Optimized Modulation of a Four-Port Isolated DC–DC Converter Formed by Integration of Three Dual Active Bridge Converter Stages

Multi-port converters have gained more and more interest in research during recent years, due to the increasing field of possible applications, e.g., DC micro grids, energy distribution in electric vehicles and more electric aircraft, and power supplies for cascaded multi-cell converters. This paper presents an optimized modulation strategy for a bidirectional multi-port DC-DC converter, which consists of the Integration of Three (3) conventional Dual-Active Bridge (I3DAB) converters into a structure that combines the primary-side full bridges into a common three-phase two-level inverter. The resulting structure features one input port and three isolated output ports. By utilizing so far unused degrees of freedom for the control of the power converter, it is shown that a reduction of the power dissipation can be achieved by adapting the primary-side duty cycles to the output power levels. According to the outcome of a comparative evaluation of conventional and optimized modulation strategies for an example system with input and output port voltages of 700 V and 3 × 100 V, respectively, and with a total nominal power of 3 × 4 kW, reductions of the conduction losses of up to 23% and reduced additional hardware efforts to achieve ZVS operation (with regard to reduced transformers' magnetizing inductances) within wide power ranges are achievable and are also expected for deviating port voltages. Thus, in combination with the presented optimized modulation strategy, the I3DAB converter is found to be well suited to multi-port applications that require bidirectional conversion capabilities, galvanic isolation, and are subject to unequal load conditions with substantially different power levels provided by the output ports.