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MCF8315A: Using FOC to drive BLDC TurboFans with the goal of reducing audible noise

Chris Esser
Prodigy 30 points
Part Number: MCF8315A
Other Parts Discussed in Thread: MCF8316A, MCF8316AEVM

Tool/software:

I am looking to drive a 100,000RPM BLDC turbofan (link below) in a way that reduces the audible noise. These motors come with cheap drive electronics that result in them being very noisy, like a dentist drill. 

I am interested in implementing FOC to drive these motors, but I am unsure if this IC can handle the extremely fast RPM of the motor, since have typically seen FOC for lower speed applications. 

My questions are:

1) Will the MCF8315A be capable of driving these turbofans?

2) Would it be expected that the audible noise from the fan would be reduced.

Turbofan motor example:

DC9-12V/7-24V Brushless Turbo Fan Motor 100000RPM

  • 0
    TI__Genius 9210 points

    Hi Chris,

    1. It'll depend on how many pole-pairs this motor has, and you can convert the mechanical RPM to electrical frequency with this equation:

      The MCF algorithm is limited to a maximum of ~1500 Hz electrical frequency. So if the motor has 2 poles (1 pole-pair), then the MCF algorithm can possibly come close to driving it at 100000 RPM (~1666.7 Hz). If this motor has 4 poles or more, then our MCF algorithm won't be able to come close to 100000RPM.

      However, another big factor is the maximum power output of the MCF8315 also depends on its thermal limitations, which is likely not sufficient to drive the motor at its rated max power without overheating.

      The MCF8316A may be able to get close to driving the 12V version at full power, but since these devices have integrated powerFETs, the actual maximum power output will be restricted by thermal limitations (which is dependent on board layout, ambient temp, airflow, cooling, etc). And it's unlikely that these devices can operate at sustained 12V 6A, or 24V 5A without triggering overtemperature shutdown. 

    2. If these motor's built-in controllers uses Trapezoidal commutation, then yes, there can likely be improvements to the acoustic performance. FOC can produce much smoother sinusoidal current waveforms with lower torque ripple, which lead to reduced noise.

    Regards,
    Eric C.

  • 0 in reply to Eric Chen
    Prodigy 30 points

    Hi Eric,

    1) I confirmed that my motor has 1 pole pair and ideally operates around 91,000 RPM. Based on your answer above, it looks like this will fall into the operational region for the electrical frequency. This application will have the drive electronics directly in series with the air flow created by the turbofan (and its a lot of air), so I'm hopeful that thermal management won't be too tricky. I'll look at the MCF8316A first

    2) They do use trapezoidal commutation, so I'm looking forward to testing it out.

    Follow up question:

    What is the easiest way to test out the MCF8316A with this BLDC motor? Is the evaluation board (MCF8316AEVM) the best route?

  • +1 in reply to Chris Esser
    TI__Genius 9210 points

    Hi Chris,

    1. Again, MCF8316A on the EVM can operate at ~70W continuously on the EVM. Anything higher may risk triggering device overtemp warning/shutdown. The thermal limit and device's maximum sustainable power output may vary depend on board layout design, ambient temp, airflow, active/passive cooling, etc.

    Yes, the MCF8316AEVM is the best route to evaluate performance.

    FYI, the latest MCF8316AEVM should come populated with the newer device version MCF8316C, which has some bug fixes and feature enhancements.

    Regards,
    Eric C.