Enhanced Analysis and Optimization of Active-Clamped Forward-Flyback for Highly-Efficient Step-Up Photovoltaic Systems

Abstract

The Active-Clamped Forward-Flyback is a topology suitable for photovoltaic applications, since it offers high efficiency across wide input/output voltage and power ranges, zero-voltage switching (ZVS) on all the switches and zero-current switching (ZCS) on the secondary side devices, while allowing high power density due to the forward energy transfer capability. However, the studies presented in the literature do not fully exploit the potential of this topology. This paper provides an in-depth analysis of its behavior that also considers the parasitic capacitances of the switches and establishes the conditions for achieving both ZVS and ZCS. In contrast to the prototypes reported in the existing literature, the proposed implementation makes the topology resonant by using a secondary-side capacitor, thereby reducing circulating currents and decreasing the number of components relative to prior solutions. Furthermore, it presents a detailed study of the current dip effect, not previously discussed in the literature, caused by the ratio of secondary to primary switches capacitances, which significantly impacts RMS currents and overall efficiency. The comprehensive analysis enables the design of a high-efficiency, high-density prototype, which is validated through a 480 W converter capable of operating with input voltage range of 24-48 V and output voltage range of 300-400 V, achieving a peak efficiency of 98.42% and a power density of 101.48 W/$in^{\mathrm{3}}$.