Research On Boost PFC Converter Operating In Pseudo Continuous Conduction Mode

Power factor correction (PFC) technology which is an indispensable component of the electrical equipment supplied by power system can effectively reduce the current harmonics and improve the power factor. Boost converter is widely used as PFC circuit because of many advantages, such as the simple topology, high efficiency and easily achieved control strategy.Boost PFC converters are generally designed to operate in discontinuous conduction mode (DCM) or in continuous conduction mode (CCM). However, it is known that the converter suffers from restricted load range in the two operation modes. Pseudo continuous conduction mode (PCCM) is a novel operation intervened between DCM and CCM. Compared with DCM Boost converter, the PCCM Boost converter has a smaller voltage and current ripple, resulting in greater capacity of taking heavy load. Besides, there is no right half plane (RHP) zero in the control to output transfer function which, however, exists in CCM Boost converter. So the PCCM Boost converter exhibits a very attractive feature on transient response. On the whole, PCCM is a novel mode with excellent performance.A novel PFC converter operating in pseudo continuous conduction mode is proposed in this paper. On the premise of studying PCCM Boost PFC converter, two side-by-side loops are established and designed to control the typical two degrees of freedom. To extend the load range of Boost PFC converter, the point that the average inductor current is higher than the average input current in PCCM is perfectly utilized, which is meet by calculating and adjusting the reference valley value of inductor current on the basis of load current. Based on which, the digital valley current control strategy of current loop and PI compensation of voltage loop is designed.To verify the theoretical analysis, the PCCM Boost PFC converter has been simulated and compared with the Boost PFC converter operating in CCM and DCM controlled by conventional technique. Simulation results show that, when the Boost PFC converter operates at high output power, the inductor current peak value in DCM operation is much higher than that in PCCM and DCM operation, which would obviously ehance the switch and EMI cost. The PCCM and CCM Boost PFC converter with low inductor current peak value and ripples have good performance for high-power application. On the other hand, if the output power is reduced, the PCCM Boost PFC converter could regulate the reference valley value of inductor current in time and keep stable operation mode, and then have sinusoidal input current. However, the input current of CCM Boost PFC converter at low output power is non-sinusoidal, resulting in a relatively low power factor. Therefore, when the overall performance including power factor, switch current stress and EMI is taken into account, the PCCM Boost PFC converter exhibits more excellent capability for wide load range application.The performance of PCCM Boost PFC converter and CCM Boost PFC converter is compared and verified by using an 70W～400W experimental prototype.