Brushless Motor ( ESC BLDC) Controller

MaxHeadRoom

Joined Jul 18, 2013
28,619
Your positional control loop to zero encoder read-backs counts can be closed-loop ensuring accuracy while the drive control loop (for motion) to correct for positional errors from the desired position can be open loop. That's not usually the case because if you have high resolution encoder data it would be foolish IMO not to let the adaptive observer use that in calculations of speed and position.
The big problem with BLDC control open loop, is the severe 'cogging' at low to medium RPM's.
 

nsaspook

Joined Aug 27, 2009
13,086
The big problem with BLDC control open loop, is the severe 'cogging' at low to medium RPM's.
That's mainly because of low resolution in waveform micro-steps with non-sinusoidal drive waveforms. It's more a problem with cheap electronics and poor algorithms that don't generate smooth torque because step changes are coarse. I see the same effect with hall based closed-loop commutation feedback for 6 step waveform drives.

https://forum.allaboutcircuits.com/threads/pic32mk-mc-qei-example.150351/post-1538714

What you see (two of the three phases on the oscope) here is on the fly 3-phase positional waveform generation (using a 32-bit PIC motor controller) using open-loop motor control with closed loop positioning control from a motor encoder for position error offsets to drive the motor to zero positional error.

https://www.microchip.com/content/d...PIC32MK_GP_MC_Familly_Datasheet_60001402G.pdf
Some typical 32-bit motor drive PWM and smoothed signals.
https://forum.allaboutcircuits.com/...troller.183667/page-2#lg=post-1690092&slide=1
 
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MisterBill2

Joined Jan 23, 2018
18,176
Note that I DID suggest a big flywheel and an elastic drive belt. That is the formula used for some belt-driven turntables, or at east it used to be used.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
That's mainly because of low resolution in waveform micro-steps with non-sinusoidal drive waveforms. It's more a problem with cheap electronics and poor algorithms that don't generate smooth torque because step changes are coarse. I see the same effect with hall based closed-loop commutation feedback for 6 step waveform drives.
It is also because of the low resolution between poles, I recall when BLDC servo's came out and a salesman told me that when using them in positioning applications i should use some kind of gearing to prevent cogging.
That only occurred when used open-loop, once I closed the loop with encoder and PID controller, they were as smooth as any high pole DC motor down to zero RPM's..
Same motor drive used in both cases.
 
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nsaspook

Joined Aug 27, 2009
13,086
Hello,

Are there any large brushless DC or permanent magnet DC motors that can readily be sourced, either new or used?

BLDC motors can of course be obtained from EVs such as the Leaf motor which is affordable and easy to find, but their voltage and rpm are too high and the current too low. They are also very difficult to custom adapt to anything because they use proprietary shafts that slip into the gearbox and their end shaft bearing is weak if they even have one.

I am looking for something a bit more industrial and universal, with a max rpm of 6000-8000, 120-200V, and a high current. Pretty much a BLDC or PMDC equivalent of a Warp9 or Warp11 motor.

Does anyone make such motors?
Can they be found in any equipment, similar to how large series motors can be obtained from old forklifts?
Do such motors even exist?

Thank you.
Sure, there are big large brushless DC motors for industrial use. Search for direct drive rotary.
IMG_20180709_110231524.jpg
IMG_20190703_153325027.jpg
 

MisterBill2

Joined Jan 23, 2018
18,176
I am thinking that a three-phase variable speed drive package should be able to drive the BLDC motor at the lower speeds. 6000 RPM is much above the normal motor speeds of 1750 RPM and 3450 RPM.
For spinning honey a slower speed will be better, and a VS drive should be usable. Check Automation Direct for a good price.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
I am thinking that a three-phase variable speed drive package should be able to drive the BLDC motor
Although a BLDC motor can be ran as a 3ph motor with the right controller, the VFD variety made with the induction motor in mind will not, or at least not for most manufactures in mind.
They have to be designed for a PM motor.
 

