Flux Control Modulation for Three-Phase Dual-Active-Bridge DC-DC Converters

Abstract

Flux control modulation (FCM) is a frequen-cy-variable modulation technique that has been originally in-troduced for the single-phase dual-active bridge (DAB). The peak flux linkage in the transformer decreases with increasing power, allowing the switching frequency to be reduced, which lowers the switching and conduction losses in contrast to the traditional single phase shift (SPS) modulation that operates at constant frequency. This paper derives FCM for the three-phase DAB. It is shown that all advantages of FCM also apply to the three-phase topology. In comparison with SPS modulation, FCM not only lowers the switching and conduction losses of the converter, but also allows a larger power rating without any increase in conduction or switching losses, while never violating saturation boundaries. Moreover, significant overload capabilities are possible with FCM. Thus, FCM has a great potential to increase the efficiency, the power rating, and overload capabilities in dc power distribution systems and high-power applications in general. The findings are validated by experiment, revealing 26 % lowered full-load losses in contrast to SPS modulation.