High Current Applications Research Articles

A Novel ZVS/ZCS Push-Pull LC Resonant DC-DC Converter for Energy Sources

In this paper, a novel soft switching push-pull LC resonant DC-DC converter for energy sources is presented. In a high step-up converter, the input of primary side possesses low voltage and high current, so the losses caused by the current account for most of the total power loss. At the same time, the high-voltage stress of the high-voltage output components on the secondary side is also a major problem. Therefore, a high-gain isolated push-pull converter with a secondary-side resonant circuit is proposed, so that the primary-side switches have zero voltage switching (ZVS) and the secondary-side diodes have zero current switching (ZCS). The push-pull structure can reduce the number of active switches, so that the total power loss on the primary side can be reduced. The converter has a resonant tank circuit arranged between the secondary side of isolation transformer and the high-voltage output rectification module. The high-voltage output rectifier module adopts a full-bridge architecture suitable for high-voltage coupling connection. The low-side power switching module adopts a push-pull architecture suitable for low-voltage and high-current applications. The resonant tank circuit uses an inductor–capacitor (LC) structure to improve the resonant tank circuit, which achieves soft switching during power transfer, increasing the efficiency of the converter and improving the electromagnetic compatibility. The main advantage of this technology is that the secondary-side leakage inductance of transformer and the resonant capacitance are connected in series to achieve ZVS for switches and ZCS for diodes. Finally, a prototype of a high-gain push-pull resonant converter was established. The converter was operated at a fixed switching frequency of 135 kHz and a duty cycle of approximately 0.5. The efficiency of the converter can reach 97.1% under experimental tests at an output voltage of 400 V and a rated output power of 500 W.

Development of Phase-Shift Full-Bridge Converter With Integrated Winding Planar Two-Transformer for LDC

This study proposes a new phase-shift full-bridge (PSFB) converter with an integrated winding planar two-transformer for a low-voltage dc–dc converter (LDC). An LDC is a dc–dc converter that supplies power to a 12-V auxiliary battery (A_BAT) and loads from the main battery (M_BAT) of electric vehicles (EVs), used in low-voltage and high-current output applications. PSFB converter is widely used as a suitable topology for such systems. In order to improve the power density, the integrated planar magnetics is designed in the proposed PSFB converter. Furthermore, the size of the transformer is optimized considering the footprint and core loss of components. To confirm the validity of the proposed converter, a 2.1-kW prototype LDC with an input voltage range of 400–800 V and an output voltage of 14 V is analyzed, and the operating characteristics are described. The proposed converter achieves a maximum efficiency of 95.4% and a power density of 5.2 kW/L.

Gate Drive Circuit Implementation for Parallel Connection of Power Devices Considering Parasitic Inductance

SiC devices are potential future power devices because of their higher switching speed and lower ON resistance than those of Si devices. Research and development efforts to apply them in medium- and large-capacity power conversion circuits are underway. However, SiC power devices in TO packages, which are general-purpose packages, are difficult to apply in high-current applications owing to their low current ratings. Therefore, increasing the capacity of power devices by connecting them in parallel is being studied. However, the current imbalance during switching due to the differences in device characteristics and variations in parasitic inductance is problem. This study proposed a current-balancing procedure focused on the parasitic inductances around power devices and gate drive circuit implementation. The proposed method was verified by conducting double-pulse tests at 300V and 200A.

Experimental investigation and comparative analysis of immersion cooling of lithium-ion batteries using mineral and therminol oil

Renewable energy can potentially mitigate the adverse effects of energy and environmental crises. The Lithium-ion battery, a storage system investigated in the present study, has a potential to increase the penetration of renewable energy technologies, due to its high mass and volumetric energy density. However, thermal management strategies are necessary for lithium-ion battery electrical storage to grow technologically and gain widespread acceptability. In the present work, a comparative study of the different cooling methods, namely, forced air cooling (FAC), direct liquid contact cooling (i.e., Mineral oil cooling (MOC), and therminol oil cooling (TOC)) with low-cost coolants have been carried out on 20 cells of 10Ah lithium-ion battery-stack at a discharge rate of 1C, 1.5C, 2C, 2.5C, and 3C. It is found that the maximum temperature of the battery module is reduced by 43.83%, 49.17%, and 51.54% for forced air cooling, therminol oil cooling, and mineral oil cooling respectively, at 3C discharge rate, compared to the natural air-cooling method.Under the experimental conditions studied, the maximum temperature of the battery pack is found to be within the desired value during forced convection cooling only up to 1.5C discharge rate, while the immersion cooling performed satisfactorily up to 2C discharge rate. This study demonstrates direct liquid contact cooling with low-cost dielectric fluids as a safe and efficient thermal management technology for high-energy density and high-current lithium-ion battery applications.

