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Conventional Al-air battery has many disadvantages for miniwatt applications, such as the complex water management, bulky electrolyte storage and potential leakage hazard. Moreover, the self-corrosion of Al anode continues even when the electrolyte flow is stopped, leading to great Al waste. To tackle these issues, an innovative cotton-based aluminum-air battery is developed in this study. Instead of flowing alkaline solution, cotton substrate pre-deposited with solid alkaline is used, together with a small water reservoir to continuously wet the cotton and dissolve the alkaline in-situ. In this manner, the battery can be mechanically recharged by replacing the cotton substrate and refilling the water reservoir, while the thick aluminum anode can be reused for tens of times until complete consumption. The cotton substrate shows excellent ability for the storage and transportation of alkaline electrolyte, leading to a high peak power density of 73 mW cm−2 and a high specific energy of 930 mW h g−1. Moreover, the battery discharge capacity is found to be linear to the loading of pre-deposited alkaline, so that it can be precisely controlled according to the mission profile to avoid Al waste. Finally, a two-cell battery pack with common water reservoir is developed, which can provide a voltage of 2.7 V and a power output of 223.8 mW. With further scaling-up and stacking, this cotton-based Al-air battery system with low cost and high energy density is very promising for recharging miniwatt electronics in the outdoor environment.

Conventionally, single phase shift control technique is used, for dual active bridge (DAB) which works efficiently at unity voltage conversion ratio and full load. However, when there is mismatch between primary voltage and reflected secondary voltage on primary side at light load, its efficiency reduces because of increased current stress and circulating power. Moreover, due to single control variable, its power flow controllability is confined. In this paper, isolated bi-directional T-type multilevel dual active bridge dc-dc converter topology is presented. It has five level voltages on both the primary and secondary side of high frequency transformer, which reduces the current stress and circulating power over wide operating range. It also has five control variables which gives extra edge for enhancing power flow controllability. Comparative analysis reveals that the proposed converter has high efficiency over wide operating range, due to reduced circulating power and current stress. Performance of the proposed T- type multilevel dual active bridge DC-DC converter topology has been verified via simulation in MATLAB.

As a novel micro-propulsion system for small satellites (from micro to nano), the ionic liquid electrospray propulsion system is a promising candidate. However, performance measurement and evaluation of the Ionic Liquid Electrospray Thruster (ILET) is one of the most challenging issues for practical application, due to the difficulties in the development of a prototype and direct measurements of micro-thrust and small flow rate. To address this issue, a Modular Ionic Liquid Electrospray Thruster (MILET) prototype is constructed, and a diagnostic system for thrust and mass flow rate is specially developed based on an analytical balance method. With the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate as the propellant, a series of experiments is carried out on the MILET prototype under a wide operating condition through changing the applied voltage to control the thrust. Under different applied voltages, the thrust and the mass flow rate of the propellant are directly measured. The propulsive performance parameters of the thruster, such as thrust, specific impulse, thrust-to-power ratio, thruster efficiency, etc., are comprehensively analyzed. Then, a performance comparison is made between the MILET and other representative ILETs. With a relatively low applied voltage ranging from 1550 V to 2000 V, the MILET achieves a quasi-constant specific impulse of 1263 s with the averaged thrust-to-power ratio of 65.2 μN/W and thruster efficiency of 40.7%. The performance of ILET is also compared with other typical electric propulsions. The results demonstrate that the ILET exhibits an excellent ability of minimalization with high specific impulse and thruster efficiency, which guarantees a great superiority in micro propulsions. Finally, the ways to further improve the performance of ILET are discussed, which further confirms the potential prospect of ILET. The present result helps to advance the development and application of ILET.

A new dc-dc converter with high voltage gain is proposed in this study. The proposed converter consists of two switches which are turned on and off simultaneously. Additionally, two Switched-Capacitor (SC) cells and one Energy Storage (ES) cell are utilized in the structure of the proposed converter. These result in high voltage gains at low values of the duty cycle. Besides, the voltage stress across the power devices is low and below half of the output voltage. Therefore, the MOSFET switches with low RDS-on and devices with reduced nominal voltage can be used in the proposed converter which in turn reduces the conduction and turn-on losses. The analysis of the voltage and current stresses of the devices is accomplished. The circuit performance is compared with other solutions in the literature in terms of voltage gain and normalized voltage stress of switches and diodes. Eventually, in order to verify the theoretical analysis, the experimental results are provided.

Electric discharge machining (EDM) routehas capability of machining hard materials. Even intricate shapes can be machined by this process. Traditional machining routes develop machining issues like tool wear and pitiable surface finish. It can be overcome by the EDM process. The objective of this work is to prepare AA6351-10wt%Al2O3-5wt%Gr composites through stir casting process. The manufactured composites were machined via EDM route and their machining characteristics material removal rate (MRR) and surface roughness (SR) were studied via Taguchi process. The results display that for MRR current is the major influencing parameter and for SR voltage is the foremostpersuading parameter.

