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Vbus > 50VDC, Motor Stops. What would cause this?

Hi,

Custom PCB based on HVKIT, F28027F CPU.

We used the HVKIT to demo our motor and have transitioned to our own PCB. Last week had a few tricky issue with the MOSFET gate driver propagation delay, but that is behind us.

Our board works fine at Vbus voltages below 50VDC. Our target working voltage is 310VDC. For some reason as we increase Vbus > 50VDC the motor starts to kick and then totally stops.  This is not a current limit or trip zone problem as neither of those conditions are met.

It looks like the PWM goes crazy after >50VDC.

Our user.h settings are not much different from that of the HVKIT, so I am wondering if anyone knows what could the cause be?

Thanks

Stomp!

 

  • I would triple check your voltage and current sense circuits. Re-do the math so you have the proper USER_ADC settings. Check the polarity of the current measurement to make sure it matches the HVKIT (it probably does if it's working below 50V). Check the USER_VOLTAGE_FILTER_POLE calculated from your voltage sense circuit.
  • Hi Chris,

    As always, thanks for your time.

    I am certain about the USER_ADC settings, and I have tripple checked the filter pole which is 342Hz.

    The image below shows the Ifb_V (CH1) and Vfb_V (CH2) as at the CPU pins.

    The frequency of Ifb_V is about 90Hz which gives about 1.8KRPM on the motor. (which is approximately what I am seeing at the motor)

    I'ts difficult to understand why my current profile looks like it does, and what the significance of the current spike at about the red arrows is.

    Would you have any additional comments?

    Thanks

    Stomp!

  • Hi Chris,

    During some more long term testing we found the gate driver was shutting down for a few uS at random points.
    We've had nothing but issues with this gate driver vendor, this is really the final straw, we're changing to another vendor.

    Thanks for your assistance which ultimately helped us find the issue.

    Cheers
    Stomp!
  • thanks for updating us on the issue. glad you found root cause!