Modular SEPIC-Based Isolated dc-dc Converter with Reduced Voltage Stresses across the Semiconductors

This paper presents the theoretical analysis, experimental results and generalized structure for N modules of an isolated dc-dc SEPIC converter. The structure comes from the integration of N conventional SEPIC converters based on the input-series and output-parallel connection. The main advantages provided by the proposed structure are reduced voltage stress across the semiconductors and division of the current stress in the output diodes. The proposed converter is presented in a generalized approach, varying the voltage stress across the semiconductors according to the number of modules used. As the converter uses more than one switch, the commands can be either equal or phase-shifted by 360 degrees /N degrees. When operating with phase-shift modulation, a multilevel converter is obtained, which brings another advantage of the structure, since there is a reduction in the volume of the input inductors (L-i(1) and L-i2) and the output capacitor (C-0). In this paper, the steady-state analysis, a dynamic model, system control and experimental results are presented for phase-shift modulation and discontinuous conduction mode (DCM). The performance of the proposed converter was verified in a prototype with four modules and the following specifications: 500 W output power, 800 V input voltage, 120 V output voltage and 50 kHz switching frequency. The converter achieved 94.42% efficiency at rated power.