The tool and die applications are preferred the unconventional machining processes as they are popular in machining the difficult to cut type complex contour/ profile. The complex profile machined on hard material. Some special materials like Stainless Steel 12X18H10T withstand its inherent properties even it exposes at higher temperature. This investigation aims to expand its application by investigating its machinability in Electro Chemical machining process for surface finish. The process parameters like gap between work material and tool, discharge current, concentration of electrolyte and applied voltage at three levels. The Taguchi approach is used for optimizing the process parameters and confirmation runs also conducted for developing the mathematical modelling. For optimizing number of experiment the Taguchi L9 is utilized for this investigation.

Pulsed electric field disinfection is an effective non-thermal water disinfection technology. Compared to conventional disinfection techniques, PEF inactivation has several advantages including no by-products. In this context, the use of silver ions in conjunction with a reverse osmosis filtration system has been proposed as a safe and cost-effective treatment approach that can be used in a point of use technologies. This system contains two silver meshes as electrodes inside a reverse osmosis membrane with the application of a pulsed electric field on it as a disinfection method, After conducting chemical and physical tests of the water samples before and after the treatment system, it was noticed that most of these characteristics were significantly affected by increasing the number of electrical impulses and the intensity of the applied voltage as a result of the increase in the ionization process of silver in water.

In General, a larger number of experimental data would be required for optimizing the performance efficiency of the electrodes in solid oxide fuel cells (SOFC), as it was likely to involve many complex chemical and physical reactions. Therefore, in this study, we have attempted the artificial intelligence (AI) technique for analyzing the performance of the anode and cathode electrodes of SOFC under various key parameters that normally influences the efficiency of the electrodes. Since the cost of SOFC elements is expensive, computational trials with the aid of AI would not only be curtailing the preparation cost but also ensures less time consumption. Among the variety of AI methods available in the literature, the Support Vector Machine (SVM) appears to be one of the excellent and effective machine learning techniques. Hence, we have developed a SVM model and predicted the maximum current density and power density of Nickel oxide-samarium-doped ceria (NiO-SDC) composite anode and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode electrodes of SOFC. The input parameters such as stack temperature, supply voltage were supplied to the SVM model and obtained maximum current density and power density as output and it decides the working performance of the electrodes. We have also predicted that the maximum current density and power density of 1160 mA cm2 and 225 mW cm2 respectively at 800 °C. To validate the results as predicted from SVM, we have experimented using Yttrium stabilized zirconia electrolyte-supported single cell with our prepared NiO-SDC anode and LSCF cathode which exhibited a maximum current and power density of 1170 mA cm2 and 227 mW cm2 at 800 °C using H2 as fuel. It has been found that that the theoretical predicted data current and power densities of the electrodes from the SVM approach reasonably agrees well with the experimental results.

Microstrip silicon detectors are one of the key trackers in particle physics experiment like LHC at CERN. There is a continuous need to improve upon various parameters of detectors like breakdown voltage, leakage current, full depletion voltage, post radiation hardness, charge collection efficiency and low thermal budget. We have introduced new doping less silicon microstrip detector for the very first time and investigated the various parameter of the detector. We have studied and compared the results of doped and dopingless charge plasma silicon microstrip detector. Our study shows improvement in Preradiation breakdown voltage of 2200 V with leakage current of 5.2 pA/um in dopingless charge plasma microstrip detector as compared to 1500 V of breakdown voltage with leakage current of 6.5pA/um as in the case of doped silicon microstrip detector.

Multilevel topologies with SiC devices for medium voltage (MV) motor drive have advantages to reduce the harmonics and device voltage stress as well as to increase the efficiency. However, with the application of SiC devices, the reflected wave phenomenon still happens in multilevel motor drive due to its high dv/dt, resulting in overvoltage at motor terminals. This paper proposed a T-type circuit based active reflected wave canceller (ARWC) to suppress the overvoltage of a M-level motor drives with reduced voltage rating of Vdc/(M-1). A coupled inductor is applied to isolate the ARWC output and the main inverter. In addition, the coupled inductor is designed with a small resistor to allow low current flowing into ARWC. The proposed ARWC configuration can be applied for general multilevel topologies. A 3-level ANPC converter with 3.3 kV SiC device is built in the laboratory. A 1.2 kV SiC module is applied in the proposed ARWC. The experimental results at 1.6 kV Vdc and 16 A (RMS) load current with and without proposed ARWC are provided and compared to verify the validity of proposed method.

