A modular DC-DC converter with collapsible input voltage of series connected modules without additional bypass switch

Modular DC-DC converters have been used in high power applications to increase both the maximum power and voltage ratings of DC-DC converters. In parallel-connected modular DC-DC converters, light-load efficiency has been reported to improve by shutting down unnecessary modules. In this paper, low voltage efficiency of series-connected converter is improved by shutting down modules to shift the input voltage of the remaining modules to higher values for higher efficiency. Moreover, minimum input voltage of the converter is also reduced and input voltage range is therefore increased. The collapse of input voltage is required during this process and energy stored in the input bus capacitors has to be discharged. The focus of this paper is to use available switches in the modules as bypass switches. A method to control these switches for operation within their safe operating area (SOA) during this process is discussed. Finally, a modular DC-DC convert prototype with input series and output parallel (ISOP) connections is built to verify this concept.