A multi-level AC or DC-DC converter using self-bypassable fixed transfer ratio modules

An AC-DC or wide-range DC-DC converter using single-active-stage, isolated modules in an input-series and output-parallel stack is presented. Individual modules are operated with a fixed input-output transfer ratio, which results in a high efficiency. A varying portion of the modules are either inserted or bypassed in the stack to provide an overall transfer ratio adjustment for the converter system. The novelty of the method is in the self-bypassing of modules without the need for external switches. This is done with a loss-free discharge of the module input dc links through an auxiliary circuit followed by placing the module switches in a cross-conduction mode. Simulation and experimental results are presented. The approach can be particularly useful for medium voltage AC-DC or DC-DC conversion in applications such as EV fast chargers.