Accurate Measurement of Dynamic on-State Resistances of GaN Devices under Reverse and Forward Conduction in High Frequency Power Converter

Because of trapped charges in GaN transistor structure, device dynamic ON-state resistance RDSon is increased when it is operated in high frequency switched power converters, in which device is possibly operated by zero voltage switching (ZVS) to reduce its turn-ON switching losses. When GaN transistor finishes ZVS during one switching period, device has been operated under both reverse and forward conduction. Therefore its dynamic RDSon under both conduction modes needs to be carefully measured to understand device power losses. For this reason, a measurement circuit with simple structure and fast dynamic response is proposed to characterise device reverse and forward RDSon. In order to improve measurement sensitivity when device switches at high frequency, a trapezoidal current mode is proposed to measure device RDSon under almost constant current, which resolves measurement sensitivity issues caused by unavoidable measurement circuit parasitic inductance and measurement probes deskew in conventional device characterisation method by triangle current mode. Proposed measurement circuit and measurement method is then validated by first characterising a SiC-MOSFET with constant RDSon. Then, the comparison on GaN-HEMT dynamic RDSon measurement results demonstrates the improved accuracy of proposed trapezoidal current mode over conventional triangle current mode when device switches at 1MHz

A GaN-HEMT compact model including dynamic r_DSon effect for power electronics converters

In order to model GaN-HEMT switching transients and determine power losses, a compact model including dynamic RDSon effect is proposed herein. The model includes mathematical equations to represent device static and capacitance-voltage characteristics, and a behavioural voltage source, which includes multiple RC units to represent different time constants for trapping and detrapping effect from 100 ns to 100 s range. All the required parameters in the model can be obtained by fitting method using a datasheet or experimental characterisation results. The model is then implemented into our developed virtual prototyping software, where the device compact model is co-simulated with a parasitic inductance physical model to obtain the switching waveform. As model order reduction is applied in our software to resolve physical model, the device switching current and voltage waveform can be obtained in the range of minutes. By comparison with experimental measurements, the model is validated to accurately represent device switching transients as well as their spectrum in frequency domain until 100 MHz. In terms of dynamic RDSon value, the mismatch between the model and experimental results is within 10% under different power converter operation conditions in terms of switching frequencies and duty cycles, so designers can use this model to accurately obtain GaN-HEMT power losses due to trapping and detrapping effects for power electronics converters

Investigation on Single and Split Output Gate Configurations Influence on the GaN-HEMTs Switching Behaviours

This work investigates the power GaN-HEMTs switching behaviour differences resulted from usage of two gate driving configurations: single and split outputs. The analysis based on simulation and experimental results show that GaN-HEMTs could switch slower and cause higher switching losses when the split output configuration is used. This is because the output capacitance (Coss) of MOSFETs inside gate driver will be charged during the turn-on process of GaN-HEMTs, and this charging process can reduce the charging speed of input capacitance (Ciss) of GaN-HEMTs. Moreover, the gate resistance and parasitic inductance are the main parameters selected for analysis, and their distribution can amplify this effect by increasing the impedance ratio of turn-on and turn-off loop. This research provides guiding suggestions for gate driver and high-efficiency GaN-HEMTs power module design.</p

DMTs and Covid-19 severity in MS: a pooled analysis from Italy and France

We evaluated the effect of DMTs on Covid-19 severity in patients with MS, with a pooled-analysis of two large cohorts from Italy and France. The association of baseline characteristics and DMTs with Covid-19 severity was assessed by multivariate ordinal-logistic models and pooled by a fixed-effect meta-analysis. 1066 patients with MS from Italy and 721 from France were included. In the multivariate model, anti-CD20 therapies were significantly associated (OR&nbsp;=&nbsp;2.05, 95%CI&nbsp;=&nbsp;1.39–3.02, p&nbsp;&lt;&nbsp;0.001) with Covid-19 severity, whereas interferon indicated a decreased risk (OR&nbsp;=&nbsp;0.42, 95%CI&nbsp;=&nbsp;0.18–0.99, p&nbsp;=&nbsp;0.047). This pooled-analysis confirms an increased risk of severe Covid-19 in patients on anti-CD20 therapies and supports the protective role of interferon