nsaspook

Joined Aug 27, 2009
13,086
I am thinking that a three-phase variable speed drive package should be able to drive the BLDC motor at the lower speeds. 6000 RPM is much above the normal motor speeds of 1750 RPM and 3450 RPM.
For spinning honey a slower speed will be better, and a VS drive should be usable. Check Automation Direct for a good price.
It won't work with varying loads at anything close to normal speeds. The three-phase drive flux must be in sync with the rotational PM flux on a BLDC or PMAC motor so you need to start slow and ramp up with a open loop induction motor VFD. You need shaft positional feedback for proper BLDC motor control.
 

MisterBill2

Joined Jan 23, 2018
18,176
Of course there is a need to read and understand the description of the driver before selecting it. I have made the error of presuming that it was a given and understood by all. My apologies for presuming such.
 

nsaspook

Joined Aug 27, 2009
13,086
Of course there is a need to read and understand the description of the driver before selecting it. I have made the error of presuming that it was a given and understood by all. My apologies for presuming such.
You used the words, "three-phase variable speed drive package". That set of terms almost always specifies a induction motor configuration that's missing the specific commutation functions and wave-forms needed for the several types of PMAC motors.
 
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MisterBill2

Joined Jan 23, 2018
18,176
You used the words, "three-phase variable speed drive package". That set of terms almost always specifies a induction motor configuration that's missing the specific commutation functions and wave-forms needed for the several types of PMAC motors.
A PM BLDC motor should be able to run like a synchronous motor, without electronic position sensing. I know that some do that.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
A PM BLDC motor should be able to run like a synchronous motor, without electronic position sensing. I know that some do that.
The ones I have come across that do not have commutation sensors, use the encoder that may be fitted to, or other means such as exercising the armature slightly at power up to determine the rotor position, from then on the position is known and the commutation is kept track of.
HVAC ECM motors use this usually.
 

nsaspook

Joined Aug 27, 2009
13,086
A PM BLDC motor should be able to run like a synchronous motor, without electronic position sensing. I know that some do that.
Sure, I've designed and built controllers for most types. The problem is without electronic position sensing, even with open-loop sinusoidal commutation, once you lose rotor/stator rotational magnetic field sync with a synchronous BLDC (load imbalance, speed changes) the motor stops (or slows making one hell of a noise) and just alternates in place instead of spinning. With a induction (asynchronous) motor the induced EMF always provides rotation torque.

1658333132806.png
Open-loop design

https://www.testandmeasurementtips....ronous-and-asynchronous-induction-motors-faq/

 
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Philip B

Joined Jul 29, 2022
2
For what it's worth, I can confirm that the GS10 series VFDs from AutomationDirect can at least somewhat control BLDC motors when set to "IM/PM SVC" control mode and SPM or IPM motor type. I'm experimenting with using a GS11N-11P0 drive to run a 160V, .75 kW SPM BLDC motor I'd like to drive a hydraulic pump. (That said, I haven't been able to get my motor running smoothly yet, which led to me stumbling across this thread in search for wisdom from people who actually know what they're talking about!)

I can also confirm that, unsurprisingly, the drive isn't very successful in turning my BLDC motor when set for V/Hz control mode / induction motor type.

Also, some VFDs actually have built-in BLDC control modes. I'm going to try out an Invertek OptiDrive E3 soon, so I'll post an update on how that goes. Seems like it might be a good solution for the OP if it works.
 

