The Primary-Side Regulation of Active-Clamp Forward Converter with On-the-Fly Output Voltage Variation

Primary-side regulation (PSR) methods have limited applicability in DC-DC converters with output inductors, such as forward converters, due to low regulation accuracy and the inability to adjust the output voltage during operation. This paper proposes a novel PSR method that accurately estimates the output voltage of an active-clamp forward converter (ACFW) to overcome these limitations. The estimator models the output voltage as a polynomial function of input power, input voltage, and clamp capacitor voltage, which are all sensed at the primary side. The polynomial is derived from high-resolution simulations and its order is optimized to minimize the computational burden on the microcontroller. The error of the output voltage regulated by the polynomial is <1% under parameter variations of ±20%. The proposed method is also capable of varying output voltage during converter operation, i.e., on-the-fly output voltage adjustment. A small-signal model is presented and validated by simulation in order to support controller design. Experimental results with a 100-kHz, 200-W ACFW hardware prototype confirmed that the proposed PSR method has 99.8% accuracy during the steady-state operation.