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) .

I have been working a bit with control of a BLDC for precise servo operations. I would recommend including a little note on using the Clarke & Park transforms which is commonly used in several high performance architectures and is a mere mathematical approach to the theory of controlling both AC and BLDC motor types.
--Tobibobi 10:29, 15 September 2007 (UTC)

[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

As I already 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)

The BackEMF of a DC brushless motor can be trapezoidal. Maybe yours was not. When designing the magnetic circuit of a BLDC motor the goal of the magnetic flux distibution in the air gap can be trapezodial or sinusoidal, or any other waveform. The goal of trapezodial BEMF is low torque ripple when driven by a flat top current pulse ( as opposed to a sinusoidal current). In other words the flat top of the trapezoid ( ie pulse with sloping sides) is "pure DC". Since you sound like an observant experimenter, try looking at the synthesized sinewave voltage pulses coming out the controller. Those variable spaced PWM pulses ( a sinusoidal distributed duty cycle) are smoothed to a sinewave current by the motor coil inductance and calling them sinusoidal may be generous indeed. Also, try thinking of the input current pulse to a trapezoidal BEMF phase at the the clipped fundamental of the Fourier series of the pulse.

Shaping the mangnets and distributing the windings for sinewave BEMF is more challenging than trapezodial. You can run a sinewave BEMF motor with flat top current pulses with only a minor degradation in efficency and a little extra torque ripple ( on big motors rotor inertia wil take care of the ripple).

Electron pond 21:25, 7 May 2007 (UTC)

Considering I designed the controller, software included, I know what's coming out is square (plus PWM when it's not running at full power)... actually, it's high, Hi-Z, low, Hi-Z, etc... Anyways, I see what you're saying. When building the motor, my goal was to get the magnets to hug the laminations as closely as possible, with 25% gaps between the magnets -- I assume this yielded the sine shape. I saw no significant difference between my motor and other DC Brushless motors, but I was not looking too carefully at the "purity" of the sine. Perhaps my own motor's power and efficiency can be attributed to the cause of its sinusoidal back-emf.

Anyways, I still maintain that BLDC motors are not going to have noticeably trapezoidal back-emf; the magnets are moving in a continuous circle. Although the receiving coil is not centered on its orbit, the coil does have the smoothing properties of an inductor, and the magnets will never make a change in their orbit so sudden that it induces a sharp trapezoid "corner". Kipperoo 01:36, 29 October 2007 (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).

  • Regenerative braking does occur in BLDC-based vehicles. The "easiest" controller design usually employs many diode-like behaviors, making current flow only one way, so this is not normally possible. If I were to lay out a controller meant to do this, I would implement a way to "switch" the motor's leads between the BLDC controller output and a rectifier connected to the battery-charging circuit... the controller would automatically activate the rectifier when the governor (device) (or program) determines that the motor needs to slow down rather than speed up. —The preceding unsigned comment was added by 74.79.164.211 (talk) 04:57, 6 April 2007 (UTC).
  • Regenerative braking is possible with permanent magnet motors. In normal two-quadrant controllers, power will flow back into the batteries if the back-EMF voltage is above the battery voltage. On vehicles employing direct-drive permanent magnet motors, such as ebikes using hub motors, this will happen whenever the vehicle's speed is greater than the motor's maximum speed (at a given battery voltage), such as on long downhills. This sort of regenerative braking can not be engaged at will and is not useful for stopping, but it can (and will) happen automatically with most any brushless controller. True regenerative braking requires extra control electronics, typically a four-quadrant controller (so called because it can operate in all four regions of motor power, positive and negative speed and torque. In the case of regenerative braking, the positive speed negative torque quadrant is salient). Such controllers more complex and consequently more expensive. —Preceding unsigned comment added by 70.225.70.76 (talk) 07:39, 24 May 2008 (UTC)

[edit] Lower noise

I don't think that the BLDCMs are more quite than the classical DC motors. The abrupt switches of the phases result in sudden movements of the coils inside the motor. When the magnetic field of a coil changes it is attracted toward another coil. This process repeats every time a phase switch occurs.

