Stability investigation of the cascade two-stage PFC converter

A stability of the cascade two-stage Power-Factor-Correction converter is investigated. The first stage is boost PFC converter to achieve a near unity power factor and the second stage is forward converter to regulate the output voltage. In this issue, low-frequency instability is detected for some operating conditions that can not be detected by the prior linear models. Therefore, nonlinear model is proposed to detected and explain these instabilities. The borderlines between stable and unstable operation is made clear. It is cleared that feedback gain of the first stage PFC and the second stage DC/DC converters are large contribution parts of the total system stability.