Analysis and Design of an Isolated High Step-Up Converter Without Voltage-Drop

This article presents a precise derivation of the prevalent voltage-drop problem in pulsewidth modulation high step-up converters with a transformer-based voltage multiplier. The corresponding solution is proposed and analyzed with an isolated interleaved full-bridge high step-up converter as an example. By introducing a resonant capacitor, the improved converter solves the voltage-drop problem caused by the reverse recovery process of the leakage inductor. Meanwhile, the zero-current switching condition is achieved for output diodes due to the resonance between the leakage inductor and the resonant capacitor. Moreover, the proposed solution can be extended to other high step-up converters with voltage-multipliers utilizing transformers or coupled inductors. The voltage-drop problem is analyzed in detail first, followed by the operational principles and steady-state analysis of the improved converter. Experimental results based on a 450-W laboratory prototype at 25-kHz switching frequency verify the validity of the theoretical analysis.