## 1 Introduction
The backflow power also leads to higher current stress on the power switches, causing an increase in conduction loss and the magnetic loss of the transformer, resulting in lower converter efficiency, especially at light loads. For better efficiency of DAB converters at light load, several control strategies were developed, such as EPS control [10; 11] or series resonant dual-active bridge (SRDAB) converters [12; 13]. EPS control can effectively reduce the current stress and reactive power and thus increase the system efficiency, but the phase-shift degrees of freedom also increase. This control method adds another degree of freedom to the converter by adjusting the time sequence between the gate signals of diagonal power switches to enhance flexibility. [PERSON]. [10] proposed a minimum-backflow-power under extended-phase-shift control (MEPS) strategy to minimize the backflow power and improve the efficiency in a wide operating range. [PERSON]. [11] presented a three-degree-of-freedom control method for DAB converters to achieve full load range ZVS under a wide voltage range. However, in practice, control complexity is high because of the number of coupled variables, making it difficult to implement. In terms of resonant converters, [PERSON]. [12] introduced a symmetrical CLLC resonant tank on the DAB with pulse frequency modulation (PFM) control to achieve soft switching during bidirectional power conversion. In [13], a dual-bridge series resonant DC-DC converter (DBSRC) developed by modifying the topology of the traditional DBSRC was introduced. The proposed circuit presents higher voltage gain, a wider soft-switching region, and larger output power than the traditional DBSRC. However, the resonant converter commonly uses variable frequency control methods, which generate higher harmonics. As a result, the converter requires the use of more complex designed EMI suppression filters. To improve efficiency at light loads while taking advantage of the large power transmission capacity of SPS control, a fixed-frequency dual-mode control strategy is proposed in this paper, enabling the DAB converter to switch the operation mode based  
Figure 3: Backflow power in SPS control. on the load. For example, the DAB converter operating at light loads is controlled by using PWM control. Nevertheless, when the converter is under medium-to-full load, the DAB converter is controlled by using the SPS control. Table 1 shows a comparison of the related studies. This paper is structured as follows:  
Section 1 introduces the DAB converter topology and its control strategies. This section also briefly mentions the purpose of this study and the paper structure. Section 2 describes the operation of the dual-mode control strategy for the DAB converter, along with its related circuit analysis. Section 3 presents the design procedure of the prototype converter. Section 4 establishes the power loss model of the converter. In Section 5, the experimental results prove the feasibility of the proposed dual-mode control strategy for the DAB converter. Moreover, the experimental data show that the light load efficiency of the proposed control strategy is higher than that of the traditional SPS control strategy. Section 6 concludes the paper.