Measuring back emf in a 3-phase BLDC motor

I am currently trying to determine the back emf generated in the floating coil of a 3 phase BLDC motor (simple RC car motor). I can currently monitor the current and the voltages supplied to each of the motor phases from the controller but I would like to eliminate the use of Hall sensors from my setup and monitor the back emf instead of the Hall outputs (to use as feedback instead). I am using a CB-68LP terminal block and the NI 6024E PCI card. To run the motor at full throttle requiers a 5 volt PWM at 60Hz and 12% duty cycle. I am no EE, just a lowly ME, so bear with my ignorance and give a girl a hand. Any suggestions? Thanks!

Hi pyrochk247,
Out of curiosity, are you using a motion controller to control the motor, or are you using the 6024E's counters to do the PWM? We don't deal with Back-EMF as a method of feedback so you'll have to forgive me if I trip up my understanding of the topic:
In the way of reading the motor windings for a simple voltage and feedback voltage, that is highly possible. Using a 6024E card you would be able to read in the analog signals and use the counters as outputs at the same time. What would be difficult about this is pulling out the Back-EMF signals from the standard motor winding voltage. I found this article:
http://www.acroname.com/robotics/info/articles/back-emf/back-emf.html
So the trick would be developing a method good enough to read the signals we desire well and rejecting the rest. If you are using PWM from the 6024E then you could do decent feedback to the motor through a PID loop.
Currently, I'm not trying to suggest anything. Rather, I'm asking to see if this idea makes sense to you.
Let me know what you think.
Justin Louie

Similar Messages

Mesauring position and speed in a 3 phase BLDC motor?

Hi!
I was wondering if you could help me with a problem. What I want to do is control and measure a 3 phase BLDC motors position and speed prefferably using a PID controller (or two!).
The position part isn't too hard (I think I got it!), but having a PID controller measuring the time from the trigger pulse to the desired position within a desired time is harder. The speed-PID controller should automatically adjust parameters so the next motor rotation will get to the exact position within the desired time.
Can anyone help me with this problem?

Could you please provide some information about the hard- and software that you are using to control the motor?
Thanks,
Jochen

BLDC Motor

Hey guys,
I have a BLDC Motor which I try to control using Xilinx FPGA.
It's a sensor-less motor and I try to close a loop using the Encoder.
My signals to the Motor are 3 Halls signals, PWM, Brake and direction.
The signals are going through the following component
http://www.google.co.il/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCkQ FjAA&url=http%3A%2F%2Fwww...
and at the end I get the 3 phases which go to the motor.
So far I've managed to rotate it by closing a loop with the encoder which by that, I get the halls (I chose the halls using the Datasheet I posted above).
I gave it a specific PWM and it rotates.
My first problem is that I actually need to give it the first push (by Hand) for it to start rotating, how can I avoid it?
Another thing is that I only have 6 selection for the halls and by that I divided the space (360 degrees). However I don't understand how can I put it in a middle point, between the flux created and a magnet?
Another thing, what is the relation between the PWM and speed?
Thanks a lot.
Assaf.

To help you troubleshoot this, what National Instruments hardware are you using to control the motor? Is it one of our motion controllers or a DAQ card?
Thanks!
Ravi A.
National Instruments | Applications Engineer

Is there a NI controller board that can control a 5-phase stepper motor?

I'm developing an application using Borland C++ Builder 6 under Windows 2000. I need to control a 5-phase motor from within my application. I have some old Keithley Metrabyte MSTEP-5 ISA boards that would work with the motor, but Borland doesn't allow direct port access to the boards to give them instructions. So, the second question would be: Would the aforementioned NI board be programmable using Borland C++ Builder 6?

