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DRV10987EVM: Maximum attainable RPM for a given motor?

Supira Medical
Prodigy 120 points
Part Number: DRV10987EVM
Other Parts Discussed in Thread: DRV10987

Hi,

I am attempting to spin a motor that has a maximum rating of 37k RPM.  Using the GUI for the EVM, I am unable to get anywhere close to this speed.

The motor has 4 poles (2 pairs), a phase to phase resistance of .306 ohms and a voltage constant of .488 V/kRPM.

Since the DRV10987 has a maximum electrical frequency of 1000 Hz, calculations suggest that the maximum speed this motor can attain is (1000/2) * 60 = 30,000 RPM.  I haven't measured the FG out using an o'scope but I estimate the RPM to be around 1500 or so, quite removed from the expected speed.

Am I limited by the motor's parameters in some way or is there something I should be doing differently, such as using an external PWM signal?

Thanks for your assistance,

Adnan

  • 0
    TI__Mastermind 24405 points

    Hi Adnan,

    Thanks for posting your question in MD forum. Minimum phase-phase resistance that the device can support is 0.6 ohms. Because the resistance is too low, at high speeds the device might trigger overcurrent protection. Can you check the fault/lock code triggered by the device? 

    Regards,

    Vishnu

  • 0 in reply to Vishnu Balaraj
    Prodigy 120 points

    Hi Vishnu,

    Thanks for your reply.

    I do see a current limit fault show up if I play with some of the parameters but I am able to have the motor run continuously at that very low speed without triggering any faults.  One thing I should mention is that I cannot get it to run in closed loop mode t all, regardless of RPM.

    Do you offer a different controller that would suit this particular motor, since the resistance is out of bounds?  However, the datasheet for the DRV10987 says that the minimum supported phase to CT resistance is 0.029 ohms (section 8.4.1.1).  How do you arrive at 0.6 ohms phase-phase?

    Regards,

    Adnan

  • 0 in reply to Supira Medical
    TI__Mastermind 24405 points

    Hi Adnan,

    Unfortunately. we do not have any devices in DRV10x (integrated FETs+control) family that can support such low resistance motors. It is true that device can support min of 0.029 ohms but we do not recommend driving motors below 0.3 ohms because we may not be able to spin the motor at maximum speed because the device might trigger over current fault. Can you share the parameters that you are currently using to spin the motor? Let's see if we could get the motor to spin in closed loop by tuning some critical parameters.

    Regards,

    Vishnu.