Recently, the use of rectifiers connected to network has increased. Since these rectifiers are nonlinear loads, they inject unwanted frequencies into network system. These harmonics create losses and overheating in transformers, excessive current in the neutral conductor of three-phase four-wire systems, distortion of the line voltage via the line impedance, electrical resonances in the power system, telephone interference, errors in metering equipment and reducing power factor. Therefore different standards are established to reduce these undesirable effects. So the use of PFC converters is compulsion. Conventional PFC converters have higher conduction Losses than rectifiers. For reducing conduction losses, the Power Factor correction block must be combined with DC-DC regulator or rectifier that the resulting converters are called single stage PFC and bridgeless PFC respectively. Since bridgeless PFC converters are usable in all electrical equipments that need to rectify AC voltage and the lowest conduction losses in all PFC converters, in this thesis soft switching techniques are used to further increase the efficiency. In literatures for reducing the switching losses the lossless snubbers, Zero Voltage Transition (ZVT) and Zero Current Transition (ZCT) techniques are applied to bridgeless PFC. Three soft switching Bridgeless PFC converters are introduced in this thesis. First proposed PFC converter prepares soft switching condition without any extra switch. This converter has fewer components than other converters that have not any extra switch. This converter is controlled by changing of switching frequency. Therefore EMI of this converter is reduced by distribution of EMI noise in frequency domain. A ZCT technique that has no extra stress on main switch is applied for second proposed PFC converter. This converter has lowest extra elements in soft switching bridgeless PFC converters. It can use any control strategy that is used in conventional PFC converter by adding three extra elements to control circuit. Therefore the conventional Pulse Width Modulation (PWM) control IC can be used. Third propose bridgeless PFC uses a ZVT technique for soft switching of all semiconductor devices. This technique has lowest conduction losses in auxiliary circuit because the number of elements that are in resonance path is reduced to two elements. It can use any control strategy that is used in conventional PFC converter by adding three extra elements to control circuit. Keywords: Power Factor Correction (PFC), Soft switching, Boost converter, Bridgeless PFC converter, Zero Current Transition (ZCT), Zero Voltage Transition (ZVT)
