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What limits the maximum RPM possible for the DRV11873?

Other Parts Discussed in Thread: DRV11873, DRV10975, DRV10983, USB2ANY, DRV10975EVM

I'm using the DRV11873 to drive a motor with 12 pole pairs and with 100% PWM modulation the maximum RPM I can get is 1200 RPM. I need at least 1400. The FG is 241 Hz which would be 241x60/12 = 1205 RPM.  Am I missing something obvious? 

  • Hi John,

    We will contact our experts on this device, and have them get back to you.

    While waiting, can you provide a little more information?
    1) When you reach 1200 RPM (FG=241Hz), what happens? Does the motor stop and restart, or does it continue to run at this speed?
    2) Are you changing speed rapidly? If so, does changing slowly allow more speed?
    3) Are you seeing voltage droops on the VCC pin that could cause the device to stop?
    4) What voltage are you using?
    5) What are the motor R and L?

    Any other details you can share (schematics/layout) will help.
  • 1) The duty cycle of the PWM input is 100%. I can't increase it any more than 100%
    2) Speed is steady state. I need to be able to switch between 2 speeds. 1400 RPM and 700 RPM.
    3) It doesn't stop, just doesn't go any faster.
    4) 12 VDC
    5) I don't know much about the motor, I was just given it as the one to use.

    The motor does not have a COM connection so I used the delta wiring to create the COM signal. The circuit is very basic. I'm using the EVAL board, I removed the onboard PWM generator and replaced it with a LTC6992 from Linear to convert a voltage to a PWM modulated output. The PWM frequency is set to 84kHz. I switch between 2 voltages into the LTC6992 to change from one speed to the other.
    Later I plan to implement a control loop that monitors the speed via the FC output and adjusts the voltage into the PWM chip to lock the speed. But I need it to get to 1400 RPM first.
  • John,

    Below are my inputs:

    1. Is motor  24-pole? I'm sure when you mention 12-pole pair it means 24-pole but just as double check to aviod any confusion for poles and pole-pairs. If motor poles are 12V, then in equation it needs to be divided by 6 and you can get your speed. 

    2. Please let us know back-emf costant of motor  i.e. Volt/Hz. This is limiting factor to achive highest speed. This constant decide how much voltage is need to achive certian speed or Hz. If it requries higher than 12V to achive 1400 rpm then you will never reach it with 12Vdc.

    Best Regards

    Milan-Motor Application Team

     

  • 1. Yes, the motor has 24 poles total. I'm using a tachometer to measure the speed. Dividing by 6 does not make the motor spin faster.

    2. The motor runs on 12V. I was hoping to use this controller to replace the original controller which is now obsolete. The motor has no problem reaching 1400 RPM with the original controller.

  • Jonh,

    Did you try to change FS logic? The resistance value to create COM, should be between 1k to 3K, I hope you would in similar range, if not, try changing these values.

    If both of these option does work, there is nothing much that can be done with DRV11873 becuase it is not tunable.

    We have another better part DRV10975 in our portfolio, you may like to experiment with this. This device has advantage over DRV11873, it provides 180 deg sinusiodal commuation and it can be tuned based on motor parameter for optimum performance.

    Best Regards

    Milan

  • I did try changing the FS logic and nothing changed. The resistors to create COM are 1.1K. 

    I would still like to understand why it is not working per the datasheet. I read something a while back about motors being designed to work with sinusoidal commutation and some are specifically designed to work with trapezoidal commutation. The controller I'm trying to replace was a sinusoidal generator and I think the DRV11873 is trapezoidal. Do you think this would limit the maximum speed?

    I'll try the DRV10975 but it is going to take a while to receive it.  

  • Unfortunately the DRV10975 requires a micro to program it. I need a stand alone solution.
  • Hi John,

    The DRV10975 requires a micro to program the internal settings for optimized operation. Once this is done the DRV10975 can operate in a similar manner as the DRV11873. In addition, the DRV10975 does not require the artificial center tap that the DRV11873 requires.