Variateur de vitesse à impact électromagnétique réduit : onduleur multiniveaux et nouvelles stratégies de modulation

Among power electronic converters, variable speed drives are responsible for high frequency electromagnetic disturbances such as common mode currents and motor overvoltages. This work aims at reducing these phenomena by using a multilevel converter controlled with new modulation schemes. A state of the art of existing attenuation techniques is presented, and the three-level neutral-point-clamped (NPC) inverter is retained as direct- to alternative-current converter topology. A new pulse-width-modulation (PWM) strategy is developed for the reduction of common mode currents generated by the inverter. The power switches commutation process is analyzed and modelled in order to establish specific constraints that maximize the efficiency of the proposed strategy. Meanwhile, the use of long cables between drives and electric machines highlights a drawback regarding motor overvoltages, which is kept under control by appropriate use of the degrees of freedom of the new PWM. Eventually, the issue of neutral point balancing is worked out. The proposed modulation strategy is experimentally implemented through a new carried-based modulator, and measurement results confirm a five-decibel gain on common mode currents upon conventional strategies while ensuring motor overvoltages limitation as well as neutral point balancing.Parmi les convertisseurs d'électronique de puissance, les variateurs de vitesse utilisés pour l'alimentation des machines électriques sont source de perturbations électromagnétiques à haute fréquence telles que les courants de mode commun et les surtensions aux bornes des moteurs. Le travail porte sur la réduction de ces perturbations par l'emploi d'un convertisseur multiniveaux associé à de nouvelles lois de commande rapprochée. Après un état de l'art des méthodes d'atténuation existantes, l'onduleur à trois niveaux de type neutral-point-clamped (NPC) est retenu comme structure de conversion continu-alternatif et une nouvelle stratégie de modulation de largeur d'impulsion (MLI) est développée en vue de réduire les courants de mode commun générés par l'onduleur. Les phénomènes entrant en jeu dans les commutations des interrupteurs de puissance sont analysés et modélisés afin d'établir des contraintes de commande permettant de maximiser les performances de la MLI proposée. Parallèlement, l'utilisation de câbles longs entre le variateur et la machine soulève une contrepartie vis-à-vis des surtensions moteur qui est maîtrisée par l'exploitation adéquate des degrés de liberté de la nouvelle MLI. Enfin, la problématique de régulation du point milieu capacitif du bus continu est abordée. La stratégie proposée est implantée expérimentalement par l'intermédiaire d'une modulation naturelle par porteuses, et les résultats de mesure montrent un gain de cinq décibels sur les courants de mode commun par rapport aux stratégies classiques tout en limitant les surtensions générées aux bornes du moteur et en assurant l'équilibrage du bus continu

A Simple Carrier-Based Modulation for the SVM of the Matrix Converter

Today, industry has not fully embraced the matrix converter solution. One important reason is its high control complexity. It is therefore relevant to propose a simpler but efficient modulation scheme, similar as three phase voltage source inverter modulators with the well-known symmetrical carrier-based ones. The modulation presented in this paper is equivalent to a particular space vector modulation (SVM) and takes into account harmonics and unbalanced input voltages, with the same maximum voltage transfer ratio (86%). The aim of this work is to propose a simple and general pulse width-modulation method using carrier-based modulator for an easier matrix converter control. Furthermore, a simple duty cycle calculation method is used, based on a virtual matrix converter. Finally, simulations and experimentations are presented to validate this simple, original and efficient modulation concept equivalent to matrix converter SVM.TRavaux de thèses financé par le pole MEDEE, La région Nord pas de calais et STIE (Schneider Toshiba Inverter Europe

