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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.

Full-bridge (FB) LLC resonant converter is a promising candidate for wide voltage range applications with multiple operation modes. By simply adjusting the gate driving signals, the FB LLC converter can be reconfigured as half-bridge (HB) LLC converter to extend the converter operation range. However, in the HB mode, the operating status of the four switches is different. One switch of the phase leg is turned on permanently and another one is turned off, while the other two switches of another phase leg are operating in high switching frequency mode. It is obvious that the thermal performances for these four switches are different, which will lead to a reliability issue from long-term perspective. In this article, the thermal balance control strategy in HB mode is proposed by interchanging all four possible circuit states to make sure the thermal stresses for all four switches are same. On the other hand, to avoid the transients during transitions of different circuit states in HB mode, a simple optimal trajectory control strategy is proposed. The analysis demonstrated that to ensure smooth and fast transition, only a constant time is required to be inserted during the transition, which requires no sensors and complicate calculation. Experimental and simulation results have been presented to demonstrate the effectiveness of the proposed strategy.

In this article, a hybrid pulse frequency modulation (PFM) and pulse width modulation (PWM) modulation strategy is proposed for the stacked structure LLC resonant converter. Three-level operation of the resonant tank input voltage is achieved by introducing the half of input voltage level due to the adopted PWM modulation strategy. Therefore, two control freedoms, switching frequency and duty ratio, are available for the proposed converter. To optimize the system efficiency performance, a power loss model based on the time-domain analysis method was built. By setting the converter power loss as the optimization objective, the optimized combination result of switching frequency and duty ratio can be found. In addition, the proposed hybrid modulation strategy can be applied for wide input voltage range application. Compared with traditional PFM LLC resonant converter, the proposed converter has better efficiency performance and the required switching frequency operating range is reduced significantly. Compared with the PWM LLC resonant converter, the resonant inductor current peak value and root-mean-square (RMS) value are reduced greatly. Finally, a 115 W experimental prototype with a wide input voltage range of 160 V--340 V was built to validate the effectiveness of the proposed hybrid modulation strategy for the stacked structure LLC resonant converter.

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.

Nano-grid (NG) clusters (NGCs) have the potential to serve as an essential configuration for future low-voltage distribution networks. To address the comprehensive energy efficiency (CEE) problem over a longer time horizon, this paper proposes an energy optimization management strategy. First of all, three typical models are developed, namely equivalent circuit model, cluster loss model and energy sharing model. In the modelling, influences of port characteristics and power transmission losses of interconnecting converters are considered to more accurately describe the cluster power flow. Then, an optimal energy scheduling mechanism with high CEE is proposed based on the three established models. The strategy decomposes the complex CEE problem into three interdependent sub-problems, corresponding to the three established models. First, ensuring the bus power quality and battery requirements are satisfied based on the proposed equivalent circuit model. Second, improving cluster self-sufficiency based on cluster energy sharing model. Third, achieving high energy transfer efficiency based on cluster loss model. Extensive simulation results demonstrate that the CEE under the proposed strategy achieves significant performance improvements, with increases of 8% and 32% in energy transfer efficiency and energy self-sufficiency respectively.

In the field of electric mobility, in particular heavy-duty electric vehicles and long-haul trucks, the energy systems are susceptible to transients with different amplitudes and dynamics due to the high power demand. With the combination of high power and long distances, the available battery technologies become insufficient as a single energy source for such a system. Thus, the integration of hybrid energy storage systems (HESSs) with different energy capabilities, such as fuel cells, battery packs, and supercapacitors, is highly required. In this context, for leveraging HESSs in an efficient way, a resonant multiwinding transformer-based converter is proposed to interconnect these different energy storage systems (ESSs) since the resonant converters are able to operate at a wider range of switching frequencies and, hence, a wider soft-switching range. However, due to the multiple resonant circuits and possible parameter deviations, the control capability might be compromised. Thus, a multiport resonant dc/dc converter embedded with variable inductors is proposed to enhance the power flow management among these different ESSs with reduced conversion stages. Further, the proposed concept can also improve the immunity to parameter deviations on the resonant by compensating for possible variations at the resonant frequencies. Finally, simulations and experimental results of a $\text{20} \;\text{kW}$ four-port resonant dc/dc converter embedded with variable inductors are shown to prove the effectiveness of the proposed concept.