Portable Prototype of Hydrogen Fuel Cells for Educational Training

This paper presents an experimental prototype of hydrogen fuel cells suitable for training engineering students. The presented system is designed to teach students the V-I characteristics of the fuel cells and how to record the V-I characteristics curve in the case of a single or multiple fuel cells. The prototype contains a compact electrolyzer to produce hydrogen and oxygen to the fuel cell. The fuel cell generates electricity to supply power to various types of loads. The paper also illustrates how to calculate the efficiency of fuel cells in series and parallel modes of operation. In the series mode of operation, it is mathematically proven that the efficiency is higher at lower currents. Still, the fuel cell operating area is required where the power is the highest. According to experimental results, the efficiency in the case of series connection is approximately 25%, while in parallel operation mode, the efficiency is about 50%. Thus, a parallel connection is recommended in the high current applications because the efficiency is higher than the one resulted from series connection. As explained later in the study plan, several other experiments can be performed using this educational kit.

AC Resistance and Leakage Inductance Estimation for Planar Transformers With Parallel-Connected Windings

Regarding the ever-increasing switching frequency of power converters, there is a lack of tools to perform a quick and effective optimization of the high-frequency transformers embedded in isolated power converters. Indeed, at high operating frequency, the geometry of the core and windings deeply impacts the overall transformer performance. Specifically, assessing accurately the current distribution in parallel-connected windings is a challenging and key issue. Winding parallelization, frequently implemented in low-voltage and high-current applications so as to decrease Joule losses, may be an ineffective solution because of skin and proximity effects. They create an unbalanced current distribution in the parallel-connected windings, which greatly impacts the ac resistance and leakage inductance of the transformer. This article proposes an innovative frequency analytical model permitting to simply and accurately compute the current distribution in the transformer windings, the ac resistance, and the leakage inductance. The proposed approach is comprehensively presented, validated using both measurements and two-dimensional finite element analysis and analyzed giving guidelines to engineers designing high-frequency transformers.

High Power Parallel Hybrid DC-DC Converter

The parallel hybrid converter (PHC) is gaining popularity for high voltage direct current (HVdc) applications. The PHC features low energy storage requirement and low conduction losses in the sub-modules (SMs). Moreover, the PHC requires lower number of SMs and switching devices. However, the existing PHC configuration needs harmonic voltage injection in the chain-links (CLs) to feed the ac grid, thereby injecting harmonic currents into the main DC-link. Additionally, the existing PHC lacks dc fault-tolerant capability. A new front–to-front dc-dc configuration called as parallel hybrid dc-dc converter (PHDC) for HVdc application is presented. The proposed PHDC eliminates the need of harmonic voltage injection and provides the dc fault-tolerant capability. Furthermore, the proposed PHDC requires lesser energy storage and smaller interlinking transformers than in the PHC used for ac-dc application. The detailed mathematical analysis with design procedure considering the dc-dc conversion application is presented. The authenticity of the proposed dc-dc converter is verified by both analytical and simulation studies. Finally, a three phase front-to-front experimental setup is tested for different operating conditions and results are presented.

Investigations on Wide-Gap Al0.21Ga0.79N Channel MOS-HFETs With In0.12Al0.76Ga0.12N Barrier/Buffer and Drain Field-Plate

This work investigates, for the first time, wide-gap Al0.21Ga0.79N channel metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) with In0.12Al0.76Ga0.12N barrier/buffer and drain field-plate (DFP) designs. High-k and wide-gap Al2O3 was grown as the gate oxide and surface passivation by using non-vacuum ultrasonic spray pyrolysis deposition (USPD) technique. A control device having the same epitaxial layers, except with In0.12Al0.88N barrier/buffer was studied in comparison. Enhanced spontaneous polarization effect, improved interfacial quality, and enhanced carrier confinement have been achieved by using the In0.12Al0.76Ga0.12N barrier/buffer design, which has successfully resulted in improved carrier transport, increased electron concentration, and high current densities. The present In0.12Al0.76Ga0.12N/AlN/Al0.21Ga0.79N MOS-HFET design with (without) DFP design has demonstrated superior maximum drain-source current density (IDS, max) of >1 (>1) A/mm at VDS = 20 V, high saturated drain-source current density at VGS = 0 V (IDSS0) of 791.1 (755) mA/mm, and low specific on-resistance (Ron, sp) of 2.83 (2.81) mΩ/cm2. High device figure-of-merit (FOM) on BVDS2/Ron, sp of 93.7 (75.4) MW/cm2 was also obtained with the three-terminal on-state drain-source breakdown voltage (BVDS) of 515 (460) V. The present design is promisingly advantageous to high-current and high-voltage power-switching circuit applications.

