Gate Loop Research Articles

A High Current High Power Density Motor Drive for a 48-Volt Belt-Driven Starter Generator (BSG) System

A 48 V Belt-Driven Starter Generator (BSG) System is featured with high output current, high starting torque, and highly efficient thermal management. This paper firstly elaborates hardware design considerations of a high power density three-phase BSG inverter to address the challenges of even current distribution among paralleled MOSFETs, small drain-source voltage spike and good thermal dissipation. In order to satisfy the high-current requirement, a careful selection of MOSFET device with high-current rating and low on-resistance has been presented. In order to suppress circulating current among paralleled devices, individual gate resistors have been placed in the gate loop of each MOSFET. In order to provide good thermal dissipation, an Insulated Metal Substrate (IMS) board and single-layer layout technique have been implemented. Multiple low-profile electrolytic capacitors are used to increase the power density of the prototype. Moreover, the use of automotive gate driver IC TLE9180 and microcontroller TC1782 makes the prototype more readily accepted by industry. An improved Interior Permanent Magnet (IPM) motor control strategy and a pump-back system based on a virtual machine concept have been implemented to facilitate the validation of the prototype under rated condition without using a real motor. The control algorithm automatically adjusts the onset of field-weakening by using an additional inverter voltage loop and takes into account the nonlinearity of the stator flux linkage by using curve fitting technique, which makes the motor drive adaptive to machine parameter changes as well as DC bus voltage fluctuation. A three-phase BSG inverter prototype with a peak power of 12 kW has been built and tested. The prototype power density has reached 20.3 kW/L. Both PLECS simulations and hardware experiments show a continuous and stable operation with up to 200 A phase current and up to 600 Hz output frequency.

Features of particle flows hydrodynamics in recirculating systems and pneumatic valves of CFB boilers

Circulating fluidized bed (CFB) technology is characterized by relatively high reactor velocity that exceed the transport velocity of medium-sized particles, and the presence of separators (mainly of the cyclone type) with a system for returning trapped particles to the reactor. These systems consist of downpipes equipped in the lower part with pneumatic valves for transporting material from the low (atmospheric) pressure zone in the cyclone to the high-pressure zone in the furnace. Pneumatic valves operate on the principle of fluidized valves, and the locking function of the valves is performed by a lifting section with an inclined return flow to the furnace (loop gate or J-valve) or a horizontal section connecting the drain to the furnace (L-valve). The report discusses the current state of development and methods for standpipe and pneumatic valve operation and calculating. A brief description of the test rigs and the results of our own studies of CFB returned system are given. The results of the work can be used for the design and commissioning of a circulating fluidized bed reactors, including systems with dual reactors for polygenerating systems and chemical looping.

A pH-independent quiet OmpG pore with enhanced electrostatic repulsion among the extracellular loops

Membrane protein pores have emerged as powerful nanopore sensors for single-molecule detection. OmpG, a monomeric nanopore, is comprised of fourteen β-strands connected by seven flexible extracellular loops. The OmpG nanopore exhibits pH-dependent gating as revealed by planar lipid bilayer studies. Current evidence strongly suggests that the dynamic movement of loop 6 is responsible for the gating mechanism. In this work, we have shown that enhancing the electrostatic repulsion forces between extracellular loops suppressed the pH-dependent gating. Our mutant containing additional negative charges in loop 6 and loop 1 exhibited minimal spontaneous gating and reduced sensitivity to pH changes compared to the wild type OmpG. These results provide new evidence to support the mechanism of OmpG gating controlled by the complex electrostatic network around the gating loop 6. The pH-independent quiet OmpG pores could potentially be used as a sensing platform that operates at a broad range of pH conditions.