In this paper, a non-isolated dc-dc high step-up converter with passive switched-inductor-capacitor network is proposed, which is applicable for the required high gain voltage low power applications, such as battery-powered LED lighting systems and high-intensity mobile discharge lamps. The proposed circuit can produce higher gain voltage with small duty cycle, which decreases the voltage stress and conduction power loss on the active switches. In contrast to other non-isolated dc converters, by using the same or analogous number of passive/active components in circuit topology, the proposed topology has lower voltage stresses across capacitors and diodes, lower inductor current stresses. Therefore, the efficiency and reliability of the circuit topology can be ameliorated. The theoretical principle, parameter design guideline, small-signal dynamic analysis, power loss analysis and performance comparison with other dc-dc non-isolated converters have been implemented. Finally, a 200 W experimental setup is built and tested with an input dc voltage of 36V–60V and an output voltage of 200V to validate the aforementioned merits of the proposed circuit.

Conventional digital LLC Synchronous Rectifier (SR) control typically uses detection circuits to sense the drain-source voltage of SR MOSFET in low output voltage applications, or gives SR duty cycle only considering the switching frequency in the microcontroller. They are difficult to be applied to the applications of 700 V high voltage and 6.6 kW high power directly due to the high dv/dt and large SR duty cycle variations, which poses serious challenge for SRs control. A bidirectional impedance-based SR driving scheme is presented for high voltage SiC LLC converter. Based on the LLC equivalent impedance, mathematical models are built to calculate the SR on-time in the forward and reverse modes, which can be tuned timely when the switching frequency and load vary. Thus, both bidirectional LLC performance with high efficiency and high immunity to the switching noise can be achieved without adding auxiliary circuits. A prototype of 300-kHz 6.6-kW SiC bidirectional LLC charger was built. Compared to the conventional SR method, the LLC efficiencies improve 0.3% in the forward and reverse modes at full load by using the proposed SR driving scheme.

We have developed a comprehensive 3D heating test simulation model of a Li-ion battery cylindrical cell and module, taking gas flow and combustion into account. The model is based on the equivalent circuit model and includes not only the heating of a cell (joule heating and thermal decomposition) but also gas ejection flow from the cell and combustion. First, the validation of the cell model for surface temperature and voltage profiles was conducted for a commercial 18650-type cell with an actual heating experiment. Subsequently, a simulation model of the battery module, composed of total 98 cells heated by a burner, was developed, and the behavior of thermal runaway was evaluated. This model makes it possible to evaluate the events that occur from the start of heating the battery module to gas ejection, including housing melting, separator shutdown, and the propagation of thermal decomposition reactions between the cells, and might be a helpful tool for designing battery cells and modules.

A Phase-shifted full-bridge (PSFB) converter is widely used in various applications due to its soft-switching characteristics. However, one of the recognized shortcomings of the PSFB converter is that it cannot simultaneously have a wide soft switching range and a small secondary-side duty cycle loss. The shortcoming hinders the high frequency and high efficiency of the converter. In this paper, the change of the energy demand of the converter on the external series inductor with input voltage and load is analyzed. On this basis, a variable saturation inductor with controllable energy is proposed to meet the energy demand and solve the problem of core heating. The controllable change characteristics of the inductor energy are studied directly instead of the controllable change of the inductance value. By adjusting the inductor energy, the PSFB can not only achieve soft switching under light loads, but also reduce duty cycle loss under heavy loads. Theoretical analysis and experimental verification are carried out on the soft switching and duty cycle loss of the converter. Since the transformer ratio can be increased due to the smaller duty cycle loss. The efficiency of the converter can be further improved.

High voltage/high power capacitor chargers are primarily interested in many industrial applications. Resonant converters have been a proper choice in such applications because of their advantages. However, the performance of the resonant converter is highly affected by the parasitic elements of the high voltage/high power transformer. Also, short circuit condition is a frequent event in high voltage applications, so that the resonant converter should be robust against the short circuit condition. This paper presents a novel LCCL resonant converter with current source characteristics used as a high voltage capacitor charger. The proposed resonant converter eliminates the undesirable effect of the stray capacitance in high voltage devices and is robust against the short circuit condition inherently. It also provides a semi-trapezoidal resonant current wave which produces a lower crest factor. Furthermore, a frequency-sweep operation is applied, which has advantages in reducing the resonant current's peak value and the resonant network's size. Simulation results show a satisfactory performance of the proposed resonant converter. Moreover, experimental results confirm the effectiveness of the proposed resonant converter in the application of capacitor charging.

High step-down dc-dc converters are widely employed in data center applications. Due to the higher step-down conversion ratio in the new generation 48V voltage regulator module (VRM), a conventional buck converter is not suitable for such applications. To conquer this problem, a novel DC-DC converter is proposed in this paper to achieve an ultrahigh step-down voltage conversion ratio for data centers. The non-isolated topology can be optimally designed to integrate both the switched-capacitor and coupled inductor techniques, which allows Zero-Voltage-Switching (ZVS) of all active switches to be achieved and improves high efficiency. In addition, the converter presents the advantages of lower voltage stress, ultrahigh voltage gain and common ground. A comprehensive analysis of the steady-state analysis, derivation of voltage gain, voltage stress and ZVS condition is presented in detail. Finally, a 30 W, 48-to-1V experimental prototype is built and tested, which validates the ultrahigh step-down voltage gain and soft-switching characteristic of the proposed converter. The maximum efficiency of the prototype is 89.1% and the efficiency is 81.4% in full-load condition.