Hybrid silicon (Si)/silicon carbide (SiC) switches are gaining increased attention for designing high-efficiency and high-power density energy conversion systems. They offer very good conduction and switching power loss performance compared to using only Si insulated gate bipolar transistor (IGBT) or SiC metal–oxide–semiconductor field effect transistor (MOSFET) devices as a result of combining the best properties of both devices. Several Si/SiC gate control strategies, gate driving approaches, and packaging considerations have been proposed in the literature. This article presents a comprehensive review and performance comparison of different Si/SiC gate control strategies, gate driver solutions, and packaging approaches that are already proposed in the literature. In addition, it aims to provide a general guideline for selecting the appropriate Si/SiC gate control approach that is suitable for different applications considering several Si/SiC switch design properties. It also aims to establish a general metrics for evaluating the performance of different Si/SiC gate driver solutions that are proposed in the literature in order to help the designer choose a suitable gate driver solution for different applications. Moreover, it highlights future research and development needs of hybrid Si/SiC switches in terms of gate control techniques, gate driver approaches, and packaging solutions in order to achieve further performance improvements and fully exploit their benefits.

Cryogenic power electronics is regarded as the next step to improve the power converter efficiency and power density. Thus, investigations on component and converter performances under low temperature operations are of great importance. Silicon carbide (SiC) devices have gradually replaced traditional Silicon (Si) devices in high voltage and high power applications. This is due to their fast switching speed and low switching loss. In this article, the performance of SiC device based power converters are investigated under low temperature operation. Firstly, the individual component performances are evaluated under low temperatures. Then, a 600 W resonant converter based DC transformer was built and tested under low temperatures. The efficiency for the tested converter with ferrite cores drops from 97.86% at room temperature (298 K) to 93.44% at 143 K. The converter power loss model under low temperature operation was developed to facilitate the understanding of converter performance at various operating temperatures.

In this article, the static and dynamic characterizations for semiconductors with different materials, including silicon (Si), silicon carbide (SiC), and gallium nitride (GaN), are evaluated and compared at room temperature and cryogenic temperature (liquid nitrogen temperature). For static characterizations, the on-state resistance and threshold voltage are evaluated. For dynamic characterizations, the turn-on switching loss, turn-off switching loss, and dynamic on-state resistance (Rds(on)) are evaluated. The results demonstrate that Si and GaN based semiconductors have improved performances with lower on-state resistance and faster switching speed at low temperature operations. For SiC based semiconductors, the on-state resistance increases significantly at cryogenic temperature. The switching speed is reduced dramatically for the evaluated 1.2 kV SiC metal oxide semiconductor field effect transistors (MOSFETs) at cryogenic temperature. This makes it less attractive for cryogenic applications. For the evaluated 650 V and 900 V SiC MOSFETs, the switching speed remains almost unchanged at low temperature. GaN high electron mobility transistor (HEMT) demonstrates a fast turn-on switching speed at low temperature, where the device's dv/dt and di/dt are almost doubled when compared with room temperature. In addition, the dynamic Rds(on) of the evaluated GaN HEMTs also decreases at low temperatures. The evaluation results can serve as guidelines for cryogenic power electronics applications. Meanwhile, the future work for semiconductors cryogenic characterizations is discussed.

LLC resonant converters are used in renewable energy applications to achieve high power efficiency conversions between different energy sources, buses, and energy storage elements. The traditional design methods for LLC resonant converters are based on a simple frequency-domain analysis (FDA). However, the accuracy of FDA is not satisfactory, especially at wide voltage range applications. To overcome the drawbacks of the traditional FDA method in wide-range applications, in this article, the time-domain analysis (TDA) is adopted to achieve accurate analysis of LLC converters. Efficiency is normally selected as the optimization objective, where the circuit components and accurate power loss models are required beforehand. To achieve a more general optimal design method for LLC converters, a simple root-mean-square (rms) current and TDA-based optimal design method is proposed. The optimal design is achieved by minimizing the converter rms current and ensuring some key design considerations. Moreover, an automatic design tool for the proposed rms-current-based optimal design method is developed, and advanced optimization algorithms are introduced to improve the optimization speed. A 2.5-kW experimental prototype is built using the optimal circuit parameters. Experimental results under different operating conditions are demonstrated, and the results are consistent with the theoretical analysis. Efficiency comparisons between the proposed optimal design method and conventional design method are made. The proposed optimal design method can improve the converter efficiency by a maximum value of 2.14%.

