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Highlights Single-atom Fe–N 4 sites embedded into graphene were successfully synthesized to exert the dielectric properties of graphene. The absorption mechanisms of metal-nitrogen doping reduced graphene oxide mainly include enhanced dipole polarization, interface polarization, conduction loss and defect-induced polarization. Excellent reflection loss of − 74.05 dB (2.0 mm) and broad effective absorption bandwidth of 7.05 GHz (1.89 mm, with filler loading only 1 wt%) were obtained. Developing effective strategies to regulate graphene's conduction loss and polarization has become a key to expanding its application in the electromagnetic wave absorption (EMWA) field. Based on the unique energy band structure of graphene, regulating its bandgap and electrical properties by introducing heteroatoms is considered a feasible solution. Herein, metal-nitrogen doping reduced graphene oxide (M–N-RGO) was prepared by embedding a series of single metal atoms M–N 4 sites (M = Mn, Fe, Co, Ni, Cu, Zn, Nb, Cd, and Sn) in RGO using an N-coordination atom-assisted strategy. These composites had adjustable conductivity and polarization to optimize dielectric loss and impedance matching for efficient EMWA performance. The results showed that the minimum reflection loss ( RL min ) of Fe–N-RGO reaches − 74.05 dB (2.0 mm) and the maximum effective absorption bandwidth (EAB max ) is 7.05 GHz (1.89 mm) even with a low filler loading of only 1 wt%. Combined with X-ray absorption spectra (XAFS), atomic force microscopy, and density functional theory calculation analysis, the Fe–N 4 can be used as the polarization center to increase dipole polarization, interface polarization and defect-induced polarization due to d-p orbital hybridization and structural distortion. Moreover, electron migration within the Fe further leads to conduction loss, thereby synergistically promoting energy attenuation. This study demonstrates the effectiveness of metal-nitrogen doping in regulating the graphene′s dielectric properties, which provides an important basis for further investigation of the loss mechanism.

Dielectric materials with excellent energy storage capability at elevated temperatures are critical to meet the increasing demand of electrical energy storage and power conditioning at extreme conditions such as hybrid electric vehicles, underground oil industries and aerospace systems. This review study summarises the important aspects and recent advances in the development of nanostructured dielectric materials including ceramics, polymers and polymer composites for high-temperature capacitor applications. The advantages and limitations of current dielectric materials are discussed and analysed. Ongoing research strategies to suppress the conduction loss and optimise the high-temperature capacitive performance of dielectrics have been highlighted. A summary and outlook will conclude this review.

Introduction. This research presents a simple single-phase pulse-width modulated 7-level inverter topology for renewable system which allows home-grid applications with electric vehicle charging. Although multilevel inverters have appealing qualities, their vast range of application is limited by the use of more switches in the traditional arrangement. As a result, a novel symmetrical 7-level inverter is proposed, which has the fewest number of unidirectional switches with gate circuits, providing the lowest switching losses, conduction losses, total harmonic distortion and higher efficiency than conventional topology. The novelty of the proposed work consists of a novel modular inverter structure for photovoltaic energy system and electric vehicle applications with fewer numbers of switches and compact in size. Purpose. The proposed system aims to reduce switch count, overall harmonic distortions, and power loss. There are no passive filters required, and the constituted optimizes power quality by producing distortion-free sinusoidal output voltage as the level count increases while reducing power losses. Methods. The proposed topology is implemented with MATLAB/Simulink, using gating pulses and various pulse-width modulation methodologies. Moreover, the proposed model also has been validated and compared to the hardware system. Results. Total harmonic distortion, number of power switches, output voltage, current, power losses and number of DC sources are investigated with conventional topology. Practical value. The proposed topology has proven to be extremely beneficial for implementing photovoltaic-based stand-alone multilevel inverter and electric vehicle charging applications.

In a capacitive power transfer (CPT) system, the coupling capacitance formed between the coupling plates is very small only in the pF or nF range, which leads to high voltage stress among the coupling plates during energy transmission, which increases the risk of an electrical breakdown between the coupled plates. To solve this problem, a novel dual-frequency CPT system is proposed in this paper, which uses the “peak clipping” effect caused by the superposition of the fundamental wave and third harmonic wave to reduce the voltage stress of the coupled plates. Through the detailed analysis of the working principle of the CPT system, it is shown that the dual-frequency CPT system can indeed reduce the high voltage stress among the coupled plate to 84.3% of the equivalent single-frequency system and can also reduce the inverter conduction losses to 90%. A 200 W prototype is designed with the proposed scheme, and the experimental results confirm the correctness of the theoretical derivation.

Electronic equipment brings great convenience to daily life but also causes a lot of electromagnetic radiation pollution. Therefore, there is an urgent demand for electromagnetic wave-absorbing materials with a low thickness, wide bandwidth, and strong absorption. This work obtained a high-performance electromagnetic wave absorption system by adding conductive carbon spheres (CSs) to the CH3NH3PbI3 (MAPbI3) absorber. In this system, MAPbI3, with strong dipole and relaxation polarization, acts dominant to the wave absorber. The carbon spheres provide a free electron transport channel between MAPbI3 lattices and constructs interfacial polarization loss in MAPbI3/CS. By regulating the content of CSs, we speculate that this increased effective absorption bandwidth and reflection loss intensity are attributed to the conductive channel of the carbon sphere and the interfacial polarization. As a result, when the mass ratio of the carbon sphere is 7.7%, the reflection loss intensity of MAPbI3/CS reaches −54 dB at 12 GHz, the corresponding effective absorption bandwidth is 4 GHz (10.24–14.24 GHz), and the absorber thickness is 2.96 mm. This work proves that enhancing conduction loss and interfacial polarization loss is an effective strategy for regulating the properties of dielectric loss-type absorbing materials. It also indicates that organic-inorganic hybrid perovskites have great potential in the field of electromagnetic wave absorption.

