Modelling and Control of Active Clamp Forward Converter with Centre Tap Transformer

This paper presents the small-signal model, controller design, open-loop, and closed-loop analyses of an active clamp forward converter with centre tap transformer (ACFCC). The centre tap transformer provides full-wave rectification at the secondary side of transformer to form a quasi-integrated topology. A clamp circuit comprises an auxiliary switch and a capacitor is used to recycle the energy stored in the transformer magnetizing inductor. However, due to the presence of the clamp circuit and the centre tap transformer, the active clamp forward converter exhibits a fourth-order power-stage dynamics. The circuit averaging technique is applied to extract the small-signal model of the power stage. Based on this model, frequency domain approach is used for stability analysis. The distinctive power-stage dynamics of the ACFCC is addressed and a feedback controller is designed accordingly. The small-signal model and experimental results with voltage-mode control applied to ACFCC are presented.