What is the difference between a front-end and a back-end converter ?

A front-end power electronic converter is a term used when a converter is connected to an ac mains/source either using a transformer or without using a transformer.

A back-end power electronic converter is one which is connected to the load. Such converter term is used frequently in a two stage power converter system.

In a two stage PV inverter system the inverter is called back-end power electronic converter whereas, the dc-dc converter connected with the solar PV module is called as front-end converter.