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HVKIT v2.0, Deceleration causes DC bus to go from 100V to 450VDC

Mark Iverson
Prodigy 180 points

I've been working with the HVKit for several weeks running a Baldor 170V, 0.5HP BLDC.

It's turning a wheel which is 14" diameter and weighs 11lbs... up to 3000rpm (altho I've only tried that once!).

I'm quite satisfied with everything so far (HVKit, SpinTac GUI, 28069MISO CCard)... operation of the motor is quite smooth once the motor is ID'd and inertia set.  Little to no overshoot/undershoot when changing speed. 

However, decelerating even a modest amount, say from 800rpm to 500rpm, causes the DC bus voltage to EXCEED 450V in a matter of ~2 seconds... that's without using the PFC section of the HVkit.  I've got a variac on the 120VAC, and jumper the rectified AC directly over to the Inverter stage.  I've already replaced numerous fuses, and even a few of the in-rush current limiters.

I assume the HVKit was not really designed to deal with dissipating the energy from a rotating mass...

Thus, any suggestions on how to go about this in my design, and/or, anything I can do in software to limit the DCBus from exceeding some set V?

Thanks,

-Mark

  • 0
    TI__Expert 8885 points

    Mark,

    HV-kit does not have dynamic barking resistor across DC-BUS and that’s the reason you are observing over-voltage across DC-Bus. It just your feeling that it is modest deceleration but reality is that your load power, speed, torques, inertia and deceleration time are of such nature that it’s creates high braking power which cannot be sustain by  HV-kit.

    I can suggest following options to reduce the over-voltage,

    1. Easiest one is to reduce the deceleration rate through software such that DC-bus remains within required limits.
    2. Increase the DC-Bus capacitor value.
    3. If above two chnages does not meet your end specification, you will need to add braking resistor across DC-bus with a series transistor/IGBT. This is involved design because there is no simple formula to calculate the value and power rating of braking resistor. I would suggest visiting http://literature.rockwellautomation.com/idc/groups/literature/documents/at/pflex-at001_-en-p.pdf to get more details on this topic. You can find similar application notes from other AC drives manufactures too.

     Best Regards

    Milan

  • 0 in reply to Milan Rajne
    Prodigy 180 points

    Much appreciate the very prompt reply, and the suggestions.

    -Mark