A Novel Modular Multilevel Converter Based on Interleaved Half-Bridge Submodules

A new Modular Multilevel Converter with Interleaved half-bridge Sub-Modules (ISM-MMC) is proposed in this article. The ISM-MMC exhibits higher modularity and scalability in terms of current ratings with respect to a conventional MMC while preserving the typical voltage-level adaptiveness. The ISM-MMC brings the known advantages of classical MMC to low-voltage, high-current applications making it a novel candidate for the sector of ultrafast chargers for all types of electric vehicles (EVs). This advanced topology makes it possible to easily reach the charging power of the EV charging system up to 4.5 MW and beyond with a low-voltage supply. To operate the new converter, a hybrid modulation scheme that helps to exploit the advantages of the interleaving scheme is implemented and explained in this article. It has been verified that the typical MMC control methods are still applicable for ISM-MMC. A comparative study between classical MMC and ISM-MMC configurations in terms of output characteristics and efficiency is also given. Furthermore, it has been demonstrated that the number of ac voltage levels is synthetically multiplied by the number of interleaved half-bridge legs in submodules. Simulations, hardware in the loop, and experimental tests are carried out to demonstrate the feasibility of the proposed topology and the implemented modulation scheme.

Development of Multicellular Converter with Magnetic Coupler for Space Charge Measurement on DC Cable

One of the main issues on high voltage direct current (HVDC) cable is the electric field distribution on the insulation induced by space charges accumulation. Indeed, the space charges can cause a local increase of the electric field, which will accelerate ageing and may lead to dielectric breakdown. The TSM is one of the techniques that allow space charge measurements. The principle of the TSM consists in disturbing the electrostatic balance of the cable insulation system using a short thermal stimulus. For this study, the thermal pulse is created by Joule effect. This paper describes the structural optimization of a multi-cell DC-DC converter and its use in a high-current application to produce thermal stimulus. The design of the converter is first presented, then a multi-objective optimization is proposed for minimizing volume and losses. Finally, experimental results using a converter prototype which confirmed the space charge measurement principle are presented.

Effect of radical scavenger on electrical tree in cross‐linked polyethylene with large harmonic superimposed DC voltage

AbstractIn this study, three kinds of radical scavenger Chimassorb 944, Tinuvin 622, and Tinuvin 770 are used to suppress the growth of electrical trees in cross‐linked polyethylene (XLPE) with transient superimposed voltage under the temperature gradient. The tree morphology, tree length, accumulated damage, and time to breakdown are used to investigate the effect of radical scavenger on the electrical treeing process. It is found that under the temperature gradient caused by the temperature rise on the high voltage side, only Tinuvin 622 can always suppress the electrical tree as the temperature gradient rises. Under the temperature gradient caused by the temperature rise on the ground side, the three radical scavengers can all suppress the electrical tree. The breakdown of electrical tree exhibits the strong DC polarity dependence. Meanwhile, energy levels of these three radical scavengers are calculated through quantum chemistry, and the results indicate that radical scavengers have greater electron affinity, smaller ionisation energy, and smaller energy gap than XLPE. According to the surface potential decay test results at 60°C, it is found that all three radical scavengers can introduce deep traps. The different performances of radical scavengers under different temperature gradients and voltages are determined by the trap distribution characteristics, the molecular structure and chemical reaction of the additives themselves. It is concluded that Tinuvin 622 has potential for use in high voltage direct current XLPE cable application.

