Isolated DC/AC Converter with ZVT based on Pulsating DC Link

An isolated DC/AC converter based on Pulsating DC Link principle is presented. It includes a H-bridge stage, operated in Phase Shift mode (PS), feeding the primary winding of the insulating transformer, followed by a full-wave rectifier, fed by the secondary winding of the transformer. The rectifier is connected to a pulsating DC link which feeds a three phase inverter stage. The switches of the inverter are turned on and off during the free-wheeling phase of the PS-H-bridge when the voltage on the dc-link is zero allowing the switches of the inverter stage to commutate in fully ZV conditions. Due to the absence of a large dc-link capacitor, an active-clamp network provides a clamp of the voltage across the inverter stage. An FPGA based modulation logic is also presented. It is conceived to perform the change of the pattern during the free-wheeling phase of the first stage. The proposed topology is typically aimed to convert a DC power to a line-frequency AC power, as required, for example, in photovoltaic applications. This solution allows us to obtain at the same time: galvanic isolation, reduction in weight and cost of the transformer in comparison with standard inverter solutions which adopt a line-frequency transformer, and high overall efficiency due to soft-switching operations of each switch of the circuit.