A novel variable duty cycle control to achieve optimal reduction of the electrolytic capacitor ripple current for DCM Boost PFC Converter

In power factor correction (PFC) converter, an electrolytic capacitor (E-Cap) is usually used, which has the shortest lifetime. The mathematical relationship between the root mean square (RMS) value of E-Cap´s ripple current and the converter´s parameters are derived in this paper for DCM boost PFC converter. The corresponding 3^rd input current harmonic is figured out for the optimal reduction of the ripple current RMS value so that the E-Cap´s lifetime can be greatly improved. A method of fitting the variable duty cycle and the simplified circuit implementation are further proposed. Compared with the constant duty cycle control (CDC), the variable duty cycle control (VDC) also achieves efficiency improvement as the critical inductance is increased and the peak and RMS current value of the power components are therefore decreased. The experimental results from a prototype of 120W are given to verify the effectiveness of the analysis.