Comprehensive analysis and comparative evaluation of the isolated true bridgeless Cuk single-phase PFC rectifier system

In the public low voltage mains the stress caused by harmonic currents is strongly increased due to the higher demand of electronic equipment in everyday use. Therefore, standards were created in order to limit the harmonic currents injected into the network, thus maintaining a high voltage quality of these networks. Hence, converter systems with active PFC are indispensable, where in general the compliance of the created directives for lower harmonics can be easily fulfilled. Typically, in single-phase systems, boost PFC converter topologies are used, which offer a wide input voltage range and a controlled output voltage. Depending on the underlying applications, a subsequent reduction and/or isolation of the output voltage based on a DC/DC-converter is needed. The major disadvantages of this converter cascading are the reduction of the overall efficiency, the large component count and the increasing control complexity. In comparison to the conventional two-stage PFC converter system, the true bridgeless Cuk PFC rectifier system can perform the PFC functionality and the galvanic isolation in a single-stage, thus eliminating the mentioned disadvantages. In this paper a comprehensive analysis of the operation, design and limits of the recently proposed single-stage Cuk concept is investigated. In addition, a comparative evaluation concerning efficiency and power density against a conventional two-stage approach based on bridgeless PFC rectifier and a subsequent LLC-resonant DC/DC-converter is presented.