Deadtime is a critical design target for soft switching dc/dc converters. On the one hand, the deadtime is necessary to ensure the safety operation of the devices in one switching leg; on the other hand, enough deadtime is required to achieve zero voltage switching (ZVS) operation. Due to the complexity of LLC converters, traditionally, the deadtime selection is either based on engineering experience or inaccurate analysis of the converter, which leads to an unoptimized deadtime. Specifically, a large deadtime will lead to efficiency degradation due to the body diode conduction during deadtime. The ZVS operation cannot be completely achieved with a small deadtime, which will also degrade the converter efficiency. Therefore, there is a demand for an accurate analysis of the deadtime effect on LLC converters. In this article, an accurate and in-depth analysis of the deadtime effect on the LLC converter is performed with the aid of the time-domain analysis (TDA). However, the proposed adaptive deadtime strategies can also be implemented based on the experiment or simulation results for those who do not have access to the TDA of LLC converters. Based on the analysis, novel adaptive deadtime strategies are proposed for the LLC converter. Compared with the traditional fixed deadtime strategy, around 1% efficiency improvement is achieved for a 125-W experimental prototype during the whole operating range.

Wide voltage gain range applications are challenging for dc/dc converters, and the system efficiency would be degraded in order to satisfy the voltage gain requirement. Inductor–inductor–capacitor (LLC) resonant converters have gained popularity owning to its high efficiency feature. However, wide voltage gain range applications also challenge the LLC converters from the following three aspects: 1) large switching frequency operating range is required to meet the voltage gain requirement, which degrades the converter electromagnetic interference (EMI) performance and challenges the optimization of magnetic components; 2) small inductor ratio is required to boost the voltage gain, which increases the resonant tank root-mean-square (rms) current and conduction loss; and 3) control instability issues may occur at both maximum voltage gain and minimum voltage gain, which reduce the converter reliability. To address these issues, in this article, a novel LLC converter with topology morphing control is proposed for wide voltage gain range applications. Three operation modes, dual full-bridge (DFB), hybrid full-bridge and half-bridge (HFBHB), and dual half-bridge (DHB), can be achieved by adopting the topology morphing control, which can cover a wide voltage gain operation range. Operational principles, design considerations, and experimental validations of the proposed converter are presented.

Large circulating current and reactive power exist for the LLC/CLLC converter in the case that fs < fr, where fs is the switching frequency and fr is the resonant frequency; on the other hand, in the scenario of fs > fr, the switching losses for both primary and secondary semiconductor devices are increased due to the large turn-off current and high di/dt related reverse recovery issue, respectively. When operating at the natural resonant frequency of inductor and capacitor or fs = fr, the regulation capability for LLC/CLLC converter is lost since the voltage conversion ratio is constant. This application is also known as dc transformer (DCX), which has been widely adopted in energy storage systems as interconnection between different units. However, due to the variation of circuit parameters, the switching frequency is different from the resonant frequency, which results in converter efficiency degradation and loss of output voltage regulation capability for two-stage applications. In this article, by sensing the output voltage and input voltage, the converter voltage conversion ratio is computed on-line. Based on the comparison result between the calculated gain and unity, the switching frequency is adjusted accordingly and the resonant frequency tracking is achieved. In addition, multiple frequency adjustment step strategy is proposed to improve the tracking speed. Various scenarios are emulated in the experiment part to examine the effectiveness of the solution.

Driving solutions for power semiconductor devices are experiencing new challenges since the emerging wide bandgap power devices, such as silicon carbide (SiC), with superior performance become commercially available. Generally, high switching speed is desired due to the lower switching loss, yet high $dv/dt$ and $di/dt$ can result in elevated electromagnetic interference (EMI) emission, false-triggering, and other detrimental effects during switching transients. Active gate drivers (AGDs) have been proposed to balance the switching losses and the switching speed of each switching transient. The review of the in-existence AGD methodologies for SiC devices has not been reported yet. This review starts with the essence of the slew rate control and its significance. Then, a comprehensive review categorizing the state-of-the-art AGD methodologies is presented. It is followed by a summary of the AGDs control and timing strategies. In this work, using AGD to reduce the EMI noise of a 10-kV SiC MOSFET system is reported. This work also highlights other capabilities of AGDs, including reliability enhancement of power devices and rebalancing the mismatched electrical parameters of parallel- and series-connected devices. These application scenarios of AGDs are validated via simulation and experimental results.

Cryogenic power electronics is both advantageous and indispensable in many applications, like deep space probe, military electric vehicle, magnetic resonance imaging etc. Among different semiconductors, the gallium nitride (GaN) high electron mobility transistor (HEMT) is the most promising candidate for cryogenic applications with significant conduction loss and switching loss reductions. Moreover, there is no carrier freeze out effect for the GaN HEMTs, which is applicable in extreme low temperature operating conditions. In this work, the efficiency of GaN HEMTs based power converters with different power levels (from several Watts to several kiloWatts) are evaluated at cryogenic temperature. Three different commercial GaN HEMTs are used in these power converters, including the Texas Instruments LMG5200 80 V GaN half-bridge power stage with integrated gate driver, the GaN Systems 650 V bottomcooled GaN HEMT GS66516B, and the 650 V top-cooled GaN HEMT GS66516T from GaN Systems. Moreover, two different cryogenic power converter evaluation methods (cryogenic chamber and liquid nitrogen channeled through cold plate) are investigated. Three of these power converters are evaluated by using a cryogenic chamber and such that the converter operating environment temperature can be regulated. One of the power converters is evaluated by using liquid nitrogen (LN2) channeled through a cold plate, where the gate driver can be designed to operate at non-cryogenic temperatures to ensure the safe operation of the system. Due to the degraded performance of conventional magnetic components, air core magnetics are used in these power converters to improve the converter efficiency. Efficiency improvements at cryogenic temperature are observed for all the GaN HEMTs and air core magnetics based power converters, which are promising for cryogenic power electronics applications.

