Efficiency and THD Optimization Based on an Interleaved PFC Converter Using Digital Controller with Integrated Valley Switching Control Feature

In this paper, a digital control optimization solution is presented to increase interleaved PFC converter performance especially the light load efficiency and THD for an interleaved PFC converter. This does not require any complex external logic. When a PFC converter is under discontinuous conduction mode (DCM), the resonation can happen between the parasitic capacitance and the PFC inductor. This usually occurs under light load condition. Depending on the instantaneous input voltage, the MOSFET needs to be turned on at the valley point or zero voltage crossing point of the Vds in order to get higher efficiency and lower THD. The proposed optimization method utilizes the both feature of integrated programmable valley of the digital controller and mathematical model of PFC converter to easily implement the valley switching and ZVS. The valley skipping is selected to maintain a relatively low switching frequency by the presented integrated programmable valley switching technique to get better light load efficiency. When the instantaneous voltage is very low, an enhanced control method which uses fixed frequency control is adopted to avoid the current distortion. The hardware test is based on a Texas Instruments microcontroller which contains integrated programmable valley switching feature. A 750W interleaved PFC converter is used in the experiment.