In HOMER, the converter component generally models any device that converts power from AC to DC (rectifying) and DC to AC (inverting). Some devices are bi-directional, meaning that it can convert power flowing in either direction, either AC to DC or vice versa. 

Some systems will use two separate devices: a rectifier for AC to DC conversion, and an inverter for DC to AC conversion. You can model these two separate devices as one system converter component, with a cost equal to the sum of both components. 

Many systems, however, contain just a rectifier, or just an inverter, and not both.