cspurr
Newbie level 1
I am doing some testing on an electric golf cart that uses an AC drive with a VFD. When the VFD is engaged via the gas petal, a relay is sealed in which applies power to the VFD. When this occurs, a huge amount of what I am thinking is common mode coducted noise is being conducted back onto the 48V battery pack DC supply. Measuring differentially, there is no significate noise, measuring referenced to earth (not sure what other reference I could use on a golf cart) as soon as the VFD is engaged, a huge 10vp 8KHz, almost squarewave is measured. The 3rd and 5th harmoic are also signigicant. I assume this is the fundamental switching frequency of the VFD, but I have not dug into that. Assuming it is conducted noise and not massive radiated, how can it be squashed? Most commercial common mode chokes are designed for much higher frequencies and present hardly any siginificant impeadance at 8KHz. There is no other reference such as earth to shunt it to? Exuse my ignorance or assumptions. I have tested with the scope probe streched out in the area of the cart to see if it is mostly radiated, and it does not seem to be. I have attached the probe to both the + and - sides of the batteries, earth referenced, and the noise only shows up when the VFD is enaged (a relay picks up and supplies power to the VFD, that is what I am referring to as engaged). Any ideas what could be done to remove this hugh swinging, relatively low frequency common mode signal? Again, excuse my ignorance or assumptions, I by no means consider myself a expert HW engineer. Thanks for any info you can provide and it is always appreciated.
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Here is a scope capture of the waveform and FFT.
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Here is a scope capture of the waveform and FFT.
