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Dual active bridge (DAB) converter has been widely used in electric vehicles (EVs) with the advantages of its simple structure and high performance. Traditional optimization strategies based on triple phase shift (TPS) of DAB cannot optimize both soft switching and current stress. To overcome this challenge, a comprehensive optimization strategy based on TPS (TPS-CO) adapted to the whole operating range is proposed in this article. The power range, current stress, and soft-switching features for TPS are detailed, and the mathematical model of TPS-CO is established. Accordingly, the optimal path method for seeking the minimal current stress in zero voltage switching (ZVS) region over full-power range is proposed. Therein, it solves the problem of zero current switching (ZCS) operation of TPS at light loads and significantly extends the ZVS range. The proposed strategy is implemented through closed-loop control. Finally, experimental results on a 1.6-kW laboratory prototype demonstrate the significant efficiency advantages of the proposed TPS-CO strategy of the DAB converter with widely varying voltage ratios and full-power range compared with the conventional strategies, and the peak efficiency can be promoted up to 2% at light loads as reported in the experimental statistics.

Silicon carbide (SiC) power devices have been extensively for high-power-density application scenarios. To increase the current rating, SiC devices are usually connected in parallel. However, the mismatching current brought by unbalanced electrical parameters can increase the current stress of a device and pose a reliability concern for the converter system. Aiming at addressing the current imbalance for paralleled SiC devices, this article reports the application of an improved active gate driver (AGD) on the paralleled SiC MOSFETs to address the current imbalance problems. The three-level driver voltage can minimize the overshoot voltage and current. The adjustable turn-on voltage and gate signal delay time can realize the current sharing of both static and dynamic processes. Current sensors and a digital controller are utilized for close-loop control. The functionality of the proposed AGD is validated in continuous operating experiments.

Cryogenic power electronics is regarded as the next step to improve the converter efficiency and power density. It is advantageous in many different applications, including aerospace, renewable energy, transportation and so on. Among all different semiconductors, gallium nitride (GaN) was found more advantageous with significant loss reduction at cryogenic temperature. In this paper, overcurrent test is performed and analyzed for a high-efficient commercial GaN high electron mobility transistor (HEMT). The experimental results demonstrate a significant improvement of the device overcurrent capability at cryogenic temperature (from 160 A at room temperature to 250 A at cryogenic temperature). The operating mechanisms behind the overcurrent test are investigated and discussed. Finally, a 5 kW GaN HEMT based cryogenic Buck converter is built and tested. Maximum efficiency of 98.5% is achieved at 1.5 kW output power and around 1% efficiency improvement can be achieved when compared to room temperature operation. Another GaN HEMT based four-switch Buck-boost converter is evaluated at cryogenic temperature, maximum efficiency improvement of 1.5% is observed when compared to room temperature.