Alright for the Universal Motion Interface (UMI-7764).
Firstly, the equipment I am focused on a is friction machine test and I would like to know if the static friction compensation (NI 7340 Series) is an important factor (probably for this kind of test)?
Then, the D550 or 650X0/X1 (Berger Lahr) are the steering cards for the 5-phase stepper motor (same manufacturer).
Here are the specifications:
- Operating voltage: 70...130 VDC
- Power input: max. 8A
- Adjustable achievement: max. 1000 W
- Rated current: 2...5 A/Phase
- Dynamic current increase by Boost I_Boost=100...190% In
max. 6A/Phase
- Engine line: Length <100m, cross section of a line >= 075 mm2
R_Lmax < 2 Ohm)
- Signal voltage for D 650.00/D 650.50: 20V...30V
D 650.01/D 650.51: 2,5V...5,25V
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- Relay contact exit change-over switch): 36 VDC / 30VAC,0,2 A
- Operating temperature: 0...55°C
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- Dampness class: "F" DIN 40400
- Mechanical dimensions:
- Weight: 1,3 kg
Moreover, I have an incremental linear encoder attached (Heidenhain LIDA 201) connected to adaptor EXE 6190B
for measuring the displacement of the stepper motor. The adaptor EXE 602, 605, 610 outputs a voltage between 1.4 and 4 volts, 1.4 and 4 volts, 0.4 and 1.7 volts, a frequency range from 0 to 50 Hz, and an operating voltage 5 volts +/-5% / 120 mA.

PXI 2527 & PXI 4071 -Questions about EMF considerations for high accuracy measurements and EMF calibration schemes?

Hi!
I need to perform an in-depth analysis of the overall system accuracy for a proposed system. I'm well underway using the extensive documentation in the start-menu National Instruments\NI-DMM\ and ..\NI-Switch\ Documenation folders...
While typing the question, I think I partially answered myself while cross-referencing NI documents... However a couple of questions remain:
If I connect a DMM to a 2 by X arranged switch/mux, each DMM probe will see twice the listed internal "Differential thermal EMF" at a typical value of 2.5uV and a max value of less than 12uV (per relay). So the total effect on the DMM uncertainty caused by the switch EMF would be 2*2.5uV = 5uV? Or should these be added as RSS: = sqrt(2.5^2+2.5^2) since you can not know if the two relays have the same emf?
Is there anything that can be done to characterize or account for this EMF (software cal, etc?)?
For example, assuming the following:
* Instruments and standards are powered on for several hours to allow thermal stability inside of the rack and enclosures
* temperature in room outside of rack is constant
Is there a reliable way of measureing/zeroing the effect of system emf? Could this be done by applying a high quality, low emf short at the point where the DUT would normally be located, followed by a series of long-aperture voltage average measurements at the lowest DMM range, where the end result (say (+)8.9....uV) could be taken as a system calibration constant accurate to the spec's of the DMM?
What would the accuracy of the 4071 DMM be, can I calculate it as follows, using 8.9uV +-700.16nV using 90 days and 8.9uV +- 700.16nV + 150nV due to "Additional noise error" assuming integration time of 1 (aperture) for ease of reading the chart, and a multiplier of 15 for the 100mV range. (Is this equivalent to averaging a reading of 1 aperture 100 times?)
