Parallel Fixed Switching Frequency CRM and DCM Boost PFC Converter with High Power Factor

Critical conduction mode (CRM) or discontinuous conduction mode (DCM) boost power factor correction (PFC) converter is widely used in low power applications for its advantages of zero-current turn-on of the switch, no reverse recovery in diode and simple control. The input current of fixed switching frequency control CRM boost PFC converter and the input current of constant duty-cycle control DCM boost PFC converter mainly contain third harmonic. Moreover, the phase of the third harmonics is opposite. This paper proposes a harmonic elimination parallel control to connect these two converters in parallel. The input current third harmonic of the parallel converter can be eliminated completely so as to improve the PF to nearly unity in the whole input voltage range. This parallel method is an interesting way to extend power, and is different from the existing method of parallel DCM boost PFC converter or parallel CRM boost PFC converter. The experimental results verify the accuracy of the theoretical analysis.