    Can you provide any information on your original controller? This may help explain the difference in speed.
  • Sure, the original controller is from Mitsubishi M56730ASP. Once the optimal settings are determined for the DRV10975 is it possible to order them pre-programmed? Or would there need to be an additional step in the assembly process that programs it? I read in the data sheet where it has an internal EEPROM to store the settings.
  • John,
    We can certainly look into to provide pre-programmed parts. It depends upon order quantities, let me know details. I can't promise though on this forum, need to talk to factory.
    Besides this, there are other means to program the parts using:
    a) Target boards works in conjunction with MSP430 launch pad. After programming, parts can be soldered to actual.
    b) You can also use provide 3-pin connector on your board with soldered parts and program them using USB to any and GUI.
    Best RegardsMilan-Motor Application Team
  • I don't know if it is just me but I finally received the DRV10975EVM and out of the box it does not run. So I connected the USB2ANY module and searched for the GUI. The user's manual does not tell you where to download it from. There is no link on the DRV10975EVM page. I finally did a search for "DRV10975EVM gui software" and it pointed me to the DRV10983 page. There was a link to the software there. After downloading it the file has no extension so made guess that it was a zip file and opened it with WINRAR. The GUI reported that the USB2ANY required a firmware update and after the update the program crashed and now will not run. Need to reboot to see if it that corrects it. 

  • Now the GUI reports the USB2ANY needs to be updated and then it just hangs forever. Looks like I'm stuck until someone can help me.
  • It finally timed out and this is the error I get now:
    Error 5000 occurred at Notifier Timed Out
    Device GUI.lvlib:GUI Wait for GUI Response via Notifier.vi:2:\Device Update
    Required.vi\DRV10983.lvlib:Main.vi

    This error code is undefined. Undefined errors might occur for a number of reasons.
    For example, no one has provided a description for the code, or you might have
    wired a number that is not an error code to the error code input.

    Additionally, undefined error codes might occur because the error relates to a third-
    party object, such as the operating system or ActiveX. For these third-party errors,
    you might be able to obtain a description of the error by searching the Web for the
    error code (5000) or for its hexadecimal representation (0x00001388).
  • It takes it about 30 minutes to finally time out. I had it continue in simulation so at least now the software starts. But when I start up I get the following message:
    An update to the device is required.
    Please make sure the power supply
    is greater than 22V and press OK

    22V power supply for what? If I click OK it goes into the 30 minute timeout cycle.
  • I really need something to try soon. This was supposed to be the 'solution' but since it did not work even with the provided motor out of the box, I'm slave to being able to configure it which requires your USB2ANY box which required a firmware update out of the box, which seems to have killed it. I am dead in the water until this is resolved. What should had been a 1 day activity is turning into a week and it's getting expensive. For 'me'.
  • John,

    We sincerely apologies for your inconvenience with DRV10975EVM. We never anticipate our customer to struggle with tools and documentations provided with EVMs, but it has happened, as you have pointed out rightly DRV10975 webpage does not provide right directions to download GUI applications. We are going to fix it soon, but for now, let me help you to start with EVM and GUI.

    Please use attached file, Store and Unzip is on separate folder, than originally stalled. Open the GUI using DRV10983-75.exe. You may see message “ Python script directory containing the script file found”, click yes to proceed. Deselect “Simulate communication” , you should be able to connect to GUI, “Connected tab should turn green”. Once this is done, you should be able to run the motor.

    Best Regards

    Milan-Motor Application Team

    DRV10983-75.zip

  • I get the error message: 

    Error 5002 occurred at DRV10983 Device Inferface.lvclass:Read Register.vi

    Possible Reason(s):

    Register reading not successful!! Please restart GUI and try again

    <Stop>    <Continue>

    Still dead in the water. 

  • John,

    The error 5002 occurs due to wrong I^2C comminication oe if EVM is not powered on. 

    Please confirm that USB cable is connected tightly between your PC/Laptop to USB to ANY board and I2C cable between USB to ANY  and EVM. Make sure to apply VCC before lauching the GUI.

    Best Regards

    Milan

  • After power cycling and reconnecting everything several times it started communicating. Not sure what the problem was but it seems to be repeatable. The problem now is the motor doesn't run. I followed the instructions in the EVM user guide and loaded the configuration parameters for the Runtian motor and it doesn't spin at all. Not sure what to do next?
  • Ok, I did nothing. Just left it on and was re-reading through the manual when I noticed that the "Display" panel was changing. It said the speed was 600,000 RPM but it was changing. So did a Speed 'OverRide' and it started turning. I unchecked the override and it now spins with the speed adjustment pot on the board. Not sure what changed.
    But now:
    1) How do I get the parameters to load into the EEPROM so I do not have to configure it via the GUI every time I power cycle the board?
    2) How many Poles does the Runtian motor have?
    3) The FG is 145Hz at max RPM. What limits the maximum RPM of this motorcontroller? Am I going to be able to get 1400 RPM with a 12 pole-pair motor?
    4) The motor occasionally stops and restarts. This cannot be normal?
  • I have arranged my schedule to work on getting this to work with our motor tomorrow morning. So if someone could answer at least question #1 within the next 12 hours I would be very appreciative.