SiC (silicon carbide) MOSFETs have been extensively used in the power electronics industry due to their exceptional characteristics. First, it was found in this study that their driving loss is larger than their conduction loss in high-frequency applications. Based on this finding, this study proposes a hierarchical driving control strategy for improving the parallel-converter efficiency of SiC MOSFETs under light loads. Efficiency under light loads is of great importance for battery-based energy storage systems. To minimize the sum of the conduction loss and driving loss in parallel devices, this study proposes a current-monitoring hierarchical driving strategy based on an active-clamped flyback converter. By monitoring the output current of the converter, the strategy minimizes the sum of the driving and conduction losses by switching the driving state under different loads. The results of simulations indicate the effectiveness of the load-current-monitoring strategy. To verify the effectiveness of this method, a principle prototype of two SiC MOSFETs connected in parallel at 12 V/5 A was fabricated and tested, and the test results showed that there was a maximum improvement of 1.4% in the converter’s efficiency when the load current was in the range of 0.5–1.5 A.

A novel Performance Optimized Carrier Stored Trench Gate Bipolar Transistor (CSTBT) with Low Switching Loss has been proposed. By applying a positive DC voltage to the shield gate, the carrier storage effect is enhanced, the hole blocking capability is improved and the conduction loss is reduced. The DC biased shield gate naturally forms inverse conduction channel to speed up turn-on period. Excess holes are conducted away from the device through the hole path to reduce turn-off loss (Eoff). In addition, other parameters including ON-state voltage (Von), blocking characteristic and short circuit performance are also improved. Simulation results demonstrate that our device exhibits a 35.1% and 35.9% decrease in Eoff and turn-on loss (Eon), respectively, in comparison with the conventional shield CSTBT (Con-SGCSTBT). Additionally, our device achieves a short-circuit duration time that is 2.48 times longer. In high-frequency switching applications, device power loss can be reduced by 35%. It should be noted that the additional DC voltage bias is equivalent to the output voltage of the driving circuit, enabling an effective and feasible approach towards high-performance power electronics applications.

In this study, polymer-derived SiC fibers fabricated using low-melting point PCS (polycarbosilane) were prepared in a mat shape for application as a microwave-assisted heating element. In addition, polymer-derived SiC blocks of various shapes were prepared under the same conditions to verify the heating behavior under the microwave. As a result, the polymer-derived SiC generated more than 1500 °C of heat in tens of seconds under the microwave. The polymer-derived SiC also exhibited different microwave-assisted heating behavior and maximum heating temperature depending on its shape. This microwave heating behavior meant that polymer-derived SiC was more dependent on the conduction loss mechanism than the dipolar loss mechanism. Therefore, as the pyrolysis temperature increased, the pi-electrons needed for the conduction loss were observed by Raman analysis and showed a tendency similar to the heat-generating behavior as the pyrolysis temperature increased.

The medium voltage DC (MVDC) type system can connect multiple terminals to a common MVDC bus, so it is possible to connect several renewable DC power sources to the common MVDC bus, but a DC circuit breaker is needed to isolate short circuit accidents that may occur in the MVDC bus. For this purpose, the concept of a hybrid DC circuit breaker that takes advantage of a low conduction loss contact type switch and an arcless-breaking semiconductor switch has been proposed. During break the hybrid switch, a dedicated current commutation device is required to temporarily bypass the load current flowing through the main switch into a semiconductor switch branch. Existing current commutation methods include a proactive method and a reverse current injection method by a LC (Inductor-capacitor) resonant circuit. This paper proposes a power circuit of a new MVDC hybrid circuit breaker using a low withstanding voltage capacitor branch for commutation and a sequence controller according to it, and verifies its operation through an experiment.

This paper introduces a mathematical design and analysis of three-phase inverters used in electric drive applications such as aerospace, electric vehicles, and pumping applications. Different wide bandgap (WBG) semiconductor technologies are considered in this analysis. Using SiC MOSFETs and Si IGBTs, two drive systems are developed in order to show the improvement in the efficiency of the inverter. The efficiency, total losses of the drive systems and the power losses of two inverters are computed and compared for both drive systems at the same operating condition. The drive system with SiC MOSFET shows much better performance compared to the drive system with Si IGBT. The SiC MOSFET system provides a 59.39%, 86.13%, and 29.76% lower conduction losses, switching losses and drive’s total losses, respectively, compared to the Si IGBT system. The efficiency of the SiC MOSFET system is 2.46%pu higher than the efficiency of the Si IGBT drive system. Moreover, this paper introduces a detailed analysis for the dc-link voltage and current ripples in three-phase inverters. Furthermore, the minimal dc-link capacitor needed to deal with the ripple current and voltage is investigated. Finally, the performance of the drive with Si IGBT is experimentally tested under different operating speeds and loads.