In this paper, a novel single switch high voltage gain DC-DC converter is presented. The proposed converter operates with continuous input current and the voltage stress across the power switch is lower compared to the competitive high voltage gain topologies. Hence, a lower rating active switch can be selected for the proposed configuration to achieve reduced conduction losses due to its low on-state resistance of the switch. The leakage energy of coupled inductor is effectively recycled to the load through the voltage multiplier used in the topology. The voltage stress across the power diode at the output side is less and hence there is an improvement in the output side reverse recovery performance. Moreover, the proposed topology has reduced aggregate diode voltage stress. A detailed comparative study is presented consisting of the steady-state analysis, working principle, efficiency and reliability evaluation of the proposed converter for continuous conduction mode. The proposed concept is verified through extensive simulation studies and from the measured results from the experimental prototypes.

To calibrate non-contact sensors with fast response and high scale factor, it is critical to develop step pulse generators capable of generating standard high voltage step pulses and accurately measuring the generated waveform. In this paper, two types of step pulse generators are designed with output voltages of 2 kV and 100 kV. The 2 kV step pulse generator can generate a step pulse with a rise time of ~300 ps and an adjustable pulse width. A step pulse with a rise time less than 5 ns and a pulse width over 1 s can be generated with the 100 kV step pulse generator. The uncertainty of 2 kV step pulse generator is then analyzed by simulations and experiments. Finally, a performance comparison with step pulse generators in previous studies is carried out. Bandwidth, linearity and repeatability of the sensors can be verified with the designed two step pulse generators.

Evaluating the robustness of power semiconductor devices is key for their adoption into power electronics applications. Recent static acceleration tests have revealed that SiC MOSFETs can safely operate for thousands of hours at a blocking voltage higher than the rated voltage and near the avalanche boundary. This work evaluates the high-bias robustness of SiC MOSFETs under continuous, hard-switched, turn-off stresses with a dc-bias higher than the device rated voltage. Under this high-bias switching condition, SiC MOSFETs show degradation in merely tens of hours at 25°C and tens of minutes at 100°C. Two independent degradation and failure mechanisms are unveiled, one present in the gate-oxide and the other in the bulk-semiconductor regions, featured by the increase in gate leakage current and drain leakage current, respectively. The second degradation mechanism has not been previously reported in the literature; it is found to be related to the electron hopping along the defects in semiconductors generated in the switching tests. The comparison with the static acceleration tests reveals that both degradation mechanisms correlate to the high-bias switching transients rather than the high-bias blocking states. These results suggest the insufficient robustness of SiC MOSFETs under high-bias, hard switching conditions and the significance of using switching-based tests to evaluate the device robustness.

Wear debris sensing is an important approach for machine condition monitoring. To date, different types of debris sensors have been developed, among which the magnetostatic inductive debris sensor is preferable for monitoring ferromagnetic debris, but the existing induced voltage model cannot be used to quantify wear debris in lube oil. Accordingly, a modeling method was proposed for the debris sensor based on a high-gradient magnetostatic field. First, a Gaussian curve is used to fit the magnetic field along the axis of the sensor. Then, time-harmonic electromagnetic field analysis and Fourier series decomposition are combined to establish an induced voltage model. Furthermore, the influence of the relative permeability, size, and velocity of wear debris and induction coil parameters on the output voltage is analyzed. The results show a linear relationship between the theoretical calculations and experimental results. Therefore, the proposed model can be used to realize quantitative analysis of wear debris, laying a foundation for optimizing the sensor structure, and extracting features from output voltage signals.

Ultra-high voltage fast vacuum circuit breakers (FVCBs) could benefit a power system by promoting transient stability. This paper presents the design and verification of a prototype 363-kV/5000-A 63-kA multiple-break FVCB. The prototype consists of two parallel-connected circuit branches in each phase. Each branch comprises three breaking units. The breaking unit, arranged on a 330-kV-class insulating platform, is a double-break FVCB driven by two independent electromagnetic repulsion actuators. The breaking units include a specially designed 40.5-kV vacuum interrupter (VI) with an extended ceramic envelope and optimized contact contours. A 4.0-nF grading capacitor is connected in parallel with each break to achieve a uniform stressed voltage distribution across the break. The prototype performs controlled switching of short-circuit current with an arcing time of 2.0 ms. The feasibility of the 363-kV FVCB is verified by a dielectric test on one break of the prototype and a series of tests on a single-phase prototype. The tests include controlled switching of a short-circuit current in a short arcing time under different transient recovery voltages following test duties T100s(b) and T100a, short-time withstand current and peak withstand current tests, a temperature rise test, and an electromagnetic compatibility tes

