A simplified approach to input voltage balancing for series connected isolated DC-DC converters

The interleaved multilevel DC-DC converters have advantages of low voltage stress of the switches and diodes and reduction of filter size. Particularly series input parallel output (ISOP) configuration is well suited for high output voltage and large output current application but input series output series (ISOS) configuration enable the utilization of low voltage rating switches in high voltage input and high voltage output applications that require galvanic isolation. The series connection of the isolated DC-DC converters at the input side also can be used for higher voltage application. While multilevel topology offers many new features, it also necessitates a balance control of the input capacitors. The paper describes the operating principles of the balancing circuit, analyzes the fundamental relationships, introduces principles of the operation of the circuit. The paper shows experimental results based on a few practical application examples. The paper discusses design of the transformer with balancing winding for ISOP, ISOS and parallel connection of the DC-DC converters to provide independent voltage balancing of input capacitors.