Research On The Bridgeless Pfc Based On Sepic Converter

In order to restrain harmonic pollution and improve power system quality, power factor correction (PFC) circuit is applied in pre-stage of power supply. Conventional PFC topology is constituted by Boost circuit, whose control is complexity, output voltage is higher than input voltage and electrical isolation is difficult to achieve between the input and output. The PFC topology constituted by flyback circuit must work in discontinuous mode (DCM), and requires large electromagnetic interference (EMI) filter. And the power consumption of rectifier will increase gradually with the increase of power.Base on the advantages of Sepic circuit, such as isolation easy, EMI small and input current continuous, the working principles of the different modes of the traditional Sepic-PFC are analyzed in details in this paper firstly. It is noted that there are several problems in the traditional circuit, such as the great loss of the rectifier bridge structure, the reverse-current recovery under the continuous mode, and so on. To solve the above-mentioned problems, a new bridgeless Sepic-PFC circuit is presented. Based on the traditional Sepic power factor corrector, this new circuit utilize the bridgeless technique instead of the pre-rectifier in the corrector .In the process of turning on the switch, the input current only flow one diode, and it can effectively reduce the energy consumption in the conduction process.The circuit works in the current DCM, so the input current can not only automatically follow the input voltage, and reduce the EMI of the input circuit, but also make the switch turn on in the low-current state and the diode turn off in zero-current, which reduce the conduction loss of the switch and the reverse-recovery losses of the diode. In this paper, the working principle of the circuit and the formula derivation of key parameters are presented. And then the small-signal mode of the bridgeless Sepic-PFC circuit is derived, and control mode of the system is established. Finally, the simulation is carried out under the PSIM simulation software.According to the theoretical analysis above, the prototype of the bridgeless Sepic-PFC circuit is made, and the design method and experimental results are given. Experimental results verify that theoretical analysis and simulation results are correct.