A Comprehensive Investigation on Short-Circuit Oscillation of p-GaN HEMTs

This article presents a study on the short-circuit (SC) instability of p-doped gate gallium nitride (p-GaN) high-electron-mobility transistors (HEMTs). Under SC condition, self-sustained oscillation occurs when a package stray inductance is introduced in a common source. The SC oscillation features some unique characteristics. With higher dc-bus voltage, the SC oscillation tends to be more unstable. The SC oscillation of p-GaN HEMTs is, thereby, a real threat to the converter operation. When the common-source inductance is eliminated or a larger gate resistor is utilized, the SC oscillation can be dampened. Due to the SPICE simulation, the self-sustained SC oscillation is reproduced. The analyses on the simulated waveforms reveal a positive feedback mechanism that excites the SC oscillation. An analytical model is, thereby, derived to analyze the instability of the positive feedback system. The analyses reveal that the SC oscillation becomes more unstable when the power loop or gate loop has smaller stray inductances, which makes some conventional oscillation suppression methods invalid. To avoid SC oscillation, some effective guidelines are proposed at the end of the article.

Online Junction Temperature Measurement for SiC MOSFET Based on Dynamic Threshold Voltage Extraction

The online junction temperature monitoring of power devices is a viable technique to ensure the reliable operation of mission-critical power electronic converters. This article provides a potential approach for the junction temperature estimation of SiC MOSFETs based on the dynamic threshold voltage. The proposed method is independent of load current variation, which eliminates the complicated calibration procedure with load current. First, the physical mechanism and the temperature dependence of the dynamic threshold voltage are analyzed. An analytical model for the dynamic threshold voltage is built to investigate the effects of gate loop parameters on the temperature sensitivity and measurement accuracy. Then, the principle of the dynamic threshold voltage measurement circuit is introduced. Finally, the proposed dynamic threshold voltage measurement circuit is experimentally evaluated through the double-pulse tests. The experimental results show that the dynamic threshold voltage of SiC MOSFET has a good linear relationship with junction temperature. The temperature sensitivity of the dynamic threshold voltage of two SiC MOSFETs is approximately 5.2 mV/°C and 19.6 mV/°C, respectively.

Differential splicing of the lectin domain of an O-glycosyltransferase modulates both peptide and glycopeptide preferences

Mucin-type O-glycosylation is an essential post-translational modification required for protein secretion, extracellular matrix formation, and organ growth. O-Glycosylation is initiated by a large family of enzymes (GALNTs in mammals and PGANTs in Drosophila) that catalyze the addition of GalNAc onto the hydroxyl groups of serines or threonines in protein substrates. These enzymes contain two functional domains: a catalytic domain and a C-terminal ricin-like lectin domain comprised of three potential GalNAc recognition repeats termed α, β, and γ. The catalytic domain is responsible for binding donor and acceptor substrates and catalyzing transfer of GalNAc, whereas the lectin domain recognizes more distant extant GalNAc on previously glycosylated substrates. We previously demonstrated a novel role for the α repeat of lectin domain in influencing charged peptide preferences. Here, we further interrogate how the differentially spliced α repeat of the PGANT9A and PGANT9B O-glycosyltransferases confers distinct preferences for a variety of endogenous substrates. Through biochemical analyses and in silico modeling using preferred substrates, we find that a combination of charged residues within the α repeat and charged residues in the flexible gating loop of the catalytic domain distinctively influence the peptide substrate preferences of each splice variant. Moreover, PGANT9A and PGANT9B also display unique glycopeptide preferences. These data illustrate how changes within the noncatalytic lectin domain can alter the recognition of both peptide and glycopeptide substrates. Overall, our results elucidate a novel mechanism for modulating substrate preferences of O-glycosyltransferases via alternative splicing within specific subregions of functional domains.

Influence of Gate Loop Inductance on TSEP-Based Junction Temperature Monitoring for IGBT

In this article, the influence of gate loop inductance on the insulated-gate bipolar transistor (IGBT) junction temperature monitoring based on the transient peak gate current temperature-sensitive electrical parameter (TSEP) methods is investigated using the time-domain analysis, SPICE simulation, and experimental work. It is observed that the peak gate current decreases considerably with increasing gate loop inductance, which was not addressed by a previous work. An improved junction temperature estimation model is developed to address this issue and is experimentally validated over a wide range of gate loop inductances. Unlike the previously reported model calibrated for a fixed gate loop inductance, the new model can provide accurate junction temperature monitoring in any power converter based on the same IGBT with a wide range of gate loop inductance values. An error of less than 6.2 °C in IGBT junction temperature estimation is demonstrated even when the gate loop inductance varies by 247%.

