Efficiency Optimization of Two Dual Active Bridge Converters Operating in Parallel

Abstract

Growing interest in dc-type energy storage systems (ESS) and dc/dc converters has led to increased power ratings of such devices, which often requires parallel connection. The process of energy efficiency optimization of such modular systems is described in literature mainly in terms of the varying power demand, but the problem is more complex and not analyzed yet in relation to varying energy storage (ES) voltage level and bidirectional energy transfer at the same time. Therefore, this article considers the input parallel output parallel (IPOP) connection of two dual active bridge (DAB) modules as a representative modular converter, and to answer a question of: how to improve (maximize) efficiency of such a system, at different power demands and varying ESS voltage, only by a turn on/off operation of the module without any circuit and control algorithm changes. The proposed solution defines an operating area (enclosing different ES's voltage levels and loading power conditions) showing where one or two modules should operate to improve the overall efficiency. A curve fitting approach and polynomial approximation of the single module's input/output power curves are utilized for the proposed algorithm based on parametric functions. After simulation study, the method is validated with two 1.4 kW SiC-based DAB converters, operating at 100 kHz of switching frequency within a wide (0-270 V) ES's voltage range.