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DRV10970EVM: Geting higher current/torque

Prodigy 90 points

Replies: 8

Views: 227

Part Number: DRV10970EVM

Hello,

I have an DRV109070EVM Evaluation Module here to drive an DF45M024053-A2 Brushless Motor from Nanotec.

The motors main datas are: rated valtage: 24V, rated current: 2,36A, phase to phase resistance: 0.8 ohms, torque constant: 0.0335 Nm/A.

I connected it like discriped in the user guide, with 15V supply voltage.

Internal voltage of the Evaluation Module just starts with lower volage (as descriped in another post) then the board works.

But it is not able to start the unloaded motor. The motor needs to be turned manually to get ist started. And when it is running the current is never more than 0.3A even when the motor is breaked manually the current goes down to 0.1A and therefore torque is minimal. According to the datasheet 1A should be possible but how can i reach that current under load?

Is it possible to get the start problems fixed and a higher torque?

Or can someone suggest a Tree-Phase Brushless DC Motor Driver which is able to generate high torque even at low speed.

Thank you for your answers!

Regards

Gabriel

  • Hey Gabrial,

    I think the problems of improper startup and not a lot of current applied lies in improper configuration of the halls.

    1) Please confirm that this is the correct datasheet for your part.
    www.farnell.com/.../1996060.pdf

    2) Can you try putting H2 = U_HP, H3 = V_HP, H1 = W_HP, with FR = 1, and using trap commutation? This is to match the driving state in the motor datasheet to the driving state in Table 1 of the DRV10970 datasheet.

    3) Are you driving the motor in sinusoidal mode or trap mode (CMTMOD pin config)? also please tell me your other configurations, like DAA

    4) make sure current isn't being limited too low by the CS pin
    Sincerely.
    sanmesh U.
  • In reply to Sanmesh Udhayakumar:

    Thank you for your answer sanmesh!

    1) Yes thats the right datasheet!

    2) I changed the connection of the Hall-elements as you descriped, an now start up works fine and I'm also getting higher currents about 0.5A with 95% duty cycle and 0.2A for low speeds.

    3) I drive the motor in Trapezoidalmode with 30° Hall placement and 10° driveangle adjustment, but also tryed sinusoidal operation but torque results where best with trap mode.

    4) I checked currentlimit setting, in the evaluation board a 24k resistor is connected between CS pin and GND, that means a current limit of 1.25A

    I hoped that it would be possible to get high torque and currents about 1A even at low speeds. Has anyone an idea to improve that?

    Regards

    Gabriel

  • In reply to Gabriel Ecker:

    Hey Gabriel,

    1) Can you apply 100% duty cycle to the PWM signal to indicate max voltage applied, instead of 95% duty cycle? It shouldnt increase the speed too much, but you can see what it does.

    2) What is the supply voltage? I know you mentioned 15V but i just want to confirm since you also said "Internal voltage of the Evaluation Module just starts with lower voltage". An estimation of the max current that can be applied is  Imax = (Vcc- Kt*SpeedHz)/RphaseToPhase. So if Vcc = 15V and Kt = 0.0335 Nm/A = 0.0335 V/Hz, and RphaseToPhase = 0.8ohms, then max current = (15V - 0.0335 V/Hz*ElecFreqSpeedHz)/0.8 ohms. To get ElectFreqSpeedHz, just see what the frequency of the FG pin is in Hz.

    3) If you want to increase current applied, put a load torque on the motor. This will slow down the motor, thus reducing kt*speedHz term, and thus making Imax bigger.

    4) What is your target rpm and what is the motor phase current you are drawing at the target rpm? Having a scope capture of the current would help too.

  • In reply to Sanmesh Udhayakumar:

    Thank you for your answer.

    1) I tryed this, but that changed nothing.

    2) I have an 15V / 5A DC power supply. The start up problem with over 10V were discussed in the forum: https://e2e.ti.com/support/motor-drivers/f/38/t/659117?tisearch=e2e-sitesearch&keymatch=drv10970evm

    3) Yes, thats clear for me.

    4)

    The first image represents the phase current with full duty cycle when i break down the motor to 100 rmp, the second is no load phase current at 5% duty cycle with about 350 rpm. I used the connection cable as shunt, its resistance is 25mOhms. So the phase current in loaded case goes up to nearly 1A, can this be true when the source is 15V / 0.2A (measured with FLUKE 87 Multimeter)? Target rpm is 100-150.

    Maybe I just need a controller which is able to drive currents around 10A.

    Regards

    Gabriel

  • In reply to Gabriel Ecker:

    ElecFreqSpeedHz at fully duty cycle= 100Targetrpm*8polePairs/60 = 13.3Hz
    max current = (15V - 0.0335 V/Hz*13.3Hz)/(0.8 ohms from motor + 0.4ohms Rdson high and low) = 12A.
    We should be able to get a lot more current.
    Can you confirm the resistance between two motor phases?

    Also the oscilloscope current capture shows voltage. Is the conversion to current the voltage/25mOhms?

    Sincerely,
    sanmesh U.
  • In reply to Sanmesh Udhayakumar:

    Thank you for your answer!

    Yes I can confirm the phase to phase resistance is 0.8ohms.

    Exactly 25mOhms ist the conversion.

    Maybe the current limit of 1.25A is the reason why no higher current can be reached. According to the datasheet DRV10970 is able for 1.5A peak output, so that high current may not be possible for this driver.

    Regards

    Gabriel

  • In reply to Gabriel Ecker:

    This may be the case for this driver. I'll also check with my coworkers as well
  • In reply to Sanmesh Udhayakumar:

    I have got an DRV8306EVM now it works fine.

    Thank you!

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