Crystal structure of Oryza sativa TDC reveals the substrate specificity for TDC-mediated melatonin biosynthesis

Plant tryptophan decarboxylase (TDC) is a type II Pyridoxal-5′-phosphate-dependent decarboxylase (PLP_DC) that could be used as a target to genetically improve crops. However, lack of accurate structural information on plant TDC hampers the understanding of its decarboxylation mechanisms. In the present study, the crystal structures of Oryza sativa TDC (OsTDC) in its complexes with pyridoxal-5′-phosphate, tryptamine and serotonin were determined. The structures provide detailed interaction information between TDC and its substrates. The Y359 residue from the loop gate is a proton donor and forms a Lewis acid-base pair with serotonin/tryptamine, which is associated with product release. The H214 residue is responsible for PLP binding and proton transfer, and its proper interaction with Y359 is essential for OsTDC enzyme activity. The extra hydrogen bonds formed between the 5-hydroxyl group of serotonin and the backbone carboxyl groups of F104 and P105 explain the discrepancy between the catalytic activity of TDC in tryptophan and in 5-hydroxytryptophan. In addition, an evolutionary analysis revealed that type II PLP_DC originated from glutamic acid decarboxylase, potentially as an adaptive evolution of mechanism in organisms in extreme environments. This study is, to our knowledge, the first to present a detailed analysis of the crystal structure of OsTDC in these complexes. The information regarding the catalytic mechanism described here could facilitate the development of protocols to regulate melatonin levels and thereby contribute to crop improvement efforts to improve food security worldwide.

The single nucleotide β -arrestin2 variant, A248T, resembles dynamical properties of activated arrestin.

β -arrestins are responsible for termination of G protein-coupled receptor (GPCR)-mediated signaling. Association of single nucleotide variants with onset of crucial diseases has made this protein family hot targets in the field of GPCR-mediated pharmacology. However, impact of these mutations on function of these variants has remained elusive. In this study, structural and dynamical properties of one of β -arrestin2 (arrestin 3) variants, A248T, which has been identified in some cancer tissue samples, were investigated via molecular dynamics simulations. The results showed that the variant underwent structural rearrangements which are seen in crystal structures of active arrestin. Specifically, the “short helix” unravels and the “gate loop” swings forward as seen in crystal structures of receptor-bound and GPCR phosphopeptide-bound arrestin. Moreover, the “finger loop” samples upward position in the variant. Importantly, these regions harbor crucial residues that are involved in receptor binding interfaces. Cumulatively, these local structural rearrangements help the variant adopt active-like domain angle without perturbing the “polar core”. Considering that phosphorylation of the receptor is required for activation of arrestin, A248T might serve as a model system to understand phosphorylation-independent activation mechanism, thus enabling modulation of function of arrestin variants which are activated independent of receptor phosphorylation as seen in cancer.

The crystal structure of the tetrameric DABA-aminotransferase EctB, a rate-limiting enzyme in the ectoine biosynthesis pathway.

l-2,4-diaminobutyric acid (DABA) aminotransferases can catalyze the formation of amines at the distal ω-position of substrates, and is the intial andrate-limiting enzyme in the biosynthesis pathway of the cytoprotecting molecule (S)-2-methyl-1,4,5,6-tetrahydro-4-pyrimidine carboxylic acid (ectoine). Although there is an industrial interest in the biosynthesis of ectoine, the DABA aminotransferases remain poorly characterized. Herein, we present the crystal structure of EctB (2.45Å), a DABA aminotransferase from Chromohalobactersalexigens DSM 3043, a well-studied organism with respect to osmoadaptation by ectoine biosynthesis. We investigate the enzyme's oligomeric state to show that EctB from C.salexigens is a tetramer of two functional dimers, and suggest conserved recognition sites for dimerization that also includes the characteristic gating loop that helps shape the active site of the neighboring monomer. Although ω-transaminases are known to have two binding pockets to accommodate for their dual substrate specificity, we herein provide the first description of two binding pockets in the active site that may account for the catalytic character of DABA aminotransferases. Furthermore, our biochemical data reveal that the EctB enzyme from C.salexigens is a thermostable, halotolerant enzyme with a broad pH tolerance which may be linked to its tetrameric state. Put together, this study creates a solid foundation for a deeper structural understanding of DABA aminotransferases and opening up for future downstream studies of EctB's catalytic character and its redesign as a better catalyst for ectoine biosynthesis. In summary, we believe that the EctB enzyme from C.salexigens can serve as a benchmark enzyme for characterization of DABA aminotransferases. DATABASE: Structural data are available in PDB database under the accession number 6RL5.