So, given the above assumptions, would it be correct to say that I could characterize the system EMF to within 8.5uV+- [700.16nV (DMM cal data) + 0.025ppm*15 (RMS noise, assuming aperture time of 100*100ms = 10s)] = +-[700.16nV+37.5nV] = +- 737.66nV? Or should the ppm accuracy uncertainties be RSS as such: 8.5uV +- sqrt[700.16nV^2 + 37.5nV^2] = 8.5uV +-701.16nV??
As evident by my above line of thought, I am not at all sure how to properly sum the uncertainties (I think you always do RSS for uncertainties from different sources?) and more importantly, how to read and use the graph/table in the NI 4071 Specifications.pdf on page 3. What exactly does it entail to have an integration time larger than 1? Should I adjust the aperture time or would it be more accurate to just leave aperture at default (100ms for current range) and just average multiple readings, say average 10 to get a 10x aperture equivalent?
The below text includes what was going to be the post until I think I answered myself. I left it in as it is relevant to the problem above and includes what I hope to be correct statements. If you are tired of reading now, just stop, if you are bored, feel free to comment on the below section as well.
The problem I have is one of fully understanding part of this documenation. In particular, since a relay consists of (at least) 2 dissimilar metal junctions (as mentioned in the NI Switch help\Fundamentals\General Switching Considerations\Thermal EMF and Offset Voltage section) and because of the thermo-couple effect (Seebeck voltage), it seems that there would be an offset voltage generated inside each of the relays at the point of the junction. It refeers the "Thermocouple Measurements" section (in the same help document) for further details, but this is where my confusion starts to creep up.
In equation (1) it gives the expression for determining E_EMF which for my application is what I care about, I think (see below for details on my application).
What confuses me is this: If my goal is to, as accurately as possible, determine the overall uncertainty in a system consisting of a DMM and a Switch module, do I use the "Differential thermal EMF" as found in the switch data-sheet, or do I need to try and estimate temperatures in the switch and use the equation?
*MY answer to my own question:
By carefully re-reading the example in the thermocouple section of the switch, I realized that they calculate 2 EMF's, one for the internal switch, calculated as 2.5uV (given in the spec sheet of the switch as the typical value) and one for the actual thermocouple. I say actual, because I think my initial confusion stems from the fact that the documenation talks about the relay/switch junctions as thermocouples in one section, and then talks about an external "probe" thermocouple in the next and I got them confused.
As such, if I can ensure low temperatures inside the switch at the location of the junctions (by adequate ventilation and powering down latching relays), I should be able to use 2.5uV as my EMF from the switch module, or to be conservative, <12uV max (from data sheet of 2527 again).
I guess now I have a hard time believeing the 2.5uV typical value listed.. They say the junctions in the relays are typically an iron-nickel alloy against a copper-alloy. Well, those combinations are not explicitly listed in the documenation table for Seebeck coefficients, but even a very small value, like 0.3uV/C adds up to 7.5uV at 25degC. I'm thinking maybe the table values in the NI documentation reffers to the Seebeck values at 25C?
Project Engineer
LabVIEW 2009
Run LabVIEW on WinXP and Vista system.
Used LabVIEW since May 2005
Certifications: CLD and CPI certified
Currently employed.