A GaN–Si hybrid integrated driver for narrow-pulse and high-current LiDAR applications

Light detection and ranging (LiDAR) is the most important active remote sensing tool and is widely used in civilian and military fields. There are a number of methods to drive laser diodes; the most common circuit topologies are capacitor-discharge resonant circuits. However, the performance of the silicon (Si)-based switching device limits the development of Light detection and ranging, such as the large figure of merit (FOM) and the stray inductance. Although different methods have been reported to resolve these problems, there are still great challenges in reducing the pressure on Light detection and ranging driver design. Hence, this work presents a gallium nitride (GaN)–Si hybrid integrated driver for a Light detection and ranging system. In the circuit, the switching power device uses GaN instead of a Si-based device, because GaN enables much better performance for pulsed-laser operation due to its near-ideal switching performance. Furthermore, a GaN push–pull driver stage between the GaN power device and the Si-based driver integrated circuit (IC) was innovatively introduced, which is integrated in the same chip with the GaN power device, thereby effectively reducing the parasitic parameters of the signal chain and enhancing the system reliability. The design and implementation of the Si-based IC and GaN IC are based on 0.18 µm 80–120 V Bipolar-CMOS-DMOS (BCD) technology and 0.5 µm p-GaN technology, respectively. The experimental results suggest that the proposed driver circuit output pulse width is 12.6 ns, and it can normally operate at 10 MHz with turn-on/turn-off delay is 11.94 ns. In addition, the driver was capable of generating approximately 8.25 A current pulses through a low ohmic load with a pulse width of approximately 12.4 ns. This work plays a vital role in promoting the development of information equipment and aerospace equipment such as precise ranging, high-efficiency power supplies, and high-speed motors.

Effect of thermal annealing on the electronic parameters of Al/p-Si/Cu double Schottky barrier heights

In this work, performance enhancements of a double Schottky rectifier diode with Cu contact on top of p-type Si and a back-side-Al contact due to an optimized thermal annealing process are reported. A decrease of the ideality factor for non-ohmic and ohmic Schottky contacts from 3.17 to 1.15 could be observed in conjunction with a barrier height reduction from 0.59 eV to 0.48 eV by thorough hydrofluoric acid treatment prior to annealing the sample for 15 min. at 450 °C in N2 atmosphere. Moreover, the barrier height and built-in voltage values decreased by increasing frequency in the ohmic contact structure. The results presented in this work demonstrate such ohmic contacts to be potential candidates for high current and low resistance Schottky diodes and applications.

Multi-layer anodes for high-current applications

In this work, we present a combination of experiments and modeling of a two-layer anode structure designed by EnPower Inc. for high-energy and fast-charge capabilities. The anode consists of lower porosity near the current collector and higher porosity near the separator with comparable active materials in both regions. A pseudo-two-dimensional electrochemical–thermal model was designed to represent the performance of this electrode. Simulations, consistent with experiments, show superior ion transport and lithiation in the multi-layer anode (MLA) compared to a conventional single-layer anode (SLA). Surprisingly, this improved transport in MLA manifests as enhanced cathode performance during high-rate discharge and this, in turn, provides higher energy density for MLA. Similarly, during fast charge, less irreversible lithium is deposited due to this improved transport in MLA, and hence MLA exhibits less capacity fade compared to SLA. Polarization analysis demonstrates marginally lower cumulative overpotential for MLA in different case studies; however, MLA cells maintain a significantly higher capacity in the same conditions and have more than double the cycle life. This means despite the apparently limited polarization benefit provided by MLA; the MLA structure can more reliably be employed in cell designs. Additional design changes are also analyzed by means of the model.

Analysis of Electrochemical Performance with Dispersion Degree of CNTs in Electrode According to Ultrasonication Process and Slurry Viscosity for Lithium-Ion Battery.

Lithium-ion batteries (LIBs) continue to dominate the battery market with their efficient energy storage abilities and their ongoing development. However, at high charge/discharge C-rates their electrochemical performance decreases significantly. To improve the power density properties of LIBs, it is important to form a uniform electron transfer network in the cathode electrode via the addition of conductive additives. Carbon nanotubes (CNTs) with high crystallinity, high electrical conductivity, and high aspect ratio properties have gathered significant interest as cathode electrode conductive additives. However, due to the high aggregational properties of CNTs, it is difficult to form a uniform network for electron transfer within the electrode. In this study, to help fabricate electrodes with well-dispersed CNTs, various electrodes were prepared by controlling (i) the mixing order of the conductive material, binder, and active material, and (ii) the sonication process of the CNTs/NMP solution before the electrode slurry preparation. When the binder was mixed with a well sonicated CNTs/NMP solution, the CNTs uniformly adsorbed to the then added cathode material of LiNi0.6Co0.2Mn0.2O2 and were well-dispersed to form a flowing uniform network. This electrode fabrication process achieved > 98.74% capacity retention after 50 cycles at 5C via suppressed polarization at high current densities and a more reversible H1-M phase transition of the active material. Our study presents a novel design benchmark for the fabricating of electrodes applying well-dispersed CNTs, which can facilitate the application of LIBs in high current density applications.