In the inductive charging scenario of an electric vehicle (EV), the charger should have the capability to flexibly regulate the output power regardless of the misalignment and EV battery voltage. This paper proposes a hybrid voltage and frequency tuning strategy for a series-series (SS) inductive power transfer (IPT) system to regulate power through 0 to 3.3kW at any battery voltages and misalignment conditions without using additional converters. A voltage tuning is used to achieve full-power of 3.3kW and partly contribute to reducing the power. When the input voltage achieves the lower limit, a frequency tuning is used to further decrease the power to 0W, achieving the regulation through 0 to full power. The practical charging region is specified by 110mm airgap, 100mm misalignment in both x and y directions, and 180V-240V battery voltage range. Experiments are carried out at various conditions, and it shows that with an input voltage range of 180V-380V and a frequency of 82.5kHz~87.9kHz, the charging power can be regulated between 100W and 3.3kW at any case in the specified working region. In addition, a peak dc-dc efficiency of 95.7% is achieved at 3.29 kW.

The study of wear-out mechanism of press-pack IGBTs (PPIs) is conducted insufficiently now. In this paper, both the numerical and experimental methods are utilized to investigate the wear-out mechanism of PPIs. After conducting an accelerated aging test, three wear-out modes are observed, fretting scratches, cracks next to the additional metallization area, and oxidation of the additional metallization area. The oxidation of the additional metallization area is the newly found wear-out mode. In order to explain the deterioration mechanism of the modes, the fully coupled multi-physical model considering the aging state inside PPIs is utilized to analyze the temperature, pressure and voltage distribution. The results show that fretting wear is the main reason for the three wear-out modes. Firstly, the fretting scratches caused by fretting wear lead to the increment of surface roughness. The junction temperature and thermal resistance of the PPI both show approximately linear increment with surfaces roughness, while the saturation voltage remains unchanged. Secondly, high mechanical pressure during fretting wear results in the fatigue cracks next to the additional metallization area. Lastly, it is found that the fretting wear also leads to the oxidation of the additional metallization area.

SiC MOSFET is a promising power device for electric drive system due to its various advantages such as high switching frequency and low loss. However, fast switching speed results in high voltage stress and can potentially cause insulation damage of the winding. Few studies have analyzed and evaluated the voltage stress, especially for the hairpin winding, which is the mainstream winding type for electric vehicle traction machines. For this purpose, this paper proposes a high-frequency equivalent circuit model to predict the inter-turn voltage stress of hairpin windings driven by SiC MOSFETs. Firstly, the working principle of the overvoltage at the winding ends is analyzed and validated by experiments. Then, the parasitic parameters are calculated before building the high-frequency equivalent circuit. A field-circuit coupled finite element method is used to consider the nonlinear parameters and to evaluate the voltage stress. Finally, a prototype is built, and the voltage stress is tested. The resultant error between the calculated and experimental maximum inter-turn voltage stress is only 1.3%, which supports the inference on the validity of the presented equivalent circuit and the method. Based on the above, a novel winding connection scheme is proposed to reduce effectively the voltage stress of hairpin winding.

A non-isolated bidirectional DC-DC converter is proposed for energy storage systems in this paper. The proposed converter is composed of three active switches, two synchronous rectifiers, two clamping capacitors and two inductors. The proposed converter has advantages of being a simple structure, a fewer number of components, a common ground, lower voltage stress, and wide voltage gain range. Compared with the conventional buck converters, the novel converter triples the effective duty cycle and lowers voltage stresses across the active switches. A 300 W/500 kHz GaN-based experimental prototype is built and tested to verify the correctness and validity, demonstrating a peak efficiency of 94.54% in step-down mode and a peak efficiency of 94.88% in step-up mode.

The insulation impedance monitoring methods such as capacitance/dissipation factor (C/DF) monitoring methods have been proposed for the online stator insulation condition monitoring. By measuring the insulation leakage currents and the phase-to-ground voltages, the groundwall and phase-to-phase insulation impedances can be calculated in frequency domain. In the existing methods, the calculation is based on the assumption that the differential mode phase-to-ground voltage decreases linearly along the stator winding and no phase angle deviation is considered. However, the phase angles of the induced electromagnetic forces in stator winding in different slots depend on the slot positions. The assumption in the existing methods neglects this phase deviation and causes errors in the monitoring results. In order to eliminate this effect, the effect of the phase angle deviation on monitoring results is analyzed in this paper. Its dependency on the turn number, the winding configuration and the frequency of the selected monitoring signals is studied. A compensation method is proposed and the compensation coefficients are calculated for different winding cases for the demonstration purpose. The online experimental results prove that the accuracy of the online monitoring results is improved after the compensation.

