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UCC28710: Isolation for BLDC Inverter

stomp
Genius 4675 points
Part Number: UCC28710
Other Parts Discussed in Thread: UCC28740

Hi,

We have used with great success the UCC28710 in several designs.

We are now building a universal input 3kW BLDC Inverter with TI's InstaSPIN Technology and wish to use the same Isolated UCC28710 design but...

A glaring problem has come up that does not seem to be easily solved: Our H-Bridge / DC Link Bus (310VDC) is powered directly from the Bridge Rectifier, the same rectifier feeding the UCC28710.

To keep the grounds the same (digital ground output from transformer and power ground from rectifier) we need to bridge the power and digital grounds that would otherwise be separated at the transformer by a isolation capacitor. The obvious issue is that doing this will break the isolation.

My question is more general in how do people approach this problem of both needing an isolated power supply for a whitegoods product, and having a high-voltage Inverter where the current and voltage sense as well as gate drive is ground referenced, without trying to implement very complex isolation?

Any pointers would be great.

Thanks

Stomp!

  • 0
    TI__Expert 7395 points
    Stomp,
    Thanks for the interest in TI and your continued use of UCC28710. Typically we see people use Y-rated caps connecting the grounds of isolated designs. This is also used for common mode EMI. So if there are multiple grounds they will use Y-rated caps between each of them.
    Like in this example: www.ti.com/.../PMP10468
    I hope this helps.
    Regards,
    John
  • 0 in reply to John Stevens
    Genius 4675 points
    Thanks John,

    Is there any reason in the operation of the UCC28710 that would prevent me from joining PGND and DGND to make a non-isolated supply?

    I understand the EMI and product safety risks, and we are looking at the necessary physical protection schemes for a non-isolated product per IEC60950.

    Thanks
    Stomp!.
  • 0 in reply to stomp
    TI__Expert 7395 points
    Stomp,
    Sorry for the delay here with the holiday season. The UCC28710 can still operate normally with the grounds connected. As long as the Vs signal and Cs are clean and good general layout and design practices are followed the controller doesn't really see the difference. If it is a non-isolated supply though you always have the option also to connect the output directly to the feedback of the controller like using UCC28740 as a non-isolated flyback.
    Regards,
    John