Rational Engineering of the Substrate Specificity of a Thermostable D-Hydantoinase (Dihydropyrimidinase).

D-hydantoinases catalyze an enantioselective opening of 5- and 6-membered cyclic structures and therefore can be used for the production of optically pure precursors for biomedical applications. The thermostable D-hydantoinase from Geobacillus stearothermophilus ATCC 31783 is a manganese-dependent enzyme and exhibits low activity towards bulky hydantoin derivatives. Homology modeling with a known 3D structure (PDB code: 1K1D) allowed us to identify the amino acids to be mutated at the substrate binding site and in its immediate vicinity to modulate the substrate specificity. Both single and double substituted mutants were generated by site-directed mutagenesis at appropriate sites located inside and outside of the stereochemistry gate loops (SGL) involved in the substrate binding. Substrate specificity and kinetic constant data demonstrate that the replacement of Phe159 and Trp287 with alanine leads to an increase in the enzyme activity towards D,L-5-benzyl and D,L-5-indolylmethyl hydantoins. The length of the side chain and the hydrophobicity of substrates are essential parameters to consider when designing the substrate binding pocket for bulky hydantoins. Our data highlight that D-hydantoinase is the authentic dihydropyrimidinase involved in the pyrimidine reductive catabolic pathway in moderate thermophiles.

S-adenosylmethionine synthases in plants: Structural characterization of type I and II isoenzymes from Arabidopsis thaliana and Medicago truncatula

S-adenosylmethionine synthases (MATs) are responsible for production of S-adenosylmethionine, the cofactor essential for various methylation reactions, production of polyamines and phytohormone ethylene, etc. Plants have two distinct MAT types (I and II). This work presents the structural analysis of MATs from Arabidopsis thaliana (AtMAT1 and AtMAT2, both type I) and Medicago truncatula (MtMAT3a, type II), which, unlike most MATs from other domains of life, are dimers where three-domain subunits are sandwiched flat with one another. Although MAT types are very similar, their subunits are differently oriented within the dimer. Structural snapshots along the enzymatic reaction reveal the exact conformation of precatalytic methionine in the active site and show a binding niche, characteristic only for plant MATs, that may serve as a lock of the gate loop. Nevertheless, plants, in contrary to mammals, lack the MAT regulatory subunit, and the regulation of plant MAT activity is still puzzling. Our structures open a possibility of an allosteric activity regulation of type I plant MATs by linear compounds, like polyamines, which would tighten the relationship between S-adenosylmethionine and polyamine biosynthesis.

Investigation of Low-Profile, High-Performance 62-mm SiC Power Module Package

Silicon carbide (SiC) power devices possess many beneficial properties for power electronics applications, but commercial 62-mm SiC power module packages with the direct drop-in replacement of Si devices limit many benefits of these SiC power devices. To fully utilize the advantages of the SiC power devices, this article presents a low-profile and high power density packaging solution of a 62-mm 1200-V/300-A SiC power module with enhanced electrical and thermal performance. The design optimizations on layout, chip placement, and terminal structure are compatible with the conventional module fabrication processes. An increase of power density by threefold is achieved with a low-profile package by reducing the height of the terminal connectors. Moreover, lower voltage overshoots of gate-source and drain-source of the proposed module are demonstrated due to low inductance in both gate and power loops. Thermal simulations show that the proposed module has a lower peak junction temperature and a more balanced temperature distribution among paralleled devices. Finally, the commercial and fabricated modules are characterized experimentally under the same conditions. Both simulation and experimental results show that the gate and power loop inductances of the proposed module are reduced by 96% and 76%, respectively. Moreover, the total switching loss and drain-source voltage overshoot are reduced by 44% and 54%, respectively, at 300 A using a 2- Ω external gate resistor.

