218VDC TO ALTERNATING CURRENT

You need custom inverter circuit that will synchornously boost the 218VDC to a step up tranformer. It is not a simple circuit but a complex one.

Did you calculated maximum current output?

Best way to have an AC transformer with step up facility. However, have a decent knowledge about what  is the output frequency you require.

THen simply use a transformer and convert it from available wall output voltage to the required AC voltage. Simple, cost effective and will do the Job.