Highly efficient electrically driven avionics have led to a renewed interest in cryogenic propulsion systems with the goal of reducing carbon emission footprint. Although cryogenic converters promise better efficiency and improved power density, the successful design is incumbent upon the appropriate switching device selection and simulation-based analyses prior to initial prototyping. In this work, a datasheet-driven compact model for a gallium nitride (GaN) Gate Injection Transistor (GIT) has been proposed and implemented in LTspice, a versatile, high performance, and free circuit simulator in order to investigate the merit of the chosen device in a power electronic system.

Drug-induced liver injury (DILI) is a life-threatening, adverse reaction to certain drugs. The onset and extent of DILI can vary drastically in different patients using identical drugs. Association studies suggested that subtle differences in DNA methylation may help explain the individual differences in DILI. However, there are very few experimental methods to confirm such associations. In this study, we established a novel DNA methylation functional detection system in human hepatocytes, using CRISPR/dCas9 for targeted modification of DNA methylation, and set four parameters to indicate the liver injury by cell model. Using this system, we validated the association of hypermethylation of CYP2D6and CYP2E1with rifampin-induced DILI. Our results revealed that, following treatment of HepaRG cells with rifampin, the methylation levels of CYP2D6and CYP2E1were inversely proportional to cell viability and glutathione content, and directly proportional to caspase 3/7 activity. We expect that our methylation detection system will serve as a useful tool in validating correlations between DNA methylation and DILI in other in vitro systems. Our results establish a foundation for future investigations to better understand the mechanisms underlying DILI and may aid in advancing personalized DILI medicine.

The cryogenic operation of power converters integrated with the superconducting electric machines can leverage the lower parasitic, lower core material, and insulation requirement to reduce weight and increase power density in aerospace applications. To that end, Gallium Nitride High Electron Mobility Transistor (GaN HEMT) has recently proven to be the most viable option for the cryogenic converter operation. However, the topology selection and optimization are greatly influenced by the current/voltage rating of the power devices. Although series connected HEMTs can increase the blocking voltage, the dynamic voltage imbalance issue stemming from device parameter fluctuations, the larger number of required isolated gate driver makes the need for single high blocking voltage devices more compelling. This is even more pronounced in GaN due to its higher operating frequency which stems from the lower input capacitance. Although 900V cascode GaN HEMTs are now commercially available, single-chip high voltage HEMTs are attractive due to their zero reverse recovery charge, and lower package bonding parasitics. In this paper, a 1200V enhancement-mode GaN HEMT from GaNPower International has been characterized at cryogenic temperature. A 63% decrease has been demonstrated in the on-resistance, Rds(on)from room temperature to -150°C. The threshold voltage shows a 1.2x increase from room temperature to cryogenic temperature (-178°C). The transconductance (Gfs) shows a 1.34x increase for a temperature difference of 175°C. The results translate to a lower conduction loss and a faster switching speed and unfold further possibility of GaN in cryogenic converter applications.

Cryogenic power electronics is an emerging technology to achieve high efficiency and high power density. As the key element of the power electronics system, the device performance should be evaluated under cryogenic temperatures. To demonstrate the differences between different materials and technologies, cryogenic temperature performance comparisons among silicon (Si) metal–oxide–semiconductor field-effect transistor (MOSFET), Si insulated-gate bipolar transistor (IGBT), silicon carbide (SiC) MOSFET, Cascode gallium nitride (GaN), and GaN high-electron-mobility transistor (HEMT) from different perspectives are made, which includes on-state resistance, threshold voltage, turn-on and turn-off times, turn-on and turn-off switching losses. The normalized values are adopted and results are drawn in the same pictures to demonstrate the differences. The results demonstrate that traditional Si devices have better performances under low temperatures. The SiC MOSFET is not suitable for cryogenic applications due to its increased on-state resistance and switching loss. Cascode GaN and GaN HEMT are promising candidates for cryogenic applications with reduced conduction loss and switching loss.