Solid-state transformers can be applied in the AC/DC hybrid distribution network. The reliability and power density of a solid-state transformer is significantly influenced by the insulation design of the isolated DC-DC converter and, in particular, its medium-voltage medium-frequency transformer. This paper proposes an insulation design method for the medium-voltage medium-frequency transformer. A novel insulation structure is adopted to reduce the volume and improve the heat dissipation performance. Optimization of insulation distance parameters is performed based on finite element method simulations. The proposed method is applied to a 60 kVA/10 kHz transformer, and the simulation results verify the improved performances with the proposed insulation design method. A prototype is developed according to the proposed scheme, and the experimental results of a DC-DC converter and the partial discharge and applied voltage tests are presented.

The galvanic isolation of solid-state transformers (SSTs) is typically realized with a medium-frequency (MF) magnetic-core transformer (MCT). Previous demonstrations indicate that achieving highly power dense and lightweight MCTs imposes several challenges on the design because of stringent requirements related to insulation and cooling. This work investigates the achievable efficiency of an optimized 166kW / 7 kV air-core transformer (ACT), which is a core part of a DC Transformer (DCX), i.e., an unregulated DC-DC SST with a voltage scaling defined by the transformer turns ratio. The ACT features relatively low complexity of the construction, comparably high coupling values, and high efficiency. Modeling, optimization, and construction of the realized ACT are explained and guidelines regarding insulation, cooling, and shielding of the magnetic stray flux are discussed in detail. Furthermore, the prototype is experimentally validated to demonstrate its full functionality. In the investigated DCX, which is based on a series resonant converter (SRC) topology, the realized ACT is found to achieve a full-load efficiency of 99.5% and an unprecedented gravimetric power density of 16.5 kW/kg. With the use of 10 kV SiC MOSFETs, the complete DCX is estimated to reach an efficiency of 99% at 166kW output power.

A three-level bidirectional AC-DC converter with H8 topology is proposed to combine the advantages of both neutral-point clamped and flying-capacitor three-level converters for medium voltage AC-DC solid-state transformer applications. The innovative H8 converter features self-balanced capacitor voltage, common-mode voltage elimination, and small capacitance of the flying capacitors. The proposed carrier-based modulation enables the H8 converter to operate under both active and reactive power conditions. A 10 kVA AC-DC converter prototype with 1.7 kV SiC MOSFETs and 3.3 kV SiC diodes verifies the feasibility and advantages of the proposed topology and the modulation method. The capacitance of the flying capacitors in the H8 converter is reduced by 45 times compared to that of the flying-capacitor converters. The H8 converter efficiency is tested up to 99% at 2 kV DC voltage. The proposed H8 converter is suitable for the next-generation PV inverter, grid-forming inverter, MV fast charger, and SST applications.

Following the continuous development of wide bandgap (WBG) devices and multilevel converter technology, medium voltage (MV) active front ends (AFEs) are becoming promising in future high-power-density and high-power applications. However, the cost issue is one of the major drawbacks, which stops the WBG devices from being widely applied in high-power areas. This paper proposes a silicon carbide (SiC) and silicon (Si) hybrid five-level unidirectional rectifier. It requires only four SiC MOSFETs with relatively low blocking voltage and four Si diodes. Meanwhile, by adding snubber capacitors, all the Si devices are with low-speed switching, and the voltage stresses of fast SiC MOSFETs are minimized. In this paper, operational analysis and carrier-based phase-disposition PWM scheme for this circuit are discussed in detail. The capacitor voltage balancing and unity power factor are both realized. Simulation and scaled-down experimental results are demonstrated to verify the proposed rectifier. Furthermore, the comparison of the hybrid five-level rectifiers is given to show the advantages of the proposed rectifier in terms of voltage stress, efficiency, and cost.

In this paper, a new triple-switch triple-mode (TS-TM) high step-up DC-DC converter has been proposed. The proposed converter consists of three switches, four diodes, two magnetically coupled inductors, and three capacitors. This converter can provide a high voltage conversion ratio with high power efficiency and low voltage stress across the power semiconductor components. Due to the low voltage stresses of the power semiconductors and implementing the coupled inductors technique, the proposed converter is a low-cost and high-efficient structure in comparison to the other similar TS-TM structures. In order to clarify the advantages of the proposed converter, the required mathematical calculations and comparison results with similar converters are presented. Also, a novel TS-TM with transformer (TS-TMTR) has been proposed to overcome the electromagnetic interface (EMI) problems. Furthermore, a 500W experimental prototype is built and its performance with different values of duty cycles has been tested to prove the claimed features of the proposed converter. 94.5% maximum power efficiency of the assembled prototype has been obtained at 260W output power.