MisterBill2

Joined Jan 23, 2018
18,176
Is this hydraulic application for a hobby type project, or for a commercial business type project. The power level is about one HP and at that point a purchased motor could be the lower cost option. But it seems that a BLDC motor should be able to run with the same drive scheme as a synchronous motor would use.
Of course, synchronous motors are NEVER used for hydraulic pumps. The speed/torque relationship is all wrong for driving a pump.
 

nsaspook

Joined Aug 27, 2009
13,086
For what it's worth, I can confirm that the GS10 series VFDs from AutomationDirect can at least somewhat control BLDC motors when set to "IM/PM SVC" control mode and SPM or IPM motor type. I'm experimenting with using a GS11N-11P0 drive to run a 160V, .75 kW SPM BLDC motor I'd like to drive a hydraulic pump. (That said, I haven't been able to get my motor running smoothly yet, which led to me stumbling across this thread in search for wisdom from people who actually know what they're talking about!)

I can also confirm that, unsurprisingly, the drive isn't very successful in turning my BLDC motor when set for V/Hz control mode / induction motor type.

Also, some VFDs actually have built-in BLDC control modes. I'm going to try out an Invertek OptiDrive E3 soon, so I'll post an update on how that goes. Seems like it might be a good solution for the OP if it works.
Did a quick lookover on the PMSVC section on the VDF GS manual. That looks like the classic sensorless kluge (it works better in theory than in actual operation on larger motors at low speeds) using open loop Flux Linkage Observer speed estimation instead of a shaft position encoder or resolver. Very tricky to tune properly for low speed dynamic operation.
https://www.mathworks.com/help/mcb/ref/fluxobserver.html

 

Philip B

Joined Jul 29, 2022
2
Is this hydraulic application for a hobby type project, or for a commercial business type project. The power level is about one HP and at that point a purchased motor could be the lower cost option. But it seems that a BLDC motor should be able to run with the same drive scheme as a synchronous motor would use.
Of course, synchronous motors are NEVER used for hydraulic pumps. The speed/torque relationship is all wrong for driving a pump.
Well... commercial/business, but I'm in early stage information gathering. I'd be fine with a 3/4 hp induction motor + contactor, but no one will quote a motor with suitable specs for less than $800. BLDC is interesting to me primarily because of power density; my machine doesn't have enough much space (hence the difficulty sourcing standard induction motors). I can get a suitable BLDC motor and a VFD for ~$500 total, and then I get the side benefits of speed and acceleration control (assuming I can make it work). I'm trying other motor types too (brushed PMDC is actually looking most likely at the moment).

Any idea why my BLDC motor would accelerate slower than the VFD ramp time, vibrate more than it should, and draw roughly full load current at no load? This VFD has a lot of settings, and I'm a little (a lot) out of my depth here. I've already plugged in the stator resistance, inductance, and Ke from the motor datasheet, and it sort of works, but it's clear that something's not right. And yes, my VFD selection could be the thing that isn't right... I tried the cheapest option first!
 

nsaspook

Joined Aug 27, 2009
13,086
A PM motor is a synchronous motor where the motor speed equals the frequency commanded by a VFD. Without a proper position sensor in open-loop you are half-guessing shaft speed and position based on BEMF and a host of motor factors that dynamically change. IF all you is to ramp and spin a fan at X speed then it will work (to varying degrees of satisfaction) with a PM motor mode VFD if tuned (most have a auto-tune function).
1659148868041.png

You really need a proper BLDC motor with some sort of position encoder (never trust sensor-less for an industrial application) and a proper designed closed-loop sensored BLDC ESC driver.
 

MisterBill2

Joined Jan 23, 2018
18,176
Like I said before: Of course, synchronous motors are NEVER used for hydraulic pumps. The speed/torque relationship is all wrong for driving a pump.
The hydraulic pumps that I am familiar with take a fair amount of torque coming up to speed, and piston types of pumps are a variable load several times per revolution. Thus they are not the best kid for a synchronous motor during starting. Besides that there certainly is that pesky matter of setting up the drive parameters.
A brush-type PMDC motor is a high performance device and can certainly deliver the torque. The tradeoff is brush life and the need for brush replacement. The good news is that they can perform well on unfiltered DC, and they can be open loop speed controlled rather simply.
 
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