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A switching control strategy to control the power flow and minimize the total power losses of the dual active bridge converter topology is proposed in this paper. The control strategy consists of driving the bridge with the largest dc voltage to generate a three-level pulsewidth-modulated (PWM) voltage waveform. This PWM is ruled by two manipulated variables: the phase shift between the primary and secondary transformer voltages and the modulation index. These variables are calculated using an algorithm that is deduced on the basis of particular calculation and analysis of converter losses, which are also presented in this paper. An experimental prototype was implemented to validate the theoretical analysis and feasibility of the proposal. The experimental results revealed that the overall efficiency of this converter can be improved up to 10% using the control strategy instead of the conventional one.

This paper presents a boundary control scheme for dual active bridge (DAB) converters using the natural switching surface (NSS). The implementation of a curved switching surface for DAB converters is a new area of research undertaken in this paper. The proposed technique brings the benefit of unprecedented dynamic performance, already developed for nonisolated topologies (e.g., buck and boost), to this more complex isolated topology. The analysis provides insight into the natural trajectories of the DAB converters and creates an accurate framework in the normalized geometrical domain. As a result, the physical limits of the converter under study become evident. Those physical limits are exploited by employing the NSS to obtain fast transient response under start-up, sudden load transients, and reference change. In addition, fixed-frequency operation is one of the key features of the proposed control scheme, which allows optimizing the design of the high-frequency transformer. Experimental results are presented to validate the NSS for DAB converters and illustrate the benefits of the normalization technique. Index Terms-Boundary control, dc-dc isolated converters, dual active bridge (DAB) converter, natural switching surface (NSS).

Dual Active Bridge (DAB) converters enable bidirectional power flow in buck and boost operating modes. This paper presents an advanced switching sequence and burst mode strategy to balance conduction, switching, and magnetic losses under light, medium, and heavy loading conditions, leading to improved operating efficiency. The implementation of the switching sequence employs the natural state-plane trajectories of the converter and contributes to higher efficiency and the ability to perform burst-mode. The proposed switching sequences improve the overall efficiency of the converter by enabling soft switching and adjusting the frequency to match the minimum RMS transformer current in the full operating range. Furthermore, it incorporates a fully controlled burstmode switching sequence for light loading conditions to further extend the efficiency gains. As a result, maximum efficiency is obtained by taking advantage of all the possible switching structures of the converter. The analysis provides insight into the natural trajectories of the converter, which produce softswitching transitions and enable the converter structures to achieve the target operating point directly. Simulation and experimental results are presented to validate the benefits of the switching sequence and illustrate the burst-mode operation.