A photovoltaic power conditioning unit for delivering power from a dc power source to an ac mains power supply output , the power conditioning unit comprising: a dc power input to receive dc power from said dc power source ; an ac power output for delivering ac power to said ac mains power supply ; a dc link coupled between said dc power input and said ac power output; a first dc-to-dc converter coupled between said dc power input and said dc link ; a second dc-to-dc converter coupled between said dc power input and said dc link ; and a dc-to-ac converter coupled between said dc link and said ac power output; wherein each of the first and second dc-to-dc converter comprises: a transformer (608a,b) having an input winding and an output winding; an input dc-to-ac converter (606a,b) coupled between said dc power input and said input winding of said transformer; an ac-to-dc converter (610a,b) coupled between said output winding of said transformer and said dc link; and wherein said output winding of said transformer has a winding tap between first and second portions of said output winding, and wherein said ac-to-dc converter comprises: first and second rectifiers , each connected to a corresponding first and second output inductor and to said winding tap; and wherein the first and second output inductors are each connected in series with an output of the corresponding first and second rectifiers, wherein the outputs of the first and second output inductors are each connected to a respective said first and second portion of said output winding, and further connected to said dc link. a dc power input to receive dc power from said dc power source ; an ac power output for delivering ac power to said ac mains power supply ; a dc link coupled between said dc power input and said ac power output; a first dc-to-dc converter coupled between said dc power input and said dc link ; a second dc-to-dc converter coupled between said dc power input and said dc link ; and a dc-to-ac converter coupled between said dc link and said ac power output; a transformer (608a,b) having an input winding and an output winding; an input dc-to-ac converter (606a,b) coupled between said dc power input and said input winding of said transformer; an ac-to-dc converter (610a,b) coupled between said output winding of said transformer and said dc link; and wherein said output winding of said transformer has a winding tap between first and second portions of said output winding, and wherein said ac-to-dc converter comprises: first and second rectifiers , each connected to a corresponding first and second output inductor and to said winding tap; and wherein the first and second output inductors are each connected in series with an output of the corresponding first and second rectifiers, wherein the outputs of the first and second output inductors are each connected to a respective said first and second portion of said output winding, and further connected to said dc link. first and second rectifiers , each connected to a corresponding first and second output inductor and to said winding tap; and wherein the first and second output inductors are each connected in series with an output of the corresponding first and second rectifiers, wherein the outputs of the first and second output inductors are each connected to a respective said first and second portion of said output winding, and further connected to said dc link. <EOS>