Method for conversion


Extract .vmdk from OVA using 7zip.
Install Virtualbox
Run from command line : VBoxManage.exe" clonemedium --format vhd infile.vmdk outfile.vhd

or for older versions of Virtualbox

VBoxManage.exe" clonehd --format vhd infile.vmdk outfile.vhd

2. qemu-img for windows
Great command line tool to convert from ova to vhd or vhdx

3. CloneVDI
There is a free GUI program out there called CloneVDI that does not require any command line and has a few extra options. Did not used this one yet.