Reliable and affordable AC/AC power conversion plays a key role in supplying various electrical equipment. Among the options available, direct matrix converter (DMC) outperforms its counterparts (e.g. AC/DC/AC), in terms of lifespan and compactness, due to its omission of fragile and bulky dc-link capacitors. However, most off-the-shelf DMC modules suffer from high input current spikes, which if unresolved, can noticeably increase current stresses and lower efficiency. Origin of the spikes and a mechanism for reducing them are hence studied in the paper, before developing a low-cost SiC-Si hybrid module for implementing DMC reliably and compactly. The developed module consists of 18 Si insulated gate bipolar transistors (IGBTs) and 18 SiC junction barrier Schottky (JBS) diodes connected in a common-collector structure. The improved reverse recovery property of the SiC JBS diodes then permits the hybrid module to operate with mitigated current spikes. To demonstrate, the hybrid module has been fabricated, tested and compared with two counterparts in terms of their input current spikes and power losses over different output voltages and switching frequencies. Experimental results have proven the expected performances of the hybrid DMC module, which collectively, can accelerate large-scale emergence of small all-semiconductor drives for industrial pumps, cooling and refrigeration systems, and others widely needed in developing economies.

The short rise time observed in the PWM voltages generated by ultrafast wide bandgap devices increases the amplitude of voltage harmonics at higher frequencies. These harmonics can excite the resonances of medium-frequency transformers (MFTs), resulting in overvoltages inside the windings during continuous operation. Without further measures, these overvoltages can lead to unexpectedly high electric fields in the insulation material, which can result in partial discharge, accelerated aging, and possible failure of the MFT. To avoid these effects, the mechanism causing the overvoltages has to be understood and quantified during the design process. Based on this, the MFT can be designed in a way that the overvoltages vanish or are tolerable. Therefore, the voltage distribution inside the MFT windings is analyzed by a fully coupled multiconductor transmission line model, which includes the damping effect of electromagnetic losses in the litz wire and the core. This method is verified by measuring the transfer functions of the voltage to ground of individual turns and their voltage waveforms during continuous operation. The waveforms indicate repeating overvoltages inside the windings. A guideline for the design verification and a simplified approach to speed-up the modeling process are presented.

This paper proposes a new dc solid-state circuit breaker (SSCB) based on silicon carbide (SiC) MOSFETs. There are two main contributions. First, a transient current commutation (TCC) is obtained in the main switch during current interruption. To achieve this, a compact and fast active injection circuit (AIC) is employed. TCC brings two main benefits: 1) it eliminates the effects of parasitic inductances in circuit connections and removes voltage oscillations on the gate of the main switch, which prevents spurious turn-on; 2) it eliminates the transient power shock on the switch during turn-off, which extends the life-time of SSCB and increases its reliability. Second, the voltage on the employed metal oxide varistor (MOV) is reduced to zero during the off-state. This extends the maximum allowable dc bus voltage on the SSCB and solves the MOV reliability issue in the SSCBs. The presented SSCB employs a time-sequence control and needs no real-time detections of the dc current, which simplify the design. LTspice simulations of 380 V/80 A and 600 V/80 A are presented, and the results are compared with MOV based SSCBs and MOV resistor-capacitor-diode (MOV-RCD) based SSCBs. Also, experiments of a 380 V/80 A prototype validate the effectiveness of the proposed SSCB in practice where the voltage on the SSCB is clamped to 721 V with a fixed response time of 9.4 μs.

Photovoltaic (PV) system's performance is significantly affected by its orientation and tilt angle. Experimental investigation (indoor and outdoor) has been carried out to trace the variation in PV performance and electrical parameters at varying tilt angles in Malaysian conditions. There were two experimental modus: 1) varying module tilt under constant irradiation level, 2) varying irradiation intensity at the optimum tilt set up. For the former scheme, the irradiation level was maintained at 750 W/m2, and for the later arrangement, the module tilt angle was varied from 0o to 80o by means of a single-axis tracker. Results show that under constant irradiation of 750 W/m2, every 5o increase in tilt angle causes a power drop of 2.09 W at indoor and 3.45 W at outdoor. In contrast, for the same condition, efficiency decreases by 0.54% for indoor case and by 0.76% at outdoor. On the other hand, for every 100 W/m2 increase in irradiation, solar cell temperature rises by 7.52°C at indoor and by 5.67°C at outdoor. As of module electrical parameters, open-circuit voltage, short-circuit current, maximum power point voltage and maximum power point current drops substantially with increasing tilt angle, whereas fill factor drops rather gradually. Outdoor experimental investigation confirms that the optimum tilt angle at Malaysian conditions is 15o and orienting a PV module this angle will maximize the sun's energy captured and thereby enhance its performance.