Wide-Bandgap Semiconductor HF-Oscillation Attenuation Method With Tuned Gate $RLC$ Filter

Wide-bandgap (WBG) transistors provide better switching performance and higher operating temperatures compared to state-of-the-art Si devices and are suited for high-frequency applications due to very short switching times. The main obstacle for implementation of WBG transistors at full potential is the high-frequency oscillation in voltage and current during switching transients. Oscillations arise from resonance due to parasitic and device inductances and capacitances. Introduction of WBG transistors depends on the elimination of these oscillations and their negative effect on the performance of power converters. Good layout practice is mandatory, but there is a limit to the reduction of these parasitics, and often, slowing of the semiconductor switching time must be applied. This article presents a simple methodology for the attenuation of the negative effects of WBG transistor high-frequency oscillations without increasing rise and fall times. The proposed methodology is based on determination of the source of feedback resonant frequency between gate and power loops using network analyzer measurement on printed circuit board and utilization of a tuned $RLC$ filter. Experimental application of the methodology shows a direct relationship between loop resonant frequency and voltage and current oscillations. The proposed method reduces power losses, high-frequency oscillations, and electromagnetic interference.

Energy flow and intersubunit signalling in GSAM: A non-equilibrium molecular dynamics study

Non-equilibrium molecular dynamics simulations of vibrational energy flow induced by the imposition of a thermal gradient have been performed on the μ2-dimeric enzyme glutamate-1-semialdehyde aminomutase (GSAM), the key enzyme in the biosynthesis of chlorophyll, in order to identify energy transport pathways and to elucidate their role as potential allosteric communication networks for coordinating functional dynamics, specifically the negative cooperativity observed in the motion of the two active site gating loops. Fully atomistic MD simulations of thermal diffusion were executed with a GROMACS simulation package on a fully solvated GSAM enzyme by heating various active site target ligands (initially, catalytic intermediates and cofactors) to 300K while holding the remainder of the protein and the solvent bath at 10K and monitoring the temperature T(t) of all the enzyme residues as a function of time over a 1ns observation window. Energy is observed to be deposited in a relatively small number of discrete chains of residues most of which contribute to specific structural or biochemical functionality. Thermal linkages between all thermally active chains were established by isolating a specific pair of chains and performing a thermal diffusion simulation on the pair, one held at 300K and the other at 10K, with the rest of the protein frozen in its initial atomic configuration and thus thermally unresponsive. Proceeding in this way, it was possible to map out multiple pathways of vibrational energy flow leading from one of the active sites through a network of contiguous residues, many of which were evolutionarily conserved and linked by hydrogen bonds, into the other active site and ultimately to the other gating loop.

A channel profile report of the unusual K+ channel KtrB.

KtrAB is a key player in bacterial K+ uptake required for K+ homeostasis and osmoadaptation. The system is unique in structure and function. It consists of the K+-translocating channel subunit KtrB, which forms a dimer in the membrane, and the soluble regulatory subunit KtrA, which attaches to the cytoplasmic side of the dimer as an octameric ring conferring Na+ and ATP dependency to the system. Unlike most K+ channels, KtrB lacks the highly conserved T(X)GYG selectivity filter sequence. Instead, only a single glycine residue is found in each pore loop, which raises the question of how selective the ion channel is. Here, we characterized the KtrB subunit from the Gram-negative pathogen Vibrio alginolyticus by isothermal titration calorimetry, solid-supported membrane-based electrophysiology, whole-cell K+ uptake, and ACMA-based transport assays. We found that, despite its simple selectivity filter, KtrB selectively binds K+ with micromolar affinity. Rb+ and Cs+ bind with millimolar affinities. However, only K+ and the poorly binding Na+ are efficiently translocated, based on size exclusion by the gating loop. Importantly, the physiologically required K+ over Na+ selectivity is provided by the channel's high affinity for potassium, which interestingly results from the presence of the sodium ions themselves. In the presence of the KtrA subunit, sodium ions further decrease the Michaelis-Menten constant for K+ uptake from milli- to micromolar concentrations and increase the Vmax, suggesting that Na+ also facilitates channel gating. In conclusion, high binding affinity and facilitated K+ gating allow KtrAB to function as a selective K+ channel.

