Optimal Utilization of the Dual-Active Bridge Converter with Bidirectional Charge Control

Abstract

This study describes a new method to optimize the utilization of the dual-active bridge converter. The optimized DAB converter utilization is defined as the maximum power displacement per Ampere of RMS current flowing through the inductor, a design target that encompasses both the control parameter (power displacement) and the quantity responsible for the majority of the losses in the converter (inductor current). Various studies have already described the minimization of the inductor current in the dual-active bridge converter, thereby employing less efficient fixed-frequency and dynamic incapable phase-shift control strategies. Bidirectional charge control though, is a recently proposed control strategy that comprises excellent dynamic behaviour and has the potential to facilitate variable-frequency operation. In order to optimize the variable-frequency operation, this paper discusses the DAB converter utilization for a fixed frequency to determine its dependency on the switching events so that this optimum can then be used with a variable frequency. Therefore, bidirectional charge control is used to describe the power displacement and the RMS current flowing through the inductor as a function of both the primary and secondary switching event. It shows that the DAB converter utilization has an optimum depending on only three variables, i.e. the primary and the reflected secondary voltage. This is demonstrated both quantitatively (numerical) and qualitatively (analytical), after which identical results are acquired through simulation. Moreover, component non-idealities that complicate the implementation and verification of the desired control, are described and included in the simulations. Finally, countermeasures for the non-idealities are both described and verified. To further explore the feasibility of the optimal utilization of the DAB converter, it should be investigated in an experimental manner in addition to the discussed simulations.