  • John,

    Good to know the progress and that you are able to run the Runtian motor supplied with kit and EVM is working. Below are answers to your questions:

    1. How do I get the parameters to load into the EEPROM so I do not have to configure it via the GUI every time I power cycle the board?

    You need to supply >22Volt so apply 24Volt to EVM. Do not connect the motor because device is not rated to run the motor at 24V. Connect USB to ANY, Launch the GUI, connect should turn green showing EVM is properly connected to USBtoANy. Enable configure and Load the Runtian CSV file via GUI, use B6 as EEPROM key and press ee-write for programming the EEPROm.

    1. How many Poles does the Runtian motor have? 8-poles
    2. The FG is 145Hz at max RPM. What limits the maximum RPM of this motorcontroller? Am I going to be able to get 1400 RPM with a 12 pole-pair motor?

    Maximum electric Hz for DRV10975 is 1000Hz. For 12-pole pair 1400rpm, electric frequency is 280Hz, which is very well within device spec.

    1. The motor occasionally stops and restarts. This cannot be normal?

    Are you saying that even at continuous maximum POT (full Clock-wise position) setting, motor does halt and start, if yes it is not normal?

    If motor start-stops happens in changing POT conditions, than the reason is that device goes into sleep mode as POT comes near to zero position (CCW). Can you please elaborate more on which condition, start-stop is happening?

     

    Best Regards

    Milan

  • Yes, what I am saying is if I leave the motor running with the POT set to maximum, after a few minutes the motor will full stop and then ramp back up to speed again. Nothing else is changing.

  • Milan Rajne said:
    1. How many Poles does the Runtian motor have? 8-poles
    2. The FG is 145Hz at max RPM. What limits the maximum RPM of this motorcontroller? Am I going to be able to get 1400 RPM with a 12 pole-pair motor?

    Maximum electric Hz for DRV10975 is 1000Hz. For 12-pole pair 1400rpm, electric frequency is 280Hz, which is very well within device spec.

    This doesn't make sense as the Runtian motor has 8-poles and the maximum frequency I see with the speed pot at 100% is 145 Hz? Why doesn't it run faster? 

  • After working with it all day, I walked through the bring up procedure in the tuning guide and the motor would not even start running. I noticed that fault code 0 was always lit. Nothing I did seemed to affect it so I unchecked the current limit box in the Lock Detect section and it would at least start spinning. I ended up going through each of the parameters and tweaking them a little to see if it looked like it improved or not and finally have it spinning continously but Fault Codes 1 and 2 are always lit and I can't seem to do anything to make them not be lit.

    Also the speed does not appear to be adjustable so it may just be by luck it is spinning and it really isn't under control. 

  • John

     Maximum speed operation , I should have been more clear nonethless, below are my inputs:

    For all BLDC motor, two things governs maximum speed i.e applied voltage and freqency. Both goes hand in hand and The motor velocity or back-emf constant (Kt) defines as ratio of voltage/Hz, tells maximum speed motor can attain. For example, take example of Runtian motor, its back-emf constant is 0.055V/Hz. So it means, at 12Volt, at ideal no-load condition, maximum Hz is 12/0.055 ~218 Hz. This is ideal maximum but in actual condition when motor runs at higher speed, it draws current and the current creates drop across stator resistance and inductance, which reduces the amount of availbale voltage for back-emf,that's why you are observing reduce speed.

    In your latest post, I assume the problem faced by you is occuring when you are trying to tune your motor. First and foremost thing to get the proper tuning is to provide right inputs to GUI for velocity constant and phase resistance. This will help in faster tuning. In order to provide right inputs, please share the GUI setting.

     The reason to not to get speed control via POT is: Either Over-ride tab is selected on display page or Cloopdis is selected on Basic setting page.

    Best Regards

    Milan-Motor Application Team

  • Thank you for the explanation. I am not a motor engineer, I am the one stuck with trying to find a replacement for an obsolete motor controller. To complicate matters I have no data on the existing motor. That being said, I've been try to tune the parameters the data sheet says causes theses faults but the faults never go away.  It would be nice to be able to tell if I'm making things better or worse while tuning but the only indication is error/no error.

