Multiphase Isolated DC-DC Converters for Low-Voltage High-Power Fuel Cell Applications

Multiphase isolated dc-dc converters allow current sharing among phases and high-frequency ripple cancellation and are very desirable for low-voltage high-power fuel cell applications. The three-phase dc-dc converters particularly are getting more attention because they share the same circuit structure as the conventional three-phase dc-ac inverters, and they have been reported to have high-efficiency operation. This paper is to compare the similarities and differences between two soft-switched three-phase dc-dc converters: one with three phase legs and the other with six phase legs. This paper will describe basic operating principle of these two multiphase dc-dc converters and compare their performance for a low-voltage, high-power fuel cell application. Two 5-kW converters have been built and tested with a fuel cell simulator. Experimental switching waveforms and efficiency profiles are shown to support the described basic principles. Major features and differences between these two converters will be discussed.