Several topologies will be reviewed with reference to the grid connection (single-phase or three-phase) to the number of power converter stages employed (single-stage or multistage) and to the type of distributed source (mainly fuel cells, photovoltaic and wind turbine). Particularly the integration of the functions of different converters and the integration of the converter with the source will be analysed in detail. In the first case the dc-link regulation, the grid side control, the rectification/inversion and the voltage boost can be performed by one step-up inverter (for FC and PV) or by a matrix converter in case of WT-systems. In the

second case the integration of the converter with the distributed source (one converter for one source) is put in comparison with the centralized solution (one converter for all the sources). Particularly the

possibility to have different distributed sources (also mixed with batteries and/or ultracapacitors with a buffer function) connected to the same converter (e.g. multilevel converter) is also discussed.

Then the design of the grid side filter (LCL-filter) adopting different criteria (cost, encumbrance, mounting problem, immunity, stability and ripple rejection) will be discussed.