Multivariable-Modulation-Based Conduction Loss Minimization in a Triple-Active-Bridge Converter

This article presents the design, development, and optimization of pulsewidth modulation (PWM) scheme of an isolated bidirectional triple-active-bridge (TAB) dc-dc converter composed of three full-bridge modules and a high-frequency planar transformer. This article aims at improving the efficiency of the TAB converter by means of conduction loss minimization. The approach utilizes multiple control variables as degrees of freedom for the converter modulation. The optimization is based on the minimization of the true rms current, formulated using generalized harmonic approximation technique. The approach constitutes of two steps: the modulation pattern with least algorithmic complexity for efficiency maximization is first found depending on the operating load and gain condition, and, subsequently, the optimum control variables are calculated using the gradient descent algorithm applied on the identified modulation pattern. An 800-W TAB converter proof-of-concept is built to verify all theoretical considerations and model-oriented analysis. While the converter has an input dc bus voltage of 160 V, the two output ports of the converter can deliver 400 W each at voltage levels of 110-130 V and 18-27 V, respectively. With the implementation of the proposed optimal phase-duty control, the experimental results show a nonunity gain light load efficiency increment up to 6.1% compared with the conventional modulation technique.