Second Harmonic Current Reduction Schemes for DC-DC Converter in Two-Stage PFC Converters

For the two-stage single-phase power factor correction (PFC) converter, its instantaneous input power pulsates at twice the line frequency, generating the second harmonic current (SHC) at the dc-bus port. The dc-dc stage is used to regulate the output voltage or the dc bus voltage in different applications, and the SHC reduction schemes for the dc-dc stage with different control objectives are discussed in this article. When the dc-dc stage regulates the output voltage, it is pointed out that the control bandwidth of the dc-dc stage is required to be high enough and the dc bus capacitor should be large enough to suppress the SHC, and the design of the dc bus capacitor is given. When the dc-dc stage regulates the dc bus voltage, a virtual impedance is added in series with the input/output of the dc-dc stage to suppress the SHC, and a virtual impedance is added in parallel with the dc bus to improve the dynamic performance. The selection and design of the virtual impedances are also given. Based on that, three specific control schemes are proposed for the dc-dc stage to suppress the SHC, and the parameters design method is also presented. Finally, a 3.3-kW two-stage single-phase PFC converter is fabricated and tested in the lab to verify the effectiveness of the proposed SHC reduction schemes.