This is not necessarily the case. It's quite possible to ramp up and down the phase current to avoid the rapid field change. This adds cost so is often not done in small motors, which can have an audible 'tick" at commutation frequency. But that's an artifact of a cheap commutator, rather than an inherent feature of a BLDC motor.60.234.130.225 02:31, 16 July 2007 (UTC)
The main problem with DC brushed motor noise is the arcing. It is certainly possible that a crappy DC controller could output more noise... well.. maybe not. Kipperoo 01:14, 29 October 2007 (UTC)

Can anyone comment on the relative electronic noise of brushless DC motors vs AC motors?165.123.243.168 18:28, 18 July 2007 (UTC)

In small (.5-1 HP) motors, there is a significant decrease in noise levels between BLDC and induction, especially when speed control is taken into account. It's one of the main reason why some HVAC systems use BLDC motors instead of AC...the current losses that make AC more inefficient also create a bunch of noise. DC motors are whisper quiet in comparison. Jeremy RBC 16:05, 19 September 2007 (UTC)
Comparing an AC motor to a DC Brushless motor is really difficult because the line is so blurred. I think this is more a question of the behavior of individual controllers. Kipperoo 01:14, 29 October 2007 (UTC)
However -- sine waves -- a function more related to AC motor controllers, will output a cleaner "noise" on one frequency (and perhaps noise on the PWM frequency). Because DC Brushless motors tend to output very square-ish waves, they will output more erratic noise. Still, other components of the circuits can make this generality untrue. Kipperoo 01:18, 29 October 2007 (UTC)

[edit] Spam

A link to electojects.com has been repeatedly added to Stepper motor, Electric motor and Brushless DC electric motor by Special:Contributions/217.53.109.235, Special:Contributions/82.201.156.201, Special:Contributions/217.53.107.168, Special:Contributions/217.53.16.164, and others.

The link in question is registered to Abdoh Ali Mohamed, Hay Swesri, Nasr City, Cairo, Egypt.[1]

I wonder if the four IP addresses listed above have any connection... Naw, couldn't be. [2][3][4][5] Egypt is a big country. Must be a coincidence.

I'm going to start patrolling wikipedia for any links to electojects.com or redirects to it and deleting them on sight. If they come back, I'll move to blacklist the address. Mdsummermsw (talk) 18:07, 28 December 2007 (UTC)

[edit] Winding connections & torque....

This article states the age old misunderstanding that a star ("wye") wound motor produces more torque but less top end, where a delta wound motor produces less torque and more top end... when infact a star/wye wound motor produces only 33% of the starting torque that a delta wound motor does

I'm not very familiar with brushless motors but I cant see how it would be any different to an AC induction motor

122.108.44.97 (talk) 06:55, 3 April 2008 (UTC)


[edit] kV rating?

May I request an explanation of what the kV rating is? I understand that it is the proportionality constant between RPM and applied voltage, but a good definition would be nice. Searching for kv on wikipedia leads here. —Preceding unsigned comment added by 87.194.171.29 (talk) 20:42, 21 May 2008 (UTC)

I've just added this - but it's still not a very good definition. Does 'K' just stand for proportionality constant, or does it mean something specific? Is "the" applied voltage the RMS 3-phase voltage? Or does "the" voltage mean the DC voltage, supplied to the motor controller?. Presumably Kv refers to the unloaded RPM - but how much does the RPM change under load? (An ideal motor has an exact relation between voltage and rpm; if there is more load, the motor simply draws more current. But a real-world motor has some resistance, so RPM drops under load, even when the supply voltage is maintained. —Preceding unsigned comment added by 87.194.171.29 (talk) 20:34, 25 May 2008 (UTC)