We have an electric vehicle with an on-board AC/DC charger for which we have designed a virtual ground at the output of the DC side to eliminate the common mode noise. (see attached picture for more info) We are currently connecting this virtual ground wire to the grid earth and it works fine. The question is can we route this virtual ground wire (16 AWG) along with other low voltage wires through a simple low voltage connector? If so, what would happen if one of the capacitors become short to the high voltage lines?
No, cannot , noise would start appearing in virtual ground from high voltage line, in normal working, and is dangerous in fault condition too...
Bhupendra,
Thanks for your reply.
Agreed. Do you expect to see current flow in case of fault? e.g. the capacitor shorts to HV and the virtual ground wire touches chassis.
--Kash
You will see high harmonic currents (noise). Your comment question, there will be no current flow since there is zero voltage difference.
I don't see why with properly specified components this would not be acceptable. Specify capacitors with a "Y" safety rating, which will make the probability of a short near zero. Y-rated caps are designed to fail open, and undergo rigorous safety agency testing to prove they are safe for line to ground use. As far as the wire is concerned, earth ground is considered safe, and in fact, your LV circuits must be operating near ground potential for safety.
That said, good design practice would have the ground wire run with the power wires. Consider the path the noise current follows. Returning the noise current separately results in a large loop that will radiate more than a properly routed line. You don't show an EMI filter on the AC side, but typically one would be included that would also have line-to-ground caps. I would consider connecting your DC side capacitors to this junction, which would allow the EMI current loop size to be minimized.
Keep in mind that the other concern with this EMI mitigation strategy is leakage current, which will limit the capacitors to fairly small values. With values dictated by safety specs, minimizing loop sizes and parasitic inductance becomes critical.
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