A high step-up isolated forward–flyback DC–DC converter with pulse frequency modulation (PFM) is presented in this paper. The proposed converter has features of both a forward and a flyback converter and can deliver energy during the turn-on and turn-off intervals in a switching period. In addition, by utilizing resonance it can achieve zero-voltage switching (ZVS) for the primary switches and zero-current switching (ZCS) for the secondary rectifier diodes. All of the power semiconductors operate under soft switching conditions. The structure of the proposed converter is simple and easily implemented. It also provides a high step-up voltage gain. The current stresses of the power devices in PFM are lower than those in pulse width modulation (PWM). Therefore, the converter efficiency in PFM is higher than that in PWM. The operation principle and characteristic of the presented converter are described in detail, and the converter performances for PWM and PFM are compared. A 160 W hardware prototype has been built, and experimental results verify the validity of the theoretical analysis.

本文介绍了一种具有脉冲频率调制（PFM）的高升压隔离正激-反激DC-DC转换器。所提出的转换器具有正向和反激转换器的特征，并且可以在开关周期的导通和关断间隔期间传递能量。此外，通过利用谐振，它可以实现初级开关的零电压开关（ZVS）和次级整流二极管的零电流开关（ZCS）。所有功率半导体均在软开关条件下工作。所提出的转换器的结构简单且易于实现。它还提供了较高的升压电压增益。PFM中功率器件的电流应力低于脉宽调制（PWM）中的功率器件。因此，PFM中的转换器效率高于PWM中的转换器效率。详细介绍了该转换器的工作原理和特性，并比较了PWM和PFM的转换器性能。已经建立了一个160 W的硬件原型，实验结果验证了理论分析的有效性。