A Novel Control to Achieve Optimal Reduction of the E-Cap's Ripple Current for Discontinuous-Conduction Mode Boost PFC Converter

In a power factor correction (PFC) converter, an electrolytic capacitor (E-Cap), which has the advantages of a smaller volume and a low cost compared with other kinds of capacitors at the same voltage rating and capacitance value, is usually used to balance the difference between the pulsating input power and constant output power. However, the E-Cap has a bigger equivalent series resistance and the ripple current flowing through it will produce loss and heat, therefore, shortening its lifetime. So the E-Cap, a component that has the shortest life in a PFC converter, decides the lifetime of the power source. In this paper, the mathematical relationship between the root mean square (RMS) value of the E-Cap's ripple current and the converter's parameters are derived for a DCM boost PFC converter. The corresponding third input current harmonic is figured out for the optimal reduction of the RMS value of the high-frequency ripple current, so that the E-Cap's lifetime can be greatly improved. A method of fitting the duty cycle and the simplified circuit implementation are further proposed. Compared with the traditional control, the proposed minimum RMS value control also achieves an 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 120-W prototype are given to verify the effectiveness of the analysis.