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Variable Frequency Drive for BLDC Motor
Controlling speed by using a VFD for BLDC motor

Hey,

Is it possible to use directly a VFD (Variable Frequency Drive) for a BLDC motor for controlling the speed? If not then please suggest me a possible solution. Also I need to have a feedback loop for checking its speed.

There are some VFDs out there that can run BLDC and PMAC servo motors. Hard to say more without details, but it is possible. But the average cheap little VFDs you can get from internet resellers will not be able to be accurate enough to handle a servo motor. You are going to need something like an Allen Bradley PowerFlex 755, a Control Techniques Unidrive, a Yaskawa A1000, something like that.

Do these devices as mentioned above provide feedback loop also for maintaining that speed?

> Do these devices as mentioned above provide feedback loop
> also for maintaining that speed?

Yes, that's the only way they can work. But again, it is not a STANDARD VFD, they need a much more capable motor modeling algorithm to make it work with any reasonable accuracy and to avoid burning up the motor. Yes, a standard VFD might make it turn, but not reliably and not without a significant risk of harm.

Hi yo'all!

EXCELLENT ADVICE!

>There are some VFDs out there that can run BLDC and PMAC
>servo motors. Hard to say more without details, but it is
---- sniped by Moderator ----

PETER MACALUA
PORT ARTHUR TEXAS

Someone correct me if I'm wrong, but there shouldn't be any problem controlling a synchronous permanent magnet motor with a vfd. Just make sure you ramp up the speed in a way that it can actually do.

The thing is, as you apply torque the speed will not slip as in an asynchronous induction motor. A synchronous motor will have the mechanical speed exactly match the electrical frequency (factoring in the number of poles), and when you apply torque there will be a phase angle difference 'delta', being the angle between the permanent magnet and the magnetic field.

So if your VFD ramps up electrical frequency too fast, at high load, weird things will happen when the phase angle passes that 90-degree maximum torque. You'll have to be careful of this with a 'dumb' VFD or frequency converter.

The drives mentioned above are probably vector drives, with internal monitoring of the current loop to observe for that kind of condition. You tell it it's a servo motor, it will be able to control speed open loop very well. Some even have feedback for position.

Either way I don't think you'll need feedback for speed with that type of motor

By James Ingraham on 25 May, 2016 - 5:42 pm

I do not believe that a standard VFD will run a BLDC motor. Why do you want this particular combination? What is it that you are trying to accomplish? With more information we may be able to suggest a solution.

-James Ingraham
Sage Automation, Inc.

> I do not believe that a standard VFD will run a BLDC motor.
> Why do you want this particular combination? What is it
> that you are trying to accomplish? With more information we
> may be able to suggest a solution.

I agree fully with what Mr. James Ingraham has mentioned.

1. In BLDC you take Hall Sensor Information and accordingly apply the phase voltages whether to be logic 1 or logic 0

2. As speed builds up the frequency is increased and it is not the other way. What I mean is frequency is not increased and speed builds up.

3. In a simple speed control system, you can derive speed information from Hall Sensor signals.

4. If the motor current is less than 8-Amps and voltage less than 70-V there are standard BLDC driver ICs (3-nos of half bridges) available. By using these standard ICs you need not get into the domain of designing boot-strap circuits for driving MOSFETs

Nandakumar

Hey

I'm trying to fabricate a small scale Laboratory stirrer. so I require running of BLDC motor, along with it I need to install integrated motion controller. Please can anybody suggest me any good manufacturers who can directly provide me the solution which I can directly purchase.

By James Ingraham on 6 June, 2016 - 4:06 pm

It is not clear to me from your response why you MUST use a BLDC for your application. Why wouldn't a stepper motor work? Here on Control.com, AMCI advertises a motor + driver + controller.

What approximate size are you looking at? 1 Watt, 10W, 100W, 1KW?

Where are you, at least by continent? Different manufacturers are more prominent in certain locations.

Here are some manufacturers of small servos, depending on what you mean by "small."

DC-powered (most of these also have larger options):
Advanced Motion Controls, AMCI, Copley Controls, Elmo Motion Control, Maxon, Infranor / Lourdes / Mesa, Quicksilver, Tamagawa-Seiki

110VAC / 220VAC powered:
Applied Motion Products, Panasonic, Omron, Electrocraft, Oriental Motor, Mitsubishi Electric, Yaskawa.

-James Ingraham
Sage Automation, Inc.