I do not believe there is an OCX / DLL for directly communicating with an AC500, although I could be wrong. I believe you will have to talk either serially or over Ethernet. The AC500 appears to support Modbus/TCP. If yours already has Ethernet, great. Modbus/TCP can be written from scratch easily, or else you can get a DLL for it. If not, you'll have to find out more about how the AC500 talks serially or else add the Ethernet hardware to the PLC.
As always, your distributor / integrator / machine builder or the manufacturer / manufacturer's rep may be able to help you.