Seebeck EMV needs temperature gradients , in your relays you hopefully have low temperature gradients ... however in a switching contact you can have all kind diffusions and 'funny' effects, keeping them on same temperature is the best you can do.
Since you work with a multiplexer and with TCs, you need a good Cold junction ( for serious calibrations at 0°C ) and there is the good place for your short cut to measure the zero EMV. Another good test is loop the 'hot junction' back to the cold junction and observe the residual EMV. Touching (or heating/cooling) the TC loop gives another number for the uncertainty calculation: the inhomogeneous material of the TC itself..
A good source for TC knowledge:
Manual on the use of thermocouples in temperature measurement,
ASTM PCN: 28-012093-40,
ISBN 0-8031-1466-4
(Page1): 'Regardless
of how many facts are presented herein and regardless of the percentage
retained,
all will be for naught unless one simple important fact is
kept firmly in mind.
The thermocouple reports only what it "feels."
This may or may not the temperature of interest'
Message Edited by Henrik Volkers on 04-27-2009 09:36 AM
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

Back up error--Out of phase

Hi,
I used take successful backup on this tape using DB13.
But now I am getting following error:
BR0061I 50 files found for backup, total size 126910.432 MB
BR0143I Backup type: offline_force
BR0112I Files will not be compressed
BR0130I Backup device type: tape
BR0102I Following backup device will be used: /dev/rmt1.1
BR0103I Following backup volume will be used: ARDB02
BR0289I BRARCHIVE will be started at the end of processing
BR0134I Unattended mode with 'force' active - no operator confirmation allowed
BR0208I Volume with name ARDB02 required in device /dev/rmt1.1
BR0280I BRBACKUP time stamp: 2008-10-02 00.39.08
BR0226I Rewinding tape volume in device /dev/rmt1 ...
BR0351I Restoring /oracle/ARD/sapbackup/.tape.hdr0
BR0355I from /dev/rmt1.1 ...
BR0278E Command output of 'LANG=C cd /oracle/ARD/sapbackup && /usr/sap/ARD/SYS/exe/run/brtools -f detach LANG=C cpio -iuvB .tape.hdr0 < /dev/rmt1.1':
Out of phase!
cpio attempting to continue...
skipping 32925310 bytes to get back in phase!
One or more files lost and the previous file is possibly corrupt
Length of file name doesn't match expected length.
BR0280I BRBACKUP time stamp: 2008-10-02 00.39.18
BR0279E Return code from 'LANG=C cd /oracle/ARD/sapbackup && /usr/sap/ARD/SYS/exe/run/brtools -f detach LANG=C cpio -iuvB .tape.hdr0 < /dev/rmt1.1': 2
BR0359E Restore of /oracle/ARD/sapbackup/.tape.hdr0 from /dev/rmt1.1 failed due to previous errors
BR0218E Checking label on volume in device /dev/rmt1.1 failed
BR0236I Perhaps volume initialization with option '-i force' required
BR0056I End of database backup: bdyybedn.aft 2008-10-02 00.39.18
BR0280I BRBACKUP time stamp: 2008-10-02 00.39.18
BR0054I BRBACKUP terminated with errors
OS is AIX 5.3
DB is Oracle 10.2
Please help me to solve this problem.
Regards

Hi,
Take a look at the note 17163 BRARCHIVE/BRBACKUP messages and codes
the solution is indicated on the error message:
BR0236I Perhaps volume initialization with option '-i force' required

How to do carrier phase measurement of any RF signal and Phase Noise measurement of any RF signal?

Hello,
Can any one give some idea to do carrier phase measurement and Phase Noise measurement of any RF signal?
Regards,
Vijay

Vijay,
A great example for measuring RF phase noise can be found in the LabVIEW Example Finder. The name of the VI is "MT RFSA Phase Noise.vi" This example performs phase noise density measurements on I-Q data acquired using RFSA. You may also want to take a look at Performing Modulation Measurements on Real-World IQ Data With Carrier Frequency Drift to see if phase measurement could be implemented: http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=EEAFD63A09CD3B79E0340003BA7CCD71&p_node=200054&p_source=External
What type of RF signal would you be analyzing? Are you trying to measure phase shift of a carrier frequency that is varying with time?
Shea C
Applications
NI

Measure pulsewidths and amplitudes of 3-phase pulse using PXI-5122

Hello,
I am trying to measure the pulsewidth and amplitude of each of the three sections of the attached pulse. Basically there will be two negative sections and a positive section in between. Each may have a different amplitude and/or pulsewidth. Is there any fairly easy way to do this on the 5122 (using CVI)? I was thinking perhaps there's a way to only capture each of the three segments separately, and let the digitizer do the relatively simple analysis. Please see the attachment for a picture of what I'm trying to measure.
Thanks!
P.S. If you can figure out a method for measuring the deadtime in between the 3 sections, and a method for determining whether the pulse is fairly square, you get extra points.
Attachments:
measure pulse.JPG ‏4 KB

determining whether the pulse is fairly square ....
Using a Histogram of all pulse values? If it is a pure pulse all values will be in two bins ....
You didn't provide a coarse time scale. Is it p/n/µ/m seconds?
So my approach out of the cristal ball:
Set up the 5122 to absolute timescale , set up trigger to 5% pretrigger with multiple shots , each shot long enough to hold one tripple pulse
fetch one shot , seperate the pulses (find slopes seperate inbetween) , make histogram.... do analysis (hope you have the time for it)
time between tripple pulse is the difference in the trigger timestamp
(In LabVIEW I would use multiple loops in parrallel with queues... )
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

Measuring Amplitudes of 3 Mixed/Staggered Phase Square Waves

I'm writing a vi intended to measure the amplitudes of three mixed signals. These signals are generated by the DAQ already to drive 3 LEDs at 9kHz/ 50% DC combined.
I was able to modify an existing example vi to create the LED drive. I was hoping to find a similar example for the data capture and analysis. I haven't been successful thus far.
Could someone please suggest a good example to get me started? Please forgive my inexperience as I have been teaching myself Lab View and thus have a very ignorant instructor.
-Thanks in advance.

