Optimal Switching Frequency Variation Range Control For CRM Boost PFC Converter

As the inductor of the boost power factor correction(PFC)converter is in series with the input terminal,the input current is continuous and the input power factor is relatively high over a wide input voltage range.In addition,the source of the switch is connected to the ground and the drive realization is simple.Therefore,it is widely used in the field of power conversion.Depending on the inductor current to be continuous or not,there are three basic operating modes: discontinuous conduction mode(DCM),critical conduction mode(CRM)and continuous conduction mode(CCM).Featuring zero-current turn-on of switch,no reverse recovery in diode and unity PF,boost PFC converter is widely used in low to medium power applications,and the power level is between DCM and CCM.However,the switching frequency of the converter varies in a wide range,especially at high input voltages,for which the ratio of the maximum to the minimum is more than ten.Furthermore,in a half line cycle,the switching frequency has an overall change with different output power.This not only complicates the design of components such as filters,but also increases the loss of switch and inductor,and affects the efficiency.For the issues mentioned above,a method of injecting some third and fifth harmonics into the input current to reduce the variation range of switching frequency is proposed in this paper,and the harmonics meet the IEC 61000-3-2 Class D standard.However,the reduction of the switching frequency variation range is realized at the cost of the PF.Therefore,a compromise scheme taking PF and switching frequency both into consideration is further put forward.The minimum switching frequency variation range and the corresponding optimal harmonics with different PF value limits are revealed.In addition to a lower frequency range,the proposed control method achieves the output voltage ripple reduction and the efficiency improvement as well.A prototype is built in the lab and tested with the two control methods over a wide input voltage range.The feasibility and effectiveness of the proposed method is verified by the experimental results.