For certain field-effect transistors (FETs) in soft-switching operation, the large-signal behavior of their output capacitance ( Co ) has shown to deviate considerably from the datasheet values. This can have a significant effect on hard-switching losses if the value of output charge is also different for a given voltage. In addition, standard hard-switching tests are incapable of fully setting apart the contributions from Co , whereas existing methods tailored to characterize Co losses in soft-switching operations subject Co to a fundamentally different charge–discharge process, and hence, might not predict the correct behavior for hard switching. To address this, first, we analyze and establish the particular charge–discharge conditions that Co undergoes in hard-switching circuits by considering a half bridge at no-load conditions. We show that the channel of the switching device incurs a fixed energy loss during the turn- on process, which is separated into co-energy and stored energy components of the top (complementary) and bottom (switching) devices, respectively. Exploiting this, a new measurement technique is developed to obtain output-charge versus voltage curves of devices subjected to actual hard switching. The experimental results for commercial Si, SiC, and GaN devices indicate that the effective charge-capacity of Co for hard switching can considerably vary from the values based on datasheets or Sawyer–Tower circuit; this could greatly undermine efficiency and thermal optimizations in the design phase of power converters.

In conventional medium voltage Solid-State Circuit Breakers (SSCBs), series-connected semiconductor switches are used with Metal Oxide Varistors (MOVs) in parallel with each of them to extend the voltage ratings of the breakers without incurring the dynamic voltage unbalance. Besides, for isolating the faults at faster speeds, the clamped surge voltages of the MOVs are always much higher than the system voltages. For those reasons, the voltage ratings of all the switches in the SSCBs have to be overdesigned according to the surge voltage values, which causes high material costs along with nonideal conduction losses in the solid-state circuit breakers employed for medium voltage DC distribution systems. To solve this dilemma, a Surgeless Diode-Clamped Multilevel Solid-State Circuit Breaker has been proposed in this paper. It offers an ultrafast isolation speed with no significant surge voltages or dynamic unbalanced voltage across the semiconductor switches. With these attributes, the proposed SSCB can potentially use the semiconductor switches rated at lower voltages compared to conventional SSCBs and have higher efficiency along with faster isolation speed. The simulation and experimental results are presented to validate the technical feasibility and practical values of the proposed solid-state circuit breaker.

A solid-liquid triboelectric nanogenerator (TENG) has attracted increasing research interest in relation to the development of regeneration energy based on water resources. The output of solid-liquid TENG remains unsolved, however, because of the low voltage output that impedes wide applications. To this end, in this work we developed a miniaturized microfluidic channel-based TENG device for highly efficient conversion of energy from the transport of a water droplet to an electrical output. We investigated an optimized design in a triboelectric material, the droplet transport and the electrostatic induction layer to provide a high voltage output and stable energy harvesting. The optimized device demonstrated maximum voltage amplitude 102 mV with an ultralow liquid consumption, 0.36 [Formula: see text], resulting in sample-energy conversion 283.33 mV/ [Formula: see text]. This novel device is expected potentially to address the limitations imposed by sample consumption in energy harvesting in the future.

In this paper, an interleaved coupled-inductor (CI) based bidirectional dc-dc converter (BDC) is proposed with a higher voltage conversion ratio (VCR). In proposed interleave CI-based BDC (ICI-BDC), the CIs can operate as both a filter inductor and a transformer simultaneously, so that the power density is improved. As a transformer, the turns ratio of CIs is used to improve the VCR with a voltage stress reduction purpose. Furthermore, the interleaved technique can well achieve the low current ripple and reduced current stress in this topology. To control ICI-BDC, the PWM plus phase-shift (PPS) control is employed, where the duty cycle is used to match the two side voltages, and the phase-shift angle is used to control the amount and direction of power flow. Uniquely, a difference value is set between the two side duty cycles The duty cycle of the high voltage side (HVS) is smaller than that of the low voltage side (LVS) by a fixed value. All the switches can achieve soft-switching even at light load condition, which can improve the transmission efficiency. Experimental results obtained from a 1-kW prototype show a high efficiency under all loading conditions, validating the proposed ICI-BDC topology and control method.

The snappy reverse recovery (SRR) and failure of high-voltage non-punch-through (NPT)-PIN diodes under extreme working conditions is of great significance to the reliability evaluation of operating diodes in actual power electronic devices. In this paper, the analysis of the physical mechanism of the diode SRR and the restrictions of the traditional PT-PIN diode model are made. Then, the traditional model for soft recovery is improved in order to accurately describe the diode SRR characteristics. Simulations of key dynamic performances of the established model agree well with the testing results. Furthermore, a suppression method for diode SRR based on the optimal RC snubber circuit is proposed. A high-voltage NPT-PIN diode used in the DC-DC converter with different RC snubber circuits is simulated using the proposed diode snappy model and tested. The comparison results show good consistency between the simulated and measured voltage and current peaks and the diode SRR can be suppressed effectively. The model developed and the results are of much importance to the prediction of the safe operation area of the diode and to the reliability improvement of power electronic device.