Bad,
Have you tried the analog data acquisition examples? The sample rate would need to be >18 kHz to meet the Nyquist criterion, but that assumes sinusoidal signals. Since you are talking square waves, you will need to sample quite a bit faster to recover the waveforms. 100 kHz or 250 kHz are probably good starting points if your device will sample that fast.
Tell us what you have tried and specifically what does not work. Do you get error messages? Does the result look wrong?
Posting you code with the data you have collected is very useful.
Lynn

Three phase AC motor model problem...

Hello, is there a way to use the 3PH_Motor from the family OUTPUT_DEVICES located in the group Electro_Mechanical but with a modified Spice model that uses only the data printed on the nameplate? I ask this question because I have to simulate power factor correction using a field of 10 motors rated at 110 kW each for my thesis, but I need the R and L of the windings in order to use the default model and I cannot find these values in catalogues.
Thank you in advance and I hope there is a way to solve this problem...
Multisim 12.0.0
Solved!
Go to Solution.

I am assuming you're looking for an induction motor.
It would be an oversimplification to model an induction motor using a fixed R,L load (In V12 of Multisim, we actually removed the 3PH_Motor and instead added a more realistic dynamic model based on a more realistic parameter set). An induction motor is in many ways like a transformer. Therefore you need the magnetising inductance, rotor and stator leakage inductances, and rotor and stator resistances. You may be able to contact the manufacturer to obtain, but I doubt you can accurately deduce them just from the name plate.
This link goes over a simple steady-state model: http://www.scribd.com/doc/13311930/Induction-Motor-Modeling-steady-State
Thanks,
Max
National Instruments

Difference between BLDC motors and Brushless Servo Motors

Hi
I am new to the concept of motors and motor control. I dont know if I have come to the right place but it would be great if anyone can help me in finding out the differences between Brushless DC motors and Brushless Servo motors. Can I use NI motion controllers to control a Brushless DC motor?
Regards,
Suman.

Suman,
Brushless DC motors and Brushless Servo motors mean typically the same thing. The word "servo" implies that a position feedback resource (e. g. a quadrature encoder) is used for closed loop control.
You can use NI motion controllers to control brushless motors. Please refer to this thread in the forums for more information.
Best regards,
Jochen Klier
National Instruments Germany

BLDC Motor Speed from Controller

In the tester I am building, I am having troubles acquiring a stable motor speed. I need a stable speed so that I can control the motor speed to 1100 +/- 50 RPM.
We have a compressor connected to a Dart 700BDC controller, and a cFP-CTR-502 counter input connected to one of the hall sensor inputs on the controller. The counter is set up just to continually counting the number of pulses (counter overflow is handled within the test application). The test application gets the counter value and timestamp from the Fieldpoint VI's approximately every 500 milliseconds. It compares these two items to the data from the previous iteration to generate an RPM. I've attached a VI that has the routine that I am currently using.
When I run the motor, I have RPM values that fluctuates beyond my 50 RPM window. Do I need to tweak my routines to display a more stable reading? Or is a different solution required?
Attachments:
Monitor Motor Speed.vi ‏13 KB

Hi OlderJohn,
The first you should try is lowering your sample time and perhaps even your proportional gain. Are you familiar with PID control. I recommend reading a great article on it here
Joe Daily
National Instruments
Applications Engineer
may the G be with you ....

Measuring power at two different point (single phase)

Hi all,
I am new user of LabVIEW 2013 with electrical power suite.
May i know how to measure two different point of single phase system using the same VI such as in DAQ power and energy example?
As I notice that there are several type of wiring available. Is only one voltage and one current availabe during 1 ph voltage and 1 current selection. Thus, when I select 3ph voltage and 2 current, the value I obtain is not seem to be true.
From the figure attached, I want to measure the voltage at current at the solar/PV to obtain the power value. Other than that, I also need to measure the voltage and current at the load such as water heater. This is a single phase configuration network.
(2 voltage and 2 current measurement at single phase)
Hope for guidance.

