use an outrageously inefficient controller, you would see that the wave is still sinusoidal.

Also, this picture might be useful in the current context: http://www.slowfly.com/press/ViolatorMotor.jpg It is a picture of the atypically small Violator, a "3D plane" (having more thrust than weight) produced by Dynamics Unlimited, which is now out of business. The Violator features a DC brushless "outrunner" motor, with the BLC-1, the world's smallest brushless motor controller. I designed the electronics, built the plane, and took the picture myself. Wiki is welcome to use it, no strings attached. Kipperoo 07:13, 24 December 2006 (UTC)

  • Okay, I did all this... I tried to address the trapezoidal shape without invalidating it. Was I a little too verbose in the picture descriptions? Kipperoo 06:10, 30 December 2006 (UTC)

[edit] Regenerative Braking

A permanent magnet DC motor can be used to charge the battery in an electric vehicle going downhill. This is especially so if gears are available so that the rpm of the DC motor can be increased. My question is: can a BLDC motor become a generator the same way. Does it depend on the controller design? —The preceding unsigned comment was added by 124.187.145.41 (talk) 00:43, 16 March 2007 (UTC).

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