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In this study, an isolated high step-up DC-DC converter with integrated cascade structure is proposed. The converter structure is equivalent to that of a cascade consisting of a boost converter and an isolated buck-boost converter. Compared with existing converters, the proposed converter can achieve a higher voltage gain with a lower transformer turn ratio. In addition, the integrated structure makes the controller more reliable and the system more compact. As the leakage inductance energy of the transformer is released to the output capacitors, the voltage spike caused by leakage inductance can be avoided, thereby reducing the voltage stress of the switches. Moreover, the zero-voltage switching (ZVS) operation improves the conversion efficiency and the continuous input current makes a small peak current. This study discusses the operating principles of the discontinuous and continuous conduction modes in detail. The theoretical derivation of the proposed converter is provided, and the ZVS principle and conditions are presented. Finally, a prototype circuit with 40 V input voltage, 500 V output voltage, and 200 W output power is implemented to verify the validity of the theoretical analysis and the performance of the proposed converter.

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