Architecture of the Cellulose Synthase Outer Membrane Channel and Its Association with the Periplasmic TPR Domain

Extracellular bacterial cellulose contributes to biofilm stability and to the integrity of the bacterial cell envelope. In Gram-negative bacteria, cellulose is synthesized and secreted by a multi-component cellulose synthase complex. The BcsA subunit synthesizes cellulose and also transports the polymer across the inner membrane. Translocation across the outer membrane occurs through the BcsC porin, which extends into the periplasm via 19 tetra-tricopeptide repeats (TPR). We present the crystal structure of a truncated BcsC, encompassing the last TPR repeat and the complete outer membrane channel domain, revealing a 16-stranded, β barrel pore architecture. The pore is blocked by an extracellular gating loop, while the extended C terminus inserts deeply into the channel and positions a conserved Trp residue near its extracellular exit. The channel is lined with hydrophilic and aromatic residues suggesting a mechanism for facilitated cellulose diffusion based on aromatic stacking and hydrogen bonding.

High Off-State Impedance Gate Driver of SiC MOSFETs for Crosstalk Voltage Elimination Considering Common-Source Inductance

The crosstalk voltage on the gate-source terminal of SiC power mosfets in a phase-leg circuit is composed of the gate-drain capacitor introduced voltage and the common-source inductor introduced voltage. The mathematical model of the crosstalk voltage indicates that to suppress two types of crosstalk voltage, there exists a contradictory requirement on the off-state gate loop impedance. This challenge reduces the effectiveness of conventional crosstalk elimination methods. As an improvement, a crosstalk voltage suppression circuit that synchronously eliminates the crosstalk voltage of gate-drain capacitance and the common-source inductance is proposed. In this article, instead of creating low-impedance gate loop in the off-state, a high-impedance gate loop is formatted to eliminate the voltage drop on the common-source inductance. Meanwhile, the potential false turn-on or the negative voltage spikes caused by gate-drain capacitance is eliminated by the precharge voltage in the gate-source capacitor. The required prestored charge is analyzed considering the nonlinear behavior of the junction capacitance of the SiC mosfets. The proposed gate driver is experimentally verified in different switching conditions.

A Study on Fastening the Switching Speed for Wide Bandgap Semiconductor Based Super Cascode

The Super Cascode is a series connected structure with a normally-off low voltage Si-MOSFET and multiple normally-on wide bandgap semiconductors. It has low switching losses compared with silicon based bipolar devices, and low on-resistance and low cost compared with other single high voltage normally-off wide bandgap semiconductor devices. In practice, however, there are inevitable parasitic inductances, which result in the increase of switching losses. The method is proposed to eliminate the common-source inductances (CSIs), such as using stack-die configuration with each device and adding an additional inductance in the gate loop of Si-MOSFET. It is numerically shown that the rise and fall times of the proposed method were 33.5% and 7.2% faster than the conventional one, respectively.

Secretory expression of the rat aryl sulfotransferases IV with improved catalytic efficiency by molecular engineering.

The rat aryl sulfotransferases IV (AST IV) has been used to catalyze 3'-phosphoadenosine-5'-phosphate (PAP) into the sulfuryl group donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS) in biotechnological production of glycosaminoglycans. The performance of native AST IV is not satisfying due to the lower catalytic activity with substrate PAP. In the present study, we achieved secretory expression of the AST IV and improved its catalytic efficiency by molecular engineering. Fusion with signal peptides Cex, YebF and PelB allow for secretory expression of AST IV and the secreted AST IV yield reached 4.21 ± 0.23U/mL, 8.67 ± 0.34U/mL and 21.35 ± 0.87U/mL, respectively. Modification of PelB further increased the secretory expression by more than fourfold, to 89.67 ± 1.34U/mL. On this basis, molecular evolution of the predicted PAP-binding pocket gate loop was performed and a positive mutant L89S/E90L with higher activity was identified. Considering the importance of the sites Leu89 and Glu90, we performed site-saturation mutagenesis and found the mutant L89M/E90Q with much higher PAP affinity (K m= 0.46 ± 0.02mM) and catalytic efficiency (k cat/K m = 1816.32 ± 12.72/s/M). The secretory expression of the AST IV variant L89M/E90Q with higher catalytic efficiency should facilitate the studies on biosynthesis of sulfated polysaccharides.