  • John,

    I can understand your restiveness to quickly get the motor running. I'm there to help in best possible way to achive your aim. But there are certain steps that you must follow to get optimize tuning with DRV10975. So let's start in step by step:

    1. First foremost is to get right value of stator resistance and velocity constant of motor: Resistance  is easy, just use multimeter to get resistance value across two terminals of motor, and enter 1/2 of its value in GUI. Velocity constant is little involved,  rotate the motor and capture waveforms across two terminals, and get the constant as explained in tuning GUI guide.  Once you know the velocity constant, you will know the maximum Hz motor can reach at 12Volt, as explained in my previous post.

    2. Second step is to get successful rotation in open loop. Check Cloop disable, and enter 1/4 or 1/5 of rated Hz at12V value in "open to close loop thershold", and fine tune start-up setting. 

    If you get succesful in this,  you can proceed for close loop tuning. I would strongly suggest to follow steps as mentioned in Tuning guide, RevB. For time being, Tuning guide is downloadable from DRV10983 EVM page: http://www.ti.com/tool/drv10983evm

    Best Regards

    Milan-Motor application Team

     

  • Just as I am about to give up, I manage to get things working. I think the problem has to do with it trying to accelerate too quickly. I walked through the tuning guide for about the 10th time and for whatever reason things started working. The GUI still shows Fault Code 0 and I haven't figured out yet how to make it go out. "Device Status" in the GUI tends to lock up the ability to refresh the Display a lot. 

  • Something bad just happened. The motor was running for about 20 minutes and then it stopped. It was frozen and making noise so I powered everything down and restarted and now the software tells me the USB2ANY isn't there. I get the following error message:
    Error 8001 occurred at Error Converter (ErrCode or Status).vi

    Possible reason(s):

    Invalid handle

    Complete call chain:
    Error Converter (ErrCode or Status).vi
    U2a Firmware Version Read.vi
    USB2ANY.lvlib:Get FW Version.vi
    DRV10983.lvlib:DRV10983 USB2ANY.vi
    DRV10983 About.lvlib:Main.vi

    Any idea what happened?

    ---update---

    I had to reboot my computer before it would talk to the USB2ANY again. The motor doesn't try to start any more and the display page has all '0's. Guess the chip is dead? It also looks like replacement parts are not available from anywhere, not even TI? 

  • John,
    Please let me know your address, I should be able to ship another EVM set to you.
    Best RegardsMilan
  • That would be very much appreciated.

  • If you could let me know when it ships and how it was sent I would appreciate it, my client would like to know how long it will take. Thank you. 

  • I received the replacement EVM kit and then had back surgery. Trying to get this to work again and this time I'm going through the tuning procedure step by step and I've run into a problem with the very first part. Getting the motor to spin in openloop mode. No matter what I do, the IC reports Fault #1, Over current. The only way the motor will spin is if I disable this fault. All the while the motor is spinning, the fault is present.

    I've disabled the acceleration current limit and set the lock detect to the maximum value.

    I measured the phase resistance of the motor as 8.6 ohms. I did the measurement/calculation for Kt and got 36.25 mV/Hz. I've tried dithering these values around and it made little to no difference. The average current consumption of the controller drops if I lower the phase resistance but the error does not go away.

    On average the controller is drawing 210mA from the power supply. Unfortunately I do not have a current probe so many of the closed loop procedures are going to be a little difficult to do. But first things first. How can I determine why the overcurrent fault is always set?
  • John,

    Resistance measurement is straight forward, just measure the value across phase to phase and ½ of it for GUI tuning. Back-emf or velocity constant is involved, so I would request share the waveform of phase-phase back-emf to just re-check the calculation.

    The reason for fault #1 is Abnormal Speed. If motor is operating normally, the motor BEMF should always be less than output amplitude. This condition for this fault is BEMF2 > U, where BEMF2 = Kt × speed, and U is input supply magnitude. So it is related to Kt. For further details refer to 9.4.7.2 of data-sheet.

    Best Regards

    Milan-Motor Application Team

  • I also had that isue "Please make sure the power supply
    is greater than 22V and press OK"

    but using provided zip file actually solved thqt.

    Thanks

  • I also had that isue "Please make sure the power supply
    is greater than 22V and press OK"

    but using provided zip file actually solved thqt.

    Thanks