High current limits in chemical vapor deposited graphene spintronic devices

Understanding the stability and current-carrying capacity of graphene spintronic devices is key to their applications in graphene channel-based spin current sensors, spin-torque oscillators, and potential spin-integrated circuits. However, despite the demonstrated high current densities in exfoliated graphene, the current-carrying capacity of large-scale chemical vapor deposited (CVD) graphene is not established. Particularly, the grainy nature of chemical vapor deposited graphene and the presence of a tunnel barrier in CVD graphene spin devices pose questions about the stability of high current electrical spin injection. In this work, we observe that despite structural imperfections, CVD graphene sustains remarkably highest currents of 5.2 × 108 A/cm2, up to two orders higher than previously reported values in multilayer CVD graphene, with the capacity primarily dependent upon the sheet resistance of graphene. Furthermore, we notice a reversible regime, up to which CVD graphene can be operated without degradation with operating currents as high as 108 A/cm2, significantly high and durable over long time of operation with spin valve signals observed up to such high current densities. At the same time, the tunnel barrier resistance can be modified by the application of high currents. Our results demonstrate the robustness of large-scale CVD graphene and bring fresh insights for engineering and harnessing pure spin currents for innovative device applications.

Analysis and small-signal modeling of simplified cascade multiphase DC-DC buck converter

One of the power converters that are often implemented in renewable energy applications is a DC-DC power converter. One of such converters is a step-down converter or buck converter whose output voltage is lower than its input. A novel DC-DC buck converter for low output-voltage and high output current applications is presented in this paper. When compared to the conventional buck converter, the voltage ratio of the proposed topology is higher. The output of this converter also has lower ripple. Thus, the proposed topology is appropriate for renewable applications. The operating principle and small-signal model analysis are discussed in detailed. Finally, a simulation studies is carried out by PSIM to verify performances of the offered topology

Control-Oriented Physics-Based Modeling and Observer Design for State-of-Charge Estimation of Lithium-Ion Cells for High Current Applications

This article proposes a physics-based control-oriented model and observer design for the state-of-charge (SoC) estimation of lithium-ion cells for applications involving high magnitude fluctuating current profiles. The physics-based single-particle model (SPM) provides enhanced accuracy due to the inclusion of electrolyte dynamics and addresses the issue of nonobservability associated with it. The computationally efficient physics-based model is utilized to design a robust observer-based SoC estimator in the framework of linear matrix inequality to guarantee fast convergence despite parametric uncertainty in the state and output equations, and unknown initial conditions. The observer performance is validated using FTP75 and US06 dynamic tests at different temperatures, and the results are compared with the standard unscented Kalman filter (UKF). The mean SoC estimation error and the integral square error of the estimated SoC for the proposed observer are at least one order of magnitude smaller than that of UKF. Furthermore, robustness to ±30% parametric uncertainty, measurement noise, and unknown initial conditions is demonstrated through Monte Carlo simulations at different temperatures.

Silver Graphite Coating for High Current Applications

Silver Graphite Coating for High Current Applications

A 1.2-A Calibration-Free Hybrid LDO With In-Loop Quantization and Auxiliary Constant Current Control Achieving High Accuracy and Fast DVS

This paper presents a high-current calibration-free analog-digital hybrid controlled LDO for large-area digital load. The proposed architecture has the advantages of an analog controller (continuous and high DC accuracy) with distributed digital power transistors (flexible and scalable for high current applications). Distinctive from the conventional digital LDOs that directly quantize the output voltage, the proposed LDO utilizes an error amplifier (EA) to pre-amplify the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{V}_{\mathrm {OUT}}$ </tex-math></inline-formula> error. Then, a 5-bit time-to-digital converter (TDC) quantizes the processed analog error signal subsequently transformed into a thermometer code that directly controls the distributed digital power transistors. This design can pull off high DC accuracy even without calibration. Besides, we implement an auxiliary constant current (ACC) circuit to solve reliability issues and to improve the stability under a large voltage dropout. Fabricated in a 28-nm bulk CMOS process with a 1.2-A load capability, the proposed LDO achieves 2- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{V}$ </tex-math></inline-formula> /mA load regulation and close to 1.5% output accuracy. By employing a wide bandwidth EA and a fast TDC, the hybrid LDO can obtain a fast transient response. The measured undershoot is 70 mV with a 0.6-A load step within 10-ns edge time, and the output voltage can scale from 0.6 V to 0.9 V within 30 ns.