Dual-Mode Isolated DC–DC Converter With Fixed-Frequency Circulant Duty Cycle Modulation for Wide Input Voltage Range

This article proposes a dual-mode isolated dc–dc (DMIDC) converter for wide input voltage range applications. Under the fixed-frequency circulant duty cycle modulation, the two operation modes of the converter and the output voltage regulation can be achieved by only controlling the total duty cycle of all lower switches of the half bridge modules (HBMs) in each bridge arm as a single control variable. Also, self-balancing of HBM capacitor voltages and zero-voltage switching of all switches can be realized. The interleaved parallel structure based on series-connected HBMs reduces input current ripple and lowers the voltage stress of switches. Compared with the LLC resonant converters with variable structure and variable frequency control, the proposed scheme only needs to control the total duty cycle without the need for other control variables and additional input voltage sampling circuit to achieve mode transition within a wide input voltage. Moreover, compared with other wide voltage range resonant converters, the proposed DMIDC converter not only has better load characteristics but also has lower voltage stress on primary devices. Finally, the performance of the proposed DMIDC is validated through experiments on a 400 W prototype with 75–300 V input and 330 V output.