Hi Lewis,
Here attached the file.
Actually I wanted to measure power two different point in a single phase system as shown in the first attachement.
Since, there is example in power quality measurement(DAQ) as shown in the second attachment.
since there is two measuring point in my measurement. May i know how to obtain two measurement voltage at the same time in DAQ?
Hope for guidance.
Attachments:
Two measuremernt point (single phase).png ‏7 KB
power & energy measurement.jpg ‏172 KB

How does Order Analysis measure phase lag, particularly super-sync amplitudes?

In recent testing of a high speed gear box, an 8X amplitude was observed (on the radial displacement probes) as the gear passed through a certain speed range. An NI4472 pci card and vi's written in 7 Express, w/ Order Analysis tool kit were configured with radial displacement probes and keyphasor as input signals. The behavior of the phase lag measurement is significant. If the phase lag of the 8X amplitude rolled as the gear passed through a particular speed range then this could suggest one particular problem, but if the phase lag remained constant then this could indicate a different problem. So, someone asked: How does the system measure phase lag of supersynchronous amplitudes?

See attached file for figure 1,2,3
The Phase measurement in the LabVIEW Order Analysis Toolkit uses the phase lag convention. Phase is defined as the angle difference measured from the peak of a vibration signal backward in time to the reference trigger point. This means the directions of numerically increasing angles are always set against the shaft rotation. The trigger point here is the tachometer pulses.
Figure 1 shows the relationship of the vibration signal and reference signal to zero degree phase. The shaft has a heavy spot and a keyway slot. When the keyway slot passes the tachometer, the tachometer detects a trigger pulse. The heavy spot causes the shaft to vibrate as the shaft rotates. When the heavy spot passes the proximity probe, the vibration reaches a peak. When the heavy spot passes the proximity probe and the keyway slot passes the tachometer simultaneously, the peak of the vibration does not lag or lead the reference trigger point. At this point the phase is zero degrees.
The other part of the convention dictates that 90 degrees means that the peak of vibration lags 90 degrees behind the trigger point. Figure 2 1illustrates the 90 degree phase. When the vibration signal reaches the peak, rotate the shaft backward (counter the rotation direction) until the keyway slot passes the tachometer. The number of degrees you rotate is the phase lag, or the phase value in machinery vibration measurement. Figure 2 shows the relationship of the vibration signal and reference signal to the 90 degrees phase convention.
For the 8x phase, the measurement is conducted in the similar way. The difference is that the 8x order component go 8 times faster than the trigger pulses. Figure 3 shows the 90 degree phases ( tacho pulse in rising edge) of the 8x order components. The phase measurement is still conducted through calculating the delay between the peak in the 8x vibration components and the trigger pulses and comparing the delay to one cycle of the 8x components. In figure 3, the signals between the two green grid lines are used to output one phase results.

Dc motor measurements

Dear ppl.
Need help to traduce oscilloscope voltage readings, to Torque, Angular speed and Back-emf from attached circuit.
Motor is a 550 watts hand-driller.
A-F mutual inductance, shaft inertia and friction are unknown and set by default.
The other parameters show its actual values.
Should I convert volts to Nm, rads x seconds and Volts directly?
Are those values logicals or outrageous?
Thanks a lot.
Solved!
Go to Solution.
Attachments:
550 watts hand driller sim.ms12 ‏70 KB

Hello danielsoy
The first thing you need to find is the relation voltage (or current) with Torque. It think there´s is an ecuation that relates current and Torque. Then, knowing the torque and the shatf inertia you can yield the angular aceleration of the wheels. Doing some numeric integration you can calculate the angular speed of the wheels. That´s the way you can approach the problem. With an encoder it would be much easier, cause you can measure angular position, speed and acceleration and with the acceleration you can yield the torque.
Hopefully this information will help you.
Omar R.
Applications Engineer

Measuring back emf in a 3-phase BLDC motor

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