Switching Network Loss Minimization through Multivariable Modulation in a Multi-Active Bridge Converter

This paper presents a unified and generalized modeling, circuit analysis and power flow optimization techniques for a n-port multi-active bridge (MAB) dc-dc converter comprised of n active full bridges and a multi-winding transformer. The work aims at improving the efficiency of the MAB converter for a wide load and port voltage gain range by proposing an optimal phase-duty control variable-based modulation strategy. The loss optimization technique constitutes of two stages: firstly, both the switching and conduction loss objective functions are equivalently formulated by relating them to the transformer winding current peaks and RMSs that are synthesized by employing the proposed generalized harmonic approximation (GHA) based computational model; secondly, a multivariable multi-constrained optimization technique is adopted in order to minimize the converter power loss for wide load-gain range. Moreover, the universal zero-voltage switching (ZVS) criteria for any MAB port is also derived by proposing a port-equivalent converter model. A 600W quadruple active bridge (QAB) converter proof-of-concept is designed and tested to validate the theoretical analysis, claims, thus verifying the applicability of the generic MAB loss optimization technique for any converter candidate under the MAB family. With the implementation of proposed optimal phase-duty control, the experimental results show efficiency increment up to 17% at non-unity voltage gain and 10% loading condition, when compared to the conventional phase modulation technique.