Analysis and Improvement of Capacitance Effects in 360–800 Hz Variable On-Time Controlled CRM Boost PFC Converters

In critical conduction mode (CRM) boost power factor correction (PFC) converters, the input filter capacitor (IFC) is used to limit the propagation of switching noise into the ac line and the inherently existing parasitic capacitance of power semiconductor devices resonates with the boost inductor to achieve soft switching, which is voltage dependent and nonlinear. However, IFC leads to the crossover distortion of the rectified input voltage and thus the zero-crossing distortion of input current, which is ignored at the utility line frequency (50-60 Hz) since the effect of IFC is relatively small in this case. However, for wide variable frequency (360-800 Hz) power system, the effect of IFC becomes severe and unnegligible, which causes the deterioration of input current total harmonics distortion (THD). Besides, the nonlinearity of the parasitic capacitance is ignored and an equivalent constant linear capacitance is used in existing variable on-time (VOT) controls, which will cause the inaccuracy of VOT control, and thus, exacerbates the input current distortion. In order to improve the input current THD at high line frequency, this article proposes the IFC compensation method to minimize the effect of IFC and a variable parameter control is also achieved to suppress the effect of nonlinear parasitic capacitance. The experimental results of an 115-Vac-input 160-W/270-Vdc-output CRM boost PFC prototype are presented to verify the effectiveness and advantages of the proposed VOT methods. With the proposed methods, the input current THD is only 2.04% at 360 Hz input with full load and 3.14% at 800 Hz input with full load.