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Original question:

BQ76952: OCC Protection in charging and regeneration

LM5060-Q1: Motor controller voltage spike polarity when we disconnect the BP MOSFET switch

REDDY Y
Intellectual 870 points
Part Number: LM5060-Q1
Other Parts Discussed in Thread: LM5060

Hi TI team
we have designed a BMS with a bidirectional MOSFET controlled through LM5060-Q1, and implemented overcurrent protection for both the charge and discharge over currents .

When overcurrent is sensed via INA240A2 and detected by the comparator, I directly send this signal to the OVP pin of the driver, causing the MOSFET to turn OFF with the built-in 9.6μs delay in the driver.

I have observed several overcurrent (OC) faults in the field. My BMS battery packs are used with different types of motor controllers. In almost all types of motor controllers, I notice that the MOSFET is turning OFF due to overcurrent faults. However, in the data, I am unable to determine whether the fault is related to discharge overcurrent or charge overcurrent. In some cases, I have observed MOSFET output voltage overshooting up to 100V.

Now, my question is, in vehicle with motor controller if the overcurrent is triggered during the regen (charging), will the BMS experience a positive voltage spike or a negative voltage spike? Conversely, if the overcurrent is triggered during discharge, will the voltage seen at the MOSFET output exhibit a negative or positive overshoot? pls explain why ?

Below is a block diagram representing my BMS for your reference. Kindly let me know the polarity of the spike the BMS experiences when the MOSFET is turned OFF due to charge or discharge overcurrent faults.

  • 0
    TI__Guru** 105301 points

    Hi Reddy,

    Thanks for reaching out!

    For current interruption during discharge (serving the load), the parasitic inductance on the battery side generates positive spike Vb+Li*di/dt on the input side and -ve spike on the motor side 

    The polarity will be reverse during current interruption while charging the battery.

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Intellectual 870 points

    Hi Rakesh,

    Thank you for the prompt response.

    While the battery is discharging in one of the 2-wheeler vehicles (stationary, parked with the center stand, and the throttle set to full- wheel rotating at maximum speed), we disconnected the battery and observed that the motor controller voltage surged to 80V from the nominal 50V of the battery. This is in a positive current scenario, and I observed a positive voltage spike.

    During regen (charging current), I haven't made any waveform observations, so I'm a bit confused about whether it would result in a positive or negative spike at the battery output when we disconnect it during regen. Please note that regen current implies that the motor controller already has a higher voltage than the battery for charging. If we interrupt the regen charging path, would it not result in a positive voltage spike?"

    Please review and feedback. 

  • 0 in reply to REDDY Y
    TI__Guru** 105301 points

    Hi Reddy,

    REDDY Y said:
    While the battery is discharging in one of the 2-wheeler vehicles (stationary, parked with the center stand, and the throttle set to full- wheel rotating at maximum speed), we disconnected the battery and observed that the motor controller voltage surged to 80V from the nominal 50V of the battery. This is in a positive current scenario, and I observed a positive voltage spike.

    Rakesh-> I would expect to see any surge voltages only in regenerative mode. Have you tested controlling the motor through a relay instead of LM5060? Do we do similar observations ?

    REDDY Y said:
    During regen (charging current), I haven't made any waveform observations, so I'm a bit confused about whether it would result in a positive or negative spike at the battery output when we disconnect it during regen. Please note that regen current implies that the motor controller already has a higher voltage than the battery for charging. If we interrupt the regen charging path, would it not result in a positive voltage spike?"

    Rakesh-> yes, we should see positive voltage spike at LM5060 output side in this mode of operation

    Best Regards,

    Rakesh

  • 0 in reply to Rakesh
    Intellectual 870 points

    Hi Rakesh
    Replied over email

  • 0 in reply to REDDY Y
    TI__Guru** 105301 points

    Ok Rami.

    Let's follow-up on email. I am closing the thread here.