Your banana looks like a basjoo, however the raised bed will certainly cause problems for you overwinter. I don't think even a basjoo would be hardy in an above ground location for winter in your zone. That would be basically the same as having it potted. Above ground potted= death in cold areas left outside.
Your best bet in my opinion would be to bring it in potted for the winter, put it in the sunniest window you have, and keep it on the dry side (water wise) over winter. Increase humidity by sitting your pot on a tray of pebbles and water to help keep down spider mites.
If your banana was planted directly in the ground and it was a basjoo, then my advice would change.
Here's a link to my e-bay guide about growing potted bananas indoors.
http://cgi.ebay.com/ws/eBayISAPI.dll...m=190155033143
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Sandy Burrell
Northern Tropics Greenhouse
1501 East Fuson Road
Muncie, IN 47302
www.northerntropics.com
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