Modélisation des perturbations électromagnétiques dans les convertisseurs statiques pour des applications aéronautiques

Depuis les années 1990, l énergie électrique a tendance à supplanter les autres énergies de servitude à bord des avions. Ceci offre des gains notables en termes de poids, volume et coûts de maintenance. L'énergie électrique remplit des fonctions de plus en plus variées grâce à la généralisation de l'utilisation de convertisseurs statiques. Ces convertisseurs sont basés sur l'utilisation de composants semiconducteurs en commutation qui génèrent des variations rapides de tension et de courant. Ce qui engendre des perturbations à haute fréquence qu'il faut limiter afin d'être conforme aux normes de compatibilité électromagnétiques (CEM). La conformité aux normes est souvent obtenue en ajoutant un filtre lourd et volumineux au système, ce qui réduit les gains apportés par la transition vers le plus électrique. Afin d'optimiser le filtre à ajouter, il est intéressant de prendre en compte la contrainte de CEM dès la phase de conception, pour cela, il faut disposer d'outil de simulation prédictive. Dans cette thèse nous proposons une méthode de modélisation des perturbations conduites émises par un système valable jusque 50MHz. Pour cela, notre travail se divise en deux parties. D'une part, nous proposons une méthode de modélisation des chemins de propagation des perturbations, incluant notamment les câbles d'énergie. D'autre part, nous proposons une méthode de modélisation des sources de perturbation en domaine fréquentiel. Cette méthode est basée sur l'utilisation de plusieurs topologies de générateurs équivalents et permet de représenter le comportement non-linéaire des convertisseurs. Cette méthode est validée expérimentalement sur un hacheur série et sur un onduleur monophasé.Since the 1990 s, electricital energy tends to replace pneumatic and hydraulic energy aboard aircrafts. This allows to reduce weight, volume and maintenance costs of the actuators. Electrical energy is used for more and more variated functions thanks to the generalization of the power converters. These power converters are based on the use of semiconductor devices in switching mode which generates sharp voltage and current variations. This leads to electromagnetic (EMC) issues. In order to obtain the compliance to EMC standards, a heavy and bulky filter is often added to the system, which lower the gain allowed by the transition to electrical energy. In order to optimize the filter added, it is interesting to take into account the EMC at the design step. Thus it is necessary to have a predictive modeling tool. In this thesis, a modeling method of the conducted electromagnetic interference (EMI) emitted valid up to 50MHz by a system is proposed. Thus our work is devided into two parts. First, we propose a modeling method of the propagation paths including power cable. Then, we propose a modeling method of the EMI sources in frequency domain. This method is based on the use of multiple equivalent generators topologies and allows to retranscript the non-linear behaviour of the converters. This method is experimentally validated on a buck-converter and a single phased inverter.LILLE1-Bib. Electronique (590099901) / SudocSudocFranceF

Semi-Analytical Model of Parasitic Capacitance of Inductor with Conductive Core

International audienc

Estimation des permittivités relatives des noyaux magnétiques pour la détermination des capacités parasites des bobines des filtres CEM

International audienc

Modelling and minimization of the parasitic capacitance of ring core inductors

International audienceHigh-frequency static converters requires inductors, common and differential mode chokes with a low equivalent parallel capacitance. To reduce it, this paper proposes first a semi-analytical model of this capacitance for inductors made with coated ring cores of nano-crystalline material. This model is based on 2D finite element method to compute the turn-turn and turn-core parasitic capacitances, taking into account loose windings. Then the total capacitance is computed thanks to an energetic approach. The model is validated against measurements performed on one core for several numbers of turns. Since the model shows that the capacitance is almost linear with the parasitic turn-core capacitance, specific devices are proposed to increase the distance between turns and core and thus decrease the capacitance. It is demonstrated that a small increase in overall volume allows to divide the equivalent parallel capacitance of a common mode choke by almost a factor of three while increasing its overall volume by only 37%