A high power density and power factor cascade buck-boost PFC under expanded high line voltage

In this paper, a control method to achieve a high power density and improve the power factor (PF) in the light load conditions for a voltage range of 180~305Vac using a cascade buck-boost PFC converter is proposed. Recently, the requirement of a 277Vac for an input voltage rather than a 240Vac has been increased in a power distribution stage. The output voltage of the PFC stage of the conventional boost PFC converter, which is widely used for the PFC stage, is increased to 450V under a voltage range of 180~305Vac compared to the output voltage (400V) under a voltage range of 180~264Vac, i.e, nominal 240Vac. Therefore, the volume of the output capacitor is also increased compared to a existing voltage range of 180~264Vac, which reduces the power density of the PFC stage. Moreover, the conventional boost PFC converter has a poor PF in the light load conditions due to the phase leading input current caused by the input capacitor. To overcome these problems, this paper proposes the control scheme using a cascade buck-boost PFC converter in order to achieve the conventional output voltage (400V) under a voltage range of 180~305Vac. Therefore, a smaller output capacitor can be used in the proposed method and achieve a high power density. Also, with proper control of an additional switch (Q1), the phase leading input current can be relieved. The concept and principles are explained and the performance of the proposed method is verified by the prototype converter with 800W conventional output (450V, 1.78A) and proposed output ( 400V, 2.00A).